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I think the term loosly refers to a scope weather it be Newtonian or any thing else has been optimized for Astrophotography in that the fully illuminated field created by a larger secondary will fully illuminate the larger imaging plain required.They also tend to be a shorter F number for faster imaging.This results in a larger than normal secondary ,not a concern for deep sky imaging but not desirable for planetary imaging.
Some times it is hard to get eyepieces to come to focus in an Astrograph as the imaging plain has been designed for a camera.
I have used a Clement focuser which has 3 inches of travel and does not protrude into the light path and has a low 1 inch profile and as such can just get my DSLR to focus with it racked all the way and to the other extream my TV 12mm Nagler I think , almost all the way out without using extensions or spacers.
With my old 12.5" Newtonian f6 it was optimised for planetary imaging with a smaleer secondary 17% If I can remember and as a result even with an optimised tube focuser design only had a 12mm fully illuminated field which is more than enough for smaller planetary cams and visual observing but not enough for a larger chip.
Astrographs quite often have other optical elements to correct for aberations and flat fielding ect ect.
Any way I have only dropped an eyepiece in the new scope twice ,it always has the camera attached.
Got some more RAW images from last night & have not had time to process them but just getting the feel for the scope and imaging times and seeing how the guiding is working. Still got some bugs there but here is another RAW converted to Jpeg and resised only.4 mins ISO800 D50
Mark
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