I would not want to discourage anyone from grinding own mirror, but as I recall the 13.1 Coulter was an f 4.5, maybe to fast for first attempt. The Coulter mirror was outstanding, the tube assembly not so much. I think someone recommended using it for a planter. I would also recommend thinking long and hard about where the focuser will be place for comfortable viewing. I have come to the conclusion that a 16" f5 would be my ideal. I would also not recommend building a large scope with another person. Make out a written contract if you do. Erik --- jimgibson00@yahoo.com wrote: From: Jim Gibson <jimgibson00@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free Date: Wed, 7 Jan 2009 03:51:27 -0800 (PST) Jay, If Brent Watson was still around he could probably tell you exactly, but I think Chuck’s amount was probably about right. I took a class from Brent about 6 – 7 years ago and as I remember it cost like $350 - $400 for the mirror kit, another couple hundred for the Craford (sp?) focuser, $75 - $100 for either the 1/4th or 1/8th wave secondary, and of course you will need at least 1 lens. But lenses are like potato chips; you can’t eat just one. We started our class in January and ordered our stuff. I got a 12.5” mirror. It took a few weeks for delivery and came with all the materials for grinding accept the grinding wheel which we made ourselves. We ground our mirrors one night a week (7 -10 pm) under Brent’s tutelage and finished our mirror and scopes, which we built at home (Carcass part), by May. Oh yeah we also made our own Ronchi (sp?) tester which you need to complete the figuring of the mirror. I kept copious notes, but like most things, there are stored away in a box somewhere…lol. I guess my point is, if you have never made a mirror before, don’t do it alone. The other point is that making your own is a very rewarding experience. If it costs you about the same either way, making a scope at least once in your armature career, I think, is very worth it. But you need the right guidance. jg --- On Tue, 1/6/09, Jay Eads <jayleads@gmail.com> wrote: From: Jay Eads <jayleads@gmail.com> Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free To: "Utah-Astronomy" <utah-astronomy@mailman.xmission.com> Date: Tuesday, January 6, 2009, 7:47 PM How hard and how long would it take to make the mirror (yes, I'm attending the SLAS meeting this month) for someone who hasn't done it before? What would the estimated cost be for the materials for the mirror? Is there anyone here or in SLAS who would be available for advice? I'm interested in making my own mirror but it depends on cost (you know, the wife/CFO). If all these add up I'd take the dob tube and the rocker box. I would assume the first step would be to make the primary mirror, then to get a secondary and a focuser. So I guess if this is a project that I can assemble over time as money comes up, I'd try it. Thanks, Jay On 2009-01-06 22:56, Patrick Wiggins wrote:
I understand the "how to make a mirror" video that we were not able to screen at the solstice party last month is going to be shown at this month's SLAS meeting.
Perhaps after watching that several people will want the carcass to use with their new homemade mirror.
Grins,
patrick
On 06 Jan 2009, at 09:48, Josephine Grahn wrote:
We have the empty carcass of a 13.1 inch blue Coulter dob, if anyone would like it. No optics, no focuser, just the empty tube and rocker box. It does have the mirror cell, but no primary mirror, and it does have the support for the secondary, but no secondary mirror. Free, you just have to pick it up. Located East side SLC.
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
Warning--- Please don't take this toungue-in-cheek comment the wrong way. WOW! Who would have thought that an offer of a "dismembered carcass" would generate so much discussion? I love this list! :) Tyler _____________________________________________
On Wed, Jan 7, 2009 at 10:17 AM, Tyler Allred <tylerallred@earthlink.net>wrote:
WOW! Who would have thought that an offer of a "dismembered carcass" would generate so much discussion? I love this list! :)
Well, assuming it's not a mastodon...
When I took the class from Brent Watson he wanted all of us (about 5 or 6 in the class) to make f8 or better scopes. Brent loved long bugger scopes and rightfully so I would say. Someone more qualified than I can tell you all the benefits of a long scope beside increased contras and increased power, but I recall there a lot of benefits…oh yeah collimation is easier too. Most everyone in our class wanted to make short (fast) scopes mainly because nobody wanted to use a ladders. I went with an f7 (the longest focal length in class) so with a 12.5” mirror which would be 87.5” focal length plus some extra I believe my sono tube was about 96” long. How do you get 96" in the car you ask? Can you get 48” in your car? I could deal with 48” so I cut the sono tube down so I had 2 48” sections. I still had sono tube left over because if I remember right it was about 12’ long when I bought it. From the extra piece I cut a 1 foot section then slit it down length wise, took some extra material out till I could get it to fit inside one of the 48” sections forming a sleeve. I went to the hardware store and got some of those clampy thingys like on a metal tool box and put 3 of them on to fasten the 2 scope pieces together. It worked great! I have a ladder and a step stool with long hold onto bars, but a lot of the time I use nothing or the step stool. Yeah, right now I would need the ladder to see M31. I love the way my scope performs. I have never been sorry about going f7, but sometimes I do think I should have listened to Brent and gone f8. Chuck Hards or someone can tell you stories about Brent fastening his like f10 to the top of his car and having it come off the tope while heading down the freeway…hehe. The mirror was just fine. Brent had a couple of 12.5” f12 or something scopes in his hanger where we took the class. The good old days. jg --- On Wed, 1/7/09, Tyler Allred <tylerallred@earthlink.net> wrote: From: Tyler Allred <tylerallred@earthlink.net> Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free To: "'Utah Astronomy'" <utah-astronomy@mailman.xmission.com> Date: Wednesday, January 7, 2009, 10:17 AM Warning--- Please don't take this toungue-in-cheek comment the wrong way. WOW! Who would have thought that an offer of a "dismembered carcass" would generate so much discussion? I love this list! :) Tyler _____________________________________________ _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
Hi Everyone, OK, I finally got this working on The Tribune's Web site. To visit the Trib's astronomy blog, called The Final Frontier, please visit http://blogs.sltrib.com/frontier The Tribune is looking at cutting some of their blogs eventually, and they'll do so based on hits and interest among readers, so please, if you enjoy the blog, pass it along to friends and family, and visit often. While I can't promise daily updates, I'll do my very best to get news up as often as possible. I'm excited to get astronomical news out to everyone, and as always, I'll happily take any news tidbits or interesting happenings. Feel free to send those to my email address at smcfarland@sltrib.com. Thanks, and enjoy! Sheena McFarland State Government Reporter The Salt Lake Tribune 90 S. 400 West, Suite 700 Salt Lake City, UT 84101 Office: (801) 257-8619 Cell: (801) 510-5567 Fax: (801) 257-8525 smcfarland@sltrib.com
Nice job Sheena. --- On Wed, 1/7/09, Sheena McFarland <smcfarland@sltrib.com> wrote: From: Sheena McFarland <smcfarland@sltrib.com> Subject: [Utah-astronomy] The official Tribune Astronomy Blog To: "Utah Astronomy" <utah-astronomy@mailman.xmission.com> Date: Wednesday, January 7, 2009, 11:26 AM Hi Everyone, OK, I finally got this working on The Tribune's Web site. To visit the Trib's astronomy blog, called The Final Frontier, please visit http://blogs.sltrib.com/frontier The Tribune is looking at cutting some of their blogs eventually, and they'll do so based on hits and interest among readers, so please, if you enjoy the blog, pass it along to friends and family, and visit often. While I can't promise daily updates, I'll do my very best to get news up as often as possible. I'm excited to get astronomical news out to everyone, and as always, I'll happily take any news tidbits or interesting happenings. Feel free to send those to my email address at smcfarland@sltrib.com. Thanks, and enjoy! Sheena McFarland State Government Reporter The Salt Lake Tribune 90 S. 400 West, Suite 700 Salt Lake City, UT 84101 Office: (801) 257-8619 Cell: (801) 510-5567 Fax: (801) 257-8525 smcfarland@sltrib.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
Just looking at this new rendition of the Milky Way from Sheena’s blog: http://blogs.sltrib.com/frontier/uploaded_images/sig05-010-783325.jpg It looks like to me we are no longer part of the Orion spur but on a main arm. Anyone know? jg --- On Wed, 1/7/09, Jim Gibson <jimgibson00@yahoo.com> wrote: From: Jim Gibson <jimgibson00@yahoo.com> Subject: Re: [Utah-astronomy] The official Tribune Astronomy Blog To: "Utah Astronomy" <utah-astronomy@mailman.xmission.com> Date: Wednesday, January 7, 2009, 11:42 AM Nice job Sheena.
Advantages to long-focus Newtonians: 1. Larger diffraction-limited area at focal plane 2. Smaller secondary mirror for a given area of 100% illumination (less total diffraction) 3. Faster grind, easier to figure 4. More forgiving, easier to collimate (relates to #1, above) 5. Excellent performance using Plossl, ortho, and other simple eyepieces Advantages of short-focus Newtonians: 1. Short tube. This is only an advantage in large apertures, where a longer scope would necessiate using a ladder to reach the eyepiece. 2. Wider field and lower power using the same eyepiece as a longer-focus scope. This is more of a "trait" than an outright advantage. "Wide field" has been used as a marketing term across the board in visual astronomy, and it's not always desireable. It's an aesthetic quality only and valued differently by different observers. A planetary observer has little use for a 90-degree AFOV eyepiece. The biggest disadvantage of a short-focus scope is that coma increases alarmingly as the focal ratio drops below about f/5 in a Newtonian. The "sweet spot", or diffraction-limited portion of the focal plane, drops below an 1/8" circle at f/4. So if your wide-angle 2" eyepiece has a field stop that's about 47 or 48 mm across, only the very center of your field is tack-sharp. The way to combat this is with expensive eyepieces such as Naglers and others that are specifically designed to correct coma. Another option is a coma corrector that allows most any eyepiece to be used, as well as correcting the focal plane for imaging. This is what I personally use, a 20-year-old Lumicon coma corrector. The disadvantage to using expensive "prescription" eyepieces, apart from cost, is reduced throughput from six, seven, eight or more elements in the eyepiece. Be sure to buy eyepieces with good anti-reflection coatings to minimize this. An enhanced coating on the mirrors themselves also maximizes throughput. That said, reduced throughput really not much of an issue with large-aperture scopes (10" and larger). Brent knows that at f/8 or higher, a Newtonian becomes an incredibly sharp telescope and the views can be amazing. Going shorter means trading sharpness across the entire field for convenience. On Wed, Jan 7, 2009 at 11:04 AM, Jim Gibson <jimgibson00@yahoo.com> wrote:
When I took the class from Brent Watson he wanted all of us (about 5 or 6 in the class) to make f8 or better scopes.
participants (5)
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Chuck Hards -
Jim Gibson -
Sheena McFarland -
Tyler Allred -
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