In The Reality of Zoom Lens Performance, I discussed reasonable expectations for zoom lenses.
Having just purchased the Sigma 14-24mm f/2.8 DG DN Art, I thought a brief discussion was in order on what I found.
I compared the two samples of the Sigma 14-24mm f/2.8 DG DN Art at 24mm, as that is the weak end of the design.
- The first sample (the one I shot on my trip) is weak on the left side, and skews its sharpness rearward on the right side.
- The new sample skews its focus strongly forward on the right side and rearward on the left side—the reverse of the first sample.
Averaging it all out, I’d say they are comparable, but quite different in their skewed planes of focus. Thus the need to thoroughly understand a specific sample of a specific lens model when aiming for optimal results.
It is why, for example, I always focused the first sample on my trip towards the top right of the frame (when focusing at distance)—this was the optimal way to do it for that sample, but the top left would be optimal for the 2nd sample.
The whole situation is ridiculous, and it’s not just Sigma. NONE of this should be taken to mean that I think Sony zooms are better, indeed I think Sony lenses are at least as prone to such issues. It is also an argument for primes, except that high performance prime lens designs suffer similar issues. Still, Zeiss Loxia lenses have been very consistent for me in terms of symmetry (my Loxia 21/2.8, 25/2.4, 35/2, 50/2, 85/2.4 all have excellent symmetry) and I rate them highly for that reason.
I don’t expect a sample to have perfect symmetry, but this symmetry variation of the Sigma 14-24mm f/2.8 DG DN Art is so strong that a comparison is absurd, that is, in the sense of determining which lens is sharper. Even just getting AF to agree on the same focus at center proved troublesome.
For my meticulous work, I am not content with lenses that are clearly weak on one side or the other: asymmetry creates all kinds of execution headaches, and complicates focus stacking even at f/8 (creates confusion when retouching because of where sharpness lands).
All that said, I made many fine images with the Sigma 14-24mm f/2.8 DG DN Art, and at f/8 it has little if any competition, excepting the Zeiss Loxia 24mm f/2.4. So I still recommend it/both.
I’ve decided to send this new sample back. Maybe in 6 months Sigma will get its act together and I will re-buy. When I do buy again (I plan to), I will probably have to try 3 or 4 samples to find one I am satisfied with.
Or maybe Sigma can read this and send me a sample to prove to me they can actually build a real lens that performs to claims. Until then, I consider all Sigma claims of performance and MTF testing to be marketing bullshit.