17-40 L and ye ole brick wall

I was deciding between 2 good candidates, the Sigma 15-30, and the Canon 17-40 L. Both are very good lenses, but I went with the Canon because of its smaller size and better construction (no exposed moving parts) . At the time, I was also under the impression that the 17-40 L was sharper--I think they are equally sharp now, though. My first copy of the 17-40 L was horrible! It was soft everywhere except at 40mm! I was very disappointed. I sent it back and got myself a second copy. It appears to be better--but still softer than I'd hoped. After some mucking around, it appears to be a focus problem, and if I focus when zoomed in at 40mm, and recompose back to 17mm, then things are pretty sharp. Here are some hand-held test shots I took with the requisite brick wall. The shutter speed was much faster than 1/500 (ISO 100) on all these shots.

Click on the pictures to see the full-size crops.

Upper left-hand corner	Middle

Links about the 17-40 L

• Sigma 15-30 vs. Canon 17-40
  
• Discussion on 15-30 vs 17-40
  
• Sigma 20 vs 17-40
  
• Canon 70-200 F/4 and 17-40
  
• Discussion on bad copy of 17-40?
  
• Zeiss vs. 17-40