Quote:
Originally Posted by LewisM
Is it wise to have the GS FL as near the main scope FL?
For instance, with my f/4 Pentax, would an f/3 guidescope (converted finder) be a good match? With my f/8 main, would an old f/9 converted Toya 50mm refractor be suitable?
I have use the f/9 GS on an f/6.3 main before with great results as well as the f/3 GS on the same scope. The f/4 Pentax surely should use the short FL GS?
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Lewis, it's the focal lengths and pixels sizes that matter. Aim for the ASP (arcsec per pixel) of the guide camera to be no more than 10 times that of the imaging camera.
EG:
Imaging - Celestron C8+Atik 314L+ -> 0.65 ASP
Guiding1 - Orion ST80+ASI120MM -> 1.93 ASP
Ratio: 2.969
Guiding2 - Orion ST80+Atik 16ic -> 3.18 ASP
Ratio: 4.892
Ron Wodaski's
CCD Calculator makes doing the math simple.