> From many of my pictures, using AF, I observed that the Depth of Field
> zone is always some distance "in-front" of my focus target. Example:
> A.....B......C
> Say C is the camera, A is the subject I autofocus on, the in-focus zone
> (whatever aperture) is always from A to B. Is this the way all modern AF
> cameras work?
> I'm using EOS30/Elan7e, EF28-105 USM, and EF50 f/1.8. I thought that
> maybe a little touching up after AF is necessary, then again, maybe if I
> understand how the AF works, I can avoid that. (holding down the small
DOF
> preview button while manual focusing is a pain - is there a DOF preview
lock
> for this camera?)
DOF is no different on an EOS than any other camera. It's 1/3rd in front
of subject, and 2/3rds in the back of subject. I'm not sure how many shots
you're judging this result on you got, but if you get focus lock on say a
person at 20 feet, you should see more in focus to the rear of the person
than to the front. It may be the perceived focus due to the relative size of
things up front. Or it may be a few photos where AF was not locked where you
wanted. In any case, you might try a test under some controlled conditions
to determine your DOF. For example, take a shot of something fairly close to
the camera, then something further, say 5 feet and 20 feet. Place targets or
objects along the side of the subject that will show focus quality. I
suppose it's possible something is mis-aligned in either lens or camera. But
somehow I doubt it. Having said that, you should not be getting results as
you describe.
I'd suggest your tests be done with the lens wide open to minimize depth
of field and show you more easily just what is actually in focus. Set the
camera for only the central focus point, and make sure your focus lock light
comes on when the subject is under the central sensor. Further tests with
the other focus points might be a good idea while you're at it, as well as a
few shots using smaller apertures.
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