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Voigtlander Nokton 25mm f/0.95 MFT - Review / Test Report - Analysis |
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Lens Reviews -
(Micro-)Four-Thirds
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Page 2 of 3
Distortion
The Nokton produces a slight degree of barrel distortion (~1.1%) which is barely an issue in field conditions.
Vignetting
As mentioned, f/0.95 is an extremely large aperture and at such settings a lens is doomed to produced a heavy light falloff towards the border of the image field. Consequently the issue is very visible at around ~1.8EV (f-stops). Stopping down to f/1.4 helps a lot already but if you'd like to reduce the vignetting to a negligible degree you have to choose an aperture from f/2 onwards.
Here's a visual illustration of the issue:
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f/0.95
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f/2
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MTF (resolution)
Ultra-large aperture lenses tend to be rather soft at max. aperture. The Voigtlander Nokton 25mm f/0.95 MFT manages to deliver a very good center performance at f/0.95 whereas the borders and corners are quite soft indeed. The contrast level is also a bit reduced but it's actually more snappy than expected here. Stopping down to f/1.4 has only a marginal effect but there's substantial increase in quality at f/2 with an excellent center and a pretty good outer image zone. The sweet spot is reached around f/4 where the lens achieves an excellent center-to-corner quality. Diffraction effects have a higher impact beyond f/8.
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 (color shadows at harsh contrast transitions) are pretty much negligible throughout the aperture range. They stay below 0.5px on the average at the image borders.
Bokeh
The quality of the bokeh (out-of-focus blur) is naturally a major aspect for such a lens and the Nokton doesn't disappoint us here. The out-of-focus highlights show a slight outlining effect at f/0.95 - this can produce a nervous bokeh in scenes with very hard contrasts in the focus transition zone. However, stopping down to f/1.4 eliminates this issue and the focus blur is smooth both in front and beyond the focus zone. There's some bokeh fringing at large aperture setting - you can spot purple contrast halos in the foreground and green ones in the image background. This is normal for such a lens though. We've taken an emphasis in the bokeh aspect in our sample images. Generally we were very pleased with the results.
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