I have been shooting with Canon 24-70 f/2.8L on my 5DII for two days now, it is a rental lenser that I picked at a reputable local camera store and I was told that is calibrated "good" copy. I wanted to try this lens before purchasing it as my standard lens for 5DII, however so far my experience has been very frustrating. Yesterday I took the lenser to the Cal Academy of Science in San Francisco and it was a total blow up, I shot several hundred shots with only a handful of good ones, mainly because of poor sharpness and color fringing. I tried the lens today as well with different outdoor subjects but results were very poor. Basically it is useless at f/2.8, nothing is sharp and at f/4 a very small circle in the center picks up in sharpness while the rest of the frame is blurry and even at f/8 corner performance is unacceptable to my standard. Chromatic aberration is extremely high and clearly present even at f/8. My main usage of 5DII is very large prints so imperfections like this is very critical to my work. I am starting to think that despite what I was told this lens may indeed by a very bad copy, I would appreciate any comments from owners of this lens who have used it on a full frame camera. I have attached some samples (all RAW files converted with DPP). It would nice if someone with a "good" copy can post some 100% crops from center and corner from a typical scenery so I can decide whether this is the lens for me or not. Thank you.