Re: [APML] C9.25 (was: Another intro)

["Tom & Lou Krajci" <krajcit@3lefties.com>]

From: "Matt BenDaniel" <matt@starmatt.com>

> John Boudreau and Sean Walker have been imaging with a C9.25 for a couple
> months. They say its field is flatter than the other Celestron and Meade
SCTs
> they have used, but the field is not totally flat. They say it has less
> mirror-related focus shift and less thermal sensitivity, too.
>
> Some of the resulting images have been posted to
> http://mysky.org/mysky/?keyword=walker

Thanks!  Maybe it's not an urban legend after all.  ;-)

Hmmmmm...when an SCT has a flatter field and less thermal focus shift...my
first guess is that the secondary mirror has a lower multiplication factor.
Most commercial SCT's have a secondary with about 5x...maybe the C 9.25's is
about 3x?

Tom Krajci

PS.  Yup, it can take some expensive optical designs to get a truly flat,
fairly good sized field.


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