Canon EF 28-70mm f/2.8 USM L - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

The level of distortion is very low for a standard zoom lens with slight barrel distortion at 28mm and marginal pincushion distortion at 70mm.

28mm:

40mm:

70mm:

The chart above has a real-world size of about 120x80cm. Possibly expect more distortions towards closer focus distances.

Vignetting

On APS-C DSLRs vignetting is extremely low and not field relevant at any focal length and aperture.

MTF (resolution)

In the lab the lens showed a very good to excellent performance across the range. In fact it proved to be slightly better than its successor here which may originate in the slightly reduced range. And it's truly as good as many fix-focals in its range which is quite baffling.

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

The lens produced a medium degree of chromatic aberrations (color shadows at harsh contrast transitions) at the image borders. CAs are most pronounced at 28mm and 40mm where the average CA pixel width is around 1 pixel at the worst. At 70mm the problem is little reduced. Overall this is a decent performance for a zoom lens. Please note that CAs can be (auto-)corrected via imaging tools.




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