Is there some way that the rest of us can get removed from this discussion?  I mean...I love astronomy...I even love you guys!  But...
K.C. Johnson
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John.Zeigler@FranklinCovey.com
Sent by: uvaa-bounces@mailman.xmission.com

10/01/2003 04:03 PM
Please respond to Utah Valley Astronomy Association

       
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        Subject:        RE: [UVAA] Scope Length



Jim,
 
No problem.  I too like the longer focal length scopes, BUT when you go above 16" diameter, you need to lower the F# to keep the scope to a reasonable overall length.  Personally, I do not like to climb much over four steps up a ladder to look through the scope.  Once I get higher than that, I get nervous when looking through the eyepiece.  The BOB or Big Ogden Bucket has a focal length just a bit over 10', and that was a bit too high for me.  So I have arbitrarily chosen a focal length about 100 - 110" that I try to design all my scopes under.  Granted the smaller scopes will be much shorter, but once I go up in aperture, I shoot for an F# that will keep the focal length below this number.  Now once I get my large grinding machine completed, I may do a mirror as large as 36 - 40", at which time I will have to go beyond my 110" limit.  But mostly we will be doing mirrors and ! kits under 24" diameter.
 
Yes I know Brent.  He taught me how to grind mirrors, and encouraged me to teach a class.  We have now taught about 70 people in the valley how to make their own telescope.  We teach the entire process from grinding their own mirror and help them build the rest of the telescope assembly.  Our first class had 47 people in it, and we were overwhelmed with the sheer size of the work involved.  Some of those people did not complete the class or their scopes, but the majority of that class, about 38-40 people came out of the class with completed scopes.  Now we limit our classes to 10-20 people so we can give each person the personal attention they need.  Our current class has people building scopes ranging in size between an 8" F6 and a 18" F6 scope being built specifically for double star observing.
 
I hope this information helps.
 
John Zeigler
www.JohnsTelescopes.com
www.MirrorKits.com
 
-----Original Message-----
From: Gibson, Jim [mailto:gibson@dpg.army.mil]
Sent: Wednesday, October 01, 2003 1:27 PM
To: 'Utah Valley Astronomy Association'
Subject: RE: [UVAA] Scope Length
John
You know, I am really glad that I asked you about this. You gave me a lot of meat to chew on.  My fantasy is to have a 36" trailer mounted scope with a lazy-boy recliner attached parallel to the scope near the eyepiece all run by hydraulics using a joystick for maneuvering.
 
OK, now back to reality. I would love to see your mount when it's done.
 
I checked with Nova and Steve Dodds can make a 22" f6, no problem. Go to 24" and there is a big jump in price. I checked with Astrosystems and they can make a 22" f6 truss tube Dobson Telekit just like Rich Tenney's f6.25 16" scope. I have a van to lug this thing around in. The juiciest piece of meat you gave me is:
 
"Even with a 32mm super wide field eyepiece, you will have 103 power and somewhere around 1/2 of a degree true field of view."
 
My 22mm Neagler gives me about 96x (12.5" mirror, 2220mm focal length) but I don't know what the true field of view is off hand. The 41mm Panoptic (which I don't own) would give me about 81x in the 22" (3352 focal length) and hopefully as much field of view as the 22mm does in my 12.5" scope. If that is true, I can live with that. The North American Nebula and the Vail Nebula would be about the only things I have seen so far that would require me to pan around. You are right I am most interested in DSO.
 
I don't know if you know Brent Watson. I took a class from him when I built my 12.5" scope and a lot of his thinking has rubbed off on me. He likes high focal rations. In your comment"
 
"Properly figured, a 22" F4 scope"
 
To me you jumped right to the bottom of the f scale when you mentioned F4. I prefer to consider the longer focal ratios then grudgingly slide down into practicability, which your comments are doing to my thinking and I appreciate that. I tend to like higher contrast and less coma problems all better in longer focal length.
 
You also made me think - I am sixty now, how long can I carry a 22" mirror mounted in a box around?  I know my 12.5" mirror is hefty. The 22" mirror is 2" thick but I don't know how much it weighs.
 
I would probably be better off going back to a 20" mirror or maybe even 18".  I looked through Lowel Lyon's 20 f4.5 at Wolf Creek last week end and it was very good. I always love looking at stuff through Rich's scope too. So, you are making me think and I thank you for that.
 
Jim
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