Re: [ATM] 7 inch spherical mirror

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

On Mon, 14 Apr 2008, Richard F.L.R. Snashall wrote:

> David Harbour wrote:
> > Is the stop the entrance pupil, and if it is, where is it located?
> Since there are no "optics" in front of it, the entrance
> pupil is located where the aperture stop is.  For the
> analysis I've been doing, that is at the very edge of the
> mirror, at its full diameter.

Well, OK. I was thinking David was asking where the aperture
stop was situated in terms of distance from the primary. For
Schmidts (those I know of), this is placed at the radius of
curvature. This stop is adjustable for a lensless Schmidt.
Looking back at what I wrote earlier on this thread, maybe
the correct way to state this is that the lensless Schmidt
can be stopped down to the point where spherical aberration
is reduced as much as desired.

I need to look back at some of my earlier simulations to see
how coma looks with the two surface profiles (parabola
vs sphere) when they are both stopped down. So that we are
all on the same page, I based some of my thinking on this
article, which is based on an F/2.5 primary (system F/ratio
will be higher):

Fawdon, P., Gavin, M. A lensless Schmidt camera. J. Br.
Astron. Assoc. 99(6):292-95. 1989

For the moment, you can download it from my website:

http://www.canit.se/~dlwebb/catadioptric/310schmidt/fawdon.JBAA.1989.pdf



Dominic

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