Chromatic Aberration occurs when different wavelengths are focused at different spots on the image sensor. It shows as a colored glow along the edge of objects, and can be quite distracting. 

 

We tested chromatic aberration on both Canon Ultra-Wide Zoom lenses at various focal lengths and aperture settings. The files were then run through Imatest, a leading application for digital image testing, for greater analysis.

Below are the Imatest results of the Chromatic Aberration tests.

 

Canon 16-35mm II @ f/2.8

Canon 17-40mm @ f/4.0

 

The two charts above are depicting the performance at the maximum apertures of each lens. With both lenses "wide-open", we can see that the 17-40 shows as much total deviation - particularly in the blue spectrum - though it's more evenly distributed, averaging to result with less overall aberration.

 

At two stops down from full open, shown in the charts below, we have a much more dramatic difference. The 17-40mm f/4.0 is tracking almost perfectly along the curve; all three wavelengths are focusing on the same spot. The Canon 16-35mm f/2.8 II, on the other hand, is showing a tighter pattern stopped-down than it did at full open, but there is still some significant drifting.

 

 

Canon 16-35mm II @ f/4.5

Canon 17-40mm @ f/6.3

Interestingly, the 16-35mm II shot at f/4.5 looks remarkably similar, if not slightly better than the 17-40mm shot at f/4.