Re: [ATM] Corrector/reducer for a fast Newtonian

[David Whysong <dwhysong@gmail.com>]

On 10/15/05, Michael Peck <mpeck1@ix.netcom.com> wrote:
> Are you sure this is specified right?
...
> In OSLO putting a dummy surface at the Gaussian focus will make it
> extend ray diagrams to the focal plane

I think this was done on OSLO.

> If I entered this design correctly it looks not so good to me. It's
> producing geometric spot sizes around 20 microns and is short of
> diffraction limited by about an order of magnitude.

I noticed that. I was comparing it to the Wynne corrector in his
paper, which is only slightly better on-axis. You're right, this isn't
so good.

> Go to the searchable ATM list archives at
> <http://astro.umsystem.edu/atm/search.html> and try a search on
> "hyperbolic astrograph". If the primary can be made somewhat
> hyperboloidal a much simpler field corrector can be designed. In fact
> Dave Rowe posted one for a similar sized telescope just a couple months ago.

I've seen it, and it looks great. But can I can get an overcorrected
mirror of this size and focal ratio from a manufacturer (on purpose)?
I have neither the experience nor facilities for grinding my own
primary mirror.

> As for focal reduction, why not save for a larger format camera instead?

I can do that - and probably will, but most larger format cameras have
substantially lower sensitivity (compared with Kodak ME chips), and
much higher price. And the field of view is limited by the coma
corrector aperture stop, which can really hurt if the focal length is
longer than you need. Even with a larger camera, it would be
beneficial to have a small image scale (and small pixels) to get the
widest possible field of view.

--
David Whysong
Astrophysics Group
University of California, Santa Barbara
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