Quick comparison: Canon EF-S 24mm v. Sigma 17-70mm mk 2


Last week I bought the new Canon EF-S 24mm F2.8 STM lens from Canon. This is a lens that only works on crop sensor cameras. STM is short for stepper motor and provides a relatively fast and quiet means of focussing. What the name doesn’t convey is that this is also a very flat lens (a so-called ‘pancake’) and at 125 grams a very light lens.

For comparison my Sigma 17-70mm F2.8-4.0 zoom lens (second edition) weighs four times as much, which may not sound like much, but when you want to travel light every little bit helps.

I bought the 24 so that I don’t always have to bring the 17-70 with me (I already have a solution for 50mm and higher).

Reviews of the 24 are glowing without fail, but when I started shooting with it, I did not notice much difference with my Sigma zoom, which is generally known as a rather pedestrian lens. So I wanted to know what’s up and took a couple of test shots on my Canon EOS 600D camera.

Note that the following is definitely not even close to what in pixel peeping circles is termed ‘scientific’. I don’t need to know what a lens does at pixel level as long as it holds up well for photos that get scaled down a couple of times, because when I publish photos it is generally at a web resolution of 1 or 2 mega-pixels.

The following photos are available at 1200 pixels wide. Click them for the full size. In every comparison the Canon photo is shown first, followed by the Sigma.

Wide shot

I expect to be using the lens a lot for this type of shot and for medium shots.

I shot using (cover your children’s eyes) the automatic setting (P). The camera chose F9, 1/320s, ISO 100 for the Canon and the same settings except 1/250s for the Sigma. The DXO Labs comparison of the two lenses suggests that the Canon lets in more light for the same F value, so that might explain the differences in shutter speed. The photos were taken hand-held and focus was acquired using CDAF on the top left white window of the nearest building.

These photos already tell me most of what I wanted to know, namely that the two lenses are similar enough that scaled down to a resolution close to what I typically use, there is no significant difference along any vector you care to choose: sharpness, colour rendition and so on.



Checking that window at 100%, you can see that the Canon seems slightly sharper, but the difference is too small to worry me. The difference may be caused by a number of variables that have nothing to do with the lens. I certainly wouldn’t leave the Sigma home over this bit of evidence.


When I look at the 100% view (not shown here) of the nearest red roof in the picture, the vertical lines separating some of the roof tiles disappear in the Sigma picture where they remain visible in the Canon picture. As you can see that sort of detail makes up a tiny proportion of the final picture. That type of detail is not something I am interested in retaining for the sort of photos I generally take. Still, it is good to see the Canon pancake do well in this respect.

Macro and close-up

Both the Canon and the Sigma have an interesting feature in that you can get very close to a subject and still get it in focus. They both advertise this as macro capability. Since 24mm is equivalent to 38mm on Canon’s APS-C cameras, you can get really close and still get a nice bit of blurry background in the photo.



What’s interesting here is the change in perspective. I shot these close-ups on a tripod and took care not to move the tripod in between photos. Note that the camera doesn’t tell you which focal length you are shooting at. I had to shoot a test scene first using measurements I got from the dimensional field of view calculator I found at one Max Lyons’ site. In English, I placed an object that was 93 centimetres wide at a distance of 100 centimetres from the sensor, zoomed the Sigma in to the point where the entire width of the object filled the screen, and kept that zoom setting for all the test photos I took with that lens.

When I looked at the EXIF data of the photos, the Sigma results said 23mm instead of 24mm. It could be that such a small difference in focal length already results in such a great difference in the photos. Or maybe the way zoom lenses are constructed cause this difference, I really don’t know.

What you cannot see here is that you can get even closer with the Canon, because it is such a small lens. The Sigma will at one point cast its own shadow in your photos.

Both photos where shot in P mode resulting in F4.0 (F4.5 for the Sigma), 1/60s and ISO 100.

The following are 100% crops (after the click).



I focused on “EOS” in “only in EOS digital cameras” for the Canon test, whereas I accidentally changed to “EOS” in “für digitale EOS Spiegelreflexkameras bestimmt” for the Sigma photo.

When you peep pixel you may notice that both lenses are nice and sharp, that the Canon has slightly more chromatic aberration (both seem well controlled though), but that the Sigma has a fairly nasty rendition of high contrast out-of-focus areas. Your may well disagree, the differences seem small. I had noticed the busy high-contrast out-of-focus areas in Sigma photos before – I’ve been shooting this lens for a while now. If the Canon does better in this area I am going to be a happy camper.

Finally I will show you two 100% crops of out-of-focus areas. I find both renditions fairly pleasant.



So here’s my conclusion.

For the type of photography I do, my copy of the Canon may be slightly better than my copy of the Sigma. I would have been happy even if the results were reversed, so this is good news. The one thing I haven’t tested is shooting the Canon wide open (F2.8) in dark environments. The shutter speeds I will be using it at are 1/60s – 1/160s, depending on the subjects. The Canon, unlike the Sigma, does not have image stabilisation, but since I will be mostly photographing people (who will move without notice), I will probably have to keep the shutter speeds relatively high anyway.

In the end it seems I have achieved my goal of getting a lighter lens for my wide-angle needs.

On a more general note, the Canon EF-S 24mm F2.8 STM seems to be a nice pancake. If your needs are similar to mine, but you need to change focal lengths a lot, you may prefer the zoom lens. Note that a new version of the Sigma tests significantly better than my version at DXO and is also smaller and (slightly) lighter.