To test how badly the canon is focusing to the front or back of the subject, the next test was done using a graduated test target at 45 degrees. The target was corrected such that the markers represent centimeters when viewed at 45 degrees. Download target. All tests were done with 50mm set 1.2m from the target. Mirror lockup was used with a 2 second timer and the central AF point only selected. 6 tests were completed, 2 with the lens previously set to minimum focus, two maximum and the last two using manual focus.
1.1 Tests with focus previously set to minimum:
Result 1) - front focusing by more than 3cm.
Result 2) rear focusing by more than 3cm. This was exactly the same setup as the above test!!!
1.2 Tests with focus previously set to maximum (infinity)
Result 1) - a bit better, rear focusing by about 1.5cm
result 2) rear focusing by more than 3cm
1.3 Tests with manual focus (my best effort)
The above tests were made with the following settings:
Shooting Mode Program AE - Tv( Shutter Speed ) 1/90 - Av( Aperture Value ) 2.8 - Metering Mode Evaluative - Exposure Compensation 0 - ISO Speed 100 - Lens 50.0 mm - Focal Length 50.0 mm - Image Size 3072x2048 - Image Quality Fine - Flash Off - White Balance Auto - AF Mode One-Shot AF - Parameters Contrast Normal - Sharpness Normal - Color saturation Normal - Color tone Normal - Color Space sRGB - File Size 1479KB - Custom Function - C.Fn:01-0 - C.Fn:02-0 - C.Fn:03-0 - C.Fn:04-0 - C.Fn:05-0 - C.Fn:06-0 - C.Fn:07-0 - C.Fn:08-0 - C.Fn:09-0 - C.Fn:10-0 - C.Fn:11-0 - C.Fn:12-1 - C.Fn:13-0 - C.Fn:14-0 - C.Fn:15-0 - C.Fn:16-0 - C.Fn:17-0 - Drive Mode Self-Timer Operation - Owner's Name - Camera Body No.0130100874
It was often not possible to get the lower AF sensors to register or focus on the landscape, no matter how much moving and refocusing was tried. The only solution is to dip all 7 sensors to the foreground landscape, then move the camera back up. This results in overexposure of the sky, which is not taken into account when the focus lock is taken on the land. Look at this classic:
This roof is about 10 meters away. I tried everything I could to get the lower AF point to focus on the roof. I tried moving the focus ring before hand to min, to max (the 70-200 has an "always on" manual focus). I tried to focus the lower AF point on the slates, the lines between the slates and everything else I could think of. I tried for several minutes. The shot here is taken WITHOUT moving the composition after focusing, i.e. the middle AF point was not near the crane at all. Either the middle AF has focused on the sky, or the AF points are not actually near the square markers, which would explain a lot. I can reproduce this shot at any time.
look at the image below, taken from a distance of about 4m, viewed using the Canon file viewer with image at "Medium" size:
The focus points have missed the subject in the foreground, i.e. the child's knees, and gone for his hat. This is OK except that his hat is not in focus. The focus is about 1m behind the man (look at the sand behind). I have about 10 examples like this from 15 shots taken. The shot was taken without focusing then moving the camera - i.e. the shutter was pressed all the way in one go.
Look at the head detail (at 100% viewed in photoshop 7). It is not sharp and it should be with this lens.
more portrait focus problems
Both sports mode and manual modes have been tried. In sports mode, the AI servo does not track the subject very well at all, resulting in 80% of pictures being out of focus. Generally the focus is behind the subject by one or two meters. See below for examples:
The subject was smoothly tracked with the center point over his body from start to finish.
Focusing on climbers is hard as it tends to pick rock which is furthest away. (close focus on this lens is .42m) OK the technique here is bad (-1/2 exposure and not using flash) - it wasn't me who took it, but the focusing is terrible. Even though the light is low, i would have expected better AF.