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Hi Merlin
For lunar and planetary imaging with webcams its normal to try to get as long a focal length as seeing will allow, so you can get at much magnification (ie image scale) as possible. f ratio is usually in the f/20 to f/50 range.
The majority of webcam imaging is done at prime focus, but for those very rare perfect nights then positive eyepiece projection will give you ridiculusly long FL for huge image scale.
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