Samyang AF 35mm f/1.4 FE - Review / Test Report - Analysis
Lens Reviews - Sony Alpha (Full Format)

Distortion

Normally - thus with activated image auto-correction - you won't really notice any relevant image distortions. In RAW mode, you can spot a barrel distortion of ~2.3% which is a bit on the high side for a prime lens.

Vignetting

Ultra-fast lenses are always prone to high vignetting on full format sensors. If you use auto-correction it's not much of an issue (except for the increase in image noise in the corners) although you will still be able to spot a light falloff of ~1.3EV (f-stops) at fully-open aperture Beyond f/1.4 it's well-controlled.

This is, of course, very different in uncorrected mode. At f/1.4 the vignetting is rather massive in this case (~2.8EV) and still very noticeable at f/2. The situation eases at f/2.8 and it's good beyond.

MTF (resolution)

Ultra-fast aperture lenses are difficult to design but the Samyang AF 35mm f/1.4 FE shows some surprising qualities in terms of resolution. "Traditionally" fast Samyang lenses had a tendency of being soft at maximum aperture. While the lens isn't perfect at f/1.4, it's actually pretty decent. The center resolution is very good and the borders/corners are very useable as well. Stopping down to f/2 lifts the quality dramatically and the results are pretty stunning between f/2.8 and f/8. Diffraction is limiting the performance from f/11 onwards.

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

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)

Lateral CAs are on a low level with an average CA pixel width between 0.5-0.7px at the image borders.

Bokeh

Sharpness and all that is one thing but you are primarily buying such a fast lens shallow depth-of-field photography. The quality of the bokeh (rendering of the out-of-focus blur) is, therefore, no secondary aspect in this case. The Samyang lens does a good job albeit with a few hiccups.

Out of focus highlights are fairly nicely rendered. At/near the image center, they have a perfect circular shape at f/1.4 and f/2. The inner zone shows a very slight onion-like substructure but it's hardly noticeable really. The more edgy aperture shape starts to show up from f/2.8 onward.

The quality of the general blur is not ideal. Contrast transitions can be slightly emphasized in the background (shown to the left below) - see "the crown" and the colors are a little washed out. The foreground blur is much smoother.

The circular shape of the discs is, as always, deteriorating towards the corners but it's actually not too much of an issue as you can see below.

Bokeh Fringing / LoCA

Boheh fringing (sometimes referred to as LoCA) is an axial color fringing effect with purplish halos in front of the focus point and greenish beyond. The Samyang AF 35mm f/1.4 FE has its share of problems with this. They are very pronounced at large-aperture settings and still visible at f/4. Please note, however, that bokeh fringing is a fact of life for most ultra-fast lenses.