We made 35mm slides for lectures on the computer and photographed the screen before we bought for the department a special projector thing to which we attached a camera. Then the film was sent for processing score we got it back and mounted the slides. Fastest we could do a lecture in was 48 hours with overnight delivery.
In the early 90s, I used to make 35mm lecture slides for my father using a variation on this process
[1], on account of my naturally superior Young Person computer skills
[2]. One of the computer programs I would have been reminiscing about when I was 17 was Harvard Graphics 3.0 for DOS. A package which - although limited in countless respects - Microsoft Office has yet to beat in terms of actual graph-drawing ability. Imagine a user-friendly version of gnuplot, with rudimentary PowerPoint-style presentation features.
I still get nostalgic for the colours that worked well on 35mm slides. Medium yellow text on dark blue backgrounds was much easier on the eye than the harsh contrast that you need on the underpowered video projectors of the early 2000s (and today's low-end projectors of equivalent spec).
[1] I *think* the hospital or the MRC or someone had a machine that would expose film directly with EPS-style vector graphics, possibly using lasers or an oscilloscope-style vector CRT or something. The image quality (in the early days of XGA displays) was phenomenal.
[2] Gen-Z-ers: Ask your parents.