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The C8 has an opening of 38mm in the baffle tube. The maximum unvignetted field the instrument can give is 1.2 degrees visually, and 1.08 degrees photographically. The maximum size field of a 1-1/4" eyepiece yields 0.86 degrees.
So there are two ways to achieve the maximum field: a focal reducer with a 1-1/4" diagonal, or a 2" diagonal. If you use a 2" diagonal, you will have to keep the field stop of the eyepieces the size of a 35 Panoptic or smaller. The eyepieces with larger field stops (31 nagler, 40 SWA, 40 Konig, 55 Plossl) will visibly vignette (the edge of the field will appear darker).
If you choose the focal reducer, you can achieve the maximum field of view with a 32 Plossl or any 1-1/4" eyepiece with the maximum field stop for that diameter (e.g.24 Panoptic, 18mmUWA, 35 Ultima, etc.). The focal reducer has other benefits: it flattens the field as well as reducing the focal length 37%, it costs less than a 2" diagonal and eyepieces, it allows the use of a less-expensive 1-1/4" diagonal and eyepieces. The original diagonal with the scope is poor, so I'd upgrade the diagonal whichever way you go to a dielectric-coated model.
Don't think about using a focal reducer with 2" eyepieces, as the reducer limits the illuminated field to 24-27mm. This would cause vignetting with nearly all 2" eyepieces longer than about 22mm or so.
True field = 57.3 x (field stop/focal length of scope). Solving for maximum field stop says it's about 42mm for a 2" eyepiece, and 26.8mm for a 1-1/4" eyepiece used with a focal reducer. That means all 1-1/4" eyepieces should work with a reducer. That's for visual use, where sensitivity to vignetting is low.
Photographically, the field stop limits are : 2"--38mm, 1-1/4" w/FR--24mm. 35mm film would work with the 2" connection, most CCDs would work with the 1-1/4".
Hope that helps you see the big picture (pun intended).
Don
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