Made between: 1980 - 1982
Optical design: 10 elements in 9 groups
Lens mount: M42, (Pentax K ver called Mir-47K 20mm f/2.5)
Covers: Full-frame (24×36mm)

More info: 

http://allphotolenses.com/lenses/item/c_1575.html

Pentax K ver
http://mattsclassiccameras.com/mir_47k.html