On Mon, 03 Dec 2007 02:52:14 -0000,
(Robert Bonomi) wrote:

In article ,
Maxwell wrote:

"Roger (K8RI)" wrote in message
...
On Sun, 02 Dec 2007 22:09:30 -0000, Jim Logajan
wrote:

At cruise RPM that effect would be completely lost. There's not a
bird or human alive that can discern stroboscopic effects of more than
a couple hundred cycles let alone over a 1000. Most of us can't even
discern 60 cps.



"Mike Noel" wrote in message
...
True, but aren't we talking about 40 cps when the prop RPM is 2400?


Seems I have heard the 16 cps is all that is required for movies to appear
continuous. I think the human eye loosed it around 12 or 13. However, we
don't seen consciously either. Hence the reason an aircraft propeller will
appear to be revolving slowly backwards at times.

Visual perception is funny and complex.

black & white films were 16 frames/second.
Color films are 24 frames/second

U.S. TV is 60 fields/second, European is 50/second.
This is driven more by the need for phospors that 'decay' rapidly enough
to not produce 'blurred' motion than perception issues.

OTOH, A significant number of people can perceive 'flicker' in conventional-
tube fluorescent lamps. which is at 120 flickers/second.

I seriously doubt they can. I can discern the flicker in *some*
fluorescent lights, but I can not discern 120 cps on a strobe. I
think what they are seeing is the "sputter" of a cold lamp or a light
that isn't starting correctly. The flicker I see in those lamps is
considerably slower than 120 or even 60 cps.

First, for any flicker the phosphor has to be defective which means
the lamp is already defective so we can't expect it to be behaving
normally.

it would be interesting to see if those same people can discern even
60 cps in a strobe.

Also, the eye -- and brain -- 'notices' things that are too fleeting for
conscious identification. Google 'subliminal' advertizing -- IIRC, lab
tests showed that injected imagery with a duration of only a few milliseconds
had 'measurable' effects.

It's controversial, but has been called one of the greatest myths of
all time. It's generally accepted they are ineffective.
http://www.sciam.com/article.cfm?art...E19&sc=I100322
According to the Scientific American article they at best distract the
viewer.

Roger (K8RI)