4) Lens sharpness, contrast and color rendition
As I reveal below, the sharpness performance of the Sigma 24-35mm f/2 is simply amazing. I was quite shocked to see the lens outperform all of the Nikkor f/1.8G primes in center resolution. In fact, based on the performance of the lens at 24mm, the 24-35mm f/2 Art now holds the crown as the sharpest lens I have tested to date, with an Imatest score of 3235 in the center of the frame at f/2.8. While that’s certainly very impressive, such performance does come at a cost – the lens exhibits some focus shift.
When focusing on a subject wide open at f/2, the lens would yield very impressive mid-frame and corner performance in the expense of center performance when stopping down to f/5.6 and smaller. Imatest showed slightly lower performance in the center compared to mid-frame and the corners at f/5.6-f/11 range, which is a sign of focus shift. To keep center resolution high, I had to re-focus at f/4 using live view and re-measure the lens performance at different apertures. Although focus shift was not significant (not a big deal for most types of shooting), you might need to check your images when shooting in the field and potentially re-acquire focus at your desired aperture using live view.
Let’s now take a look at some Imatest numbers at different focal lengths:
The Sigma 24-35mm f/2 Art is a stunner at 24mm. Its wide open performance is superb and when stopped down to f/2.8, I was able to reach such high performance that no other lens has demonstrated before.
At 28mm, the lens gets a bit weaker at wide apertures, but not all that far from 24mm. By f/4 it reaches superb levels of sharpness and stopping down to f/5.6 results in excellent mid-frame and corner sharpness.
Zooming in to 35mm does not drastically change the overall picture – the lens performs amazingly well here, reaching best overall performance at f/5.6.
It is hard to understand just how good the above numbers are without comparing them to other lenses. Check out the lens comparisons section, where I put each focal length side to side with the Nikkor f/1.8G primes!
With such a wide coverage and a maximum aperture of f/2, I would not expect this lens to produce stunning bokeh – that’s just not what the lens is designed to do. If you need a solid portrait lens capable of rendering beautiful, creamy bokeh, you will be better off with a dedicated portrait lens in the 50mm+ range. However, if you often shoot wide open and you want to see how well the lens does in terms of rendering out of focus subjects, I have included a couple of images captured in the f/2 to f/4 range in this review. In short – not bad, but not great either. Out of focus transitions look pretty smooth, but if you are concerned about highlights in the background, you should be aware that this lens won’t do magic. Lenses such as the 24-35mm f/2 with aspherical elements tend to perform poorly with background highlights, showing “onion-ring” bokeh.
Here is a sample image captured at f/2:
Most lenses heavily vignette when shot wide open, especially on a full-frame body. As expected, the Sigma 24-35mm f/2 vignettes quite a bit wide open, with vignetting levels falling sharply when stopped down beyond f/2.8. Here are the vignetting levels measured by Imatest:
As you can see, vignetting is quite strong at f/2, measuring over 3.5 stops at close focus. Vignetting is not that noticeable at infinity, although it is still on the heavy side. If it bothers you, it is relatively easy to fix in post-processing software like Lightroom and Photoshop.
7) Ghosting and Flare
The Sigma 24-35mm f/2 Art handles flares and ghosting very well. When shooting against a very bright source of light such as the sun, if the light source is in the extreme corners, you might see some flare and ghosting in your images, which is normal and expected from most wide angle lenses. The provided lens hood is light and not overly obtrusive, so I would keep it on the lens at all times. When using the lens with filters, I got in the habit of reversing the lens hood and keeping it on the lens, although it made the focus ring a bit tougher to access in situations when I had to focus manually. Please keep in mind that using UV and other filters can potentially introduce more flares and ghosting to your images.
Unfortunately, distortion is the weak spot of the Sigma 24-35mm f/2, as it exhibits both barrel and pincushion distortion at different focal lengths. Take a look at the below chart, which illustrates the distortion behavior of the lens:
As you can see, the lens exhibits pretty strong barrel distortion measuring around 2% at 24mm, which gets significantly reduced at the 28mm mark (non-existent at around 30mm) and then transitions into pincushion distortion at 35mm.
9) Chromatic Aberration
Lateral chromatic aberration levels stay very light (below 1 pixel) at all focal lengths, which is quite impressive:
Most similar lenses typically stay in the 1.5 to 2.5 pixel range, so the performance of the 24-35mm f/2 is surprisingly good here.
10) Infrared Performance
Unfortunately, the Sigma 24-35mm f/2 suffers from hot spots, most likely due to use of aspherical elements. They are subtle, but definitely visible, especially when stopped down to f/8 and smaller range. I ended up converting my IR images to black and white, since the hot spot in the colored versions looked pretty bad and it was impossible to work with.
On the next page of this review, we’ve compared this Sigma against other lenses on the market around these focal lengths: