Hi, I have been walking around for quite some time with a general question about front or back focus issues. I have read many posts regarding the subject, but have not yet found the answer to my question. Perhaps the question will establish my lack of intellect, but I'll give it a try anyway. Why, if the camera's AF sensor uses the lens for focussing, and one can see through the viewfinder that the object is in focus, why o why can front or back focus occur? I mean it is TTL AF we're talking about. So if the sensor says it's in focus, it should be sharp right? I have a hard time accepting that on pro level bodies front/back office issues occur. Thanks!