In order to test my theory of back-focusing with this lens, I set up a little test rig: I used pink insulation foam as a backdrop due to its plainness to deliberately make it difficult for the camera to focus on it, thus (in theory) isolating the targets better. The camera rested on teh black case at bottom and I used each AF point to try to focus on the various targets as indicated in the above image. Between each of three shots I focused elsewhere, forcing the AF to reacquire the target for each shot. I used a blue line to approximate the focal plane across the image and a red box of course to indicate the desired target. You'll see I get better at this as we proceed through the AF points, as I sort of figured out how this was working. Finally, all shots were ISO-800, f/1.4, and 1/640s. I wanted to keep shutter speed up to reduce the possibility of motion blur; lighting was 4 x 60w bulbs in the cieling and 1 x 90w bulb about 3 feet to the right of the test rig. So! Let's get to it: The center AF point is supposed to be the most accurate, but in all three of these shots, plus a few others I took, it consistantly back-focused by maybe a quarter of an inch? To be fair, its target was a difficult one, and perhaps I would have had better performance with something that stuck up a bit as opposed to just an opening in the T-square. For the "2 O'clock" AF point, another difficult target, the back edge of the small metal ruler. Performance was simliar to the center point, back focusing a bit. Also, difficulty acquiring this target in the first place. The 3 O'clock AF point I found to be the most accurate. This could, again, be attributed to the target, which stuck up a bit providing lots of edges for the camera to see. Still, I was pleasantly surprised. The 4 O'clock point was again a tougher one for the camera. Originally it was the edge of the small ruler again, but it had so much trouble acquiring the target that I added a dime to the area to give it more edges. Some back-focusing but overall not too bad. The 6 O'Clock point also showed some back-focusing initially, until when I looked at the lens itself I found that the little medallion in the label was about an inch closer than perhaps the closest focus distance. So this data may be totally invalid. The 7 O'clock point I expected to be tough; the dog's paw in the bookmark. Surprisingly it did fairly well. The 9 O'clock point had performance similar to the 3 O'clock point: pretty darn good, and this time the target was not "sticking up in the air," it was the back-edge of the bookmark. If anything, it may have front-focused that spot a smidge. The 10 O'clock point also had excellent performance, the knot on the bookmark yarn. Finally, the 12 O'clock point was really disappointing. The target was sticking up and had lots of edges, but it was consistantly back-focused. Conclusions: clearly the camera does better with higher-contrast targets. I almost feel like re-shooting this whole series again with pop-up targets. But the PS took me a long time. Really the biggest surprise I guess was the 12 O'clock point. Questions? Comments? Suggestions?