Recently I am noticing some back focus problems with my sigma 15-30 on a 10D. First thought is may be I focused it wrong. I searched the forums here and on dpreview and photo.net and used the chart with vertical lines on a 45 degree plane. Everything seemed fine then. Here are the list of questions I need help for:
1. How can I conclusively test the back focus problem for this particular lens?
2. Would it be a good idea to trade the sigma 15-30 to get a canon 17-40 F4L?
3. Is there anything else I should do if I decide to keep the 15-30?
As always I sincerely appreciate your help.
pramod../
