Canon EF-S 18-135mm f/3.5-5.6 STM IS - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortions

Typical for many "super" zoom lenses the Canon exhibits an extreme amount of barrel distortion at 18mm (~4.2%). However, this is not really an issue anymore from 24mm onward with a pretty mild distortion of about 1%. Typical for such lenses the distortion type switches from barrel to pincushion after the first quarter of the range.

Move the mouse cursor over the focal length text marks below to observe the respective distortions
18mm 24mm 50mm 135mm

Vignetting

It's fairly common for dedicated APS-C lenses to show a more pronounced vignetting at max. aperture settings. The Canon lens is no exception here especially at 18mm with a rather extreme peak vignetting of 1.55 f-stops at 18mm @ f/3.5. At 135mm @ f/5.6 it's also somewhat hefty at 0.9EV respectively. As a general rule you should generally stop down a bit to avoid the problem.

MTF (resolution)

As already mentioned Canon hasn't an exactly impressive history when it comes to "super" zoom lenses but, surprisingly, things are quite different here now. The EF-S 18-135mm f/3.5-5.6 STM IS has no obvious weakness in terms of resolution. The center performance is generally on a very high to even excellent level at mainstream aperture settings. The border and even corner performance is very good except at 135mm @ f/5.6 where we were able to see a more pronounced drop in the image corners. There is a bit of field curvature but not to a worryingly degree. Typical for such lenses the centering quality is a bit varying along the range but this is simply the price you have to pay for the combination for extreme range and IS here.

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)

The level of lateral CAs (color shadows at harsh contrast transitions) is not bad but they can be obvious unless you correct them. The problem is most obvious at 18-35mm with an average CA pixel width of 1.3-1.8px at the borders. It is a far lesser issue at from 50-135mm though.




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