Just for comparision I have created a quick test A12 28mm vs M mount with various lenses...all OOC jpeg at А mode.
f 2.8-4-5.6-8
Lens used within test:
А12 28мм
Konica M-Hexanon 28/2.8
Voigtlander Skopar 21/4
Yashica ML 24/2.8 (C/Y)
center crop at f5.6( downsized to match A12 focal range)

A12 28mm vs lens module compare by olvych, on Flickr
Voigtlander Skopar 21/4 is turned out to be good
original shots are here-
http://www.flickr.com/photos/olvych/set ... 937042204/
f 2.8-4-5.6-8
Lens used within test:
А12 28мм
Konica M-Hexanon 28/2.8
Voigtlander Skopar 21/4
Yashica ML 24/2.8 (C/Y)
center crop at f5.6( downsized to match A12 focal range)

A12 28mm vs lens module compare by olvych, on Flickr
Voigtlander Skopar 21/4 is turned out to be good
original shots are here-
http://www.flickr.com/photos/olvych/set ... 937042204/