Sigma has a wide variety of ultra-fast lenses in their lineup. Among them is the Sigma 24mm f/1.4 DG DN ART. At a price of around $800 USD, it may not be cheap, but compared to the Sony FE 24mm f/1.4 GM ($1400), it’s almost a bargain. As always, this raises the question of whether Sigma has taken some shortcuts to make this happen, so let’s see.
Sigma emphasizes that the lens is especially aligned to astrophotography which has probably the highest quality requirements in terms of edge-to-edge sharpness – something that has traditionally been difficult to achieve for such fast wide-angle lenses.
The Sigma 24mm f/1.4 DG DN ART does certainly not disappoint regarding its build quality. As a member of the “ART” series of lenses, it is built to professional standards. It feels very sturdy and uses a dust- and splash-resistant design. For what it is, it is also fairly lightweight – just 510g – and compact. The broad, rubberized focus ring turns smoothly. It can also be disabled via a “Manual Focus Lock” (MFL) switch – probably related to the optimizations for astrophotography. The dedicated aperture ring has a nice click-action to it. A de-clicked mode has also been implemented. A petal-shaped lens hood is part of the package.
The Sigma lens uses an older-style STM (Stepping Motor) for autofocusing. However, it’s still pretty snappy and noiseless so there’s nothing wrong with this approach here. Manual focusing works, as usual, “by-wire”. An image stabilizer has not been implemented, but that’s rather normal for lenses of this speed class.
| Specifications | |
|---|---|
| Optical construction | 17 elements in 14 groups (2x FLD, 1x SLD, 4x aspherical) |
| Number of aperture blades | 11 (rounded) |
| min. focus distance | 0.25m (max. magnification 1:7.1) |
| Dimensions | φ75.7×97.5mm |
| Weight | 510g |
| Filter size | 72mm |
| Hood | petal-shaped (bayonet mount, supplied) |
| Other features | Rear filter holder, manual focus lock switch, dust- and splash-resistant, de-clickable aperture ring |
Distortions
The Sigma 24mm f/1.4 DG DN ART is well corrected in RAW images with a mild barrel distortion of 1.3%. Auto-correction can handle the rest without losing a significant amount of image quality in the corners.
Vignetting
Ultra-large aperture lenses tend to produce very high vignetting at max aperture, and the Sigma lens is no exception here. In RAW images and f/1.4, the vignetting exceeds 3EV (f-stops) in the image corners. Stopping down to f/2 reduces this by an f-stop, and the light falloff doesn’t go below 1EV, even at medium aperture settings.
Auto-correction reduces the vignetting by ~1.4 EV (f-stops) at f/1.4, and the light falloff is reasonably well corrected from f/2 without any real improvement beyond.
MTF (resolution) at 42 megapixels
The Sigma 24mm f/1.4 DG DN ART doesn’t fully convince in the resolution chapter. The dead center quality is very good at f/1.4, but there’s already a drop near the center, and the outer image field is soft, especially in the corners. Stopping down to f/2 boosts the quality quite a bit, with the borders/corners now reaching good levels. The quality peaks in the f/2.8 to f/8 range, with an excellent center and good to very good outer image field. As usual, diffraction takes its toll from f/11, although the setting remains usable. f/16 and beyond should be avoided.
The field curvature is low. The centering quality of the tested sample was good.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure of sharpness. If you want to know more about the MTF50 figures, you may check out the corresponding Imatest Explanations.
Chromatic Aberrations (CAs)
Lateral CAs have an average width of 1 to 1.5 px at the image borders. This is still fairly low. Auto-correction can handle the rest.
Bokeh
You won’t (or shouldn’t) invest in an f/1.4 lens if you aren’t interested in some kind of shallow depth-of-field photography, so let’s have a look at the quality of the out-of-focus zones.
Out-of-focus highlights are nicely rendered for a wide prime lens. The inner zone of the discs is relatively clean. There’s, however, a fairly pronounced outlining of the discs at f/1.4. This is reduced at f/2. The circular shape (near the center) remains intact up to f/2.8 thanks to no less than 11 aperture blades.
When looking at the highlight rendering across the whole image field, there’s only a mild deterioration of the circular shape with only the extreme corners being somewhat more distorted. Stopping down to f/2.8 fixes the corner discs.
The rendering quality in the focus transition zone is very good for a wide-angle lens. The more critical image background is silky smooth, while the foreground bokeh is a bit more nervous, albeit not terrible.
Bokeh Fringing / LoCA
LoCAs, or bokeh fringing, is a color fringing effect on the Z-axis. It shows up with a purplish tint in front of the focus point and a greenish tint behind – and it’s nearly impossible to fully correct in post.
The Sigma 24mm f/1.4 DG DN ART isn’t apochromatically corrected, and it shows (as with most fast lenses). At f/1.4, the color tint is very obvious. As usual, stopping down helps but the issue is still very visible at f/2. Traces remain at f/2.8 and f/4.
Sun Stars
Sun stars are an aperture effect that is produced when shooting pointy light sources – typically during nighttime.
As mentioned, the Sigma lens uses no less than 11 rounded aperture blades to optimize the bokeh, which is usually not good news for the sun star rendering. However, it turns out that things aren’t that bad.
There aren’t any “usable” rays from f/1.4 to f/5.6. Some more noticeable rays appear at f/8 with good results at f/11 and f/16. 11 aperture blades result in 22 rays, which is a bit much, though.
Competition
As always, there are numerous alternatives available in E-mount. There is, of course, Sony’s own FE 24mm f/1.4 GM (center below). As already mentioned in the introduction, it’s a much more expensive lens, but it does have an edge in terms of sharpness. Both aren’t ideal at f/1.4. When looking beyond f/1.4, there are a couple of further lenses, of course. Noteworthy ones are the Sigma 24mm f/2 DG DN Contemporary (shown to the right), the Zeiss Batis 25mm f/2 and the Samyang 24mm f/1.8 FE. We haven’t tested them yet. The Sigma and Samyang received some pretty impressive feedback in other tests on the web, so if you don’t need the extra half-stop, you may wish to dig deeper here. The Zeiss lens may be something for you if you like Zeiss colors.
Sample Images
The Sigma 24mm f/1.4 DG DN ART left us with some mixed impressions - especially following the outstanding results that we've seen from the Sigma 35mm f/1.4 DG DN ART. The center performance is generally excellent, but the borders/corners leave a bit to be desired at f/1.4 - and being advertised as a lens suitable for astrophotography, that's certainly not ideal. Stopping down to f/2 improves the outer image field a bit, but it is only critically sharp from f/2.8 onward. Image distortions are low, as are lateral CAs. The vignetting is very high at f/1.4 which is to be expected, of course, so auto-correction is needed here. The quality of the bokeh is impressive. Wide-angle lenses, even primes, usually struggle here, but the Sigma lens delivers comparatively clean and smooth results here. Axial CAs are noticeable at large apertures.
The build quality of the lens is impressive, thanks to a tightly assembled combination of metal and durable plastic parts. Combined with a dust- and splash-resistant design, it is certainly good enough for professional use. The AF is fast and noiseless. Videographers will certainly appreciate the de-clickable aperture ring.
Overall, the Sigma lens represents good value but it isn't an obvious choice. We'd rather see its strength in general photography and videos but less so in astrophotography.
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Optical Quality
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Build Quality
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Price / Performance