Canon EF 40mm f/2.8 STM

By Jim Fisher

The Canon EF 40mm f/2.8 STM ($199.99 direct)? lens is one of the smallest you'll find for Canon cameras. Its pancake design barely juts out from a camera when mounted. It can be used on full-frame and APS-C D-SLRs, and provides smooth autofocus for video recording when paired with the EOS Rebel T4i?. Even though it doesn't have a fast f/1.4 or f/2 aperture, the EF 40mm is a solid performer. It can be utilized by Rebel owners and pros with full-frame rigs alike, which is why we're giving it our Editors' Choice award for standard-angle prime lenses.

At just 0.9 by 2.7 inches (HD) and 4.6 ounces, the EF 40mm is one of the smallest autofocus lenses you'll find that can provide full-frame image coverage. The Pentax DA 40mm f/2.8 Limited, the kit lens for the K-01 ?mirrorless camera, is smaller, but only covers an APS-C image circle. It uses 52mm filters and has a focus-by-wire design?there's no physical connection between the focus ring and the lens barrel, so moving it when the lens is set to manual focus simply causes the STM focus motor to adjust the focus. If you usually live in autofocus mode this won't be an issue, but it doesn't have the same tactile feel as lenses where there is a physical connection for manual focus.

I used Imatest to check the performance of the lens when paired with the full-frame EOS-1Ds Mark III??D-SLR. Even at its maximum aperture the sharpness is well in excess of the 1,800 lines per picture height that denote a sharp image. At f/2.8 it records 2,247 lines, and its sharpness increases incrementally as you stop down?it tops out at 2,663 lines at f/5.6. Distortion is a nonissue, as the lens only exhibits 0.4 percent barrel distortion, an amount that is negligible in real-life shooting conditions.

The EF 40mm f/2.8 STM is the total package as far as lenses go. It's compact, inexpensive, sharp, and shows minimal distortion. The STM motor makes it a great companion to the T4i, and the full-frame coverage means that it will remain useful to APS-C shooters if they decide to move up to a full-frame camera. The only real problems with the lens are its focus-by-wire system, which will only bother manual focus shooters, and its f/2.8 maximum aperture?but if Canon had pushed the design to f/2 it would undoubtedly have been a larger, more expensive optic, and likely not as sharp wide open. The advantages of the lens greatly outweigh its drawbacks, earning the EF 40mm f/2.8 STM our Editors' Choice award for standard-angle prime lenses.

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