I have had this lens for about 4 years and the problem has been here since day 1. Shooting close of just one or two people images are sharp. However when backing up for about 15 feet or more the images become not sharp at all. The further back the blurrier and I focus on someone in the front row. Like in this image, the back wall is more in focus which makes me think the further back I get the more the middle focusing point is changing to focus on the back, is that possible? as on this one, I focused on the brides face. I took 3 pictures focusing on #1 bride, #2 groom and #3 woman in the back to the bride's left shoulder and all 3 have the very same result and I did use a tripod. Should I try to focus on a bigger body part like the torso the further back I go? I shot this with a Canon T5I and it doesn't have AF focus adjustment. Before then I shot with a 50D with it and did the adjustment but with negligible results.
Any one got any solutions? Can't really afford to send it to Canon but I'll get the money some way if I have to if it will do any good.