The effects in 2001 are breathtaking. Have you ever watched all the windows in the spaceships and stations? They aren't just white matte fakeouts, but actual filmsets with extras moving around overlaid with the model work. Building these sets, filming the inserts from the right angles and compositing that onto the final film in a purely optical process took an enormous amount of labor. I wonder why noone ever talks about that.
There’s a scene in a cockpit that was filmed with rear-projected computer screens and black windshields. That film was stored and later re-exposed filming a miniature moon landscape filmed through the windshield of a miniature black cockpit viewing a miniature moon base with black windows. That film was stored again then re-exposed to film people walking around through the windows of a full-sized black moon base.
The worst part of it: this is chemical film. Copying degrades image quality. So you want to do every step on a the same strip of film. But make one single mistake and you'll have to redo everything from scratch. Digital compositing is a godsend compared to that process.
