Cosina
Voigtländer Nokton 58/1.4 and Pentax 50mm lenses
What follows are some images showing the performance of the Nokton 58/1.4 compared to several Pentax 50mm lenses, especially the A50/1.4.
Disclaimer: This is a test by a layman, who does not really know what he is doing.
Conclusions:
1. Resolution: The resolution performance of all tested 50mm lenses is very good. One is reaching the sensor limit already at f1.4. Only the M50/1.7 shows a slight weakness in the corners fully open. The Nokton is flawless.
2. Contrast: The Nokton shows very good contrast values! At f4 it is the best of all tested lenses.
3. CAs: Normal CAs, both longitudinal and transversal, are very weak and difficult to detect. Enforcing fringing (longitudinal CA), the Nokton looks about the same as the A50/1.4 but with slightly better performance at exact focus.
4. Flare: The Nokton shows slightly stronger flare compared to the A50/1.4. This is similar to the Ultron 40/2.0, which also showed stronger flare compared to the FA35/2.0.
5. Bokeh: The Bokeh of the Nokton and the A50/1.4 is virtually identical. This is not really surprising since both feature an identical lens design. The most important point, which is influencing the bokeh in this case, is that the Nokton's focal length is 8mm longer compared to 50mm lenses. This reduces the DoF and gives a more blurry out-of-focus area, which is clearly noticable in the images.
The circle of confusion looks like in most modern lenses today: A smooth Gaussian transition in the foreground and a bright border in the background ("over-corrected spherical aberration").
Now let's have a look at f1.4 of the same lens:
Also here, fully open, the spurious resolution can be seen. Even in the corner the phenomenon can be perceived.
So much for the alleged softness of the f1.4 lenses.
Resolution at Infinity:
Note that the Nokton has an 8mm longer focal length.
I have scaled down the Nokton image accordingly.
The A50/1.4 shows a slight weakness at f1.4 in the corners, but the difference is only slight. At f4.0 both are identical.
Do not give much on the absolute numbers (depends on lighting) and not even much on the exact position of the points. The values have been obtained from only one image each and the error is probably quite high. Nevertheless I think one can say that the contrast of the Nokton is good!
To give an impression of how big the difference is, on the real photo, here is a comparison of the Pentax A50 at f1.4 and at f4.0 in a 100% crop. The Nokton looks similar.
a) by turning the focus ring in small steps:
Please note that it is impossible to do this stepping 100% identical for two lenses. Slight differences in the focus distance are unavoidable.
How this looks in real life, can be seen here:
Front and back Bokeh of a hedge:
f1.4
A different kind of Bokeh:
An image consisting almost exclusively of Bokeh.
This is on the beach, setting the camera on the ground and shooting against the sun.
The reflecting grains of sand create a prism-like appearance.
