This is an uncommon M mount Leitz Elmar 5cm f3.5, released in 1954 alongside the M3. Leica would later produce a redesigned f2.8 version, but this is the original from the first year of production. Very light haze and dust, minor internal glass flaws, no fungus or any other artifacting that will affect imaging. Cosmetic condition is very good, with light barrel wear.