This is completely synthetic.
Rendered by computer.
The image an files are public domain.
I only rendered it into a 3-D stereogram.
The two (virtual) cameras are the equivalent of a couple of feet apart, focused on the base of the tree.
The problem is that it is hard to view because the interocular distance is too far apart as relative to the scene. If the cameras were closer together or if they were focused on a point farther in the distance, it would be easier.
As it is, now, it is pretty hard to view unless you are about arm's length away from it. Even then, your eyes tire quickly and you can't hold it in focus for very long. You'll end up with a headache.
I learned this mostly by experimentation and reading articles on the internet. I have an advantage in this case because, being completely CGI, I can quickly redo the image if it isn't right.
Thus, might I suggest, if doing it with film that you try a few different camera setups just in case. Better to burn a little extra film than to have to make two or three trips.