Showing Stereo Images
In addition to on slides, 3D images can be shown printed on photo paper or digitally displayed on screens. There are a few other methods, such as anaglyph (the kind you use red and blue glasses for) and lenticular prints, but these lack the image quality of the methods above. I’ve seen printed stereo images from the early 1900’s that were extremely sharp even when magnified, but since they are reflecting light rather than having light projected through them, this method lacks some of the luminosity and punchy colors that illuminated slides have. Current high-resolution displays can look pretty good, but have noticeably less resolution than slide film when seen magnified in a viewer. As such, they don’t yet capture that feeling of looking through a window into the world.
Stereo slides can also be projected. Stereo projectors from the era can be found fairly often on eBay, and require specialized screens and 3D glasses. I have yet to try this out.