The Canon EF 40mm f2.8 STM is a very interesting addition to the Canon EF lens catalogue. The company’s first EF pancake lens, it makes even the chunkier EOS DSLRs look and feel much more compact, and can turn smaller models into something you could more easily squeeze into a large pocket. After all, it’s almost half the thickness of the already pretty compact EF 50mm f1.8 II.
In this respect it’s a fun lens to use, but thankfully it’s more than just a pretty face. The optical performance, as illustrated above, is very respectable even on a full-frame body with the aperture wide open. Sure there’s the usual darkening in the corners at f2.8 but it’s easily corrected in software and underneath you’ll find crisp details. Close the lens to f4 or better still f5.6 and the corner detail looks great. Meanwhile in the middle of the frame the detail is crisp and sharp even at f2.8.
The focusing is also quieter than the basic EF 50mm f1.8 II and better-suited to continuous autofocus in movies, making it a more versatile option in this respect. The price is also sufficiently low to make it an attractive, low risk option.
For full-frame owners though, the EF 40mm f2.8 STM is a much more attractive prospect. It delivers coverage that’s much more usable as a general-purpose lens, and is arguably more versatile than a 50mm. As mentioned earlier, the optical quality is surprisingly good on a full-frame image, with sharp details right into the corners at f2.8, and excellent results at f4-f5.6.For full-frame owners though, the EF 40mm f2.8 STM is a much more attractive prospect. It delivers coverage that’s much more usable as a general-purpose lens, and is arguably more versatile than a 50mm. As mentioned earlier, the optical quality is surprisingly good on a full-frame image, with sharp details right into the corners at f2.8, and excellent results at f4-f5.6.So what’s not to like? Well most obviously on a cropped body the 64mm equivalent coverage feels uncomfortable, neither being wide enough for general purpose use, nor long enough for portrait work. Indeed I’d recommend cropped body owners looking for a light and affordable prime stick with the eternally popular EF 50mm f1.8 II, which lest we forget typically costs 30-50% less, while sporting a focal length and focal ratio which are much more conducive for portrait work. Plus the optical issues suffered by this lens in the far corners of a full-frame image at large apertures are mostly avoided on bodies employing the more forgiving cropped sensor size.
It also doesn’t have to worry about competing with a 50mm for portrait use as it would on a cropped body. Instead full-frame owners would simply go for an 85mm or 135mm for portrait work, and leave the 40mm as a walkaround lens, something its size makes particularly appealing.
So while I wouldn’t recommend it to most cropped-frame Canon owners unless they’re desperate for the smallest lens, it genuinely makes sense for full-framers: small and light, great quality into the corners, and a focal length that’s ideal for general-purpose use. It’s a shame the aperture isn’t a bit brighter, but that’s the compromise with a lens this small. Overall, a recommended walkaround lens for full-frame Canon owners, who fancy something a little different from the norm.