Ask A Scientist© General Science Archive

name         Josh K.
status       student
age          14

Question -   Some guy I keep talking to argued with me that the eye
can only see an equivilency of 24 frames per second.  But I do not think
that's a fact. When I rotate a sprite at 60 or 80 fps it is quite
different than that of 40 or 30 fps.

Can someone clear this up for me? Thanks.
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When an image strikes the retina the nerve impulses last approximately
1/25 sec. This is why motion pictures appear to move continuously, even
though the number of frames/sec. is not extremely fast. This is also why a
TV screen does not flicker. If you have seen some "old time movies" from the
20's and 30's they appear "jerky" because at the time the technology did not
allow for frames to appear quickly enough to "fool" the eye, and the eye was
able to resolve successive frames.

There is another effect that may be coming into play also, and that is a
"strobe" effect. A strobe light flickers very short pulses of light at
variable controlled speeds. If some object is rotating in front of the light
at some multiple of the pulse speed, it will appear to stand still. If the
strobe light is speeded up or slowed down slightly the image will appear to
move forward or backward slowly.
Vince Calder
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