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[ATM] 3 Inch Off Axis Schmidt Camera?
Hello! I've just finished my 11 inch classical cassegrain. As I consider
my next project, I am considering what to do with a 112mm blank. Before
beginning the cassegrain project, for a separate project that I have since
abandoned, I ground the blank and have 85% polished it to f1.5.
The mirror is too small for a classical Schmidt camera - the corrector
would be about 75mm, and 35mm film would create up to 60% obstruction.
So, I wonder if I could use this blank for an off-axis schmidt camera.
The corrector plate would have to be polished as if the primary was about
275mm, giving the corrector a size of about 180mm, which I could then trepan
down to the size I would need. An advantage to an off-axis design would be
that it would bring the film out of the telescope tube for easier handling
and smaller filters could be used. Additionally, I could focus the system
like a view camera, using a loupe-type magnifier to focus bright stars or
planets on the film holder.
Questions:
1) What would the image circle of a 75mm Schmidt camera be? Would it
even cover 35mm film?
2) Would a radius of curvature of the film of about 175mm be too
severe - would the film crinkle in the holder?
3) What would the sky coverage of such a system be?
4) How close to perpendicular to the light path can the corrector
plate and film cassette be in order to avoid unacceptable astigmatism? I
think I can focus the
primary onto the film well enough, but I haven't satisfied myself
that I can align the film holder cassette and the corrector plate to within
tolerances to avoid
astigmatism.
5) Most importantly, is such a system reasonably doable?
Thank you for your help. Best regards.
Mike
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