This is a Tanack 135 finder for 35mm rangefinder cameras (such as Leica). This is nicely made finder in very good shape. This finder has an adjustment dial on the viewing side that compensates for parallax. There is a bit of internal haze, but not enough to impact use. This finder was made by Tanaka Kōgaku, a legendary Japanese camera company, and is both highly collectible as well as usable!
Price: $30 plus shipping.