Base Line Selection
For general purpose stereo photography, where the goal is to duplicate natural human vision and give a visual impression as close as possible to actually being there, the correct baseline (distance between where the right and left images are taken) would be the same as the distance between the eyes. When images taken with such a baseline are viewed using a viewing method that duplicates the conditions under which the picture is taken then the result would be an image pretty much the same as what you would see if you were actually there. This could be described as "ortho stereo."
An example would be the Realist format that was so popular in the late 1940s to mid 1950s and is still being used by some today. When these images are viewed using high quality viewers, or seen with a properly set up projector, the impression is, indeed, very close to what you would see if you were there.
The baseline used in such cases will be about 50mm to 80mm. This is what is generally referred to as a "normal" baseline, used in most stereo photography. There are, however, situations where it might be desirable to use a longer or shorter baseline. The factors to consider include the viewing method to be used and the goal in taking the picture. Note that the concept of baseline also applies to other branches of stereography, such as stereo drawings and computer generated stereo images, but it involves the point of view chosen rather than actual physical separation of cameras or lenses.
Read more about this topic: Stereoscopy
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