Originally Posted by 6spd

Man, I've been having a bitch of a problem lately. I've been encountering focus issues with multiple lenses for probably 6 months or so. Hesitant to ship my lenses and body to Canon for calibration, I've been doing a bunch of tests to try and narrow down what the problem is. The pics were consistent in that the focus was soft, not front or back focused, and the aberration was terrible. I had a breakthrough tonight though. I use a UV and CPL filter on all my lenses and pretty much never took them off. I remembered reading somewhere, I think amazon, that filters can cause issues with some stuff, I didn't remember. So... I took the filters off, snapped some shots of the Fiancee reading on the couch (she was not happy) and looked at the results. Sharp pics. Tested a bunch more and all the shots were sharp, even at apertures as wide as 1.8. What a f*cking headache. I'm gonna take some car shots outside tomorrow and see what results I get. Hopefully positive ones.

BTW, live view sharpness was perfect, even with the filters on. Probably because its so much more accurate vs the viewfinder.