Samsung NX 20mm f/2.8 ( W20NB ) - Review / Lab Test - Analysis
Lens Reviews -
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Lens distortion is usually auto-corrected either in the camera directly or in Capture One (Samsung's RAW converter). However, it is possible to disable this feature.
The native distortion characteristic of the NX 20mm f/2.8 is below average - a barrel distortion of ~3.6% will be visible in many scenes.
There is some light fall-off (~0.86EV) in the corners at max. aperture which can be visible in some scenes. However, the issue is more or less resolved from f/4 onward.
As a little update we've provided the quality ratings for the scenario with and without distortion correction.
Distortion auto-correction DISABLED:
The resolution characteristic of the NX 20mm f/2.8 is very good although not outstanding. The center performance is already very high at max. aperture. The border quality is fine whereas the corner region is quite soft. There's a substantial boost when stopping down to f/4 with an excellent center and very good borders/corners. This is also the peak performance setting of the lens. The quality remains about as high at f/5.6 before diffraction reduces the potential. The lens is still very usable at f/8 and f/11 but you should avoid to go beyond (nor is this really necessary for mainstream images).
Distortion auto-correction ENABLED:
The distortion correction may fix this issue but, as a side effect, the image gets "stretched" and up-scaled
to the original size. However, due to the image cropping it does also reduce some corner issues.
The center performance is only marginally impacted by this but the corner stretching doesn't come for
free - you are roughly loosing about a 3/4 quality mark here across the aperture range.
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
MOVE YOUR MOUSE CURSOR ACROSS THE IMAGE TO OBSERVE THE RESULTS WITH ENABLED AUTO-CORRECTION!
Chromatic Aberrations (CAs)
Lateral chromatic aberrations (color shadows at the image borders) are relatively well-controlled with an average CA pixel width at or below 1px on the average at the image corners.
Pancake lenses cannot be perfect - the small size simply implies some compromises. However, the Samsung NX 20mm f/2.8 does a pretty good job actually. At f/2.8 you have to live with some corner softness and quite high vignetting. However, the center resolution and contrast is already very decent here. The results are very sharp when stopping down to medium aperture settings. Diffraction is a limiting factor from f/11 onward. Lateral CAs are usually nothing to worry about. A primary weakness of the lens is the heavy amount of barrel distortion. That said, most users will probably prefer to enable distortion auto-correction anyway.
The build quality of the lens is very fine which is, of course, typical for most prime lenses. There're simply few moving parts here. The AF speed is pretty high and the acoustic noise level is less audible. The best news is, however, the low pricing of the NX 20mm f/2.8 - it is already available for less than 180EUR/280US$ so going really small doesn't require a fortune.