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Anonymous
related:
[ "Some of the more expensive dSLRs like the Canon 1DSMKIII etc have f/4 and even f/5.6 sensitive AF sensors, which makes them fast and accurate even with a much slower (max aperture) lens"
reply- "I dont think you've said that right. I understand the specs to be:
45-point TTL 19 cross-type points, require F2.8 or faster lens * Center cross-type point requires F4.0 or faster lens 26 assist points, require F5.6 or faster lens *
So with a 2.8 or faster its great, all 45 points engaged, 19 crosses.
With an f4 - one cross, 18 crosses become lines, and the assist points work. Damn and $8000 camera with a $6000 400 F4 DO lens and I get 1 cross sensor?
With a 5.6 - no crosses, 19 lines and 26 assists
5.6 plus - no crosses, 19 lines, no assists. So by the time you've got out here your AF system isnt that far ahead of the 11 point A700. " ]
Also, a little touted "feature" of an f/2.8 and faster lens is that some of the AF points are f/2.8 sensitive, and makes them lock focus, much faster and more accurately, when a lens with a maximum aperture of f/2.8 (or larger), is mounted.
Note that the f/2.8 sensitive AF sensors are active, even if a lens with a *max* aperture of f/2.8 (or larger) is stopped down to f/4 or f/8 or whatever and obviously is a plus in ALL lighting conditions.
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