Leica Summicron-M 50mm f/2 Ver.4 without serial number

Brand: Leica
Production Code: 11817
Condition (appearance): A-
Condition (Optical): A-
Item Included: Front Cap, Rear Cap
Product ID: BZ0064
product description

introduced the "air" lens between elements in this design as well as the reduction of aberration by the last element with wider diameter. 6 elements 5 groups.