Most of you know I’ve been very impressed with Sigma’s new Art lenses. Their 35mm f/1.4 Art I still think is the sharpest 35mm prime lens made. The 50mm f/1.4 Art is also superb.
When I heard about the Sigma 24mm f/1.4 Art lens, I had some mixed emotions. I was excited that we might get a 24mm lens of similar quality to their 35mm. But the logical side of me thought that perhaps Sigma had bitten off a bit more than they could chew this time.
Designing a wide-aperture 24mm lens is much more difficult than designing a fast 35mm lens. Even the best 24mm f/1.4 lenses (I consider the Canon 24mm f/1.4 L to be the best current offering, although that’s arguable) still have distortion, aberrations, and some edge softness.
But when our first five copies of the Sigma 24mm f/1.4 arrived, I swiped them from intake and took them over to the testing lab for a quick look and MTF testing on our optical bench. We already had results from the Canon 24mm f/1.4 L, the Nikon 24mm f/1.4 ED AF-S, and the Rokinon 24mm f/1.4 lenses in our database to compare them to.
For those of you who don’t speak MTF, I’ll summarize a bit. In the center 1/2 of the lens (from 0 to 10mm) the Sigma clearly is more contrasty and has better resolution than even the Canon lens, especially at higher (40 lp/mm and 50 lp/mm) frequencies. In the outer part of the image (from 15mm to 20mm) though, the Canon and Sigma are about the same. The Sigma is better than the Nikon all the way out to 15mm, but again, in the outer areas there is either no difference or the Nikon is slightly better.
The Rokinon is a rather different lens. It doesn’t resolve as well as either the Nikon or the Canon, and not nearly as well as the Sigma in the center of the image. The Rokinon’s advantage is that its curves remain flat almost to the very edge of the image circle, and again in this outer 1/4 of the image it is as good as the Sigma, or perhaps a bit better.
What the MTF curves suggest, then, is that Sigma has made the best resolving 24mm lens in the center of the image, but at the outer edges they’ve run up against the same aberrations and problems that designers of 24mm lenses have always faced, and haven’t managed to overcome those.