Sony FE 28mm f/2 (SEL28F20) - Review / Test Report - Analysis
Lens Reviews - Sony Alpha (Full Format)

Distortion

The Sony FE 28mm f/2 is one of the few lenses where Sony prohibits the deactivation of the automatic distortion compensation in the camera. Thus normally, users will just experience near-distortion free images (0.2% barrel distortion).

Despite Sony's coding, it's still possible to reveal the native distortion characteristic - e.g. in CaptureOne. It's not terrible at 3.7% but, of course, nothing that Sony can be overly proud of.

Vignetting

The native vignetting of the lens is on the high side at 2.9EV (f-stops) at maximum aperture. Stopping down to f/2.8 helps but if possible stop down to at least f/4. The issue isn't negligible at any setting though.

Thus it's a good idea to leave image auto-correction activated for this aspect as well. However, even so, the light falloff remains very noticeable at f/2, less so beyond.

MTF (resolution)

The resolution is a bit of a mixed bag. The center is very good at f/2 but the quality drops rapidly the more you approach the corners. The near-center is good whereas the outer image field is dismal for a prime lens. Stopping down to f/2.8 improves the broader center quite a bit whereas the borders/corners remain soft. The situation changes at f/4 with a great central performance and a good to very good outer zone. The overall peak performance is reached at f/5.6. Diffraction sets in at f/8 with an impact on the image center and there's a global decrease in quality at f/11. f/11 remains very usable though.

The centering quality of the tested sample was Ok.

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)

Image auto-correction will take care of lateral CAs (color shadows at the image borders). It's a lossless procedure so it doesn't have any negative impact.

However, the native CA characteristic is just mediocre especially considering that this is a recently designed prime lens. The CAs can be noticeable at f/2 with a width of ~1.7px on the average at the image borders - and more so in the corners.

Bokeh

According to Sony, the lens has been optimized to delivering a very smooth bokeh (out-of-focus blur). We'd at least partially agree with that.

When looking at the focus transition zones, the bokeh is very silky image background (shown to the left below). The less critical foreground blur (to the right) is almost as good.

Out-of-focus highlights aren't quite as clean though. As you can see below, the inner discs have a busy substructure which is not ideal. However, the disc edges are nicely feathered though and the circular disc shape remains mostly intact at f/2.8 and also at f/4.

As usual, the shape of the discs deteriorates towards the edge of the image field - this is a mechanical vignetting effect related to the diameter of the lens opening. The deterioration is visible from the midfield but remains on a relatively moderate level at the borders. Stopping down to f/2.8 restores the circular highlight shape for most of the image field, more so at f/4.