Studio Tests (Full frame)
The Sigma 35mm F1.4 DG HSM delivers truly excellent results on full frame cameras - again it's at least as good as anything else in its class. Sharpness is pretty impressive even wide open, and superb across the frame at F5.6. However distortion and vignetting are higher than on APS-C, as is normally the case.
|Sharpness||At F1.4, central sharpness is already extremely high, and the corners aren't bad at all. Stop down to F2 and the central sharpness reaches dizzying heights. By F4 sharpness is excellent right across the frame, with the very best results achieved at F5.6 - F8. Diffraction starts to take the edge off thereafter, but there's still no reason not to use F16 if the additional depth of field is required.|
|Chromatic Aberration||Lateral chromatic aberration is exceptionally low. You may see a little fringing towards the edges and corners if you go looking for it, but it's scarcely worth worrying about.|
|Vignetting||Vignetting is, as usual, much stronger on full frame compared to APS-C, with a 2 stop drop in brightness in the extreme corners at F1.4. This is pretty much what we'd expect from a fast prime, and no better or worse than other 35mm F1.4 lenses.|
|Distortion||Distortion becomes more visible on full frame compared to APS-C, but at 0.8% barrel it's not likely to be visible, let alone objectionable, with anything other than highly geometric compositions. Again the Sigma is no worse than other fast 35mm primes - if anything it's slightly better.|
As you'd expect, it's a similar story on full frame to what we saw on APS-C when shooting at the lens's minimum focus distance. The image is a little soft wide open, but the center sharpens up very well by F2.8. Stop down to F8 and the image is sufficiently sharp across the frame, and free from chromatic aberration, that you could use this lens for copy work if you were prepared to correct the slight barrel distortion. Very, very impressive.
Specific image quality issues
As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. The Sigma 35mm F1.4 DG HSM turned out to live up the promise shown in the studio tests, performing consistently well at all subject distances and in a wide range of lighting conditions.
It's not unusual for fast primes to struggle with flare when shooting into the light - all that glass means there's plenty of surface area for internal reflections. The Sigma 35mm F1.4 however seems remarkably resistant - pointing the lens directly into the low winter sun scarcely fazes it at all. As usual you'll get best results using the hood by default (and it'll also help protect the front element).
In the first example below we've deliberately placed the sun at the edge of the frame and stopped right down to F16, which makes any flare patterns most resolved and distinct. Sure enough there's some radial streaking from the light source, but what's impressive is how little effect there is on the right side of the frame.
The second example illustrates a tricky situation shooting a backlit subject with an APS-C camera, using a fairly-normal working aperture of F8; here the sun is directly impinging on the front element and the hood can't help at all. Again the lens has handled this pretty well, without any excessive patterning or streaking.
|Canon EOS 6D, F16, sun at edge of frame||Canon EOS 650D, F8, sun just outside frame|
Our studio tests reveal that the 35mm F1.4 exhibits very low lateral chromatic aberration (colour fringing towards the corners of the frame), and our real-world shooting shows that Sigma has also done an impressive job of minimizing longitudinal CA too (i.e. colour fringing around out-of-focus elements at large apertures). The overall result is very impressive - there's scarcely anything to worry about here at all.
The examples below are effectively torture-tests for the two types of CA. The first shows negligible fringing along high-contrast edges in the corner of the image on full frame, which is a pretty impressive result. The second shows some colour fringing around high contrast out-of-focus elements when the lens is shot wide open - magenta in front of the plane of focus, cyan behind - but for such a fast lens it's really very low.
Lateral Chromatic Aberration
|F8, Canon EOS 6D||100% crop, bottom right|
Longitudinal Chromatic Aberration
|F1.4, Canon EOS 6D||100% crop|
The tests show that the 35mm F1.4 exhibits about 2 stops vignetting wide open, which is pretty typical for its class. The fairly gentle falloff pattern means it's not especially intrusive - in many real-world images it will disappear into the natural variations of brightness across the frame. In fact, in many cases we prefer an image with a touch of vignetting to one without - it can help frame the subject. It's also trivial to correct in post-processing when necessary (but note that in-camera corrections won't work with this lens).
The rollover below compares an image shot at F1.4 using the Canon EOS 6D with a version that's had the vignetting corrected using Photoshop's generic lens correction tools. There's no inherently right or wrong answer here - which you prefer is very much a personal choice.
|Canon EOS 6D, F1.4||Vignetting corrected in PS|
Background blur ('bokeh')
One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and/or a large aperture. Its fast F1.4 maximum aperture means the Sigma can give usefully-blurred backgrounds when used carefully, if that's what you're after.
Much of the time, the character of the blur is quite attractive, and the transition from in-focus to out-of-focus regions is rendered smoothly. Where the Sigma can fall down, though, is with complex backgrounds, which it can render in a distinctly fussy fashion. The answer to this, of course, is to choose your backgrounds carefully (which is one of the most important tenets of photography anyway); it's also important to bear in mind that out-of-focus regions which appear ugly viewed onscreen at 100% can look much better in print.
The examples below were both shot on the EOS 6D, and give an idea of the how the lens renders out of focus regions wide open at F1.4. The distant background in the first example doesn't look very pretty when viewed close-up, with point highlights on the fountain showing up as bright rings, and the tree branches a jumble of green and magenta. But the crops displayed here represent a large print (~24"/60cm wide), which you may well not examine quite so closely.
|EOS 6D, F1.4||Background details (50%)|
|EOS 6D, F1.4||Background detail|
In the second sample the story is more complicated; on the whole the lens has drawn the out-of-focus areas quite attractively. But again point highlights to the lower right are reproduced as hard-edged bright rings, and the sign upper left shows plenty of CA. We wouldn't consider this as reason not to buy the lens unless you have very specific tastes or requirements, though.