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Old May 7, 2005, 10:42 PM   #1
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I have a simple question. I just bought a Sigma 70-200mm f/2.8 zoom, which mounted on my Digital Rebel is equivlalent to 112-320mm with the 1.6 crop factor. Now my question is, if I use a 1.4x teleconverter will I get the full 40% more over the 112-320mm equaling 157-448mm? and will it still just knock me down one stop to f/4? I guess that was two questions, but I know you guys can handle the presure. Thanks for the help.
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Old May 8, 2005, 12:16 AM   #2
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Yes, the 1.4 TC is a real multiplication of the lens focal length. So at max zoom it is a real 280mm lens. The 1.6 crop of the Canon applies to any lens mounted on the camera. SO with the 1.6 crop you have an effective 448mm :-) .

And yes to your second question too, the loss in 1 F-stop only applies to the 1.4 TC itself.

Peter.
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Old May 8, 2005, 9:19 AM   #3
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Thanks Peter, I was pretty sure that was the case, but just needed a second opinion.
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Old May 9, 2005, 9:35 AM   #4
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if you look on sigma's web site, under the 70-200 2.8, they talk about the use of their teleconverters and have it listed as 98-340 when used with 1.4x tc!! hmm.... even great engineers can make math mistakes too...
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