I've noted (certain others have also) that the Oly tubes are 7mm, 14mm, and
25mm while the Vivitar are 12mm, 20mm and 36mm. I also know the tubes can
be stacked in various combinations for additional lengths.
Is there a rationale for the various lengths? Are there certain lenses in
combination with one or more tubes that will give specific magnification?
If I understand it correctly, a 50mm lens with the Oly 25mm tube will give
1:2 if the lens is focused to infinity. Not that a specific magnification
is important to me . . . but curious why Oly would make one set of sizes
and Vivitar another.
(Reportedly there is no difference in the quality of the glass in them, so
that is cannot be a factor.)
Thanks,
-- John
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