Canon EF 40 mm f/2.8 STM
4. Image resolution
Let’s glance at a graph below to see how the tested lens fares in the frame centre, on the edge of the APS-C sensor and on the edge of full frame.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
When it comes to the performance in the frame centre you can only praise it. At the maximum relative aperture the tested lens reaches 34 lpmm so a result which guarantees you sharp and useful photos. The Canon 2.8/40 reaches the peak of its possibilities by f/4.0 and f/5.6 where it gets to the value of almost 45 lpmm. It is a very good result, you can even say excellent if you remember we deal here with one of these „pancake” devices which never break resolution records.
We don’t have any reservations conserning the performance on the edge of the APS-C sensor either. Although officially at the maximum relative aperture the lens doesn’t reach the value of 30 lpmm you can say that even there the lens fulfills our usefulness criteria, taking into account the margin of measurement errors. On stopping down the image quality improves but that improvement is not especially effective. Those results are good for sure but they won’t bowl you over.
The edges of full frame are often the Achilles heel of „pancakes”. Taking it into account, our assessment of the Canon’s 2.8/40 performance shouldn’t be negative. Perhaps the maximum aperture is not exactly completely useful but it really lacks little to be so. After stopping down by one stop you get very decent photos. It is worrisome, though, that further stopping down is not especially efficient and in the wide range of apertures, from f/4.0 to f/11, we get just decent results, on the level of 30-32 lpmm.
To sum up: we are pleasantly surprised with the achievements of the Canon 2.8/40. It really performs more like a typical „prime”, without showing the characteristic weaknesses of „pancakes” in an evident way.