Telescope Reviews: Help with focal reducer for Celestron EdgeHD

I have tried to get an answer to this problem from Celestron and Astro-Physics without any good results. Maybe there is no answer possible, but I thought I would try here in this forum where there are probably some sharp scope builders and opticians hanging out.

As some of you know by now, Celestron is coming out with the EdgeHD line of scopes, which seem to be a standard SCT with a corrector lens of some kind inserted somewhere in the baffle tube to give a large corrected flat field at a point behind the scope. The scope is f/10, not the optimal ratio for imaging, and they plan to eventually come out with a reducer for the scope. Since no one knows how soon that might be, I would like to purchase the scope and use another brand of reducer for now.

Since the scope is a flat field corrected instrument, it seems to me that a reducer made for a flat field corrected scope like the petzval design or corrected RC scope should work with the C11 EdgeHD. The only problem I have is knowing where to place the non-correcting reducer along the light path. I understand that the optimal distance to chip from the physical back of the C11 is 144mm (5.75"). If I insert a non-correcting 0.75x focal reducer made by Astro-Physics which has a focal length of 700mm and requires a distance from reducer to chip of 175mm [(700 - 175) / 700 = 0.75], then where in the light path should it go to provide the reduction without deterioration to the image produced by the corrected optics of the EdgeHD scope? The way Astro-Physics has it set up is to place the reducer just behind the optical back of the C11's tube on standard C11's or anywhere in the light path of a non-corrected refractor.

So, not knowing what the corrector lens really does in this scope, can anyone make any general statements about reducing a corrected scope? Is is doable? Do people use non-correcting reducers on corrected scopes of other designs like Petzval refractors or corrected D-K designs? Are there any general optical principles that can be applied here to figure this one out?

Thanks for any help.

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Hunter Wilson| Lexington, Ohio

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