An max aperture opening of f/5.6 or wider is required for the 5D to autofocus

[znxlegion]

What does this mean? If I go to 2.8 the camera wont autofocus?


Does this apply to all cameras?





Thanks in advance

[peety3]

All cameras with phase detection AF (which is most if not all of today's DSLRs) depend on aperture to present light rays in or out of phase. The camera AF sensor has certain minimums based on the camera model.


During normal operation (i.e. composition of the picture), the lens aperture is kept wide open, also known as the maximum aperture of the lens. The camera auto-focuses during this time, and is dependent on that max aperture. If you or the camera has chosen a smaller aperture (somewhere between max aperture and min aperture, obviously), the lens aperture is changed before the shutter opens and returned to max after the shutter closes.


Any Canon DSLR with a model number higher than 1 requires a max aperture of at least f/5.6 to properly auto-focus. f/2.8 is larger, and is therefore fine. With an f/2.8 lens, the center AF point probably becomes a higher-precision (dual-axis) focus point. 1-series DSLRs require a minimum aperture of f/8, and the center point becomes higher-precision at f/4 in most or all of those models. Other focus points in the 1-series might become higher-precision and/or dual-axis if a lens f/2.8 or larger is attached.

[znxlegion]

Thanks for the quick reply!


I completely misunderstood what I was reading. Thanks for clearing that up.