Post your animated GIFs thread (56k takes a bus)

Chaos

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Rotor blades syncing with the framerates of the camera, probably.
 

Eye-Q

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Rotor blades syncing with the framerates of the camera, probably of course.
FTFY

The Kamov-helos are famous for their coaxial contra-rotating rotors, thus making the rear rotor unnecessary since there is no yaw momentum. In that Video/GIF the upper rotor rotates with almost exactly a multiple of the shutterspeed of the camera. That's why the picture is only exposed when the rotor is in the same position.
 

chaos386

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FTFY

The Kamov-helos are famous for their coaxial contra-rotating rotors, thus making the rear rotor unnecessary since there is no yaw momentum. In that Video/GIF the upper rotor rotates with almost exactly a multiple of the shutterspeed of the camera. That's why the picture is only exposed when the rotor is in the same position.
Anorak mode:

The shutter speed and frame rate of a video camera are two separate things. Frame rate is how many images the camera records per second, usually somewhere between 24 and 60. Matching the frame rate to the helicopter's rotors isn't enough to get the effect in the GIF, though, since the rotors would normally just be a blur. Getting them sharp like that involves only capturing light for a fraction of each frame, and this is where the shutter comes in. High-end video cameras have a spinning disc in front of the film/sensor that blocks the light for part of each frame (it's shaped like a pie that's had a few slices cut out of it). Most movie cameras have what's known as a "180-degree" shutter, where the disc is half a circle, and this combines with 24 fps to make the traditional movie look. For something like the GIF above, the shutter might be something like 2 degrees (so the shutter is almost a complete circle, with a tiny sliver left open), so the camera only records light during a tiny fraction of each frame, removing almost all motion blur.
 
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