Re: [APML]: Guidescope?

["Andrea Ricciardi" <mc7624@mclink.it>]

 ----
From: gharding <gharding@concentric.net>
To: astro-photo@nightsky.com
Date: Thursday, August 28, 1997 2:35 AM
Subject: [APML]: Guidescope?

>
>Hi,
> 
>  For about a year I have been taking astro-photos with my trusty 35mm
>camera attached to a Meade 8" LX50, using the celestron radial guider.
>Just recently I have purchased the Meade 216xt CCD camera and have tried
>to use it as an autoguider with the radial guider.  This has proved to
>be extremely frustrating and time consuming.  I can rarely find a
>suitable guidestar, not to mention the impossible task of focusing and
>centering a  dim star on the small TC-255 chip.  So I have come to the
>conclusion that I need a guidescope.  However, I do not know which scope
>to get.  I would like to get a small refractor, but would a 70mm or 80mm
>aperture(like that on the Televue Ranger) be large enough to guide on
>faint stars? Or maybe I should try a C90 or an old 2045S, or maybe the
>ETX.  If I choose one of these scopes, would the Losmandy mounting rings
>be rigid enough to limit flexure?  Also, would it be worth it to check
>Astromart for used scopes?  Any advice would be greatly appreciated.
>Thanks in advance!
>
>              Eric
> 

Find a good 80mm. with about 1000mm. of focal lenght, better 1200mm. , so
that you could guide your scope at f/6.3. If you plan to use it at f/10,
buy a good 2x barlow, like the Meade apo one. I don't think you need an
expensive scope like the Ranger: a "normal" 80mm. will work ok. Somebody on
the list reported some troubles with the SC primary mirror: personally I
never used a guidescope with my old C8. The first times you use an
autoguider, it may seems difficult to use it: I've find very important to
use an about parafocal eyepiece to find a rough focus and refine it. It's
about impossible to find anything when you are a bit out of focus.

Andrea.