I purchased a used (duh!) 5D recently. I discovered quickly that it does not focus the 50 1.8 very well in low light, such as after dark in a large living room lit by 3 or 4 60W bulbs. It does not matter whether I use a flash with 'focus assist' or not. I just started playing with the 85 1.8 and am getting the same results. Both lenses seem to work (focus) fine in good light. I can take either of them outside, even in heavy clouds/overcast and get good results with my 5D. Both lenses work fine, in almost any light on my 60D. Is this normal behavior for the 5D? Is there an AF sensor I can clean, or something? I am using center-point only. This makes the camera just about unusable in poor lighting, even with a flash. Does my 5D have a problem, or am I spoiled by the 60D? Oh, it seems to work OK with my 24 2.8. And it works well, with all my lenses, outdoors.