i used the canon f/2.5 11.5mm - 138mm almost entirely @ f2.8 for about 3500' feet of film recently. i noticed that there's a significant amount of color fringing around highlights. it only occurs when the backlight is more than 4 stops over. it's not so noticeable in closeups, because your eye is elsewhere; it's more a wide shot where you have a character coming in from a brightly backlit door, say, and the eye is looking carefully at the detail. the lens is really solidly built, and feels great, but i have a feeling that optically there's a better choice out there. the rental house, abel cine tech had an angenieux f/2.1 11.5 - 138 that was out: we were just a student film getting a deal on what was there. my nikon full frame primes (@ f2.8 not wide open) on a digital still camera with a 23mm x 13mm size sensor control CA color fringing better. i also intercut the zoom with a zeiss 16mm T 1.3 used @ f/2.8. the prime controls flare better, controls CA slightly better, and is about the same sharpness. overall the director was very happy with the results and actually enjoyed the lens imperfections.