Canon EF-S 17-55mm f/2,8 USM IS - Retest @ 15mp / Review - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

The EF-S 17-55mm f/2.8 USM IS exhibited average distortion figures for a lens in this class. There's a relatively pronounced degree of barrel distortion (2%) at 17mm. This evens out very shortly beyond and starting from around 24mm you can expect mild pincushion distortion which increases continuously towards the long end of the zoom range (1.15%).

Move the mouse cursor over the focal length text marks below to observe the respective distortion
17mm 24mm 35mm 55mm

The chart above has a real-world size of about 120x80cm (taken from the initial review).

Vignetting

Dedicated APS-C lenses have a reduced image circle lens and they tend to produce higher vignetting figures. Unfortunately the Canon lens is no exception to the rule here. At f/2.8 the lens shows very pronounced vignetting around 1EV at all focal lengths with a peak of ~1.5EV at 17mm. Stopping down helps to reduce the problem and from f/4 onwards it's reasonably well controlled.

MTF (resolution)

The EF-S 17-55mm f/2.8 USM IS is Canon's best shot in this lens class and it does certainly show up in the resolution figures. The center resolution is very good+ to excellent throughout the range and neither the borders nor the extreme corners showed a significant weakness during the tests. There's only a very marginal weakness at 35/50mm @ f/2.8 but even so the lens remains perfectly usable here.

The lab findings were generally reflected during the field tests but the performance seem to decrease at very close focus distances. This is nothing unusual but don't expect wonders in near-macro scenarios.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Lateral chromatic aberrations (color shadows at harsh contrast transitions) tend to be a weak spot of most zoom lenses in this range but the EF-S 17-55mm f/2.8 USM IS produces an unusually moderate degree of around 1px at the image borders. This may be visible at 100% magnification but it's not relevant on prints and Canon DPP can correct this flaw during post-processing anyway.

Bokeh (out-of-focus blur) @ 55mm

The Canon EF-S 17-55mm f/2.8 USM IS may appear as a perfect lens for portrait photography but keep in mind that it is only equivalent to a full format "27-88mm f/4" lens with respect to its depth-of-field capabilities. Nonetheless it is interesting to analyze the bokeh (the quality of the out-of-focus blur).
Low contrast transitions are handled relatively well but hard contrasts are rendered quite harsh and you can spot some "onion"-like substructures in highlights upon closer observations. This doesn't really improve at f/4.

The rather mediocre highlight rendition gets also obvious in field conditions - see the following example (see also the 6th image in the sample image section):




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