A Simple explanation of Persistence of Vision

I have decided to write a post about Persistence of Vision. I figure it is fitting being as that is the name of this Blog.
To put it simply, Persistence of Vision is the ability of the mind to interpret a fast succession of still images as a moving image. In the early days of Motion Picture production, it was decided that the projection of 16 still frames per second would give the appearance to the viewer of a moving image (speeds as low as 10 frames per second would still give the illusion of motion, but would have a jerky, strobe effect, much like the stick figure flip-books we played with as kids).  Most early films where therefore shot at 16 frames per second. With the advent of sound pictures, the frame rate was increased to 24 frames per second to better accommodate the audio track (which at the time was printed on the film projection print). As a result, many early silent films were later accidentally screened at 24 frames per second giving them the sped up look that many of us associate with early silent films.

Persistence of Vision example

The images above were shot in 1878 in an early attempt to study the way horses run. It is important to note that these images were taken by 10 separate still cameras triggered by mono-filament "trip lines" that the horse was running through, and were never intended to be a moving image. (This system is also the basis for the "Bullet Time" effect from the motion picture "The Matrix" that used hundreds of cameras that fired in sequence along a path thus giving not only a slow motion shot, but also a "moving camera" effect.) The bottom right image is the previous 10 images played one after the other at a rate of 16 frames per second. As you can see, the horse appears to be running smoothly even though you are actually just looking at the 10 still images being shown in rapid succession (on a loop). 

All modern forms of moving image technology still rely on these principles. Most films are still shot at 24 frames per second. Some are shot at 30 frames per second. The analog video signals we grew up with were based on 120v 60hz power that required images to be interlaced. interlacing split the frame into 2 fields with 60 fields or 30 full frames being shown per second on NTSC systems. PAL systems used 50hz power, and therefore showed the images at 50 fields, or 25 full frames per second.

There is a growing belief that showing movies at 48 frames per second will give a more realistic experience to the viewer. The 2013 film "The Hobbit" Directed by Peter Jackson will be the first major motion picture to be shot and released in 48fps.
Persistence of Vision is the basis for many "special optical effects" commonly used in the motion picture industry. Cell animation, and stop motion animation are both fine examples. Each uses individually shot still frames that, when shown at 24 frames per second, give the viewer the illusion of smooth, fluid motion.
Time Lapse photography Also uses the principles of Persistence of Vision. Time lapse is created by shooting still frames at a slow interval, and then playing them back at a higher frame rate. The following Video was shot at a rate of 1 frame every 5 seconds.

* Check out my other blog for some real cool vintage photos

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