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Schmidt Newtonian

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Posted by Robert May on June 19, 2006 01:27:08 UTC

I generally don't do raytracing of such a design as when you build it right, there is really no need to do so.
There is a calculator on the web for doing the calculations for a Schmidt corrector for the vacuum pan method and I'd suggest that you run the corrector dimensions through that to find out how much vaccuum to use if you haven't already done so. I'd suggest that you do the corrector on both sides for a mirror that short of a focal length as a single side will probably not be possible with any reasonable success. You want to keep the vacuum as low as possible to keep the glass from breaking.
The corrector, properly done will co9rrect the light rays so that a spherical primary can be used and will give fairly good images. Probably the biggest error that you will see is astigmatism way off from the center of the axis of the scope. Making the corrector incorrectly will, of course, bring coma into the field of view, either of the positive (normal Newt directions) or negative. You will know only after you have built the scope whether you did the corrector correctly.
I'd also suggest that you make the primary mirror a bit larger than the corrector as you are interested in not vignetting the image by the primary, an inch increase for every two inches of the image plane size desired.

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