Question about MFA procedure

Started May 5, 2012 | Discussions thread
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ppage
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Question about MFA procedure
May 5, 2012

As far as I know the only purpose of doing a MFA on any lens is to correct for possible front or back focus problems. The procedure is to use the widest aperture to reduce depth of field thus making any focus problems more evident. So why is it that the recommended distance between the camera and the reference target is 50 times the focal length of the lens? Wouldn’t a shorter distance, by further reducing the depth of field, make any focus problem more obvious?

What am I missing?

Thanks,
Peter

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Canon EOS 70D Canon EF-S 10-22mm f/3.5-4.5 USM Canon EF-S 17-55mm f/2.8 IS USM Canon EF 100-400mm f/4.5-5.6L IS USM Canon EF 70-300mm f/4-5.6 IS USM +1 more
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