Canon EF-M 22mm f/2 STM - Review / Lens Test - Analysis
Lens Reviews - Canon EOS (APS-C)

Distortion

In terms of distortions, Canon did a great job. It's absolutely negligible which is astonishing really.

Vignetting

On the downside vignetting isn't really a strength of the Canon EF-M 22mm f/2 STM. At fully open aperture, there's a heavy amount of light falloff in the corners - it's actually a bit beyond our usual APS-C scale here. Stopping down to f/2.8 reduces the issue but it remains visible in critical situations even when stopped down to medium apertures. This is probably where cost cutting measures of this very affordable lens are most obvious.

MTF (resolution)

Pancake lenses are usually pretty good regarding their resolution characteristic although they rarely achieve top results. While we have yet to test further EF-M lenses, the Canon EF-M 22mm f/2 STM follows this general guidance. The center quality is excellent at f/2 and the borders are also impressive but the corners are soft here. Stopping down to f/2.8 lifts the corner results but the real boost sets in at f/4 where images are very sharp across the frame (notwithstanding Depth-of-Field, of course). This high level is kept at f/5.6. Image softening due to diffraction is getting more obvious from f/11 but that's a physical limitation.

The centering quality of the tested sample was Okay. Field curvature is moderate but visible.

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)

The amount of lateral CAs remains moderate with an average CA pixel width of around 1px at the image borders. This aspect is usually taken care of by the camera's auto-correction or in Canon's RAW converter.

At f/2 you may sometimes spot a hint of purple fringing in scenes with extreme contrasts.