I have been interested in close-up/macro stereo photography, since I got my first real camera, a Minolta X-700 in 1988. Instead of the standard 50mm lens, I elected to buy the 50mm Macro lens for a lot more money (the lens cost as much as the camera body, if not more). That was a lot of money and I had to think long and hard before making the decision. But we only live once, so I decided to go for it. This is one of the best decisions I have ever made. I used this lens extensively in my research and for personal 3d photography. At some point I had acquired all Minolta macro photography equipment including Bellows, and microscope lenses. Even though I eventually sold all the Minolta equipment, I kept the macro lens (see picture) and at least one X-700 body.
Two methods are used go get a lens to focus closer than its minimum focusing distance: 1. Extension, 2. Close up lenses. We will look at these methods in subsequent postings.
Regarding the math behind 3d macro photography, you only need to use two formulas:
1. The fundamental lens formula: 1/f = 1/I + 1/I', where f = focal length of the lens, I = distance of object from film plane, I' = distance of image from film plane. See also this blog.
2. The basic stereoscopic formula: P = FB/I = FB (1/Imin – 1/Imax), where P is the stereoscopic deviation, F is the focal length of the recording lens, B is the stereo base, I is the distance of the subject from the camera (Imin is the minimum distance, Imax is the maximum distance, Imax – Imin is the range of depth in the scene.) See also this blog.