Quote:
Originally Posted by Willow127mm
I try to use the rule of 600 when trying to avoid star trailing and came up with 600\div by 1500 focal lenth =0.4 of a second which seemed questionable.Am I using the wrong sum?
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I believe the "Rule of 600" (and similar rules of thumb) is for eliminating star trails on fixed (non-tracking) cameras. With your camera mounted on a tracking Alt-Az mount, you have already dealt with the overall issue of stars trailing across a fixed field of view, but you still need to deal with "Field Rotation" - see my previous post.