Ability to AF at low aperture

Started May 23, 2012 | Discussions thread
mmullen
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Re: Ability to AF at low aperture
In reply to Thorbard, May 23, 2012

Thorbard wrote:

It is not, however, more difficult for the camera to focus at these apertures. But at a wide aperture the depth of field is shorter than at a narrow aperture (higher number eg f8) so the autofocus has to be more accurate for the shot to appear sharp.

There is something more than that going on here. Even when a lens with a maximum aperture of f/2.8 or wider is shot at f/4, it will have a larger focus variation when a HP AF sensor is in use and conditions are not conducive to it (lower light levels and/or lower contrast subjects) than when a regular precision AF sensor is selected. The detrimental effects can start to happen even at relatively modest light levels (around EV 5).

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Mike Mullen

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