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Old Sep 13, 2005, 5:42 PM   #1
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Sorry if this is a stupid question.

If I purchase a lens such as the Sigma 70-200mm f2.8 HSM it has an effective focal length of 105-300mm when used with my digital camera. Is the lens still an f2.8 or will that also change?

Thanks for your help.

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Old Sep 13, 2005, 6:04 PM   #2
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Yes, it stays the same.
F2.8 is F2.8 :-) the F number is a ratio of the lens apature diameter to the real focal length.

The effective focal length X factor of the cameras that crop is caused by them thorwing away a good chunk of the image circle produced by a full frame lens.

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