I tried twisting and pulling on the projector lens (40.5g) by hand to remove it, and to my surprise it popped out quite easily with a twist and a tug.

I assume film or translucent still images would've been placed behind this lens that focused the projection on a surface/screen, focusing it to make the projection clear and magnifying it.

Length: 40.0mm

Width/Diameter: 15.8mm