Re: [APML] C 9.25 for AP?

["John Boudreau" <jeboud@mediaone.net>]

Hi Grant,

I took a few film shots this summer through a C9.25 that belongs to Sean
Walker. I'd say for an SCT, it's the way to go if you plan to shoot at f/10
only. I didn't try a reducer, but that's because some time ago I had seen
some reducer shots with one and the shots definitely had more problems with
a reducer than the typical SCT. These scopes are commonly used with reducers
for CCD work, but since the CCD chips are typically much smaller than 35mm
film, the resulting off-axis aberrations aren't really a problem there. I
was autoguiding off-axis with a Lumicon NEG. A full frame 400F result of
M27, focused about 1/4 field from center, is posted at:
http://people.ne.mediaone.net/jeboud/temp.htm

The big advantage of this scope for astrophotography is that with a
secondary magnification of about 3x, it's not as sensitive to focus change
due to a temperature drop during the exposure like a typical SCT with a 5x
secondary. I know that my 12" SCT doesn't beat it by much resolution-wise,
during a long exposure. And the stars images near the field edge used for
the off-axis guider have noticeably less coma than those of the typical SCT,
making my ST4 happy :o)

The best OAG for this scope may be the shortened version of the Cassegrain
Easy Guider sold by Lumicon. Apparently some C9.25 users have had trouble
reaching focus with the full-length CEG, because the scope doesn't quite
have as generous an amount of focus travel as other SCT's. I'm not sure, but
I also believe that the shortened CEG doesn't come with a reducer. The short
CEG should also give a better selection of guide stars than the NEG that I
used. I just happened to already own the NEG.

Hope this helps,

John Boudreau
jeboud@mediaone.net
http://people.ne.mediaone.net/jeboud/astro.htm
----- Original Message -----
From: "Grant" <GB1029@inter-linc.net>
To: <astro-photo@seds.org>
Sent: Tuesday, October 23, 2001 2:23 AM
Subject: [APML] C 9.25 for AP?


>
> I recently dug up as much info as I could find in the archives on the C9.2
5.
> It seems there are some good & bad things regarding the 9.25's AP
usefulness.
> In particular, I read that the scopes' optics were funky and probably
would
> cause
> problems with a reducer.  Does anyone have any additional info on what
type
> of problems might be caused?  Additional vignetting? etc..  Anyone out
> there using this scope successfully?
> I was considering trading up my LX10 setup for the OTA and using it w/ my
G-11.
> Don't want to do anything I'll regret though.
>
> Regards,
> Grant
>
>
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