Canon EF 300mm f/4 USM L - Review / Test Report - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

As expected for a fix-focal lens the level of distortion is absolutely negligible (0.276%). Same goes for EF 1.4x II tele-converter combination (-0.177%):

300mm:

300mm + EF 1.4x II = 420mm:

The chart above has a real-world size of about 120x80cm. Possibly things may get a little worse with extreme close-ups.

Vignetting

Vignetting is basically a non-issue with the lens - at least on a 1.6x DSLR. Wide-open the vignetting doesn't exceed ~0.3 f-stops which is pretty negligible. When combined with the Canon EF 1.4x II tele converter the problem is even less pronounced.

MTF (resolution & chromatic aberrations)

The lens delivered a very impressive performance in the lab across the tested aperture range. In its naked configuration the lens is capable to deliver excellent results without any significant drop in corner performance. When combined with the EF 1.4x II tele-converters the performance is (naturally) reduced slightly but it still reaches very good figures here except at f/11 where we can already see diffraction effects. So for tripod-based photography the lens is obviously superior to its successor.

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)

Similar to most other tele fix-focal lenses chromatic aberrations (color shadows at harsh contrast transitions) are very low and usually nothing to worry about.

The situation gets a little worse when attaching the Canon EF 1.4x II converter but even here the issue is still quite acceptable.




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