Re: [APML] piggy back guide scope size

[Larry McManus <lmcmanus@clearpointadv.com>]

Thanks for the info. Unfortunatly I can't use an off axis guider because the
Hasselblad uses a 2" id fitting to connect to the scope so I am stuck using
a seperate guide scope if I want to do any long exposures. Do you know if
300mm is enough for guiding?
Larry


on 10/15/02 2:58 PM, KGKIRKLEY@aol.com at KGKIRKLEY@aol.com wrote:

> 
> In a message dated 10/15/02 4:49:54 PM, lmcmanus@clearpointadv.com writes:
> 
> << Can anyone give me a minnimum size for a guide scope to go on my sc. I have
> a 6 x 6 Hasselblad connected to the visual back of my 8" sc and I need to
> come up with a setup to allow me to guide on long exposures.
> 
> Larry  >>
> 
> Larry:
> This depends on how you intend to guide.
> 
> If by 'sc' you mean Schmidt-Cassigrain, you need to know that most SC systems
> suffer from 'mirror slop', which is the slow rotation of the mirror on it's
> thimble,  as the mount tracks, which results in trailed star images. It is
> best to lock the mirror in place (various ways) and use a rear mounted
> focuser. An Off-Axis-Guider body can also be used.
> 
> If you haven't locked the mirror in place and use a separate guidescope, you
> will run into trailed star images due to the mirror movement.
> 
> Kent Kirkley
> 
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