Canon EF 28-70mm f/3.5-4.5 II - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

The lens shows some barrel distortion at 28mm changing to negligible pincushion distortion at the long end. A decent performance for a zoom lens.

28mm:

40mm:

70mm:

The chart above has a real-world size of about 120x80cm or 40x the focal length. Expect more distortions towards closer focus distances.

Vignetting

Typical for many full format lenses on APS-C DSLRs vignetting is no big issue thanks to taking advantage of the sweet spot of the lens. Vignetting is basically negligible expect maybe at 70mm where you may consider to stop down a little in extremely critical situations in order to eliminate the remaining artifacts.

MTF (resolution)

In the lab the lens was pretty capable to live up to its reputation. At 28mm the quality is already pretty good at wide-open aperture and its increasing a little bit to excellent levels at medium apertures. At 40mm and 70mm the lens is even a little better. It may be surprising but according to the local Imatests the lens is only beaten by the EF 28-70mm f/2.8 USM L and even here it´s quite close.

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)

Chromatic aberrations (color shadows at harsh contrast transitions) are pretty well controlled. It's only a real problem at 28mm at wide-open aperture where the average CA pixel width exceeds 1.4 pixels at the border. At smaller apertures as well as at longer focal lengths CAs remain well below 1 pixel which can be considered as good. a relatively minor problem with this lens with an average pixel width of less than 1 pixel except at 28mm beyond f/8 (see also the left roof in the last sample shot below).




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