Zeiss Batis 18mm f/2.8 (Sony FE) - Review / Test - Analysis
Lens Reviews - Sony Alpha (Full Format)

Distortion

In numeric figures, the Batis 18mm f/2.8 shows a very low degree (1%) of distortions for an ultra-wide lens. However, a single number can't express the realities here. Uncorrected images show a rather pronounced mustache-style distortions which can be disturbing when having straight lines in your scene. Thus if you can sacrifice a bit of quality, you should use image auto-correction.

Move the mouse cursor across the image for viewing the distortion chart with auto-correction.

Vignetting

Zeiss lenses tend to have at least one disease - vignetting. It just doesn't seem to be a primary design objective in Oberkochem (Zeiss HQ). At fully open aperture there's a very heavy amount of vignetting (~3 EV/f-stops). To be fair - this is rather normal for a full format ultra-wide lens. However, the vignetting decreases only by just more than one EV when stopping down. A minimum light fall-off of ~1.7EV (f-stops) at f/8 is certainly not something to rave about.

Enabling vignetting auto-correction solves most of the issue (unsurprisingly). You'll still spot some vignetting at f/2.8 but it's quite acceptable beyond.

MTF (resolution)

The Zeiss Batis 18mm f/2.8 has a highly impressive resolution characteristic. The center and near center is tack sharp at f/2.8. The border quality is also very good at fully open aperture whereas the far corners are just Ok here. Stopping down to f/4 improves the center zone even further and also lifts the corners to very good levels. The corner do still improve a little at f/5.6. Diffraction effects kicks in at f/8 and gets noticeable at f/11. That may be a little surprising but f/8 should be good enough for "infinity scenes" anyway. Avoid f/16 and beyond.

The centering quality of the tested sample was very good. Field curvature is very low for an ultra-wide lens.

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

Note: There was an error with the center values at f/8 and f/11 (corrected).

Chromatic Aberrations (CAs)

The Zeiss lens produces a very low amount of lateral CA (color shadows at harsh contrast transitions) starting with an average CA pixel width of 0.5px at f/2.8 and a maximum of 0.7px at f/11. This is unusually good for an ultra-wide lens.