Re: [ATM] 32" Focal ratio

[Michael Lindner <mikell@optonline.net>]

On Tue August 2 2005 7:03 am, polaraligned wrote:
> Observatory Scope is very sucessful with 
> this design. 

Successful in what way? Perhaps you can ask them for names of clients to 
contact to ask about their experience using the scope? They should be happy 
to provide references.

On their web site they talk about being like a cassegrain so you can baffle it 
like a cassegrain (as if that were an advantage). Cassegrains are difficult 
to baffle, and do not perform as well as a similarly baffled newtonian 
because the light path is pointing straight up the tube - very hard to keep 
stray sky light from coming in. My friends who have SCTs are always 
complaining about poor baffling and low contrast. Right away that raises a 
red flag with me.

I would strongly advise you to tilt the secondary to the side rather than have 
it aim straight back at the primary (doesn't have to be a 90 degree tilt in 
the optical path, but at least get the focal plane outside of the path of 
incoming light). Aside from making it easier to baffle effectively, you can 
eliminate having to worry about temperature differences from your camera 
distorting the view.

Another thing is to think about what pixel size you will be using. Since you 
are designing the scope around the camera you can optimize the focal length 
for the pixel size and field of view you want.

Clear skies.
-- 
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net
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