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Hi Rod,
To determine the focal point and hence the focal length, reinstall the old focuser, since it fits the scope tube, and then take a piece of vellum/tracing paper or cooking parchment/wax paper and some how mount it across the end of the focuser as if it were a lens cap (perhaps use tape) and then point the scope during daytime at an object at infinity and bring the scope to focus on the tracing paper surface. You now have your focal point and can have a measure of the focal length, bearing in mind that it's measured from somewhere within the optics. You can also make a determination from the field of view, but not as accurately.
Best
JA
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