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Originally Posted by hogly52
Starkler,
With your formula, I'm assuming that the tube inner diameter you refer to is the focussing sight tube diameter, ie. it's either 1.25ins or 2ins? Also, once using the correct length sight tube, what is the correct position for the focusser, in or out?  |
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Graeme, for a sight tube to fit a 1.25 inch focuser, the length is F x the
inside diameter of the sight tube. ie 1.25 inch minus 2x the wall thickness of the sight tube.
A correctly sized sight tube will alow you to visually align the secondary mirror to the edge of the sight tube, while simultaneously being able to see all of your primary mirror reflected in the secondary. Adjust the focuser so that this happens. This allows you to align your secondary easily and accurately.