Asahi Kogaku M37 Takumar 50mm f/3.5 Type I
The front element group can be removed by a rubber gripping tool which grants access to the front element and aperture mechanism.
By removing three headless screws the aperture control ring can be removed exposing aperture mechanism assembly.
Below is the view of the disassembled optical group. Left to right: 1) retaining ring that releases entire optical assembly group; 2) aperture assembly; 3) aperture control ring; 4) front element group.
Takumar 500mm f/4.5 Exploded Diagram