Slide bar

From Photo-3d

This technique involves using a purchased or constructed slide bar and a single camera to make both exposures. The author has used an aluminmum plate with the edges folded to make a support against which the camera can rest, with a ruler glued to the back to determine the amount of image separation. The drawback to this technique is that the subject must be stationary between the two exposures. In spite of this, I have taken numerous successful landscape stereo pairs this way. -- Joel Alpers

If something moves between the time that the two pictures are taken, you may cause retinal rivalry.