Specifications

Built quality and autofocus

The two Canon have similar built quality; they are solid as a rock and they look very professional; both are weather sealed, while the Sigma has no sealing. The Sigma has a pretty good built quality, too, even though the Canon are a little better. All three lenses does not extend during zooming.

The Sigma has a fixed hood, while the Canon have small removable hoods. A big difference between the Sigma and the Canon is that the Sigma can not use filters due to its protruding front elements, while the Canon can use any filter. Personally I never use filters so I don't care, but if you like filters, keep in mind this difference :-)

All three lenses have true ultrasonic AF motor with full time manual focus. The Canon 16-35 II has the fastest AF, thanks to its bright f/2.8 aperture, but overall they are all pretty good. None of them has image stabilization: even though I take the majority of my landscape photos with the camera on tripod, sometimes I handhold the camera, and in these situations image stabilization would help a lot. I really hope to see stabilized wide-angles in future... 

Image quality comparison

I have tested the lenses on my Canon 1Ds MarkIII (21 megapixel, FF). The lenses was mounted on tripod; I have used mirror lock up and self timer. The following images are 100% crop from the unprocessed RAW file. I have tested the lenses both wide open and at f/11. For most of my landscape photos I use apertures between f/8 and f/16, but wide open performance may be important for night photos.

12/16/17mm, wide open:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

12/16/17mm, f/11:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

In this first comparison I have tried the lenses at their shortest focal length: the Sigma is at 12mm, while the Canon are at 16 and 17mm. In the center, all lenses are about the same, both wide open and at f/11. In the corners, wide open, the Sigma 12-24 and the Canon 16-35 II are about the same, while the Canon 17-40 is a bit softer; at f/11, instead, the Canon 16-35 II is the winner, followed by the Canon 17-40 and Sigma 12-24.

17mm, wide open:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

17mm, f/11:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

Here, instead, I have tested all the lenses at 17mm. Wide open, the Sigma 12-24 is the best in the corners (but keep in mind that wide open for the Sigma means f/5.0, while the Canon are at f/2.8 and f/4), while the Canon 16-35 and 17-40 have better image quality in the center. At f/11, the Canon 16-35II is clearly the best, followed by the Canon 17-40; the Sigma 12-24 is good in the center but soft in the corners (surprisingly, at f/11 it is worse than wide open, in the corners).

24mm, wide open:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

24mm, f/11:

	center	corner
sigma 12-24
canon 16-35
canon 17-40

At 24mm, the differences are small. Wide open all the lenses gives similar image quality (but again, remember that the Canon 16-35 is at f/2.8, the Canon 17-40 is at f/4 and the Sigma 12-24 is at f/5.6); at f/11, the two Canon are slightly sharper, but it is a small difference.

35/40mm, wide open:

	center	corner
canon 16-35
canon 17-40

35/40mm, f/11:

	center	corner
canon 16-35
canon 17-40

At the longest focal, both the 16-35 and the 17-40 are soft in the corners, in particular wide open, while they are very sharp in the center. The 16-35 is the winner, even though you have to stop down to get relatively sharp corners.

Flare

	wide open	f/16
sigma 12-24
canon 16-35
canon 17-40

In terms of flare, the Canons are the best, while the Sigma shows a little more flare, in particular wide open. It is interesting to note, too the different "sunburst" generated by the three lenses at f/16: the 16-35 and the 17-40 are similar (even though I prefer the look of the 16-35), while the 12-24 creates a completely different sunburst with six rays (less pleasing, in my opinion).

Distortion

Sigma 12-24 at 17mm	Canon 16-35 II at 17mm
Canon 17-40mm at 17mm

Even though I don't care much about distortion - you can correct it very easily with Photoshop - it is interesting to see the difference. The Sigma has almost no barrel distortion, while the Canons have much more distortion (the 16-35 is a bit better than the 17-40, but none come close to the Sigma).

Vignetting

	f/4	f/16
sigma 12-24
canon 16-35
canon 17-40

At f/16, all thee lenses are about the same, but at f/4 there is a clear difference - the Sigma 12-24 and the Canon 17-40 have a quite strong vignetting, while the Canon 16-35 is much better in this respect.

Conclusions

In terms of optical quality, the Canon 16-35 II is the winner, by a slight margin. The Canon 17-40 and the Sigma 12-24 comes surprisingly close, and they are much cheaper! The Canon 16-35 II has also the advantage of high built quality and very wide aperture, but you have to evaluate if these advantages are worth the price, depending by your budget and your necessities.

Personally, I still prefer the Sigma 12-24...it is not very bright and it is a bit softer than the Canons at some settings, but its angle of view is truly unparalleled, and for its price it is a bargain.

Do you have comments or questions?

If you have comments or questions about this article, feel free to ask in the Juza Nature Photography Discussion Forum!