Review Canon EF 40 mm f/2.8 STM @ Canon 650D (C APS-C)


To our great surprise, Canon launched not only the Canon 650D, but also two new lightweight and compact lenses in June 2012: Canon EF-S 18-135mm f/3.5-5.6 IS STM and Canon EF 40 mm f/2.8 STM pancake lens. The Canon EF 40 mm is Canon’s first pancake lens in the EF series lenses. According to Canon, this lens is ideal for photographers who are looking for a versatile, compact, and lightweight lens for portrait, reportage, travel or landscape photography. How good is such a small Canon pancake lens?LENS-EF-40mm-product

Canon EF 40 mm f/2.8 STM @ f/4
ResolutiondemoCanon650DCanon EF 40 mm f/2.8 STM @ f/8

The size of the Canon 40 mm makes it a good partner for Canon cameras with an APS-C sensor, but in terms of focal length, it is a good choice for a camera with a full frame sensor. A 40 mm lens on a camera with an APS-C sensor has the same field of view as a 64 mm lens on a camera with a full frame sensor. The 64 mm focal length of the Canon 40 mm makes it not a perfect standard lens, a perfect short telephoto nor portrait lens on the Canon 650D.

The Canon 40 mm pancake yields very sharp images. Click on the right picture for a larger crop. Light reflections on the water resulted in much more limited star bokeh, in comparison to the Canon 17-55 mm or Canon 17-85 mm under the same conditions. Click on the left image for an illustration of the diffraction bokeh / star bokeh.

Construction and autofocus

On this tiny 40 mm lens, Canon has still found enough space for an AF switch, which is much more user-friendly than choosing MD/AF in a menu.

The Canon 650D quickly focuses in combination with the Canon 40mm STM, but not that quickly. The lens is stationary during focusing, but not very quickly. The steps AF motor (STM) provides improved AF during live view video. At present, the Canon 650D is the only Canon camera offering that option.

In-camera lens correction

The test of the Canon 40 mm STM is performed on a Canon 650D, with the camera correcting for vignetting and chromatic aberration. The graphs below are based on jpg files created with the Canon 650D. Users of RAW files might observe – in theory – higher vignetting and chromatic aberration, since RAW files are not corrected by the camera. Our test shows that there is little difference between RAW and JPG files for vignetting or chromatic aberration.Lensafwijkingscorrectie

Image stabilization

The Canon EF 40 mm 2.8 STM has no built-in image stabilization. Given the relatively low focal length and maximum aperture of f/2.8, this is acceptable.


Vignetting can often be a problem for a pancake lens. Nevertheless, with the Canon 40mm pancake, the amount of vignetting is low. Only at f/2.8, the vignetting is visible, for example if you take a picture of a clear blue sky. However, after stopping down just 1 stop, vignetting is no longer visible. This good performance is not due to the in-camera lens correction. In the RAW files, we measured even lower values ​​for vignetting with Imatest than for the jpg files.


The Canon 40 mm shows little distortion. It will not bother you, even in critical applications such as architecture, photography.Canon-EF-40-mm-distortion


The circular, seven-blade diaphragm delivers reasonably attractive background blur. At full aperture, the bokeh in the center is nicely circular, but @ f/2.8, the bokeh changes towards the corners in cat eye bokeh due to vignetting. At f/4, the vignetting disappears and the cat’s eyes changes into beautiful circles. Click here for a larger crop of the bokeh image.


With only 6 elements in 4 groups and a 18 mm front lens, there is almost no glass to arouse internal reflections. In addition, the lens elements are coated to minimize reflections.
In practice, we encountered no flare, apart from a slight star-bokeh, which we have shown at the top of the page. Under extreme circumstances in the studio, we still managed to cause flare and ghosting (move your mouse over the image). However, you will not encounter such extreme situations in real life.


In terms of resolution, the Canon 40mm pancake lens combined with the Canon 650D performs better than all other Canon lenses at a focal length between 50 mm and 80 mm (full frame equivalent) that we have tested so far on a Canon camera with an APS -C sensor. Moreover, among these lenses previously tested by CameraStuffReview are illustrious names as the Canon 24-70 mm, Canon 17-55 mm and the Canon 24-105 mm. The resolution in the extreme corners is nearly equal to the resolution in the center at all aperture settings. Above f/11, the resolution decreases due to diffraction.Canon-EF-40-mm-resolution

Chromatic aberration

The Canon 40mm STM shows no chromatic aberration. This applies to both RAW and jpg files. The Imatest measurement results of Canon 650D jpg files are shown here.Canon-EF-40-mm-chromatic-aberration

Conclusion Canon EF 40mm f/2.8 STM review


  • Compact
  • Good quality: very high resolution, very low distortion and chromatic aberration, low vignetting.


  • Less common focal length for a camera with an APS-C sensor
  • No built-in image stabilization

In terms of focal length, the Canon 40 mm pancake lens on an APS-C sensor camera is too large for a standard lens and too short for a telephoto / portrait lens. Nevertheless, in terms of price and image quality, it is an excellent lens. Chromatic aberration, vignetting and distortion are all perfectly low. The sharpness of the Canon 40 mm pancake lens in combination with the Canon 650D is better than all Canon lenses that we have previously tested at a focal length between 50 mm and 80 mm (converted to full frame) on a Canon camera with an APS-C sensor. The sharpness in the extreme corners is nearly equal to the sharpness in the center, at all apertures. Excellent.


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