Mount: Pentax PK
Build quality: good
Filter thread: 58mm
Infrared Mark: yes
Super bright, super cheap, surprisingly good. Takes some practise to truely utilize this lens when wide open. Portraits are great with it.
This lens is fairly cheap for such a bright lens. It was distributed in Germany by Quelle/Porst and was produced by some other company. Which? I don't know.
Blown highlights are terrible when wide open. Underexpose slightly to fight that. For such a cheap lens., performance is very respectable. The cheapest Pentax 50mm 1.2 will cost several hundred bucks more.
You can find shots with a macro converter and the Revuenon 55mm 1.2 here: