Zenitar 1.9 / 50mm
MC Zenitar-M 1.9/50mm, bought by Christophe on eBay in January 2010 (55$).
According to www.zenitcamera.com two versions of this lens have been achieved: first a small series in 1990, body length 54mm, then the model "1991", length 44mm, produced from 1991 to 1994. Both versions have existed in M42 screwmount (Zenitar-M) and K bayonet (Zenitar-K). This lens is part of the second series. The body is almost identical to that of an Helios 44M-4, the optical part has smaller dimensions.
MC Zenitar-K 1.9/50mm, received in may 2010 with an AM2 bought by Irina for Christophe.
Bayonet version. The marking makes me think of a lens produced in very small series.
MC Zenitar-K 1.9/50mm, bought by Irina for Christophe, delivered October 18, 2013.
Marking different. The rear lens has a splinter.
Tests: Please note that these tests were made with the means at hand, not in a "scientific" way. See here.
Comme le 1.7/50 excellent au centre dès la pleine ouverture. Et comme lui produit à peu d'exemplaires alors qu'il aurait avantageusement succédé à l'Helios 44.