Meyer Lydith 30/3.5

The photo shown in the MCA post are taken by Pentax K100D with Meyer Lydith 30/3.5 which has a 42mm thread mount, often known as M42 mount. It has 5 elements in 5 groups, and minimum focusing distance is 0.33 meter or 1.1 feet. It is believed to be a simplified design of his brother Meyer 29/2.8. From my own knowledge, there are three versions in the production line of East German 30mm series, both share the same design but in two different names, Meyer and Pentacon.