70-inch field trip report
Did you get a break in the clouds? See anything good? Impressions? I'm off to bed, 4 AM comes awfully fast. I'll read your reports in the morning.
On 27 Oct 2013, at 20:39 , Chuck Hards wrote:
Did you get a break in the clouds? See anything good? Impressions?
I'm off to bed, 4 AM comes awfully fast. I'll read your reports in the morning.
That thing is HUGE. Walking from my car to where I thought the 1.8 was set up I could not see it and started to wonder if I'd gone to the wrong house. But then I came around a large tree and was confronted by the even much larger 1.8. Wow! And I love the flag up on top. The best we got weather wise was thin clouds. But adding to the fun was a very nice and near vertical pass of ISS that was easily visible. Ken Porras had his camera ready and snapped a series of shots of ISS passing through the superstructure of the scope. Nice! Chances are we'll get another chance to look through the scope but for today I was just satisfied to look at it. Of course ATS after was also fun. BTW, Mike said his priority is getting the scope out to the public with getting it completely finished coming second. One of the spots he hopes to "plant" it for a while is SPOC. Hmmm, anyone want to spring for a simple building to house it in at SPOC between road trips? Once again, that thing is HUGE!!! :) patrick
I don't think SLAS should put up a building just to house anyone's private scope. My 2 cents' worth. -- Joe On Sunday, October 27, 2013 9:51 PM, Wiggins Patrick <paw@getbeehive.net> wrote: On 27 Oct 2013, at 20:39 , Chuck Hards wrote:
Did you get a break in the clouds? See anything good? Impressions?
I'm off to bed, 4 AM comes awfully fast. I'll read your reports in the morning.
That thing is HUGE. Walking from my car to where I thought the 1.8 was set up I could not see it and started to wonder if I'd gone to the wrong house. But then I came around a large tree and was confronted by the even much larger 1.8. Wow! And I love the flag up on top. The best we got weather wise was thin clouds. But adding to the fun was a very nice and near vertical pass of ISS that was easily visible. Ken Porras had his camera ready and snapped a series of shots of ISS passing through the superstructure of the scope. Nice! Chances are we'll get another chance to look through the scope but for today I was just satisfied to look at it. Of course ATS after was also fun. BTW, Mike said his priority is getting the scope out to the public with getting it completely finished coming second. One of the spots he hopes to "plant" it for a while is SPOC. Hmmm, anyone want to spring for a simple building to house it in at SPOC between road trips? Once again, that thing is HUGE!!! :) patrick _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".
What about a stripped-out bus? ;-) You know, it's not out of the realm of possibility that Mike bequeaths the telescope to SLAS or a similar outreach-oriented organization when the time comes. Something for the next generation of SLAS to think about. Stay on good terms with Mike. A gentleman on Cloudy Nights generously sent me a 100mm eyepiece in a 4" barrel, to give to Mike for FREE, which I did Sunday morning. He about squealed with delight when I handed it to him. He knows the exit pupil will be too large for the 70", but it has possibilities as a very wide-field, low-power finder eyepiece. BTW, thanks to Jay's blog, SPACE.COM is interested in doing a piece on Mike and his scope, so stay tuned for that! And kudos to Jay for having his blog read by the managing editor of SPACE.COM! On Sun, Oct 27, 2013 at 11:28 PM, Joe Bauman <josephmbauman@yahoo.com>wrote:
I don't think SLAS should put up a building just to house anyone's private scope. My 2 cents' worth. -- Joe
You want pre approval to give it in a will, seriously how many of you would really want it?
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
You know, it's not out of the realm of possibility that Mike bequeaths the telescope to SLAS or a similar outreach-oriented organization when the time comes. Something for the next generation of SLAS to think about.
Stay on good terms with Mike.
A gentleman on Cloudy Nights generously sent me a 100mm eyepiece in a 4" barrel, to give to Mike for FREE, which I did Sunday morning. He about squealed with delight when I handed it to him. He knows the exit pupil will be too large for the 70", but it has possibilities as a very wide-field, low-power finder eyepiece.
BTW, thanks to Jay's blog, SPACE.COM is interested in doing a piece on Mike and his scope, so stay tuned for that!
And kudos to Jay for having his blog read by the managing editor of SPACE.COM!
On Sun, Oct 27, 2013 at 11:28 PM, Joe Bauman <josephmbauman@yahoo.com>wrote:
I don't think SLAS should put up a building just to house anyone's private scope. My 2 cents' worth. -- Joe
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Just tossing-out ideas, Erik, maybe far-fetched, maybe not. I should have known you'd have the shovel of poop ready to dump on it. Seriously, it's got to go somewhere when Mike passes-on, may as well be an outreach-oriented astronomy club or similar institution. I personally couldn't handle it, you are correct in that few individuals would be able to. That's why I suggested eventual institutional stewardship. It's a genuine piece of history now, it would be a shame to see it go to scrap one day. Q: What's better than owning a 70-inch telescope? A: Having a friend or belonging to a club with a 70-inch telescope! On Mon, Oct 28, 2013 at 1:12 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
You want pre approval to give it in a will, seriously how many of you would really want it?
There you go Chuck throwing out insults as usual, grow up man.. Do you really think SLAS would want it? We gave away an 18 inch scope because no one wanted to take it Star Parties. My point was that he will need to make arrangements and check and make sure he is giving it to someone who uses it. .> Just tossing-out ideas, Erik, maybe far-fetched, maybe not. I should have
known you'd have the shovel of poop ready to dump on it.
Seriously, it's got to go somewhere when Mike passes-on, may as well be an outreach-oriented astronomy club or similar institution. I personally couldn't handle it, you are correct in that few individuals would be able to. That's why I suggested eventual institutional stewardship. It's a genuine piece of history now, it would be a shame to see it go to scrap one day.
Q: What's better than owning a 70-inch telescope?
A: Having a friend or belonging to a club with a 70-inch telescope!
On Mon, Oct 28, 2013 at 1:12 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
You want pre approval to give it in a will, seriously how many of you would really want it?
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Hardly an insult, Erik, just an observation of you in typical form *after*you pooped all over my post. You threw the first volley, always quick to dump on an honest suggestion, never looking at possible positives first. Always the negative. Always. Always. I'm sure Mike will do whatever he wants to do with the scope, when he's no longer able to campaign it, regardless of what you, I, or anyone else thinks. And whomever gets it, if anyone, I'm equally sure will be eager and happy to take over where he leaves off. On Mon, Oct 28, 2013 at 2:42 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
There you go Chuck throwing out insults as usual, grow up man.. Do you really think SLAS would want it? We gave away an 18 inch scope because no one wanted to take it Star Parties. My point was that he will need to make arrangements and check and make sure he is giving it to someone who uses it.
Ah, bait, I get it., and you just keep it up.
Hardly an insult, Erik, just an observation of you in typical form *after*you pooped all over my post. You threw the first volley, always quick to dump on an honest suggestion, never looking at possible positives first. Always the negative. Always. Always.
I'm sure Mike will do whatever he wants to do with the scope, when he's no longer able to campaign it, regardless of what you, I, or anyone else thinks. And whomever gets it, if anyone, I'm equally sure will be eager and happy to take over where he leaves off.
On Mon, Oct 28, 2013 at 2:42 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
There you go Chuck throwing out insults as usual, grow up man.. Do you really think SLAS would want it? We gave away an 18 inch scope because no one wanted to take it Star Parties. My point was that he will need to make arrangements and check and make sure he is giving it to someone who uses it.
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interesting question, you may be surprised if you ask if someone is selling.
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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Speaking of large telescopes for sale, I have sadly decided that after I retire at the end of this school year, I will no longer have a place to store the famous (or infamous, as the case may be) 22 inch Brent Watson Dobsonian. It is currently being stored (and used) in the observatory at my high school, but I just don't have room in my already crowded garage. I'd be willing to sell it for what I paid Brent for it: $750! I'd be willing to deliver it to northern Utah locations. Anyone interested? Wayne Sumner -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Monday, October 28, 2013 2:58 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
interesting question, you may be surprised if you ask if someone is selling.
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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I may be interested Wayne, but I recall that it was a longish f/ratio. How long is it? Thanks, C. On Tue, Oct 29, 2013 at 6:56 AM, Wayne Sumner <WSUMNER@dsdmail.net> wrote:
Speaking of large telescopes for sale, I have sadly decided that after I retire at the end of this school year, I will no longer have a place to store the famous (or infamous, as the case may be) 22 inch Brent Watson Dobsonian. It is currently being stored (and used) in the observatory at my high school, but I just don't have room in my already crowded garage. I'd be willing to sell it for what I paid Brent for it: $750! I'd be willing to deliver it to northern Utah locations. Anyone interested? Wayne Sumner
The focal ratio of Brent's 22 inch is f6.3 as I recall. That would make the focal length about 11.55 feet. Brent, is that correct? -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, October 29, 2013 7:47 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I may be interested Wayne, but I recall that it was a longish f/ratio. How long is it? Thanks, C. On Tue, Oct 29, 2013 at 6:56 AM, Wayne Sumner <WSUMNER@dsdmail.net> wrote:
Speaking of large telescopes for sale, I have sadly decided that after I retire at the end of this school year, I will no longer have a place to store the famous (or infamous, as the case may be) 22 inch Brent Watson Dobsonian. It is currently being stored (and used) in the observatory at my high school, but I just don't have room in my already crowded garage. I'd be willing to sell it for what I paid Brent for it: $750! I'd be willing to deliver it to northern Utah locations. Anyone interested? Wayne Sumner
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139.5 inches. That is 11.625 feet. From: Wayne Sumner <WSUMNER@dsdmail.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 8:24 AM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter The focal ratio of Brent's 22 inch is f6.3 as I recall. That would make the focal length about 11.55 feet. Brent, is that correct? -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, October 29, 2013 7:47 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I may be interested Wayne, but I recall that it was a longish f/ratio. How long is it? Thanks, C. On Tue, Oct 29, 2013 at 6:56 AM, Wayne Sumner <WSUMNER@dsdmail.net> wrote:
Speaking of large telescopes for sale, I have sadly decided that after I retire at the end of this school year, I will no longer have a place to store the famous (or infamous, as the case may be) 22 inch Brent Watson Dobsonian. It is currently being stored (and used) in the observatory at my high school, but I just don't have room in my already crowded garage. I'd be willing to sell it for what I paid Brent for it: $750! I'd be willing to deliver it to northern Utah locations. Anyone interested? Wayne Sumner
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Brent, how thick is the mirror and what is the substrate? Is the coating standard aluminum? What is the secondary size, and do you recall the fully illuminated image diameter? You ground and figured it yourself, right? Do you recall the specifics of the figure accuracy? My mind is whirling... On Tue, Oct 29, 2013 at 8:34 AM, Brent Watson <brentjwatson@yahoo.com>wrote:
139.5 inches. That is 11.625 feet.
From: Wayne Sumner <WSUMNER@dsdmail.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 8:24 AM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
The focal ratio of Brent's 22 inch is f6.3 as I recall. That would make the focal length about 11.55 feet. Brent, is that correct?
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto: utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, October 29, 2013 7:47 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I may be interested Wayne, but I recall that it was a longish f/ratio. How long is it?
Thanks,
C.
On Tue, Oct 29, 2013 at 6:56 AM, Wayne Sumner <WSUMNER@dsdmail.net> wrote:
Speaking of large telescopes for sale, I have sadly decided that after I retire at the end of this school year, I will no longer have a place to store the famous (or infamous, as the case may be) 22 inch Brent Watson Dobsonian. It is currently being stored (and used) in the observatory at my high school, but I just don't have room in my already crowded garage. I'd be willing to sell it for what I paid Brent for it: $750! I'd be willing to deliver it to northern Utah locations. Anyone interested? Wayne Sumner
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The mirror is pyrex, 1.125 inches thick and is supported on an 18 point flotation cell. The coating is Beral, a coating that was popular years ago, but I haven't heard much about it since. The secondary is 3.1 inches minor axis. That gives right around 1 inch fully illuminated circle. The spider is a bicycle rim and spokes with the bycycle hub holding the secondary. I believe only eight of the spokes are populated. I ground and polished the mirror with a little help from my friends. Vague recollection of the mirror accuracy is between 1/4 and 1/8 wave. I know that on the right nights planetary images were spectacular. That only happened once or twice per year as I recall. The mirror had to be in the cell just right (relatively simple), and the seeing had to be exceptional (harder to get). I always said that the 22 inch began to show objects the way they looked in photographs. The telescope is large, but was designed to go into the back of my Chevy Malibu station wagon with the tube sitting on a roof rack on top. That is why it is a 22 inch and not a 24 inch. Design of the plywood parts was done with John Dobson, and follows the design philosophy of the 24 inch he built. It is VERY stable. He provided me the tool to grind the mirror, which I broke just prior to finishing the rough grinding. I still remember sitting in his apartment in San Francisco and asking him how he ground mirrors so quickly. His response was "What takes you so long? Mirror grinding is cave man's work - eat well, sleep well, and work like hell!" The concrete form tube is very resilient. It blew off the top of my truck near Nephi one night and bounced down the freeway at 56 mph ending up in the median. The roof rack was totally destroyed, but I had a star party I had to do in Panguitch the next Friday. I bought a new roof rack but had no time to do anthing else. I transported the tube and scope to Panguitch and assembled the scope. I did not even have to change the collimation! I miss those times. From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 9:02 AM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter Brent, how thick is the mirror and what is the substrate? Is the coating standard aluminum? What is the secondary size, and do you recall the fully illuminated image diameter? You ground and figured it yourself, right? Do you recall the specifics of the figure accuracy? My mind is whirling... On Tue, Oct 29, 2013 at 8:34 AM, Brent Watson <brentjwatson@yahoo.com>wrote:
139.5 inches. That is 11.625 feet.
Getting back to Mike Clements telescope, there's an article in todays Salt Lake Tribune that has photos of the mammoth thing. I can not figure out what sort of reflector it is. It sort of looks Newtonian except that I am not sure where the eyepiece is located. It looks as though it might be half way up one of the trusses and is at an odd angle while the secondary mirror is on a less than 45 degree angle. _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".
You're exactly right. The secondary reflects the light path back down the tube at an angle, and is intercepted outside the edge of the primary mirror. It was done this way to reduce the needed truss length, and keep the viewing position much closer to the ground. A shorter ladder can be used this way. The secondary mirror is round, not elliptical. I missed seeing Sheena on Sunday by just a few minutes, over at Steve's. On Tue, Oct 29, 2013 at 11:15 AM, M Wilson <astro_outwest@yahoo.com> wrote:
Getting back to Mike Clements telescope, there's an article in todays Salt Lake Tribune that has photos of the mammoth thing.
I can not figure out what sort of reflector it is. It sort of looks Newtonian except that I am not sure where the eyepiece is located. It looks as though it might be half way up one of the trusses and is at an odd angle while the secondary mirror is on a less than 45 degree angle.
_______________________________________________
So, is there a name for this type of configuration? I'm betting it isn't Newtonian. When is there going to be another SLAS field trip to Mike's scope? I didn't see the last anouncement until after the outing was filled. ________________________________ From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 11:49 AM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter You're exactly right. The secondary reflects the light path back down the tube at an angle, and is intercepted outside the edge of the primary mirror. It was done this way to reduce the needed truss length, and keep the viewing position much closer to the ground. A shorter ladder can be used this way. The secondary mirror is round, not elliptical. I missed seeing Sheena on Sunday by just a few minutes, over at Steve's. On Tue, Oct 29, 2013 at 11:15 AM, M Wilson <astro_outwest@yahoo.com> wrote:
Getting back to Mike Clements telescope, there's an article in todays Salt Lake Tribune that has photos of the mammoth thing.
I can not figure out what sort of reflector it is. It sort of looks Newtonian except that I am not sure where the eyepiece is located. It looks as though it might be half way up one of the trusses and is at an odd angle while the secondary mirror is on a less than 45 degree angle.
_______________________________________________
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Optically, it's still basically a Newtonian. Some people call them "low-riders" and there are a couple of other names being tossed-around. The nice thing about it, besides ergonomics, is that the secondary doesn't need to be quite as good as in a standard Newtonian. A mirror at a 45-degree angle should be much better optically than the primary. A mirror reflecting at a much reduced angle can be figured to about the same tolerance as the primary, and still produce a "diffraction-limited" image. I think Patrick organized the last outing as a SLAS function. I've taken a lot of Mike's time lately so I want to back-off for a bit and get this article done before I personally start pestering him for another viewing session. Others should get a chance before I get back in line, anyway. We are lucky that Mike is such a nice guy and his main point of building this telescope is so as many people as possible can look through it. On Tue, Oct 29, 2013 at 12:06 PM, M Wilson <astro_outwest@yahoo.com> wrote:
So, is there a name for this type of configuration? I'm betting it isn't Newtonian.
When is there going to be another SLAS field trip to Mike's scope? I didn't see the last anouncement until after the outing was filled.
On 29 Oct 2013, at 12:06, M Wilson wrote:
When is there going to be another SLAS field trip to Mike's scope?
Steve and Mike seem very open to the idea. Just do as I did and ring up Steve to arrange a time and then put the word out and collect names. Best to keep the numbers down in part due to limited parking at Steve's place but also because the way the scope operates it would take a long time to get a large group through. patrick
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
You're exactly right. The secondary reflects the light path back down the
tube at an angle, and is intercepted outside the edge of the primary mirror. It was done this way to reduce the needed truss length, and keep the viewing position much closer to the ground. A shorter ladder can be used this way. The secondary mirror is round, not elliptical.
I missed seeing Sheena on Sunday by just a few minutes, over at Steve's.
On Tue, Oct 29, 2013 at 11:15 AM, M Wilson <astro_outwest@yahoo.com> wrote:
Getting back to Mike Clements telescope, there's an article in todays Salt Lake Tribune that has photos of the mammoth thing.
I can not figure out what sort of reflector it is. It sort of looks Newtonian except that I am not sure where the eyepiece is located. It looks as though it might be half way up one of the trusses and is at an odd angle while the secondary mirror is on a less than 45 degree angle.
_______________________________________________
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True, but a smaller secondary would also mean a taller ladder. As built, the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built. Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror. And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture. There are always trade-offs. On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are. The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute. True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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Pretty sure that this post is going to generate some comments/corrections. I am staying out of it. Got my bag of popcorn and a soda; this could get interesting. Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 3:29 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are. The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute. True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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_______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options". This message and any attachments are solely for the use of intended recipients. The information contained herein may include trade secrets, protected health or personal information, privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. If you are not an intended recipient, you are hereby notified that you received this email in error, and that any review, dissemination, distribution or copying of this email and any attachment is strictly prohibited. If you have received this email in error, please contact the sender and delete the message and any attachment from your system. Thank you for your cooperation
LOL! On Tue, Oct 29, 2013 at 2:15 PM, Hutchings, Mat <mat.hutchings@siemens.com>wrote:
Pretty sure that this post is going to generate some comments/corrections. I am staying out of it.
Got my bag of popcorn and a soda; this could get interesting.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto: utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 3:29 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
I don't understand your "true aperture" claim. It makes no sense. The aperture is 70 inches with the resolution of a 70 inch scope. The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches. Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time. He plans to add motor drives for tracking. The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X. Again, Mike knew this in advance. On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope. These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim. Just out of curiosity, what is the diameter of the secondary in the Grim scope? From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I don't understand your "true aperture" claim. It makes no sense. The aperture is 70 inches with the resolution of a 70 inch scope. The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches. Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time. He plans to add motor drives for tracking. The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X. Again, Mike knew this in advance. On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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So, the Grim has the effective resolution of a 20" unobstructed scope and the light gathering power of a a 28 inch unobstructed scope. Mike's scope will have a 1.75 magnitude advantage over the Grim. Another rule of thumb is that for every magnitue increase in light gathering power, there are about 10 times more stars visible. That isn't quite that much for deep sky stuff, but closer to maybe 7 or 8. Mike's scope should show about 50 times more stars and maybe a bit more than an order of magnitude more deep sky objects. That is a pretty big difference! The resolving power of Mike's scope will be more than twice as good as the Grim - assuming the seeing will support it. Dawe's limit for Mike's effective 41 inches is about 0.11 arc seconds. Seeing to support that is pretty hard to come by. Read almost never. BTW, Dawe's limit is pretty close to the theoretical resolution as calculated in your physics book - at least for the apertures I've worked with. From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:42 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter The Grim has a 10-inch secondary. On Tue, Oct 29, 2013 at 2:39 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
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I was thinking the Grim was larger.
So, the Grim has the effective resolution of a 20" unobstructed scope and
the light gathering power of a a 28 inch unobstructed scope. Mike's scope will have a 1.75 magnitude advantage over the Grim. Another rule of thumb is that for every magnitue increase in light gathering power, there are about 10 times more stars visible. That isn't quite that much for deep sky stuff, but closer to maybe 7 or 8. Mike's scope should show about 50 times more stars and maybe a bit more than an order of magnitude more deep sky objects. That is a pretty big difference! The resolving power of Mike's scope will be more than twice as good as the Grim - assuming the seeing will support it. Dawe's limit for Mike's effective 41 inches is about 0.11 arc seconds. Seeing to support that is pretty hard to come by. Read almost never. BTW, Dawe's limit is pretty close to the theoretical resolution as calculated in your physics book - at least for the apertures I've worked with.
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:42 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
The Grim has a 10-inch secondary.
On Tue, Oct 29, 2013 at 2:39 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
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Ah, I get it. I was referring to the theoretical resolution of an unobstructed aperture, wheras you and Erik were talking about the effects of diffraction caused by a secondary obstruction. But if you assume the 40-inch in the argument to be of the same optical configuration, with a similar sized secondary by percentage of aperture, we are back on an even playing field. And calling effectively a 41 inch aperture is misleading without specifically referring to resolution. I consider myself schooled on this point. Thanks, Brent. The Grim does have the same limitations of field of view, but because it is driven, that limitation isn't so bad. Large objects still cannot be seen in a single FOV. One of the penalties of long focal length, with generally comes with large aperture. On Tue, Oct 29, 2013 at 2:39 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary.
The Grim must have a significantly larger field of view, and there are many objects that are just to large for it, it bet the 70 has a longer list.
The trib article mentioned that Mike seemed a little surprised by the small field of view with 1st light. As a preference I prefer the faster optics like f4 rather than f6. Ah, I get it. I was referring to the theoretical resolution of an
unobstructed aperture, wheras you and Erik were talking about the effects of diffraction caused by a secondary obstruction. But if you assume the 40-inch in the argument to be of the same optical configuration, with a similar sized secondary by percentage of aperture, we are back on an even playing field. And calling effectively a 41 inch aperture is misleading without specifically referring to resolution.
I consider myself schooled on this point. Thanks, Brent.
The Grim does have the same limitations of field of view, but because it is driven, that limitation isn't so bad. Large objects still cannot be seen in a single FOV. One of the penalties of long focal length, with generally comes with large aperture.
On Tue, Oct 29, 2013 at 2:39 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary.
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It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party. My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope. These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim. Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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The popcorn is done. But my, was it an informative discussion. Thanks to all the contributors. I was too "yella" (yellow for you yankees) to jump in.... Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party. My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor. The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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A 6" refractor is a very nice scope. My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good. The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this. Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor. The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16. A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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I'm 6'4", and plan on a very low profile rocker/mirror box. This should get the eyepiece down low enough for me, but again, I will probably go slightly faster than f4 just to make sure. I will need to bring a ladder or step of some kind for most others to view through the scope. Yes, someone would do well to buy the 16"! Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 7:24 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16. A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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Well there you go, at f4 you may be right. The only thing that would have made mine lower would have been using thinner plywood. A certain height is always needed for the mirror box to swing easily. I think the low profile designs are good because of larger diameter of the altitude bearings, it makes it easier to adjust friction. I should probably check it out at one of your ATM sessions.
I'm 6'4", and plan on a very low profile rocker/mirror box. This should
get the eyepiece down low enough for me, but again, I will probably go slightly faster than f4 just to make sure. I will need to bring a ladder or step of some kind for most others to view through the scope.
Yes, someone would do well to buy the 16"!
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 7:24 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16.
A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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of course the low profile rocker/mirror box do make large scopes more portable.
Well there you go, at f4 you may be right. The only thing that would have
made mine lower would have been using thinner plywood. A certain height is always needed for the mirror box to swing easily. I think the low profile designs are good because of larger diameter of the altitude bearings, it makes it easier to adjust friction. I should probably check it out at one of your ATM sessions.
I'm 6'4", and plan on a very low profile rocker/mirror box. This should
get the eyepiece down low enough for me, but again, I will probably go slightly faster than f4 just to make sure. I will need to bring a ladder or step of some kind for most others to view through the scope.
Yes, someone would do well to buy the 16"!
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 7:24 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16.
A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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You are certainly welcome at any ATM session. However, don't expect to see much being done on the 21" project currently. I need to sell the 16" before much more happens on the 21". One scope finances the next... Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Wednesday, October 30, 2013 11:42 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Well there you go, at f4 you may be right. The only thing that would have made mine lower would have been using thinner plywood. A certain height is always needed for the mirror box to swing easily. I think the low profile designs are good because of larger diameter of the altitude bearings, it makes it easier to adjust friction. I should probably check it out at one of your ATM sessions.
I'm 6'4", and plan on a very low profile rocker/mirror box. This should
get the eyepiece down low enough for me, but again, I will probably go slightly faster than f4 just to make sure. I will need to bring a ladder or step of some kind for most others to view through the scope.
Yes, someone would do well to buy the 16"!
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 7:24 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16.
A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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Yup, with a wife and family you generally need to be practical. I would certainly suggest your 16 to Rich. I do live near your house and have thought about checking out one of the sessions. My only possible project is upgrading my focuser, which mainly just requires cash.
You are certainly welcome at any ATM session. However, don't expect to
see much being done on the 21" project currently. I need to sell the 16" before much more happens on the 21". One scope finances the next...
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Wednesday, October 30, 2013 11:42 AM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Well there you go, at f4 you may be right. The only thing that would have made mine lower would have been using thinner plywood. A certain height is always needed for the mirror box to swing easily. I think the low profile designs are good because of larger diameter of the altitude bearings, it makes it easier to adjust friction. I should probably check it out at one of your ATM sessions.
I'm 6'4", and plan on a very low profile rocker/mirror box. This should
get the eyepiece down low enough for me, but again, I will probably go slightly faster than f4 just to make sure. I will need to bring a ladder or step of some kind for most others to view through the scope.
Yes, someone would do well to buy the 16"!
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 7:24 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
With a 20 inch f4 at the zenith you needed about one step. Had a ladder that we added a half step. I think you will need some sort of ladder, unless you are very tall. We selected a secondary size some where in the middle of min and max, as I recall 3.5 inches. Collimating was not difficult, of course you can always make it more difficult than is needed if you get obsessed, a Cheshire usually worked fine.
Sounds like someone would be fortunate to get your 16.
A 6" refractor is a very nice scope.
My 16" is f5.6 and its secondary mirror is 2.6" M.A. The secondary is very nice and was handmade by Louis Wilkinson (an early optician for Cave Optics). I have a hand written note from him stating the quality of the mirror; it is very good.
The 21" will be an f/4 or slightly faster. The secondary will be in the 4" to 4.5" range. The main goal is for me to be able to stand flat-footed at the scope when it is pointed at the zenith. Ladders don't bother me, but would rather not have to carry one around. With the current generation of parabola correctors, one does not need to shy away from fast focal lengths (at least for coma issues). Figuring a fast, larger optic is another beast. Then there is collimation, which needs to be right on the nut with a fast, fat optic But what the hey, I can man up and do this.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 5:43 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Good luck with 21 inch btw, I did a 20 f4 and enjoyed the views a great deal. What is your f ratio and secondary size? A question for your 16 inch as well.
Personally I have given up on building and did get cured from aperture fever, very happy with a 6 inch refractor.
The popcorn is done. But my, was it an informative discussion. Thanks to
all the contributors. I was too "yella" (yellow for you yankees) to jump in....
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Tuesday, October 29, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
It will for certain be a different view than the Grim. I would still like to hear people's impression anyway. Let's hope Mike is willing to set it up for a 3 or 4 hour SPOC star party.
My apologies for the error in light gathering vs resolution, you can put the popcorn away Matt.
The 41 inch aperture comes from the rule of thumb that resolution is approximated by the diameter of the primary minus the diameter of the secondary. That is 41 inches, and is an approximation of the resolution. The light gathering power, however is equal to the square of the primary minus the square of the secondary. That is NOT 41 inches, but is very close to a 64 inch scope.
These are not new rules, and I am certain that Mike has looked at them multiple times. He is not in the dark - well, all astronomers are up in the night I guess. I am sure that Steve knows all about the tradeoffs employed in this scope as well. This has got to be a fantastic telescope, and will do really well against any other amateur scope available including the Grim.
Just out of curiosity, what is the diameter of the secondary in the Grim scope?
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 2:17 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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What are you looking for in a focuser, Erik? I have several on-hand and could possibly save you some bucks. On Wed, Oct 30, 2013 at 10:41 AM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Yup, with a wife and family you generally need to be practical. I would certainly suggest your 16 to Rich. I do live near your house and have thought about checking out one of the sessions. My only possible project is upgrading my focuser, which mainly just requires cash.
Have my eye on the moonlight focusers and they have back plates that would easily mount on my tube assembly. Astro projects are low on my priorities at this point, the stars are not going any where anytime in the foreseeable future. My Jaegers with a JMI Moto Focus works fine for now, I mainly want to do it for cosmetic reasons.
What are you looking for in a focuser, Erik? I have several on-hand and
could possibly save you some bucks.
On Wed, Oct 30, 2013 at 10:41 AM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Yup, with a wife and family you generally need to be practical. I would certainly suggest your 16 to Rich. I do live near your house and have thought about checking out one of the sessions. My only possible project is upgrading my focuser, which mainly just requires cash.
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and what about a 40 inch with a 5 inch secondary.
Or how about a 70 inch f4 with a 10 inch secondary. Please share the math, my telescope building texts are buried away. The motors will be a good addition. I don't understand your "true aperture" claim. It makes no sense.
The aperture is 70 inches with the resolution of a 70 inch scope.
The clear surface area of the 70 inch with a 29-inch secondary is 3,188 square inches. The clear surface area of a 40 inch with a 10-inch secondary is 1,178 square inches.
Yes, it does have a very small true field even at a 7mm exit pupil. Mike knows this, knew it well ahead of time.
He plans to add motor drives for tracking.
The usable magnification range is a low of about 280X up to whatever the seeing will allow, but probably less than 400X.
Again, Mike knew this in advance.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
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Erik, I haven't done the math so these numbers could be off a tad. But not much. I'm running short of time so if someone else wants to do it to the inch before I can, go for it. A 40 inch Newtonian with a 5 inch secondary would have to be about an f/8 or slower. That means about a 24-foot-long telescope. The ladder needed to observe objects near the zenith would have to be about 12 feet taller than the ladder needed with the 70-inch folded configuration. Compromises must be made, I think Mike made some good decisions with the mirror. On Tue, Oct 29, 2013 at 2:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
and what about a 40 inch with a 5 inch secondary.
Or how about a 70 inch f4 with a 10 inch secondary.
Please share the math, my telescope building texts are buried away.
The motors will be a good addition.
A 70 inch with a 10 inch secondary in a Newtonian configuration would have to be of similar f-ratio, f/8-ish, or over 45 feet long with the eyepiece somewhere near 40 feet. Again, a too-tall ladder and probably unstable in any kind of breeze at all. On Tue, Oct 29, 2013 at 2:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Or how about a 70 inch f4 with a 10 inch secondary.
Chuck, I must admit that I was taken back by the size of the secondary. However, after doing the math I think the tradeoffs have been made very well. I look forward to have a peek through the behemoth. It should be a real treat. From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 3:43 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter A 70 inch with a 10 inch secondary in a Newtonian configuration would have to be of similar f-ratio, f/8-ish, or over 45 feet long with the eyepiece somewhere near 40 feet. Again, a too-tall ladder and probably unstable in any kind of breeze at all. On Tue, Oct 29, 2013 at 2:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Or how about a 70 inch f4 with a 10 inch secondary.
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yes, he adapted well to the optics he bought.
Chuck,
I must admit that I was taken back by the size of the secondary. However, after doing the math I think the tradeoffs have been made very well. I look forward to have a peek through the behemoth. It should be a real treat.
From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 3:43 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
A 70 inch with a 10 inch secondary in a Newtonian configuration would have to be of similar f-ratio, f/8-ish, or over 45 feet long with the eyepiece somewhere near 40 feet. Again, a too-tall ladder and probably unstable in any kind of breeze at all.
On Tue, Oct 29, 2013 at 2:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Or how about a 70 inch f4 with a 10 inch secondary.
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The resolution is indeed more like a 41 inch scope, but the light gathering power is equivalent to a 64 inch unobstructed apreture scope. This certainly will do better than the Grim by almost a magnitude. Interestingly, if the secondary mirror were only 20 inches in diameter, the light gathering power would only increase by about 10%. I believe Chuck referred to this a day or so ago. From: Erik Hansen <erikhansen@thebluezone.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 1:29 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are. The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute. True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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Brent, why is that? Because of atmospheric limitations? Increased aperture = increased theoretical resolution. Large professional telescopes have very large secondary obstructions yet enjoy better resolution. We are great bunch of armchair quarterbacks, aren't we? It must be remembered that the telescope was built around a serendipitous mirror acquistion. Mike didn't have the option of "shopping" for any desired diameter. On Tue, Oct 29, 2013 at 2:30 PM, Brent Watson <brentjwatson@yahoo.com>wrote:
The resolution is indeed more like a 41 inch scope, but the light gathering power is equivalent to a 64 inch unobstructed apreture scope. This certainly will do better than the Grim by almost a magnitude.
Interestingly, if the secondary mirror were only 20 inches in diameter, the light gathering power would only increase by about 10%. I believe Chuck referred to this a day or so ago.
I think it is more correct to say it has the magnification of a 70inch scope. Magnification does increase resolution to a point, they are 2 different things.
The resolution is indeed more like a 41 inch scope, but the light
gathering power is equivalent to a 64 inch unobstructed apreture scope. This certainly will do better than the Grim by almost a magnitude. Interestingly, if the secondary mirror were only 20 inches in diameter, the light gathering power would only increase by about 10%. I believe Chuck referred to this a day or so ago.
From: Erik Hansen <erikhansen@thebluezone.net> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Tuesday, October 29, 2013 1:29 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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Eric, that is dead wrong. You are getting the resolution of a 70" and the light gathering power of a 63.7" scope. On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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-- Siegfried
Siegfried, in my opinion, Erik's only misstep was equating an obstructed 70" scope to an unobstructed 41 inch. Large unobstructed telescopes are not practical. It would be better to compare apples to apples and just leave the secondary obstruction out of any arguments. Keep the playing field level. There's nothing to be gained from downgrading a particular configuration because it isn't a theoretical, unobtainable best case. The hypothetical 63.7" scope if obstructed similarly would have even less light-gathering power. The same argument can be made for resolution. Don't compare large obstructed reflectors to large unobstructed reflectors unless it's just a mental exercise. Otherwise the only practical information will come from talking about small shiefspieglers and refractors, entirely different animals from huge, fast reflectors. On Tue, Oct 29, 2013 at 6:22 PM, Siegfried Jachmann <siegfried@jachmann.org>wrote:
Eric, that is dead wrong. You are getting the resolution of a 70" and the light gathering power of a 63.7" scope.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net
wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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-- Siegfried _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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The hypothetical 63.7" would be an unobstructed aperture and assumes 100% light transmission in both systems. The formula taking diameter of the primary less the diameter of the secondary gives an approximation for the system contrast, not resolution. The 70" would therefore have the planetary contrast of a 41" unobstructed telescope. The resolution depends strictly on the aperture, otherwise interferometers would make no sense. Given all else is equal, an unobstructed telescope of X aperture will have the same resolution as an obstructed telescope of the same aperture. On Tue, Oct 29, 2013 at 6:48 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Siegfried, in my opinion, Erik's only misstep was equating an obstructed 70" scope to an unobstructed 41 inch. Large unobstructed telescopes are not practical. It would be better to compare apples to apples and just leave the secondary obstruction out of any arguments. Keep the playing field level. There's nothing to be gained from downgrading a particular configuration because it isn't a theoretical, unobtainable best case.
The hypothetical 63.7" scope if obstructed similarly would have even less light-gathering power.
The same argument can be made for resolution. Don't compare large obstructed reflectors to large unobstructed reflectors unless it's just a mental exercise. Otherwise the only practical information will come from talking about small shiefspieglers and refractors, entirely different animals from huge, fast reflectors.
On Tue, Oct 29, 2013 at 6:22 PM, Siegfried Jachmann <siegfried@jachmann.org>wrote:
Eric, that is dead wrong. You are getting the resolution of a 70" and the light gathering power of a 63.7" scope.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net
wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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-- Siegfried _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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-- Siegfried
Resolution and light-gathering are two different critters. That's why interferometry works with telescopes operated in tandem. -- Joe On Tuesday, October 29, 2013 7:26 PM, Siegfried Jachmann <siegfried@jachmann.org> wrote: The hypothetical 63.7" would be an unobstructed aperture and assumes 100% light transmission in both systems. The formula taking diameter of the primary less the diameter of the secondary gives an approximation for the system contrast, not resolution. The 70" would therefore have the planetary contrast of a 41" unobstructed telescope. The resolution depends strictly on the aperture, otherwise interferometers would make no sense. Given all else is equal, an unobstructed telescope of X aperture will have the same resolution as an obstructed telescope of the same aperture. On Tue, Oct 29, 2013 at 6:48 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Siegfried, in my opinion, Erik's only misstep was equating an obstructed 70" scope to an unobstructed 41 inch. Large unobstructed telescopes are not practical. It would be better to compare apples to apples and just leave the secondary obstruction out of any arguments. Keep the playing field level. There's nothing to be gained from downgrading a particular configuration because it isn't a theoretical, unobtainable best case.
The hypothetical 63.7" scope if obstructed similarly would have even less light-gathering power.
The same argument can be made for resolution. Don't compare large obstructed reflectors to large unobstructed reflectors unless it's just a mental exercise. Otherwise the only practical information will come from talking about small shiefspieglers and refractors, entirely different animals from huge, fast reflectors.
On Tue, Oct 29, 2013 at 6:22 PM, Siegfried Jachmann <siegfried@jachmann.org>wrote:
Eric, that is dead wrong. You are getting the resolution of a 70" and the light gathering power of a 63.7" scope.
On Tue, Oct 29, 2013 at 1:29 PM, Erik Hansen <erikhansen@thebluezone.net
wrote:
I was not suggesting a smaller secondary, I was suggesting a smaller primary with a more efficient design.> The true aperture is 41 inches, so you are getting the resolution of a 41 inch scope, my point is a 45 inch primary with a more conventional secondary would give same light gathering with probably same ladder height as a 70 inch with a 29 inch secondary. I doubt it puts the Grim to shame, it would be interesting to compare the 2 at SPOC, and hear what the comments are.
The other issue, is what is the largest field of view with the scope? With some eyepieces any object centered will not be there long. The time it takes someone to climb down the ladder and another one up, the object will be out of the field of view....will they have more than a minute or less than a minute.
True, but a smaller secondary would also mean a taller ladder. As built,
the observing position when pointed at the zenith is only about as high as you'd need to go with the 22" that Brent built.
Reducing the secondary diameter also only gains a very small percentage of the total area of the 70" mirror.
And the diffraction effects from a 40% obstruction won't be an issue with deep-sky objects, and should be offset by the increased resolution of a massive 70-inch aperture.
There are always trade-offs.
On Tue, Oct 29, 2013 at 12:45 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
of course the draw back is you get a shorter tube but a 40% obstruction of the primary, probably could have a used a smaller mirror, to reduce tube length, and get similar light gathering.
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Got a 16" that is... And it gets used often, so it is in great condition. Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Rich Allen Sent: Monday, October 28, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter Are any of these 20 and 24 inch scopes for sale? :) Rich Allen On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
_______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options". This message and any attachments are solely for the use of intended recipients. The information contained herein may include trade secrets, protected health or personal information, privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. If you are not an intended recipient, you are hereby notified that you received this email in error, and that any review, dissemination, distribution or copying of this email and any attachment is strictly prohibited. If you have received this email in error, please contact the sender and delete the message and any attachment from your system. Thank you for your cooperation
is it for sale? In my opinion 16 inches is just about the cut-off for practical scope.
Got a 16" that is... And it gets used often, so it is in great condition.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Rich Allen Sent: Monday, October 28, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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Yes, it is for sale. Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Monday, October 28, 2013 5:55 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
is it for sale? In my opinion 16 inches is just about the cut-off for practical scope.
Got a 16" that is... And it gets used often, so it is in great condition.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Rich Allen Sent: Monday, October 28, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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Why?
Yes, it is for sale.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Monday, October 28, 2013 5:55 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
is it for sale? In my opinion 16 inches is just about the cut-off for practical scope.
Got a 16" that is... And it gets used often, so it is in great condition.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Rich Allen Sent: Monday, October 28, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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Thanks for the kind words, Chuck. You are right, I am making a 21". Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Monday, October 28, 2013 8:03 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter Not speaking for Mat, but I know he's building a 21-inch at present. He's an accomplished ATM and master mirror maker. On Mon, Oct 28, 2013 at 5:54 PM, Erik Hansen <erikhansen@thebluezone.net>wrote:
Why?
Yes, it is for sale.
Mat
_______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options". This message and any attachments are solely for the use of intended recipients. The information contained herein may include trade secrets, protected health or personal information, privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. If you are not an intended recipient, you are hereby notified that you received this email in error, and that any review, dissemination, distribution or copying of this email and any attachment is strictly prohibited. If you have received this email in error, please contact the sender and delete the message and any attachment from your system. Thank you for your cooperation
Because I am making a larger one. Mat -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Monday, October 28, 2013 7:55 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Why?
Yes, it is for sale.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Erik Hansen Sent: Monday, October 28, 2013 5:55 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
is it for sale? In my opinion 16 inches is just about the cut-off for practical scope.
Got a 16" that is... And it gets used often, so it is in great condition.
Mat
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Rich Allen Sent: Monday, October 28, 2013 4:53 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Journey to the 1.8 meter
Are any of these 20 and 24 inch scopes for sale? :)
Rich Allen
On 10/28/2013 1:12 PM, Erik Hansen wrote:
SLAS members have many 20 and 24 inch scopes you rarely see used any more. What about a stripped-out bus? ;-)
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_______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options". This message and any attachments are solely for the use of intended recipients. The information contained herein may include trade secrets, protected health or personal information, privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. If you are not an intended recipient, you are hereby notified that you received this email in error, and that any review, dissemination, distribution or copying of this email and any attachment is strictly prohibited. If you have received this email in error, please contact the sender and delete the message and any attachment from your system. Thank you for your cooperation
I agree. But then, this isn't an official SLAS board, and I don't know if individuals can offer such a thing. Mike may also prefer to keep the scope at his home. So much for the speculation. From: Joe Bauman <josephmbauman@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Sunday, October 27, 2013 11:28 PM Subject: Re: [Utah-astronomy] Journey to the 1.8 meter I don't think SLAS should put up a building just to house anyone's private scope. My 2 cents' worth. -- Joe
participants (10)
-
Brent Watson -
Chuck Hards -
Erik Hansen -
Hutchings, Mat -
Joe Bauman -
M Wilson -
Rich Allen -
Siegfried Jachmann -
Wayne Sumner -
Wiggins Patrick