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theoretical and usefull max focal length
Hi,
Not the best day out there so Ive been inside thinking again. I want to make an 8" F9 but then I was thinking F10? at what point do I loose out, there is only so much light so there must be a point where I should stop . Where does the point lie? where would a longer focal ratio begin to deliver poorer preformance? (planetry only and ignore length issues for the theoretical max)
Roger
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