EDIT: After looking into this more, it is NOT a 5D Mark III issue. It happens with the D800 as well, along with many other cameras before them. It is a field curvature issue caused by wide angle lenses. It is just more noticeable with large aperture ones due to the shallower DOF.
Just wanted to share my findings today to see if others experience the same issue.
At first, I thought it was limited to my 35L, but does the same exact thing with my 24-105L. The shallow DOF of the 35L just shows it much more.
I calibrated my 35L to my body using Focal... Extremely reliable AF performance using center point. Never misses. Switch to any of the outer cross AF points and lens front focuses quite a bit. You can see the DOF scale shift over... Checked on multiple targets at various distances on a tripod (so distance does not change) and consistently the DOF scale shifts to the left once I switch to outer AF points. Resulting in soft shots wide open using outer AF points at large apertures.
I thought it was just limited to that lens, but then I tried it with my 24-105... Under 50mm, it shows the exact same behavior. Over 50mm, it does not appear to do the shift.
Almost like with wider lenses, the outer AF points are having trouble locking on. I plan to try my 135L next to see if that does it as well... If my theory is correct, it will not shift due to the FL. And from my shooting with it so far, have not seen this happen either.
Just wanted to share this with everyone though. I plan to send to Canon if firmware does not address this issue with the AF.
Just wanted to share my findings today to see if others experience the same issue.
At first, I thought it was limited to my 35L, but does the same exact thing with my 24-105L. The shallow DOF of the 35L just shows it much more.
I calibrated my 35L to my body using Focal... Extremely reliable AF performance using center point. Never misses. Switch to any of the outer cross AF points and lens front focuses quite a bit. You can see the DOF scale shift over... Checked on multiple targets at various distances on a tripod (so distance does not change) and consistently the DOF scale shifts to the left once I switch to outer AF points. Resulting in soft shots wide open using outer AF points at large apertures.
I thought it was just limited to that lens, but then I tried it with my 24-105... Under 50mm, it shows the exact same behavior. Over 50mm, it does not appear to do the shift.
Almost like with wider lenses, the outer AF points are having trouble locking on. I plan to try my 135L next to see if that does it as well... If my theory is correct, it will not shift due to the FL. And from my shooting with it so far, have not seen this happen either.
Just wanted to share this with everyone though. I plan to send to Canon if firmware does not address this issue with the AF.
Apr 12, 2012 at 07:25 PM
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