I was watching Ice Road Truckers last night, which is sponsored by Craftsman, so they kept running this commercial for one of their cordless tool lines.
They show one clip where the guy is drilling into a piece of wood attached to a tree - steps to a tree house maybe - with a wood boring bit. Maybe it was an optical illusion, but I'd swear the drill is running backwards - counter clockwise. I rewound my DVR a bunch of times, and ran it it slow motion. It sure looked to me like the bottom of the bit was coming up and the 3/8" marking was going away from, not coming towards the viewer.
If you watch TV films closely you can see the same thing with cars wheels in close-ups. I recall seeing this a lot on the old Bonanza TV series with the wagon wheels.
It is a function of the filming process.The film image is a mirror image of the actual event.
Ah, the strobe light "stroboscopic" thing. When the frequency of the camera shutter is a little different than the frequency of the drill (in RPM) the drill can appear to be going slowly forward.... or slowly backward.
I'd agree except for one issue. When I run the commercial in slow motion, it appears that the 3/8" marking on the bit is rotating away from the viewer. Would the wagon wheel effect still be present in a slow motion viewing of the object?
That's a digression. . What we have been discussing is 'timing'; as each part of something rotating (in the case of wheels it could be identical-looking spokes for example) comes into each frame of a film or TV picture. It may then appear to be ahead of or behind the one seen in the preceding frame. So the item my 'appear' to rotate either forwards or backwards.
Mirror or not; viewing film is a matter of the optics used and how the film is then projected onto either a screen or into a TV transmitter.
It was possible in some film installations, for example, to adjust the focal length etc. of the projector so that the picture could be seen reversed and/or perhaps upside down!
Almost right. It is _not_ a mirror image, it is a simple strobe effect. Were it a "mirror image" every rotating object would appear to run backward as would everyting in the movie.
The stroboscopic wagon wheel effect of old TV shows was the result of the frame rate of the film being different than the 60hz standard of television timing.
I don't know-- but I was playing with my new toy [Bosch impact driver as recommended by John in another thread] today and in full sun, at just the right speed, if you stare at the bit it looks like it reverses direction. I know it didn't because the screw kept going in.
Okay, so what does the 60hz timeing of TV have to do with the strobing in the movie theaters? Answer: Nothing. In the theater is it due to the frame rate of the projector and/or the camera that did the filming.
The strobe effect is well known and is (or used to be) a standard demonstration in HS physics.
Either one early suggestion is what's happening, he's coming OUT of the hole (or maybe he's just TESTING the gears in the drill?, or even knowing it'll be on a tv series, watched by people from HERE, sabototaging us by planting a flame-war seed?), or it's that old cowboy-movie-effect of wagon-wheels APPEARING to be turning BACKWARDS (while in full flight from the indians).
Easy demonstration. Look at the TV.
Now, either spread out your fingers and WITH ALL POSSIBLE SPEED wave your hand back and forth between your eyes and the tv.
Better, put a FAN between you and the tv, and look THROUGH the fan at the tv.
Better yet, no tv, put TWO fans together, and through both look out the window or somewhere bright enough -- unless the fans are going at the EXACT same speed (in which case you're looking at ONE fan with WIDER blades), you'll see a slow movement of an "artifact" (someone please say it with a bit more care and accuracy) invented (as is everything visual, I guess) by your brain.
Or, get two not-so-well-tuned pianos and simultaneously hit the same key on each. Here that warbling sound? Similar effect. Maybe. Maybe I've gone way too far off on a tanget from wagon-wheels.
Someone can surely improve on what I'm saying.
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