Sigma 16mm f/1.4 DC DN Contemporary (Sony E-mount) - Review / Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)

Distortion

The Sigma lens can take advantage of Sony's auto-correction algorithms and if you choose to activate it, there's little to worry about regarding image distortions. At less than 0.2% they are barely noticeable.

The original characteristic of the Sigma 16mm f/1.4 DC DN Contemporary isn't quite as glorious with a fairly heavy barrel distortion of about 2.8%.

Vignetting

We can see a similar pattern when it comes to vignetting. With activated image autocorrection, you can spot just a little bit of light falloff (0.7EV / f-stops) at f/1.4 and f/2. Surprisingly, this can't be said about the original vignetting despite the very large front element. At over 1.8EV (f-stops) at f/1.4, it's rather massive for an APS-C format lens - although that's still mild compared to full format counterparts. Stopping down to f/2 helps a lot already and the issue is mostly gone from f/2.8 onward.

MTF (resolution)

The resolution of the Sigma 16mm f/1.4 DC DN Contemporary varies quite about across the aperture range. The center quality is very good at f/1.4 already but there's a rather steep drop in quality in the outer image field. The borders are merely good here and the corners are downright soft. Stopping down to f/2 boosts the quality across the frame with an excellent center, very good borders and good corners. The quality is pretty impressive at medium aperture settings though. The corners have fully recovered at f/2.8 and images are very sharp across the frame. The peak performance is reached at f/4 although the quality plateau is very broad from f2/8 all the way up to f/8. Diffraction effects are getting somewhat more pronounced at f/11 although this setting remains very usable.

The centering quality of the tested sample was acceptable only. The field curvature is low.

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 for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Lateral CAs (color shadows at contrast transitions) are very low peaking at an average CA pixel width of less that 0.5px at f/1.4. At medium aperture settings the CAs are virtually non-existent.

Bokeh

"Bokeh" is a Japanese word referring to the way, out of focus blur is rendered. There are two main aspects - out-of-focus (background) highlights and the rendition of contrasty objects in the focus transition zones. Given its ultra-large aperture, this is, of course, an important playground for the Sigma 16mm f/1.4 DC DN Contemporary. Let's have a look at the "highlights" first.

Wide-angle lenses tend to show rough out-of-focus highlights but the Sigma is actually among the best in its class here. The inner zone of the highlight discs is very smooth with just a hint of a sub-structure. The edges are feathered rather than "sharp" which is how it should be really. Stopping down maintains the circular shape at f/2 and you can only see a hint of a more edgy aperture shape at f/2.8.

Typically, the shape of the discs deteriorates substantially towards the corners but the Sigma is capable of maintaining a near-circular shape even at f/1.4. This is quite impressive and probably relates to the large front element of the lens. Stopping down improves this a little bit still.

If you are wondering about the strange halos of the discs at the borders - this is related to the shape of the photodiodes used in the setup in conjunction with the field-of-view of the lens.

The general rendition of out-of-focus areas isn't quite as good, unfortunately. The background blur is decently smooth but the contrast suffers somewhat (shown to the left below). The foreground blur (to the right) is rather distracting with a substantial amount of smearing.