Before EXIF data landed on the scene through the rise of digital photography, film cameras could superimpose the current date directly onto your photos, allowing you to see when you shot each one as you flipped through an album. If you’ve ever wondered how that date was included, here’s an interesting 14-minute teardown by Applied Science that reveals the secret.
Since the date is seen on the negative itself, the physical components behind the system need to be extremely small. And as this teardown shows, they are — it’s a tiny micro LCD projector backed by a tiny incandescent light bulb that fires every time you press the shutter.
Since the date module on the camera isn’t pressed up against the film plane itself, simply displaying the date on the LCD screen wouldn’t allow any date to be recorded on the negative. Thus, the module needs to be a projector that forms the image of the date onto the film from a very short distance away.
To achieve that short projection distance, the light source is a tiny grain-sized incandescent bulb that’s placed at a distance by using a folded optical path that has a mirror bouncing light.
If you liked the video above, you can find more science and teardown videos over on the popular Applied Science YouTube channel.