[Chaos-l] Guide Scopes and Such

[Bryan]

Assuming your exposures are long enough to need a guide scope, the 
disadvantage to a separate telescope for guiding is differential flexure. 
Any small movement by one scope without the other will produce non-round 
stars. Also, in the case of the SCT, the primary mirror has a nasty habit of 
shifting slightly as the telescope tracks. The guide scope does not see this 
movement. They invented off-axis guiders for this problem when doing long 
exposure film work. I have a Lumicon off axis guider for my SCT that 
produced some nice 40 minute film exposures. I tried the separate guide 
scope when doing film work without any luck.

Hopefully you can integrate shorter exposures to eliminate the need for 
guiding.

Bryan

----- Original Message ----- 
From: "Robert Nielsen" <robertnielsen at nc.rr.com>
To: "Chapel Hill Astronomical Observation Society" <chaos-l at rtpnet.org>
Sent: Friday, March 23, 2007 9:49 AM
Subject: [Chaos-l] Guide Scopes and Such


>A question for all the experts in the club (I readily admit I am not one):
>
> I just saw a picture of a setup from a guy who is doing simple
> astrophotography with the Meade DSI.   He bought a "cheap" (roughly
> $75-$100 refractor ... from Meade ... one of the ones that Jon and
> John and everyone else don't buy at the mall) mounted it on his
> bigger scope and used it as a guide scope.  What does everyone
> think?   Seems like a good idea to me (since you really aren't
> working for optical clarity ... and everyone said the mall refractors
> aren't bad optically ... it's the mount that sucked).
>
> Of course, I would love to have one of the TMB wide-field refractors,
> so I could switch and use it for astrophotography as well.   Just
> can't afford it yet.  If I get mounting rings (which yes, I realize
> might cost more than the guide scope), I should be able to use those
> later as well.
>
> It's just a thought.   What does everyone else think?
>
> Robert
>
>
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