Autofocus confusion

[Greg D]

I'm having a problem with AF, and don't know if it's me or the equipment or...  (Camera in question here is a Canon 40D, usually with 24-105L, sometimes 70-300 IS.)
The issue is that when shooting moving subjects (and I'm not talking race cars and cheetahs here, just my dogs running around in the yard) my keeper rate is essentially zero.  Lots of shots are okay at a glance, but aren't really sharp.  Same results regardless of AF mode used, IS on or off.  The thing that's puzzling is that I have a good many shots taken last year (with a different 40D and 28-135 IS or 70-300 lens) that are fine - maybe not tack-sharp, but better than anything I can produce now.  But when shooting "test shots" with my current gear (i.e. brick wall type shots) it appears sharp - can't do any better focusing manually with live view.  Shooting a yardstick, it doesn't appear to front- or back-focus (maybe a hair more DOF in front of the target digit than I'd expect, but target is still sharpest).  Looking at metadata from my older good shots, it does seem that the sharpest ones have very high shutter speeds (1/2000 or faster), but some are slower and still good (better than current shots at higher speeds).  Maybe my expectations of AF are too high, but the differences seem too consistent to be just dumb luck.  Any ideas?
(Sorry for being long-winded, any help appreciated.)

[DarkPenguin]

What AF mode?

[ErikKaffehr]

Hi,

Yes, a good question. Another question: Can you see where the camera does focus? Can you see any correlation between spot of focus and AF-sensor chosen. If you take wall shots at full aperture, are corner equally sharp?

Best regards
Erik

What AF mode?

[PeterAit]

I'm having a problem with AF, and don't know if it's me or the equipment or...  (Camera in question here is a Canon 40D, usually with 24-105L, sometimes 70-300 IS.)
The issue is that when shooting moving subjects (and I'm not talking race cars and cheetahs here, just my dogs running around in the yard) my keeper rate is essentially zero.  Lots of shots are okay at a glance, but aren't really sharp.  Same results regardless of AF mode used, IS on or off.  The thing that's puzzling is that I have a good many shots taken last year (with a different 40D and 28-135 IS or 70-300 lens) that are fine - maybe not tack-sharp, but better than anything I can produce now.  But when shooting "test shots" with my current gear (i.e. brick wall type shots) it appears sharp - can't do any better focusing manually with live view.  Shooting a yardstick, it doesn't appear to front- or back-focus (maybe a hair more DOF in front of the target digit than I'd expect, but target is still sharpest).  Looking at metadata from my older good shots, it does seem that the sharpest ones have very high shutter speeds (1/2000 or faster), but some are slower and still good (better than current shots at higher speeds).  Maybe my expectations of AF are too high, but the differences seem too consistent to be just dumb luck.  Any ideas?
(Sorry for being long-winded, any help appreciated.)

I don't know about Canons, but the Nikons I use have a "continuous servo" AF mode designed for just the scenario you describe - tracking moving subjects. Make sure you are using the right mode.

[Greg D]

What AF mode?

Either mode - AI servo or AI focus - produce similar results.  BTW, I generally use the center AF point, but tried it letting the camera select - results were worse, if anything.

[Ken Bennett]

Are you choosing a specific focusing point, or letting the camera choose?

With my 40D, I find the best setting for moving subjects to be continuous focus using all focusing points. I get more keepers that way than using just the center point (probably because it's too easy for the center point to move off the subject during shooting.)

While the focusing ability of the 40D isn't as good as my 1D Mark II, it's been surprisingly decent.

[DarkPenguin]

This behaves differently than another 40D?  You might check to see if anything has gotten into the AF wells.

[Greg D]

Hi,

Yes, a good question. Another question: Can you see where the camera does focus? Can you see any correlation between spot of focus and AF-sensor chosen. If you take wall shots at full aperture, are corner equally sharp?

Best regards
Erik

As far as where the camera does focus, sometimes it appears to slightly front-focus, so I tried deliberately focusing slightly behind my subject, but this produced no different result.  Most often, even the sharpest point is still soft.

[Jonathan Wienke]

Post some samples so we can see the image AND the metadata.

[Greg D]

Post some samples so we can see the image AND the metadata.

Thanks to all for the replies.  I took another good look at shots taken with my previous 40D (to make sure that my disappointment with my current results are not a result of faulty memory and "standards creep") and I can only conclude that there's got to be something wrong with this one.  Pics taken with the same methods under similar conditions and showing similar metadata are far better than anything I can come up with from this camera.  Checked my invoice and found (to my surprise) it's just barely still in warranty, so it's on its way back.

[SandroD]

could be something wrong with your camera... could be also problems with shooting settings. what AF do u use? ai servo? do u use multiple exposures? center point af? etc.