Voigtlander Nokton 17.5 mm f/0.95 Aspherical review - Coma, astigmatism and bokeh

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Voigtlander Nokton 17.5 mm f/0.95 Aspherical

26 September 2012

Arkadiusz Olech

7. Coma, astigmatism and bokeh

The coma is very keenly felt both by f/0.95 and by f/1.4. To tell you the truth the stopping down by 1 EV stop from the maximum relative aperture doesn’t influence that aberration almost at all. An abrupt decrease of the coma can be noticed only after another stopping down of the Nokton, to the value of f/2.0. By that aperture the coma is already just medium but still visible.

Voigtlander Nokton 17.5 mm f/0.95 Aspherical - Coma, astigmatism and bokeh

There are a bit less problems with astigmatism but it doesn’t mean that aberration has no negative impact whatsoever on the image quality. An average difference between vertical and horizontal MTF50 values amounted to 13% - a noticeable level.

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Looking at photos, presented below you can find out how defocused images of light points look like. There are no significant concentric rings and sharp edges so it might suggest that the blurred area will be nice. The influence of the spherical aberration, already discussed earlier, and vignetting, which will be described in the next chapter, is clearly visible for a change. The appearance of the circle by f/0.95 is a classic example of a badly corrected spherical aberration and, simultaneously, for some users a perfect way to get a great bokeh of defocused areas.