This DIY video is really interesting and shows how photographer Mathieu Stern takes an old cinema projector lens and adapts it to a modern mirrorless camera to get some really wonderful and unique look to your shots.
You can find all sorts of old used projector lenses online (for example on e-bay), for this project, Stern used an ISCO MC 65 mm cinema projector glass made in Germany. It has diaphragm so you are forced to shoot at f/2 all the time, although as a fun relatively small specialized DIY lens (that cost around $100) isn’t bad at all.
The main issue with these lenses is that they are not really designed to be mounted on to cameras (surely not on modern DSLR or mirrorless cameras). Stern had to find a way to adapt them in such a way so that he will be able to attach them to his Sony
Stern had an old Helios 44mm housing (with no glass) and with some robber, the projector lens fits perfectly inside and all he needed to add was a M42-nex (e-mount) flat adaptor to get infinity focus working and he was able to attach it to his Sony A7 III camera and go out and shoot.
The results are actually very nice and the colors seem really punchy and the center is very sharp with a nice falloff in the corners which gives the lens an interesting character.