The SMC Pentax-M 50mm F4 Macro lens. From what I understand there are 4 versions of this lens going back to 1964. The first three bore the name Takumar and had metal bodies. (Macro Takumar 1964-66) (Super Macro Takumar 1966-71) (SMC Macro Takumar 1971-77). This 4th version bears the name Pentax and has a lighter plastic body and was made from 1977 to 1984 all were 4 element lenses. It's still sought after today as a great macro lens for digital photography and they go for around $100.00 or more on ebay, the earlier Takumar versions go for even more. Luckily I got mine in a “free bin”. These photos were taken with the lens attached to my Pentax Super Program loaded with Kodak Pro Image 100. All are hand held so the focus point isn’t where it should be on some of the photos. Use of a tripod would have certainly improved things but I’m too impatient to use tripods most of the time!