The Sigma 18-35mm f/1.8 DC HSM is the worldu2019s first zoom lens with an f/1.8 maximum aperture, but itu2019s not as expensive as you might think. Richard Sibley and Andrew Sydenham compare the lens with the Canonu2019s premium EF 16-35mm f/2.8L II and find out how good it is
Just a quick glance at the resolution charts of the Sigma 18-35mm f/1.8 DC USM reveal that it is a great lens. With an MTF 50% resolution of around 1000lp/ph at f/4, regardless of the focal length, the 18-35mm can actually resolve as much as some of the 50mm lenses we tested previously (see AP 20 July), which is impressive for a relatively wideangle zoom lens.
However, the Sigma is really at its sharpest when shooting at around f/4 at its 18mm setting, which is the equivalent of a 27mm field of view on a full-frame camera. This is good news for those looking for a mid-range zoom lens for landscapes, especially as even at the edges there is only a moderate decrease in sharpness. The only downside is that the minimum aperture is only f/16, rather than f/22. Obviously, landscape photographers will want to maximise depth of field, but thankfully the lens is still acceptably sharp at f/11 and even at f/16 diffraction isn’t so bad that it is unusable.
The images below were taken at the 35mm focal length of each of the lenses. The lenses were focused on the point highlighted, and are shown enlarged.
The Sigma 18-35mm f/1.8 lens resolves fractionally more detail than
the Canon 16-35mm f/2.8 lens, with both lenses at their sharpest between
f/5.6 and f/8
Image: Taken with Sigma 18-35mm f/1.8 DC HSM lens at f/1.8
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/2.8
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/4
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/5.6
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/8
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/11
Images: Taken with Canon 16-35mm f/2.8L II (left) and Sigma 18-35mm f/1.8 DC HSM lens (right) at f/16
Image: Taken with Canon 16-35mm f/2.8L II lens at f/22
Looking at the real-life images above, the differences between the resolution of the lenses are put into a different perspective. There is only a slight difference between the resolving power of the Sigma 18-35mm f/1.8 and the Canon 16-35mm f/2.8 lens. Overall, the Sigma appears slightly sharper in every comparable image, and there also seems to be slightly more contrast in the images taken with the Sigma lens. Of course, the additional contrast is down to the coating on the lens, and when shooting an MTF chart with its many fine converging lines, the extra contrast will help to differentiate the lines, producing better results in the test. So, under test conditions, the Sigma does produce more detailed images, but in real-world results the difference is less noticeable than the results would have us believe.
Vignetting is so minimal across the different focal lengths of the Sigma lens that it should really be of no concern. The Canon 16-35mm has an even better performance, which is most likely due to the fact that it is a full-frame lens being used on a camera with an APS-C-sized sensor.
As expected from two lenses with such complex designs and wide focal lengths, there is quite a bit of curvilinear distortion present at either extreme. At the shortest focal length the distortion will require some correction, either in-camera or when editing raw images. The results of the distortion for both lenses at their widest field of view are remarkably similar, although the Canon lens has the advantage at the 24mm focal length setting and by around 28mm the distortion is almost zeroed. At 35mm, both lenses begin to show pincushion distortion. The pincushion distortion is fairly minimal and with some subjects images it won’t even need correction.
It would be difficult to talk about the Sigma 18-35mm f/1.8 DC HSM without mentioning the performance of the lens at f/1.8. The lens coating and level of contrast mean that the performance is excellent and the lens has a lovely smooth out-of-focus bokeh. Combined with the shallow depth of field produced, the lens is great for taking mid-length portrait images when set to its 35mm focal length, with the aperture throwing any distracting backgrounds nicely out of focus.
Overall, the image quality of the Sigma 18-35mm f/1.8 DC HSM lens is excellent, especially when you consider that it is a world first.