>>3550445>>3550446>What's the reason this lens is so huge?Because it's a 50mm F/0.95 try find a smaller lens with those spec, you can't.
It's actually a Canon rangefinder lens from the 60s and only worked on the Canon 7 because it had to be mounted with an external bayonet mount.
Pic related notice the top camera (Canon 7) has external bayonet mount additional to the M39 screw mount (Leica thread mount) where as the bottom camera (Canon P) only has the screw mount.
https://global.canon/en/c-museum/product/s43.html 