Re: [APML] Off Axis Guiding Help

["Alson Wong" <alsonwong@earthlink.net>]

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 
> 
> 
> _______________________________________________
> Astro-Photo mailing list
> Astro-Photo@seds.org
> http://seds.org/mailman/listinfo/astro-photo


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