The Canon EF 40mm f/2.8 STM pancake lens has been around long enough that most people have stopped thinking about it. That's a mistake, especially now that used copies are selling for cheap and the lens adapts cleanly onto modern mirrorless bodies.
Coming to you from Christopher Frost, this thorough revisit takes a lens Frost wasn't happy covering the first time and puts it through a proper test on two demanding modern sensors. He mounts it on the Canon EOS R5 with its 45 MP sensor and the Canon EOS R7 with its 32.5 MP APS-C crop sensor, both via adapter. On full frame, sharpness at f/2.8 is strong in the center, though the corners show low contrast at wide open due to coma smearing. Stop down to f/5.6 and the image is sharp corner to corner, staying that way through f/11. That's a solid result for a lens at this price, regardless of age.
On the R7's APS-C sensor, the story is a little different. The center holds up well from f/2.8, but the corners need f/5.6 or f/8 to come fully together. Frost notes that on a 24 MP sensor or lower, the corners would likely look fine at wider apertures. The lens weighs just 130 g, uses a metal mount, and controls are minimal: an autofocus/manual switch and a narrow manual focus ring that turns loosely and responds slowly. There's no weather-sealing and no image stabilization built in, though it works with the R5's in-body stabilization without issue.
A few things are worth knowing before you buy. The autofocus motor is audible and slow, and Frost is direct about it: it makes a whirring sound that a camera's internal microphone will pick up, and it slows down further in video mode. If you shoot sports or anything that needs fast autofocus, this isn't the right tool. Bokeh is actually a pleasant surprise here, with smooth out-of-focus backgrounds in most situations. There's some coma at f/2.8 in the corners, but it clears up by f/5.6. Frost also covers distortion, vignetting, flare resistance, sun stars, and longitudinal chromatic aberration in detail, and the results are worth seeing for yourself.
The 40mm focal length sits close to what the human eye sees on a full frame body, which makes it a genuinely useful and unobtrusive focal length for everyday shooting. If you already own a Canon EF-to-RF adapter, picking up one of these used is a decision that's hard to argue against for general use. Check out the video above for the full breakdown from Frost.
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