Editing Pulfrich effect (section)

==Demonstration==

[[File:Pulfrichdemo.jpg|thumb|Imagine a camera which starts at position X and moves right to position Y. If a viewer then watches this segment with a dark lens over the left eye, then when the right eye sees the image recorded when the camera is at Y, the left eye will be a few milliseconds behind and will still be seeing the image recorded at X, thus creating the necessary parallax to generate right and left eye views and 3D perception, much the same as when still pictures are generated by shifting a single camera.]]

In the classic Pulfrich effect experiment, a subject views a pendulum swinging in a plane perpendicular to the observer's line of sight. When a neutral density filter (a darkened lens—typically gray) is placed in front of, say, the right eye, the pendulum seems to take on an elliptical orbit, appearing closer as it swings toward the right and farther as it swings toward the left, so that if it were to theoretically be viewed from above, it would appear to be revolving counterclockwise. Conversely, if the left eye is covered, the pendulum would appear to be revolving clockwise-from-top, appearing closer as it swings toward the left and farther as it swings toward the right.

A similar effect can be achieved by using a stationary camera and continuously rotating an otherwise stationary object. If the movement stops, the eye looking through the dark lens (which could be either eye depending on the direction the camera is moving) will "catch up" and the effect will disappear. One advantage of this system is that people not wearing the glasses will see a perfectly normal picture.