Voigtlander Nokton 50mm f/1.5 Aspherical (on Sony NEX) - Review / Lab Test Report - Analysis
Lens Reviews - Sony Alpha/NEX (APS-C)
Article Index
Introduction
Analysis

Distortion

The Nokton produces an absolutely negligible amount of barrel distortion (~0.1%).

Vignetting

Typical for full format lenses it shows no really significant light fall-off when used on an APS-C camera. You may spot a medium amount of vignetting at f/1.5 (0.7EV) but the issue is pretty much gone by f/2 already.

MTF (resolution)

The Voigtlander lens delivers mixed for our resolution tests. The center quality is very high at f/1.5 and f/2 whereas the borders aren't quite as good - actually just "fair" to be honest. The center is lifted to excellent quality at f/2.8 whereas the borders see a slight improvement into good territory here. The peak performance is reached around f/5.6 with an excellent center and very good borders. Diffraction effects start to have a higher impact at f/11 but the quality remains easily on a very good level at this setting.

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 (color shadows at harsh contrast transitions) are pretty much negligible at large aperture settings. The aberration increases towards medium aperture settings but it's never really a problem regarding a peak of roughly 1px on the average at the image borders (f/8-f/11).

Bokeh

The bokeh (out-of-focus blur) has both a shiny side and an ugly one. Out-of-focus highlights show an "onion-like" substructure which can be distracting at times. The problem doesn't really improve when stopping down. The blur in the critical focus transition zones is quite smooth both in the image foreground and background.

Bokeh Fringing / Longitudinal Chromatic Aberrations (LoCA)

LoCAs (non-coinciding focal planes of the various colors) are a color fringing effect. It is also referred to as "bokeh fringing". If you have a look at the samples below you will notice that the out-of-focus halos show different colors - magenta (red + blue) in front the focus point and green beyond. This is most obvious at f/1.5 and f/2 but you can still spot traces at f/4. This is a fairly normal behavior for a lens in this class.

Move the mouse cursor over the f-stop marks below to observe the respective LoCAs
f/1.5 f/2 f/2.8 f/4

Verdict

The Voigtläander Nokton 50mm f/1.5 Aspherical is one of the more interesting lenses for Sony NEX users - on paper at least. As of the time of this review Sony has yet to release a fast "dedicated" prime lens for the system. The Nokton "behaves" like a 75mm f/2.1 so it may appear like a obvious choice for portrait photography. Within this special scope it performs fine thanks to a very high performance in the image center - the borders are much less impressive at large aperture settings. If you stop down to f/4 and beyond the lens is capable of delivering very good results across the image frame. Images are basically free of distortions and vignetting is usually nothing to worry about either. Lateral CAs are absent at f/1.5 and f/2 although you may spot traces of them at smaller aperture settings. The quality of the bokeh is generally good but not stellar either regarding the rather rough out-of-focus highlights. The lens produces some bokeh fringing but even with Leica or Zeiss you cannot avoid that entirely. The build quality is on a very high level which is quite typical for most Leica M-mount lenses. So all-in-all it isn't really a perfect lens but it's fairly affordable on the used market. If you feel an itch you should make sure that you can live with the usage limitations of such an adapter solution though.

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