Iranian photographer Alireza Rostami has been researching and fine-tuning different lenses for years. One day, one of his test subjects was an MC Zenitar-M 2s 50 mm F/2.0. While disassembling the lens, Rostami discovered that he could affect its bokeh pattern by making minor changes to the optical scheme.
Zenit MC Zenitar-M 2s 50mm F/2.0 was produced by the Krasnogorsk Optical and Mechanical Plant starting in 1995. The lens had a plastic body and manual focus and aperture adjustment. Its optical scheme used 6 elements with antireflective coating, which were combined into 4 groups. The modification of the lens, made by Rosts, consisted in turning the third group of elements in the opposite direction.
Rostami filmed the entire remaking process on video, which is available at: youtube.com/watch?v=p1YrVzrsmac. In it he shows in detail how to disassemble the lens and change its optical design. Schematically, his idea is as follows:
Using an M42-EF adapter, Rostami mounted the converted Zenitar on a Canon 6D camera and this is what he got: