Canon EF 17-40 mm f/4.0L USM
6. Distortion
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The tested lens is designed for the full frame and on an APS-C detector should have good results as far as the off axis aberrations are concerned. And that is the situation indeed. The distortion is corrected accurately and even at the wide filed of view – 17 mm – its value reaches an acceptable level of –2.74%. It is worth adding that the Canon 17-85 mm had weaker results of –5.7% and the Canon 17-55 mm had a result similar to the L-grade lens one. The lenses of other firms noted much weaker results. The Tamron 17-50 mm had results of –3.7% and the Sigma 17-70 mm of as much as –4.0%.
The geometric distortions become almost completely absent when we increase the focal length. At 28 mm barrel distortion is present but its value reaches only –0.41%. The situation is even better at 40 mm, where the distortion becomes pincushion but its level reaches only 0.15% and is almost invisible.
