Canon EF 11-24mm f/4 USM L - Review / Lens Test Report - Analysis
Lens Reviews - Canon EOS (Full Format)

Distortion

Canon emphasizes that while the lens has an extreme range, the distortions are low. We wouldn't sign this as such. At 11mm we have measured a barrel distortion of 4.5% which is rather hefty actually. To be fair - Canon is exploring undiscovered lands here so we certainly applaud to them that it isn't more than that really. The issue has eased substantially at 14mm (1.8% barrel distortion) and it's negligible beyond.

Vignetting

The amount of light falloff is, unsurprisingly, excessive at 11mm @ f/4 (3.3 EV/f-stops) but remember that the "natural" vignetting ("cosine fourth" law) takes its toll here as well. Stopping down to f/5.6 improves this drastically but better stick to f/8 or f/11 to tame the issue to a reasonable degree (unless you are after this effect). The same applies to the 14mm setting albeit at a slightly lesser degree. The 18mm and 24mm settings are much better at fully open aperture (1.8EV and 1.3EV respectively) and f/5.6 is sufficiently corrected already.

MTF (resolution) at 50 megapixels

The resolution characteristic varies substantially across the zoom range. Of course, the most difficult setting remains the 11mm setting. The center quality is absolutely stellar even at f/4. However, the borders/corners are soft here. The extreme corners show CAs with a width of up to 8 (!) pixels which has certainly also affected our tool here . Stopping down lifts the quality in the outer image region but not quite as much as you would have hoped. The best quality is reached at f/8 with good to very good borders and fair corners. At f/11 diffraction is already limiting the results.
The situation changes completely at 14mm and 18mm. The center remains outstanding but the borders/corners are MUCH better. The borders are good to very good at f/4 whereas the corners are fair here. However, the corners are boosted to sharp quality at f/5.6 already.
The performance goes a little downhill at 24mm again with softer results at f/4 and f/5.6 but f/8 is decent actually.

The centering quality of the tested sample was good but not perfect.

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

MTF (resolution) at 21 megapixels

Why are the MTFs sometimes "better" on 21 megapixels compared to 50 megapixels ? There are two reasons for this. Lateral CAs are lower in terms of pixel widths at 21mp simply because the pixel density is also lower. Extreme CAs that may exist at 50mp are therefore less affecting the measurements at 21mp. Generally we are also using a certain degree of sharpening during the image conversion (just like in real life images) and because the 21mp results are "sharper" on pixel level they are relatively more receptive to sharpening.

Upon popular request we have revisited the lens once more for an analysis at 21 megapixels. As you can imagine the results are substantially "better" compared to the 50 megapixel MTFs. The center performance remains, of course, outstanding. The borders are good at 11mm @ f/4 whereas the corners are still fairly soft here. Stopping down pushes the borders to good to very good levels and the corners are catching up nicely. At 14mm and 18mm we can observe a further improvement with generally very good borders/corners. The quality of the outer region decreases slightly at 24mm but not by much.

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 (Border CAs)

We got used to rather low lateral chromatic aberrations (color shadows at harsh contrast transitions) lately but the Canon EF 11-24mm f/4 USM L is an extreme lens so it doesn't really come as a surprise that the results are a bit soso at least at 11mm where we measured an average CA pixel width of around 3px at the image borders. As already mentioned this is getting amplified in the far corners with an excessive CA width of up to 8 (...) pixels. However, remember again that this is based on the EOS 5Ds R so the CAs are magnified according to the pixel density here. The CAs are much better at 14mm (around 2px) and not much of an issue beyond.

Note: These are the results at 50 megapixels.

Flare

Such extreme ultra-wide lenses, especially with a bulb-like front element, are very prone to flare in back-light. However, Canon applied its new magic - Subwavelength Coating (SWC) as well as Air Sphere Coating (ASC). The result is actually pretty much surprising. We took a couple of shots straight into the sun and the results only suffered from low glare and few ghostings - much less so than e.g. the Nikkor AF-S 14-24mm f/2.8 ED or some others. Of course, nothing is perfect and if you are pushing it, you will see more issues than in this sample shot (taken at f/11) below.

Note: This image is also available in our sample image section.