This is a Carl Zeiss Jena (East Germany) Flektogon 35mm, a famous lens, from the later MC red letter series. With a bright f/2.4 aperture and a 6-group, 10-element lens construction, you can enjoy the Flektogon's characteristic sharpness even at the edges. There are no noticeable scratches on the front or rear elements, and no balsam separation is visible. Based on the serial number, it was manufactured around 1980. Both the aperture and focusing helicoid operate smoothly. Carl Zeiss Jena exported select, high-quality lenses to West Germany. The red letter MC models, in particular, were considered select items and were rarely available in the East. Since there is no corresponding category for M42 mount, it is listed under the full-frame Sony α series, which is well-regarded (please purchase a mount adapter separately). Designed for full-frame 35mm, it can also be used on APS-C cameras, providing a 50mm equivalent focal length, making it perfect for beginners interested in antique portrait lenses. M42 adapters are available from various manufacturers, so why not customize your full-frame mirrorless camera? It will be shipped via Yu-Yu Mercari delivery service. Thank you for your consideration.