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Hello James,
I asked Mark Suchting a similar question when I picked up my 12.5" conical mirror from him.
From memory there were a couple of issues to consider with conicals:
- The shape of the conical itself, in that you can design conicals with different edge thicknesses which affects their flexure. I believe that earlier conical mirrors may have had thicker edges, but of course that means heavier mirrors and is probably why they have trimmed them down.
- The difficulty of figuring a conical mirror due to flexure. Again from memory, I think that a 16" is near the limit of what can be achieved with current conical blanks (with some difficulty). I think that this may have been more the determining factor rather than the flexure in the actual mounting and use of the conical mirror in a telescope.
Mark, please jump in if I have gotten anything wroing here ...
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