Lens review

Canon EF 40 mm f/2.8 STM

8. Vignetting

As you see, there is still nothing worrisome here. At the maximum relative aperture the vignetting reaches a moderate level of 24% (-0.80 EV) and by f/4.0 it decreases to an imperceptible value of 9% (-0.27 EV).

More problems you can encounter on full frame and thumbnails, presented below, show it very well.

The maximum relative aperture gives us a lot of reasons to complain – in its case you should take into account the fact that brightness loss in the frame corner might reach as much as 52% (-2.1 EV). On stopping down the aperture to f/4.0 the level of this aberration decreases to 30% (-1.04 EV). Further stopping down is not as effective, though. By f/5.6 the vignetting is 21% (-0.67 EV) and by f/8.0 it gets to 19% (-0.60 EV). Implementing higher aperture values doesn’t decrease the vignetting any further.