Quote:
Originally Posted by multiweb
Visually I couldn't tell how mirror spacing affects field illumination but if you stick a CCD at the back, shortening the distance between primary and secondary will increase vignetting. Having said that if the spacing primary/secondary is shorter than recommended you will see increased spherical aberration in your in/out of focus airy discs. You lose the symmetry and some rings get brighter so the light is no longer focused at the same point.
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Thanks Marc, at this stage the scope is visual only, for the Encke Gap Challenge, etc, so I actually don't have a camera to stick on it (other than a DSLR), and I am wary of touching the primary adjustment, beyond normal tilt control to get an evenly lit ring all around my Cheshire, and final tuning with star testing.
As the scope uses a parabolic primary, and hyperbolic secondary, the risk of Spherical Aberration cannot come from the mirrors, other than positioning imho, and I have not noticed uneven ring brightness in my star testing to date.