Too many of my pictures with this lens had not been in sharp focus. I knew it wasn't camera shake because I'd used high shutter speeds. To do this test (the number circled in green is where I put the focus point) I had the camera on a tripod and used the self timer to trigger the shutter release. I also tested my Tamron 90 macro and my Canon 17-40 and both focused on the correct button, so I assumed it was the lens....and then members of the lens forum at dpreview told me I didn't do the test properly, that I needed a flat target, so I printed out a set of numbers to test further...