Why 46" is a good size camera slide for taking 3D pictures.

The main reason for having twin cameras at all is so that we can (somehow) snap the shutters simultaneously. And the latter
because any moving objects in our scene will not register correctly in the final 3D picture if the motion isn't frozen.
In fact, improperly positioned objects in a stereo presentation will cause discomfort and actually distract attention from other
parts of the picture that are correct.

Some typical moving objects are: People, animals, vehicles, leaves, flags, rushing water, waves, and so on. But some of
these objects are less important than others especially at larger distances. For example, individual leaves (typical tree leaves)
will not be discernable at distances larger than about 200 feet. At this distance only the shape of the tree should be still.
In a strong wind, when tree branches are swaying, the distance would have to be increased to 800 - 1000 feet. But let's say
that we will not go out to take 3D pictures on a stormy day.

There is a rule of thumb that says the cameras should be separated a distance of 1/30 the distance to the nearest object
in the picture. This isn't an exact science, and some say that at larger distances the ratio is even smaller (1/100 for example).
So we need to be concerned about small moving objects located up to about 200 feet from us. And using the 1/30 rule,
for 200 feet we need a camera separation of about 6.7 feet.
Unfortunately, a camera slide of nearly 7 feet is hard to manage, and that's why I've decided to build a slide that's managable,
namely 4 feet long. If the rule of thumb was 1/50, my slide would be perfect! So it depends on whose thumb we are talking about:)





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