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RE: [APML] Off Axis Guiding Help
Bill, Steve, Bert, Alson,
Thanks very much for the suggestions. There were a few that I havn't
tried, and some that are different ways of looking at things I was
already doing. Maybe the biggest help is to know that others have
succeeded.
I do have the Wil Milan and Jim Janusz tutorials printed out and dog
eared. I have suspected that a focal reducer on the ST4 might help, as
the stars on the pickoff prism don't look too bad through a 25mm
eyepiece, but I hope to not spend that money right now.
I really like Alson's suggestion of establishing the orientation of the
OAG before final focusing the main optics.
Another thing I'm going to add to my list is to not attempt to use the
SCT/OAG/ST4 combo in conditions that are too funky, think I'll stick to
the refractors if things are moving around too much.
I really appreciate the help, I'm going to build myself an archive
document of all of your suggestions, and hopefully, in a dark cycle or
two will post some results.
Eric Barber
PowerPlace Software
-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of Alson Wong
Sent: Wednesday, August 06, 2003 6:32 PM
To: Discussion of Film Astrophotography
Subject: Re: [APML] Off Axis Guiding Help
Eric,
I have used the same setup, right down to the Nikon F3, although I don't
have the Bisque eyepiece. Instead, I use a 9mm reticle eyepiece with a
parfocalizing ring. This is how I set up my exposures:
1. Frame the object in the camera and achieve rough focus.
2. Put a long focal length eyepiece into the guiding port (I use a 26mm
Plossl). Center a guide star by adjusting the mount and/or by using the
rotational and radial adjustments on the OAG. 3. Achieve final focus for
the camera. I use a SureSharp rhonchi grating which works best on bright
stars. 4. Move the scope back to the object and recenter the guide star
using the telescope mount controls only. Do not make any adjustments to
the OAG that may throw off the camera focus. 5. Insert the parfocal
eyepiece. Adjust the focus of the guide star by moving the eyepiece in
or out of the guiding port. If you have the 0.6x reducing lens in place,
you'll be using an eyepiece extender. The best way to focus with the
parfocal eyepiece is to fully insert the eyepiece into the extender and
then focus by moving the extender in or out of the guiding port. That
way the ST-4 will be in focus if you fully insert it into the eyepiece
extender. 6. When guide star focus has been achieved, replace the
eyepiece with the ST-4. You may need to make minor adjustments to get
the ST-4 perfectly focused.
I prefer to do the initial centering of the guide star (Step 2) before
performing final focus for the camera (Step 3) because making rotational
adjustments to the OAG may throw off the camera focus. When using an OAG
with the ST-4, use Faint Mode, since it gives you a larger centroid to
work with. The star images when using an OAG are distorted and Faint
Mode usually works better.
Alson
----- Original Message -----
From: "Eric Barber" <ppsupport@cox.net>
To: <astro-photo@seds.org>
Sent: Wednesday, August 06, 2003 4:26 PM
Subject: [APML] Off Axis Guiding Help
> Greetings,
>
> I am trying to get up and running shooting film through my C9.25 SCT.
> I have had decent success using a side by side refractor set-up, but I
> am batting a big zero on getting the ST-4 to guide with the 9.25 and
> the Lumicon Cassegrain Easy Guider.
>
> I was wondering if there is some kind soul who has been down this road
> that might give me some advice, either on or off list. My main issue
> seems to be guide star acquisition through the OAG, possibly focus of
> the guide camera as well.
>
> My equipment in this endeavor:
>
> Losmandy G11
> C 9.25
> ST-4
> Lumicon CEG
> Nikon F3
> Numerous extension tubes for the OAG etc.
> And even, the Software Bisque parfocal eyepiece...
>
> My intent, when I realized that I had somehow fallen into this
> astrophotography thing was to just acquire a nice APO refractor and be
> done with the SCT. Current economy has put that on hold though.
>
> The one manually guided (but trailed slightly) shot I acquired through
> the 9.25 tantalized me enough to know that good things could be
> accomplished with the setup...
>
> http://members.cox.net/ppsupport/M8.htm
>
> Anyway, thanks in advance.
>
> Eric Barber
> PowerPlace Software
>
>
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> Astro-Photo@seds.org http://seds.org/mailman/listinfo/astro-photo
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