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tour ×  There must be a mathematical description of the
difference that an extension tube makes to a lens -- is it
something that can be easily described?  (For example, with
teleconverters you can say things like "a 2x teleconverter will
turn a Y-mm lens into a 2Y-mm lens, and will lose you 2 stops."
Is there something similar for extension tubes?)  If there's
nothing much you can say about magnification, in general, what
about the change in closest focal distance? Is that also lens-
dependent?  What about if we factor out the lens: is there any
general way to compare the effects of (say) a 12mm and a 24mm
extension tube on the same lens?  share|improve this question
add comment  3 Answers  up vote 10 down vote accepted  I do
believe there are some formulas you can use. To Matt Grum's
point, I have not tested these with zoom l