Re: how much of what we see is black?

From: Jim Carlile (email suppressed)
Date: Wed Oct 31 2007 - 11:53:54 PDT

In a message dated 10/31/2007 4:12:20 A.M. Pacific Daylight Time,
email suppressed writes:

The illusion of movement in cinema is not due to the persistence of vision
(by which all frames would mesh together in the brain) but rather by the phi
phenomenon. I thought this was common knowledge. The phi phenomenon allows us
to perceive those little blinking lights around a theatre marquis as smooth

A light that blinks on the left of the visual field followed by a light that
blinks on the right of the visual field will be perceived as one light
moving from left to right, provided that there is a 30 millisecond gap of black
between the two flashes.

Right. The critics of POV are not denying that it exists, just that it does
not explain how we see moving pictures. TV scanning works differently than
film projection, which may explain why cats can watch TV, if they can...If POV
were correct, we wouldn't necessarily see the dark 'frames,' but we would see
a piling up of them which would carry over onto the bright ones. And we
wouldn't be mentally ignoring it-- if we are, then it's not POV.
Again, if we slow down the projector to 4 or 5 fps, we don't see much of a
difference in darkness. If POV were true, we would.
A correction, too... about the original question of how much we see is
"black." The correct answer is that it depends on the projector and the sector
size of the shutter blades. The shutter is a circle with 360 degrees. Old
fashioned shutters had an open angle of about 180. So the 2 or 3 blades took up
half the total circle, with the film pulldown sector slightly larger to avoid
But newer projectors shave down the blades to allow more light on the
screen-- some super 8 machines had blades as small as 43 degrees, and hobbyists
have even carved them down to 25 or less. That gives an almost 300 degree open
sector, so the percentage of light vs dark time is much greater than 1/2. It
means that most of the time we're in the light.

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