Simulated 3D—Pulfrich Effects
Using a neutral density filter (a sunglass lens) over the right eye click this link to view a Pulfrich video on YouTube.
Strange as it may sound, if 2D video is shot with the camera moving to the left or right, or if an object is spinning, it can be viewed in 3D. To do so, you cover one eye with a dark filter, perhaps the lens from an old pair of dark sunglasses, and leave the other eye uncovered. The phenomenon, known as the Pulfrich effect
, was first described by the physicist Carl Pulfrich in 1922 and has been used in films, game 3Ds and television shows including an episode of the TV show "3rd Rock from the Sun" in May of 1997. With enough research you may be able to locate a copy of this episode (it's the last show in the second season). You view the Pulfrich sections with one lens of a pair of dark sunglasses held over your right eye.
Pulfrich glasses made for the episode on 3rd Rock from the Sun. The glasses have one dark and one clear lens. Courtesy of
This effect won't work with still images or vertical movement. It only works when subjects are moving horizontally. One explanation for the effect is that light is delayed while passing through the filter over the covered eye. Since the image of a moving subject is seen by each eye at slightly different times
the images will be slightly different and interpreted in the mind as a stereo pair. When videoing, the speed of the camera relative to the distance of the subject affects the illusion. Faster camera movement intensified it because there is greater parallax. Interesting, the direction of movement will affect the
placement of the stereo window.
- When a subject is moving right to left and the right eye is covered, homologous points are seen by the left eye before the right so the object appears behind the stereo window—an example of positive parallax.
- When a subject is moving left to right and the right eye is covered homologous points are seen by the right eye before the left so the object appears in front of the stereo window— an example of negative parallax.
To see the effect yourself, use a string and an object such as a spoon to create a pendulum. Hang it from the ceiling or other support and set it to swinging back and forth parallel to you. When viewed with a dark kens it will appear to be moving elliptically and be closer to the filtered eye. The darker the lens you use the more pronounced the effect.
You can also see the effect at work if you shoot a 2D video out of the side window of a moving car as nearby objects move by very quickly and more distant objects do so more slowly. When you view the video clip through a dark lens, the scene will appear to be in 3D.
Here Kara wears a pair of sunglasses with one lens removed. The remaining dark lens is over her left eye.