Lens review

Canon EF 300 mm f/4L IS USM

4. Image resolution

The graph below shows the Canon’s EF 300 mm f/4L IS USM performance in the frame centre based on the strength of RAW files from an EOS 20D.

First, let’s look how the lens fared without a converter (red dots). Here, the behaviour is difficult to be faulted – the lens did a great job indeed. As soon as from the maximum aperture the image quality is very good; on stopping down to f/5.6 it even becomes excellent. It is worth notice that the lens’s performance is better than that of a Sigma 100-300 f/4 set at 300 mm or a Canon 100-400 mm set at 300 mm.

When the lens cooperates with a converter, the situation is a bit less rosy though. At the maximum aperture we just border on the 30 lpmm decency level and only by f/8.0 we can start speaking about good quality images. It’s worth stressing that the Canon 100-400 mm at 400 mm fared better in our tests than the Canon EF 300 mm f/4L IS USM with a converter attached. By f/8 the difference becomes negligible and within the margin of error but by f/5.6 the zoom performs significantly better than the prime lens with a converter.

It often happens that good zooms can rival the primes for sharpness in the frame centre but usually they lose the competition at the edge of the frame. Here we deal a situation that clearly proves that rule – the Canon EF 300 mm f/4L IS USM puts both to the Sigma 100-300 mm and the Canon 100-400 mm in their place. It doesn’t concern the performance with a converter, though, when the lens + converter set fares significantly worse than the Canon 100-400 at 400 mm.

At the end of the chapter we traditionally present our test charts crops and, in addition, a field comparison of our tested lens with a lot cheaper Canon 70-300 mm IS set at 300 mm.

Comparison with a Canon EF 70-300 IS USM