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Old Dec 19, 2005, 12:23 PM   #1
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If I use a 200mm (70-200) and a 20D (1.6 crop factor) plus an extension tube (1.4),
what is the correct resulting focal length?

200 x 1.6 x 1.4 = 448mm

200 x (1.6 + 1.4) = 600mm

Which would be correct?
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Old Dec 19, 2005, 1:45 PM   #2
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Jan.....
448mm is what you will have if you are using a 1.4x tele converter...If you are asking about a 1.4 "extension tube", this is used to help in macro photography, not increase your focal length...Your first calculation is the way to figure it for telephoto mm's...
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Old Dec 19, 2005, 2:14 PM   #3
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Thanks, I meant tele-converter.
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