Sigma 20mm F/1.4 Art Lens Review – Moonlit Night

by Sebastian WöberNovember 26^th, 2015

The Sigma 20mm F/1.4 Art Lens is one of the fastest wide angle full-frame lenses available today, and certainly the most affordable in its class. I took the new lens for a spin at night and shot in near total darkness with a Sony a7S II.

I was really excited when the Sigma 20mm F/1.4 Art Lens was announced last month and released just a few days ago. It is easily one of the most intriguing lenses I have seen. Why? Because for me 20mm is a stunning extreme wide angle focal length and this lens brings us great image quality, worthy of 4K video and at the same time it is exceptionally fast.

With an open aperture of F/1.4 and with great performance the seemingly high price of $899 is surprisingly low and for me competes with the most professional lenses available.

Right click, open this image in new window to see it in full 3840pixel resolution.

With the introduction of the new Sony a7S II, we can now shoot brilliant 4K video in extreme lowlight conditions. As we found out just recently, this new Sony mirrorless camera is even more powerful in lowlight than its predecessor, the original a7S.

So there was no question when this lens arrived at our office I went out and shot the whole evening just with this lens and entirely at F/1.4. You can observe the result in the video above which I hope you will enjoy. For me it was a pure enjoyment I can tell you, to realize that I needed to get far out of the city in order to push this camera/lens combination to its lowlight limits. I walked through forests, empty parking lots and ended up at a castle and many times the only light source was the moon. I could not see what the camera saw, it was my “night vision device” and the sky was not (!) blue, as it appears to be in the video.

Coming back to the editing table I was very happy to find out that the Sigma 20mm F/1.4 Art Lens indeed performed very well at its lowest aperture. I pushed the camera to 25,600 and 51,200 ISO max, as in my tests I felt those were the breaking points when it comes to noise for an HD result. In terms of exposure I tried to expose “bright”. In lowlight it is important not to use the dark side of the spectrum too much, because this is where the noise is and it has to be cut off.

I shot everything in the Slog2 Gamma and graded the film with a “lowlight” LUT I created for this project, that retained most of the spectrum, lowered the dark areas and accented the highlights only slightl. I wanted to go for a low contrast look and I’m pretty happy with the result. I’ve heard otherwise, but personally I do recommend shooting lowlight in Slog2 as this for me is the perfect starting point for a balanced grade.

One thing I did notice about the Sony a7S II in lowlight is that there’s apparently some kind of “trick” going on in extreme lowlight. When I filmed my feet walking on grass I realized that there’s some ghosting introduced at ISO 51,200. In the shot below you can see multiple frames in one frame.

Ghosting effect at high ISO speeds on the sony a7S II

Either this is a result of some kind of internal “temporal noise reduction” (this is how it looks to me) that appears on fast moving objects and patterns OR it might also be a result of the low temperature I filmed at (-1 C°). I did not notice the effect in any other shots but this one.

How Good is the Lens?

Sigma 20mm F/1.4 Art Lens

For this Sigma 20mm F/1.4 Art Lens Review I used the EF version of the lens together with a Metabones Adapter on the Sony a7S II in both 4K video and stills mode. This is not a scientific lens test, because of the lack of reference lenses, but there are a few important things I could observe and want to show you about this lens.

While this lens / adapter / camera combination is really not ideal for stills photography I took photos with our high resolution test chart in order to see how good the lens performs on a quality 4K photo / video image.

Left: Sigma 20mm Lens @ F/1.4 | Right: Sigma 20mm Lens @ F/8.0

The image above is a shot of our test chart in two different F stops. We can see quite a strong vignetting at F/1.4 in comparison to F/8.0. Personally I like vignetting and I often apply it to my shots in post, but it certainly also darkens your image further than you would like. This means that when you shoot wide open you must know that you are losing about half a stop of light due to vignetting.

Here we can also observe distortion, which, for a 20mm lens seems very low. These two attributes (vignetting and distortion) can be corrected in post, but sharpness and chromatic aberration is something that cannot be fixed with plugins, so these for me are the most important factors when it comes to lens quality.

Top-Left corner of the test chart to observe chromatic aberration and sharpness

Here’s a crop of the top left corner of the test chart shot at F/1.4 with the Sigma 20mm F/1.4 Art Lens. We can see of course that the leftmost edges of the shot are softer, yet at the same time the kind of sharpness to me is unlike other lenses I’ve seen shot wide open. Certainly a kind of sharpness absolutely pleasing and mostly sufficient for 4K. If you want a totally clean image, the softness goes away gradually when the lens is stopped down until about F/5.6.

In terms of chromatic aberration there is very little of that. Again absolutely stunning performance from this lens in comparison to other lenses I’ve seen. In my video I did not notice any chromatic aberration in any of the shots.

Build Quality

One thing you should know: This lens is not lightweight. With 960 grams it is lighter than your full fledged cine lens, but it is  double or triple the weight of other mirrorless prime photo lenses you might use for video. That said, the build quality is very nice. The lens feels solid and well made with no flimsy parts.

The focus can be set to manual and the lens has an analogue focus ring (unlike most Sony photo lenses). Unfortunately there are no hard stops making it hard to use the lens with any focus gears or focusing tools. Also the focus throw is very narrow and considering the lens has a thin depth of field it can be hard to focus manually at times. The lens is clearly design for the photographer in mind. This is a drawback we’re already used to as mirrorless and DSLR video shooters, but it’s not ideal for some applications and doesn’t provide the best ergonomics.

Conclusion

This lens kept its promise offering superb quality and while it is made for photography with some ergonomic drawbacks for video it is still among my favourite lenses of all time. The kind of shots I could achieve with this lens, without any noticeable quality loss is amazing and opens up new possibilities for people who like lowlight shooting. Furthermore this lens opens up your path to shallow depth of field at wide angles, which is rarely seen outside of high end professional productions.

The biggest highlight about the Sigma 20mm F/1.4 Art Lens for me is its price though. At $899 the value for money you get is very high and makes it an affordable option for shooters working with a Sony a7S II.

I hope you enjoyed this review. You can download the source video from Vimeo to take a closer look at the shots in HD. Let us know your own observations and thoughts about the lens in the comments.