LensRentals Nikon AF test just posted

Started Sep 14, 2012 | Discussions thread
Andre Affleck Senior Member • Posts: 2,362
Re: Unfortunately, no info on fast lenses wide open

Andre Affleck wrote:

Essentially the AF sensors only receive light from regions at the f2.8 diameter even if the lens aperture is larger than f2.8. With faster lenses, light from wider apertures beyond f2.8 do not reach the AF sensors, so the accuracy at f1.4 is no better than f2.8. However, since the DOF is 1/4 1/2 the size, the resulting accuracy is reduced by 1/4 1/2.

Correction: Reduced by 1/2

So one can always expect to get worse results shooting wide open with faster than f2.8 lenses, and the reduction in accuracy will be a straight ratio of DOFs. There's really no point in testing AF at 1.4 since it will be the same results as the f2.8 data, divided by 4 divided by 2.

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