RE: ATM 6in F/10

[Klaus Peter Schroder <schroder@ast.cam.ac.uk>]

Hi David,

you were asking for an optimum size of mirror for
planetary viewing with F=60" fixed.

In my opinion, I would go (again, in my own case) for
10" f/6. This is still convenient to use (20-25 lbs
of OTA-weight for a leight-weight truss to which mirror
contributes 10 lbs, 30-35 for a rigid truss for deep-sky
astrophotography as in my case) - on the other hand, you
have sufficient resolution for even those rarer nights
of good seeing. I can do 350x on planets then and 550x
on the moon (mostly, however, seeing only permits 220x
and 350 times, respectively). As pointed out her very
often, it is however essencial to get a good surface,
say, twice as good as the l/4 wavefront criterion or so.

Just my opinion on this matter.  :-)

Cheers, Klaus-Peter