The Brian May Archive of Stereoscopy has led a movement for June 21st to be established as Stereoscopy Day. When I first heard the date and who was behind it, I thought that's what happens when your lead guitar player is also a solar system astronomer. But it turns out it's when Sir Charles Wheatstone first presented his paper on the stereo effect in 1838.
Pinhole Photography and Stereoscopy are linked almost at birth. The first mention of someone taking a pinhole photograph is in Sir David Brewster's 1860 book, The Stereoscope. Although I don't think he questioned Wheatstone's precedence, what I remember about reading the book was frequent, sometimes a little snarky, criticism of Wheatstone. He might've been a little miffed that Wheatstone got credit for the date. Brewster also decided pinholes weren't practical and used lenses for his investigations.
Like pinhole, stereoscopy is as simple as it can be. It's always surprising how little it takes. You just take two images, coplanar and level, with a bit of a distance between them. You can do this at once in a camera that takes two pictures side by side, or one regular camera, moving it over carefully for the second exposure, often known as cha-cha.
I loaded three pinhole cameras - all with 6x6cm formats - a 45mm stereo camera, a 60mm stereo camera (both with 6cm baselines between pinholes) and a regular single chamber camera at 100mm with which I intended to play with cha-cha, both for too close and too far away stereo.
There are several ways to present stereo pairs for viewing. I'm going to use two in this post.
First is the most natural method, cross-eyed viewing, with the left view on the right and vice versa. You cross your eyes to make a double image. As the left and the right sides of the pair overlap in the middle, they fuse into stereo and depth is revealed. Note that you still see three pictures. It's the one in the middle that's 3D. That may seem unnatural to you, but they're just scanned (or printed) as they appear together on the negatives with no other manipulation or equipment. It does take some learning to view them. I created an exercise with simplified graphics at this link and have been told it does make it easier to learn.
The second is with anaglyphs, where the left and right views are rendered in red and cyan and overlaid on top of each other. Viewing through a red lens on the left eye and a cyan one on the right eye tricks the brain into calculating the depth. You of course need an appropriate pair of spectacles.
If you want to play along and you've got a lorgnette, Brian May's Owl, Google Cardboard or an Oculus rift, here's a link to a PDF with the pictures set up for stereo viewers, in the same order they're in the blog. If you've got a regular Stereocard Viewer, they should print 7 inches wide.
I started with the 45mm stereo camera with paired 6x6cm images. I built and used it primarily for the Then and Now exhibit at the Oshkosh Public Museum which was suppose to compare (not recreate) archival and contemporary views. Looking through the archives, they had hundreds of stereocards. In addition to pinholes on the axis, it has additional pinholes 10mm above the axis in order to maintain parallel verticals in the buildings I intended to photograph. They were presented with the old picture on one side of a card, and my new interpretation on the other.
Our giant hosta and the daisies seemed like the kind of a 3 dimensional object that would benefit from stereoscopy. Not the most dramatic in-your-face depth, but it does reward a quiet look around.