Stereoscopy - Base Line Selection - Variable Base For "Geometric Stereo"

Variable Base For "Geometric Stereo"

As mentioned previously, the goal of the photographer may be a reason for using a baseline that is larger than normal. Such is the case when, instead of trying to achieve a close emulation to natural vision, a stereographer may be trying to achieve geometric perfection. This approach means that objects are shown with the shape they actually have, rather than the way they are seen by humans.

Objects at 25 to 30 feet, instead of having the subtle depth that you would see if you were actually there, or what would be recorded with a normal baseline, will have the much more dramatic depth that would be seen from 7 to 10 feet. So instead seeing objects as you would with eyes 2 1/2" apart, you see them as they would appear if your eyes were 12" apart. In other words, the baseline is chosen to produce the same depth effect, regardless of the distance from the subject. As with true ortho, this effect is impossible to achieve in a literal sense, since different objects in the scene will be at different distances and will thus show different amounts of parallax, but the geometric stereographer, like the ortho stereographer attempts to come as close as possible.

Achieving this could be as simple as using the 1:30 rule to find a custom base for every shot, regardless of distance, or it could involve using a more complicated formula.

This could be thought of as a form of hyperstereo, but less extreme. As a result, it has all of the same limitations of hyperstereo. When objects are given enhanced depth, but not magnified to take up a larger portion of the view, there is a certain miniaturization effect. Of course, this may be exactly what the stereographer has in mind.

While geometric stereo neither attempts nor achieves a close emulation of natural vision, there are valid reasons for this approach. It does, however, represent a very specialized branch of stereography.