It is 35mm day (Lens, not Film) at LensRentals: Canon EF 35mm f/1.4L & EF 35mm f/2 IS versus Sigma 35mm f/1.4 DG HSM resolution tests by Roger Cicala: No Canon can beat that Sigma.

This is a nice lens with a very nice IS system at a fairly high price
Canon EF 35mm f/2 IS USM
Canon EF 35mm f/2
Canon EF 35mm f/1.4L USM

"Looking at the average (mean) for center, average, and corners shows a bit more about the lenses. The old 35mm f/2 does quite well in the center and mid-lens areas, but it’s pretty awful in the corners. The new 35mm f/2 IS and the classic 35mm f/1.4 L do much better in the corners, with the 35 L (stopped down to f/2) clearly better than the new f/2 IS. But the Sigma does better than any of them.

As always, remember these are just one measurement of resolution. There’s a lot more to a lens than resolution, of course.

Our new toys let us do some other measurements as well. Chromatic aberration is low for the Sigma and the new IS f/2 lens at 0.7% and 0.9% respectively at the lateral edges. The Canon 35mm L is higher at 1.3% and the original 35mm f/2 far worse at almost 2%. The Sigma also had the lowest distortion at 1% barrel, with the 35L higher at 1.3%, and both the new and old 35mm f/2 versions at 1.4%.

One other thing that’s interesting is to compare sagittal and tangential MTF lines from center to corner on the lenses. Below are the measurements for Canon 35mm f/2 IS and the Sigma 35mm f/1.4. Notice that these show MTF30, not MTF50 as we reported above, so the numbers are different. I didn’t put the graph of the Canon 35L up, but it’s nearly identical to the f/2 IS graph below."

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