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

["Jeff Crilly" <jlcapml@sbcglobal.net>]

> Joe:
> The old guiding 'rule of thumb' was that for manual guiding, the guidescope 
> should be equal to or greater than the imaging instrument.
> When the St-4 came along, it was discovered that it guided well at 1/2 the 
> focal length of the imaging instrument.
> When the St-V came along, it will guide with a much shorter focal length 
> guidescope, such as the efinder which is 100mm fl.
> All that being said, I think the Borg 45ED-St-4 combo might be too short for 
> your 1000 mm imaging focal length.
> Another possibility would be to but a 2x or 3x barlow lens before the St-4 
> resulting in a 600mm or 900mm guiding focal length. If you do, be sure the 
> entire optical train is flexure free.
> 

My understanding is that the ST-4 cannot do centroiding on the guidestar,
hence the need for a bit longer FL.

The STV (and PC-based guiding software used with other cameras) does
centroiding which allows for subpixel guiding.  For  the ST7E + 200mm lens 
(from my calculations) I get just under an arcsec guiding 
resolution (assuming 1/10 pixel resolution by the ccdops autoguider software.)

jeff

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