Re: [APML] Guidescope thoughts...

["Chris & Jennifer Cook" <ccjd@ix.netcom.com>]

Hi John -

>Chris, one of the problems with a very light (and usually cheap) refractor
>guidescope is the thinwall aluminum tubing used for many of these scopes.
>The tubing actually deforms slightly with even moderate force from the tube
>ring adjustment screws (sometimes referred to as "oil canning" as it
usually
>springs back to shape after the force is removed). Without getting into all
>of the other flexure sources in the focuser and any adapters, this alone
can
>be a flexure problem. This would probably be less noticeable with a smaller
>dia guidescope tube; say, a 60mm scope should have less of this problem
than
>an 80mm one.


I was thinking about that last night.  There is so much cheap s**t on the
market it's scary.


>But why not go with an OAG? IIR, you don't use a field flattener with the
5"
>ED, so a Lumicon 2" NEG should work easily with your setup without any
>modifications at all. Are you cropping the frames from the 5" at all? That
>would remove much of the vignetting and  prism shadow problems, which are
>not too bad in my NEG setup for my TV85 anyway. If you've ever used an OAG
>with your C8 in the past --- they work out a LOT easier with a refractor.
>You should even have an easier time finding suitable guidestars with the
>5"ED than I do with my TV85.
>
>Another possibility is the 2.7" medium format OAG made by Lumicon, intended
>for the AP focuser. It may be worthwhile to give Lumicon a call and see
what
>it would take to adapt it to the Meade 2.7" focuser and 35mm camera. This
>may be your best bet.



I did find a Vixen 60mm f/11.7 through Orion like Matt has.  I think I'll
try this guy first and see what happens.
I had the same Vixen 60mm back around 1989 but at that time it was sold
under Celestron.  It was an excellent little scope and very well built.  Now
I'm bummed I sold it.

As far as OAG's, they are the most reliable for eliminating flexure and will
be the way to go if the 60mm fails to perform.


>**And these OAG's could also be used for guiding a FLI MaxCam with an ST4
><VBG>.**


<G>


Chris

==================
Chris Cook
Astronomical Photography
www.abmedia.com/astro







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