Samyang AF 14mm f/2.8 FE - Review / Test Report - Analysis
Lens Reviews - Sony Alpha (Full Format)

Distortion

Ultra-wide lenses tend to produce a heavy amount of image distortion and the Samyang AF 14mm f/2.8 FE is no exception here with a barrel distortion of ~3.8%. However, it's worth noting that Samyang improved this quite a bit compared to their early MF 14mm f/2.8. Correction profiles are readily available for the lens and if applied, there's barely any distortion to speak of.

Vignetting

Another typical issue with ultra-wide lenses is vignetting. This is pretty much unavoidable. However, the light falloff is comparatively moderate at ~2.3EV (f-stops) and f/2.8. This is, of course, very visible but we've seen a lot worse. Stopping down improves the issue but the vignetting stays just above 1.4EV even at f/11. That's all less of a problem with activated auto-correction which reduces the vignetting down to ~1.2EV at maximum aperture and it's just noticeable from f/4 onward.

Below is an example of the raw vignetting at f/2.8.

MTF (resolution)

The Samyang AF 14mm f/2.8 FE struggles a bit with respect to resolution although you can't expect such a lens to be perfect anyway. On the positive side, the dead center is very sharp at f/2.8 and the broader center zone is also pretty good. However, the outer image field is soft. The center zone improves quite a bit at f/4 but the corners remain unimpressive. The best results are achieved around the f/8 mark. The center quality is impressive and the borders are good at this setting. The corners are at least acceptable. Stopping down further doesn't increase the quality any further due to diffraction effects.

The field curvature is moderate. The centering quality of the tested sample was Ok. It's worth noting that the image quality decreases substantially at close focus distances.

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 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.

The native CA characteristic is reasonable for such a lens. The CAs vary between a width of 1.3px and 1.6px on the average at the image borders. This can be visible but it's not really severe yet.