Voigtlander Ultron 40 mm f/2 SL II Aspherical
4. Image resolution
On the Nikon D3x you get a bit lower MTF50 values than on the Nikon D200. In this case we assume the decency level starts near 30 lpmm and the best lenses, tested on the D3x, reach results near 46 lpmm. How does the Voigtlander 2/40 fare here? The maximum relative aperture brushes against the 30 lpmm level which should be considered an asset of such a small and relatively fast lens with the angle of view wider than the standard one. The image quality improves significantly on stopping down although it doesn’t reach record levels anywhere. The highest results we get by f/4.0 and f/5.6, where the MTF50 values reach almost 44 lpmm. This is a very good performance, perhaps even a splendid one, but not outstanding. On the one hand you should expect really high resolution values from such an expensive fixed-focal lens; on the other hand, though, the combination of its parameters and small physical dimensions might be a huge hindrance to breaking any records.
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At the edge of the APS-C/DX sensor the maximum relative aperture is not useful. The stopping down by one EV brings us closer to that usefulness significantly. From f/4.0 including the images are sharp and fully useful. What’s interesting, on passing to the full frame edge you don’t see the image deteriorating significantly. F/2.0 and f/2.8 apertures are not very useful but near f/4.0 you can hardly have any reservations concerning the image quality. On the one hand such a performance doesn’t bowl us over, on the other hand no other f/1.4-f/2.0 full frame lens, with the focal length ranging from 35 to 50 mm tested by us so far, had sharp full frame edge near the maximum relative aperture. Even the expensive and cult Leica Summicron-M 50 mm f/2.0 became useful only on stopping down by 1-2 EV.
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