A personal hobby of mine is the modification and repurposing of old film camera lenses. Here is a collection of those with links to videos (ongoing video project):

Canon 40mm F1.9 (Canon AF35ML)

Due Oude Delft 50mm f.75 modified to ~90mm f1.1

Olympus Infinity 35mm F2.8

Yashica 45mm F1.4 (Yashica Lynx 14)

Nikon 35mm F2.8