Persistence of Vision
Overview: Persistence of vision is the optical illusion that occurs when the visual perception of an object does not cease for some time after the rays of light from it have ceased to enter the eye.
Supplies: Box of POV supplies that includes screw gun, color wheel, zoetropes, praxinoscope, flip books
Objectives: Observe the various types of ways our vision retains an image
Setup:
- Lay out the various POV items on the table
- Insert the screw end of the color wheel into the screw gun
How to run the demo:
- The praxinoscope has a viewfinder to look through to see the “movie” when the wheel is spun
- The zoetrope “movie” is see by looking through the slits as the image is rotated
- The color wheel rotation happens when the trigger on the screw gun is used
- Flip through the pages of the flip book to see the “movie” in the book
What’s Happening?
When the frequency of something flickering in motion is too high for the visual system to discern differences between moments, light and dark impressions fuse together into a continuous impression of the scene with intermediate brightness. The eye and brain retain the impression of an image for a time of about 1/30 of a second, depending on the brightness of the object.
Different technologies take advantage of human persistence of vision. For example, when we watch a movie, it feels like a continuous experience even though the screen is dark about half the time. Films show one new frame every 1/24 of a second. The eye retains the image of each frame long enough to give us the illusion of smooth motion. Even newer TV and computer monitors take advantage of our failure to notice the constant and steady refreshing of images.
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