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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