can I convert a newtonian telescope to a schmitt-casegrain ?
I have a 10″ newtonian mirror in a semi-working home made telescope. Can I send the primary mirror to a lab and have them cut a hole in it to make a schmidt casegrain ? I know I need a special secondary concave mirror, but can they drill a hole in the primary mirror once its coated or do I have to pay for a new coating ?
I think you run a considerable risk of scratching the mirror when the hole is bored. Cassegrain mirrors are usually bored before grinding and polishing. Also, as stork5100 points out, the figure of a Newtonian mirror is wrong for a Schmidt-Cassegrain.
But the bigger difference is that Cassegrain systems are generally based on a short focal ratio primary. You could build a classical Cassegrain based on your Newtonian mirror, but it would probably be f/30 or longer. The primary in a typical SCT is around f/2.
You’re also going to have to figure a way to make that corrector plate if you want a Schmidt-Cassegrain. (And the secondary is convex, not concave.)
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