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Reviewing the Canon EF 40MM F/2.8 STM lens

Kelly Lynch explores the STM and brings you the essential information you need to know


19 September 2012


Kelly Lynch explores the STM and brings you the essential information you need to know

Canon’s new standard fixed 40mm lens is so slim and light (just under 3cm protruding from camera body to lens cap edge and weighing 130g) it can slip into a gear bag or pocket with little bother. The company already has a healthy stack of 50mm lenses on their books, each with wide apertures, like f/1.8, f/1.4 and f/1.2, which might leave one wondering why introduce a 40mm f/2.8 STM lens — what’s its point of difference? The STM signifies it has ‘stepping motor’ technology, designed to smoothly and silently autofocus with cameras constructed with the Movie Servo AF feature, like Canon’s new entry-level EOS 650D, to eliminate ugly whirring sounds generated by autofocus. Canon has also recently produced another STM lens, the 18–135mm f/3.5–5.6 IS.

Unfortunately during the review period no 650D model was available to trial in conjunction with the lens so I can’t report on its performance with that camera, but mounted on a 5D Mark III it is impressive how very quiet the autofocus is. I also tried it on a 5D Mark II but autofocus doesn’t work in video mode and manual focus movement records as a distinct shuffling sound.

This lens has a metal mount and truly lives up to the ‘pancake’ label: from the rear it is hard to tell a lens is even attached as nothing protrudes in front. It is half the depth of Canon’s 50mm f/1.4 USM. Its rubber focusing ring (very narrow with a 5mm width) moves with ease and flicking the auto/manual focus switch takes a concerted effort with a thumbnail because of its positioning so close to the camera body.

As a pancake lens it lends itself to being a discreet piece of kit for street, documentary or travel photography — for still shots it autofocuses quickly with little noise as the lens protrudes in and out, albeit a tiny distance. Its focal length also makes it ideal for portraiture and videoing.

The aperture range extends from f/2.8 to f/22 and I was really impressed with the sharpness of images shot between f/4 to f/16. In unscientific testing there were no signs of vignetting, and flare only occurred when the lens was pointed almost directly at the sun.

If you plan to use the lens for movie making you’ll want to be using either the EOS 650D or 5D Mark III to really take advantage of its features — but if it’s a very reasonably priced, lightweight, standard fixed lens for stills you’re after then this is a lens that’s hard to look past.

This review is from D-Photo issue 50. Get your copy here.


  • Focal length: 40mm
  • Maximum aperture: f/2.8
  • Minimum aperture: f/22
  • Image stabilization: No
  • Aperture blades: Seven
  • Optical construction: Six elements in four groups
  • Minimum focus: 0.30m
  • Maximum magnification: 40mm
  • Dimensions (WxH): 68.2×22.8mm
  • Weight: 130g Filter: 52mm