by ʇolɐǝz ǝɥʇ qoq

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Given lighting is not a problem, can you hit a limit where you have too much extension tubes (a very long tube) and the quality of the image will suffer? For example a diffraction limit will be hit for the adjusted F-Stop or something like that?

What are the variables that come into play here.

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up vote 11 down vote accepted

Yes, if I put 68 mm of tube (36+20+12) behind my 12-24 lens, I can't focus on a subject because the focus point is behind the front lens.

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Can you explain the three numbers? – Reid Jul 19 '10 at 16:26
@Reid: I have a kit with three extension tubes, one 36 mm one 20 mm and one 12 mm. – Guffa Jul 19 '10 at 16:44
Oh, OK. I thought that you were presenting a computed answer (i.e., 68mm was theoretically significant somehow), but instead you're relating a personal experience. Thanks for the clarification. – Reid Jul 19 '10 at 17:01

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