![dslr test chart dslr test chart](https://i.ytimg.com/vi/Ml8MUyzLamM/maxresdefault.jpg)
Looking a bit beyond the APS-C scope it is worth to mention that the lens didn't perform quite as well during our corresponding full format test so the straight-forward idea of buying it now for an APS-C DSLR and using it at a later stage on a full format DSLR may not be as desirable as it may appear. The quality of the construction is next to perfect. Typical for most wide-angle zooms chromatic aberrations can be visible but the problem remains comparatively low. You may spot some barrel distortion when using the lens at 17mm but it's not all that bad. Vignetting is very well controlled - at least when using it on an APS-C DSLR. It's generally very sharp and contrasty across the image field. The Canon EF 17-40mm f/4 USM L is a very good performer without a significant weakness. The problem is almost negligible when stopping down to f/5.6 or beyond. The problem is most pronounced at f/4 with average CA pixel with just over 1px. If you want to know more about the MTF50 figures you may check out the corresponding Imatest ExplanationsĬhromatic aberrations (color shadows at harsh contrast transitions) are fairly moderate for a lens in this class. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. Please note that the MTF results are not directly comparable across the different systems!īelow is a simplified summary of the formal findings. Thereafter diffraction effects introduce a negative effect (unavoidable). The peak quality is reached between f/5.6 and f/8.
![dslr test chart dslr test chart](https://m.media-amazon.com/images/I/81WGJzQF5KL._AC_SX425_.jpg)
The borders are generally very sharp as well although it helps to stop down a little (f/5.6) - same goes for the extreme corner performance. The center quality is on a very good to excellent level throughout the tested range. The EF 17-40mm f/4 L showed a very good performance in the lab. aperture without disturbing edge shading. Move the mouse cursor over the focal length text marks below to observe the respective distortionĪPS-C DSLRs such as the EOS 50D can take advantage of the sweet spot of full format lenses so vignetting The charts below show the findings based on the initial test - the distortion characteristic cannot change just by mounting the lens to a different (APS-C) DSLR. Compared to native APS-C lenses this is fairly moderate. At 24mm there is very slight barrel distortion whereas at 40mm the problem is negligible. The lens produces a quite strong degree of barrel distortion at 17mm (~2.5%).