Samyang 50mm f/1.2 AS UMC CS review – Image quality

To achieve optimum focus with this lens you’ll either have to rely on the judgment of your eyes or put your camera’s manual-focus assist settings to good use. I discovered my sharpest results were captured using focus peaking in combination with a magnified screen view. This approach was quickly adopted for a majority of the test images that support this review, but with such a fine margin for error at f/1.2 I found myself stopping down to f/1.8-f/2.8 quite frequently.

This starburst effect was achieved by stopping the lens down to its minimum aperture setting of f/16

Our lab results confirmed my real-world findings and at f/1.2 the sharpness at the corner of the frame is virtually identical to that at the centre. To achieve optimum sharpness from this lens you’ll want to close it down by a stop or two. Centre sharpness improves considerably between f/2 and f/2.8, and the sweet spot between centre and corner sharpness is found close to f/4. Acceptable images can be produced between f/4 and f/11, beyond which diffraction starts to take its toll on sharpness. Corner shading was observed in images taken at its widest aperture settings, but things quickly improve when the lens is closed to f/2 and f/2.8.

Purple fringing was traced along high-contrast edges when the widest aperture setting (f/1.2) was used

A close inspection of images taken towards the light revealed some minor purple fringing along branches and high-contrast edges. This was a relatively easy fix in Lightroom. Our distortion chart reveals the lens renders straight lines well, with no evidence of barrel or pincushion distortion.