What follows are some images showing the performance of the Ultron 40/2.0.
As a comparison I chose the Pentax FA 35/2.0, which is generally accepted as a very good performer.
Conclusions up front:
Resolution:
Both top in portrait range from f2.0 on.
The FA35 has a weakness at f2 when focussing at infinity.
(Perhaps this is only my copy.)
Contrast:
both identical, both top
CA:
FA35 shows stronger transversal CA
Flare:
FA35 much better
The Voigtländer Ultron SL II 40mm f2.0 is a very good lens for an unbeatable price.
If you are not so much concerned with flare you will get a really top lens.
Disclaimer: This is a test by a layman, who does not really know what he is doing.
Resolution:
Resolution has been tested using the USAF test sheet, tripod, MLU and manual focussing, using a focus array of 20-30 images each.
Of each lot the sharpest image has been selected by visual inspection.
Resolution at a distance of 3m: 100% Crops
Resolution at infinity: 100% Crops
(remember, this is the best out of ca. 20 shots)
Contrast:
Contrast has been measured using the method described here, using Image-J.
Contrast at f2.0:
Contrast at f5.6:
To show how good the FA35 is,
here a comparison of the FA35 at f2.0 against the FA28 at f2.8:
(this is from another test, therefore the x-axis differs to above)
Chromatic Aberrations:
1. Longitudinal CA (Purple Fringing):
The FA35 shows stronger longitudinal CA.
FA35 left, Ultron right
2. Transversal CA 200% Crop
This is the worst example I have found for the FA35. It is normally not that strong.
FA35 left, Ultron right, both f2.0
(Perhaps this is only my copy and has to do with a slight focus error of the FA35 at infinity. Further tests needed.)
Flare:
The Ultron shows stronger and more colorful flare.
FA35 left, Ultron right
Another one from the Ultron: (different angle)
Example with the close-up lens at f2.0 and ca. min. focussing distance: