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Spinner strobing as a "Bird Strike Countermeasure"
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. 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. |
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Spinner strobing as a "Bird Strike Countermeasure"
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Spinner strobing as a "Bird Strike Countermeasure"
U.S. TV is 60 fields/second, European is 50/second. And it takes two interlaced fields to make a frame, therefore US broadcast TV standard (NTSC) is actually only 30 frames per second. Europe's PAL and SECAM standards are both 50 interlaced fields per second, yielding 25 actual frames per second. |
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Spinner strobing as a "Bird Strike Countermeasure"
Maxwell writes:
Seems I have heard the 16 cps is all that is required for movies to appear continuous. Motion pictures use 24 ips, repeated once, giving 48 fps (24 images shown twice each). The motion is smooth as long as the image isn't too bright, large, or fast-moving. Sometimes a stroboscopic effect can be seen in the latter cases. It can be hidden by allowing image elements to blur. You can see this effect very clearly on TV (30 ips in the U.S.) when sporting events are showing that have been recorded with high shutter rates in the cameras. Each image is sharp and it's easy to see that a succession of individual images is being shown on the screen, even at 30 ips. I think the human eye loosed it around 12 or 13. Higher than that. Twelve images per second tends to look noticeably jerky. Hence the reason an aircraft propeller will appear to be revolving slowly backwards at times. Not when being observed directly. That only happens in movies and video due to the interaction between the imaging rate and the rotation rate of the propeller. |
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Spinner strobing as a "Bird Strike Countermeasure"
"Mxsmanic" wrote in message ... Maxwell writes: Seems I have heard the 16 cps is all that is required for movies to appear continuous. Motion pictures use 24 ips, repeated once, giving 48 fps (24 images shown twice each). The motion is smooth as long as the image isn't too bright, large, or fast-moving. Sometimes a stroboscopic effect can be seen in the latter cases. It can be hidden by allowing image elements to blur. You can see this effect very clearly on TV (30 ips in the U.S.) when sporting events are showing that have been recorded with high shutter rates in the cameras. Each image is sharp and it's easy to see that a succession of individual images is being shown on the screen, even at 30 ips. I think the human eye loosed it around 12 or 13. Higher than that. Twelve images per second tends to look noticeably jerky. Hence the reason an aircraft propeller will appear to be revolving slowly backwards at times. Not when being observed directly. That only happens in movies and video due to the interaction between the imaging rate and the rotation rate of the propeller. Wrong again you clueless twit. |
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Spinner strobing as a "Bird Strike Countermeasure"
Wolfgang Schwanke schrieb:
Hz flicker CRT televisions, and most people don't notice it. Americans who've grown up with 60 Hz NTSC report noticing bad flicker with European PAL televisions. But they see at last twice the same colour... :-) |
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Spinner strobing as a "Bird Strike Countermeasure"
Roger (K8RI) writes:
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. Birds have much better vision than human beings, and I don't believe anyone has tested their ability to discern stroboscopic effects. And the front fan on a turbofan is turning at around 40-50 revolutions per second, not thousands. |
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Spinner strobing as a "Bird Strike Countermeasure"
"Mxsmanic" wrote in message ... Roger (K8RI) writes: 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. Birds have much better vision than human beings, and I don't believe anyone has tested their ability to discern stroboscopic effects. And the front fan on a turbofan is turning at around 40-50 revolutions per second, not thousands. Guess again. |
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Spinner strobing as a "Bird Strike Countermeasure"
Maxwell writes:
Guess again. It wasn't a guess. |
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