Re: [ATM] 7 inch sphereical mirror

[Dominic-Luc Webb <dlwebb@canit.se>]

On Sun, 13 Apr 2008, David Harbour wrote:

> > Perhaps another way of answering this question is to decide over what
> > field of view one would want a decent visual image.  I may be mistaken,
> > but won't coma be an issue here?
> > Matt

Did I miss something? My understanding was that coma is the
price paid when you make a parabola. Spherical aberration is
what you get with a sphere. At some point, the trade-off
between these two defects should be considered. Coma increases
as one progresses off axis. I think an F/10 can perform very
well. This scope is in the range of a lensless Schmidt, and
there are some very impressive images out there of objects like
Andromeda galaxy covering something like 3 degrees of sky.


Dominic

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