Lens review

Voigtlander Nokton 17.5 mm f/0.95 Aspherical

26 September 2012
Arkadiusz Olech

4. Image resolution

When it comes to the Micro 4/3 lenses the older brother of the tested device, the Voigtlander Nokton 25 mm f/0.95, has set an unattainable standard so far, reaching as high as 82 lpmm. All other lenses, tested by us on the Olympus E-PL1 body, went to 75-80 lpmm at most. It’s also worth adding here that the Nokton 0.95/25 at the maximum relative aperture got 32 lpmm so didn’t reach the decency level, set near 42 lpmm.

Knowing these results you can assess how the Nokton 0.95/17.5 compares. An appropriate graph is presented below.

Voigtlander Nokton 17.5 mm f/0.95 Aspherical - Image resolution

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Two interesting things can be noticed here. The tested lens doesn’t copy the record achievements of its older brother because it can go to less than 79 lpmm at most (but of course in itself it is an excellent result). In the next chapter you can find out why – the spherical aberration, not corrected perfectly well, is the main culprit. The fact that the Nokton 0.95/17 at the maximum relative aperture goes near 40 lpmm, providing almost useful images, is a kind of consolation. A useful image at f/0.95 aperture is no mean feat and here the lens definitely deserves to be praised a lot especially that, on stopping down, the resolution improves steeply so by f/2.0 it amounts already to 74 lpmm, a very high level indeed. Some system “pancakes” have huge problems with reaching such a value at all and the Nokton manages to get there by f/2.0, a very decent aperture fastness.

Overall here you can see clearly the advantage of f/0.95 aperture even if it is moderately useful. Usually lenses reach the peak of their possibilities after stopping down by 2-4 EV. When you use such an extreme aperture fastness as f/0.95 and you correct the lens properly it will start working in the diffraction limit (so without any optical aberrations) after stopping down to the area near f/2.0-f/2.8; small wonder such an instrument can squeeze the sensor dry and break resolution records. Slower constructions by f/2.0 or f/2.8 still suffer from noticeable axis and off-axis aberrations so it is impossible for them to come near any record values.

A wide angle of view and a great fastness is actually the very prescription for any resolution problems on the edge of the frame. The tested lens didn’t manage to avoid them all – the results by f/0.95 and f/1.4 are really very weak. Fortunately between f/1.4 and f/2.0 the imaging quality improves dramatically so the lens reaches the level of full usefulness and keeps it practically until f/16.

Below we present some crops taken from our testing chart photos saved as JPEG (the lowest sharpening level) along with RAW files, used for the analysis above.

Voigtlander Nokton 17.5 mm f/0.95 Aspherical - Image resolution