[ATM] Newt imaging vs visual design tradeoffs -- ideas?

[Scott Carson <scottcarson@austin.rr.com>]

Looking for some recommendations for an 8" f/6 Newt that I'm assembling.

I'd like to be able to use the scope for both astrophotography and 
visual observing which of course have divergent size requirements for 
the secondary.  Seems 20% or less central obstruction (CO) [1.52" 
diagonal] is recommended for the best visual observing versus a +29% CO 
[2.14" diagonal] that I'll need to get adequate camera sensor 
illumination using my Canon 300D DSLR (27mm sensor frame).

So, I was hoping I could hear from others that have already been down 
this road? 

Design possibilities so far...  hoping someone has some better option(s)?

-- Two locations for the primary mirror plus two secondaries (one small 
and one large).  use a crayford focuser.  One setup optimized for 
imaging and one for visual use.   Suspect this solution would end up 
being a hugh "hassle" in the real world, ie, I'd probably seldom if ever 
go to the trouble of moving everything around not to mention the 
additional collimination time required.

--  Use a sled focuser with the camera attached very close to the sled 
surface to minimize the distance between the camera sensor and diagonal. 
  Based on some NEWT calculations, seems a 1.83" diagonal would be a 
decent compromise for imaging and visual use.  So far this design option 
seems most promising, but not sure how well the collimination can be 
maintained throughout the 2" - 3" focuser range which also moves the 
attached diagonal?   btw, I have perused the internet and located a 
couple of sled focuser implementations, but the examples are limited. 

--  Use one diagonal, low profile crayford focuser, and eyepiece 
extension tube(s) [for visual] and accept the compromises.  
Unfortunately the calculated vignetting with a 1.83" diagonal will be 
pretty signficant for my Canon 300D even using a low profile crayford.  
So I'd probably have to use a 2.14" diagonal and accept the visual 
observing compromises do to the larger CO.

--  build two scopes... much two expensive considering the divorce 
expenses!  :-)

Thanks for any recommendations you can give me.

Scott



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