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Old 12-02-11, 01:20
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petrochemist petrochemist is offline  
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Quote:
magnification = ext tubes / focal length + 1 x 1.6 (crop factor) = 2.8444444
I'm not sure about the +1 part (I remember the guide that when extension + focal length you get 1:1)
In addition I think it applies to having the lens focused at infinity. If the lens is focus closer the ext tubes part becomes Total extension as focusing the lens adds extension internally.
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