While still remembering Canon's unfortunate mistake with the 17-85 IS USM model, we were very curious to see the test results of the new lens. We have to honestly admit we were a bit disappointed. Even with a wide-open aperature, the chromatic aberration is clearly visible and reaches a 0.11% level regardless of the focal length. Fortunately, to solve the problem in 17-30 mm focusing all you need to do is stop down the lens. This, however, does not work with a 55 mm where the aberration never falls below 0.1%.
You could probably let it go with a lens 2 or 3 times cheaper than that one. However, in the case of the Canon 17-55 IS USM, which aspires to be a competition for L-grade lenses, these results are not very promising. Nevertheless we have to admit that it's an improvement in comparison with the Canon 17-85 IS USM.
