This is a vintage Cosina-made Carena lens, sold in Germany in the 1970s by the Porst photo chain.  History below.  Rare prime 50mm lens, these are commonly found as 35mm or 135mm kit lenses sold with a body with a brand-name prime.  This is a quality lens of the Tessar design, very sought-after for portraiture as they are softer wide-open than modern plasmats, and have a more pleasant out-of-focus rendering ('bokeh').  But from f8-16, they are as sharp as most period plasmats.  So this is an ideal portrait lens for use on a mirrorless or for cine work.

Comes with generic front an a Minolta MD cap on the rear.