#MK wrote:
f the F = 1900mm,

I wonder if he meant fl 900 (which would make it f/6)?

and a 6 inch mirror is 150mm, then is the F-Ratio: f/13 [roughly]?
Hence, it wouldn't be quite curved,

Could be left spherical, which makes it easier to make, but f/13 is a
bugger under the Foucault test. The shadows are very indistinct.


and whilst magnification would be high, would this be any good for
planetary observation

In theory it could be very good, as you could have a minute secondary.
Play with NEWT (ATM software on my web site) to see what I mean.


Best,
Stephen

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