Unlike the previous Sekor SX and TL 2.8/35mm lenses which were Tessars with a wide angle front converter, the CS 2.8/35mm is a more modern wideangle construction. Its performance is said to be excellent. Since I never did use a CS or a Sekor E 2.8/35mm (which has the same optical construction) I can't compare this Mamiya lenses with other contemporary 2.8/35mm lenses. Most of the 2.8/35mm from around 1980 are excellent performers, and much easier to get and to use than the CS 2.8/35mm, though.  


Mamiya CS 35mm f28 lens section
MAMIYA SEKOR CS 35mm 1:2.8                 
(6 Linsen / 5 Glieder)