Applied Science is a delightful gem of a YouTube channel - I recommend to have a browse through the archive of videos if this presentation style and content interests you. Ben is a great presenter of complex topics.
I was picturing the engineers who must have done like a 1000 iterations of this stuff before they were able to come up with a crystal clear image on the film.<p>What an adventure it must be to make these things and one day finally having the joy to see the whole world use your inventions like this.<p>Having never worked on any hardware I can only imagine how much fun (and test of patience!) it must be to use/bend the laws of physics to make such things.
As a side note one thing you learn over the years is to always put the date on things and make sure the year, four digits, is there too not just the month and day.
The 1977 camera mentioned halfway through the video might have been the first consumer camera that superimposes the date, but it was common for aerial photos to have metadata like that added to the margins, like <a href="https://map.geoportail.lu/aerial/1977_30000/pdfs/0181.pdf" rel="nofollow">https://map.geoportail.lu/aerial/1977_30000/pdfs/0181.pdf</a>
I loved watching this video. I'm working on a product that turns your phone into a disposable camera that automatically mails you 4x6 prints (<a href="https://latercam.com" rel="nofollow">https://latercam.com</a>). People have been asking for date imprinting and I found the video while researching.
TL;DR: there is a little light, a mirror and a small see-through LCD screen forming a projection through the back side of the film. Since the distance between the light source and the LCD screen is relatively large, the light acts as a point source and you don't need a lens for the image formation.