Re: [APML] Mini Borg 45ED & ST-4 Autoguider

["William R. Mattil" <wrmattil@ix.netcom.com>]

Stuart Heggie wrote:

>Joseph - I tried to guide my 800mm newtonian with a 180mm lens and it didn't work. Not saying it
>couldn't but I wasn't really interested in spending a lot of film and clear nights figuring out
>why. So, one data point for you. Maybe 300mm would do it. Can you put a barlow in the light path?
>Then you'd have 600mm guiding 770 and I bet that would work.
>  
>

Stuart,

I don't think this data point has any relation to Josephs question due 
to the nature of a Newtonian.  It is, IMHO, impossible to use a seperate 
guidescope with a Newtonian and get resonable results. There are simply 
far too many sources of minute flexure in a Newtonian optical train. The 
bulk of the problem in my research was the secondary holder and 
secondary. Not the spider which I found curious. but I was able to 
absolutely pin down the point of flexure and chose to use an off-axis 
guider instead of redesigning the entire OTA.


Just my experience here, and an awful lot of wasted film :(


Regards

Bill
-- 

William R. Mattil  :  http://www.celestial-images.com


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