The Industar 61 was produced at the FED factory in Kharkov, Ukraine. It is a "normal" lens for M39 (Leica screw mount) and M42 (Pentax screw mount), with a focal length from 52-55mm, depending on the production run. It has four elements in three groups and the six-blade iris provides a range of apertures from f/2.8 to f/22. It is commonly found on rangefinders made by FED and Zorki. Its brand name Industar refers to the class of similar 4-element/3-group lens constructions of the whole soviet photo-optical industry.
The Industar 61 L/D is possibly the most highly regarded lens for Ukrainian Leica copies apart from the 35mm Jupiter-12. In an L/D or L/Z version of this lens, the L indicates that the lens has (slightly radioactive) Lanthanum in it, and D indicates M39 mount while Z indicates M42 mount. Most examples are multi-coated and are marked as such with MC. Some Industar 61 L/Z bear the logo of LZOS, probably having been made by that company.