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Could someone explain this optical illusion, slowly and w/o big words
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If the rotors go around 30 times in one second and you are filming at 30 frames per second it would look like they are still just like that.
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The helicopter is attached to a big crane that's out of shot and you cant see the cable because they are using Spiderman thread which is extremely thin but very strong!
Honestly - Its so simple to explain....don't know why you didn't know that
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Yeah you got me there. I thought I saw the ultimate proof that secret alien anti gravity technology is now also available for civil aircraft. But the spiderman thread is a much more logic explanation.The helicopter is attached to a big crane that's out of shot and you cant see the cable because they are using Spiderman thread which is extremely thin but very strong!
Honestly - Its so simple to explain....don't know why you didn't know that
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Easy, the visual-fx /cgi guys where having a lazy day and couldn't be bothered to make the props spin 
Eureka!!!!! A solution to DJI's rattling prop issue - DON'T LET THEM SPIN AT ALL!!!
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Ever had an instance where your brain grasped the explanation, but your eyeballs were refusing to accept it?The helicopter is attached to a big crane that's out of shot and you cant see the cable because they are using Spiderman thread which is extremely thin but very strong!
Honestly - Its so simple to explain....don't know why you didn't know that
The blades on a helicopter are spinning at a fixed rate and the pilot only changes the pitch to increase or decrease lift. If that matches the frame rate then you will get this effect.
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does anybody know what the actual frame rate used in this case was? or if its possible to figure out the right rate looking through the live video downlink? or is the downlink frame rate a muddling factor to figure it out on the fly?Ever had an instance where your brain grasped the explanation, but your eyeballs were refusing to accept it?
was this luck or intentional?
very cool either way!
A bit more complex than previously stated...
A photo at 1/30th of a second is blur unless the camera is very stabile, on a tripod. Portrait photography is usually done 1/60 - 1/125th of a second shutter speed. Sports and action photography is usually done at a 1/250 - 1/500, you can stop a tennis ball in motion clearly at 1/750+ if you increase too much you loose light and need faster film/high ISO/ or large aperture lens. The beauty of the video camera is that it put 30 frames together for one second, but the shutter speed is not 1/30, it is actually much much higher 1/1500 to 1/2000. Because the video is shot during a bright mid day sun the shutter speed is fast providing a sharp image of the rotors. In a coincidence the slow rotor head speed of the helicopter is perfectly matched with the frame rate and appears as if it is not moving at all...
Check out this YouTube video
Polish hind MI-24 in strange maneuver!!!
A photo at 1/30th of a second is blur unless the camera is very stabile, on a tripod. Portrait photography is usually done 1/60 - 1/125th of a second shutter speed. Sports and action photography is usually done at a 1/250 - 1/500, you can stop a tennis ball in motion clearly at 1/750+ if you increase too much you loose light and need faster film/high ISO/ or large aperture lens. The beauty of the video camera is that it put 30 frames together for one second, but the shutter speed is not 1/30, it is actually much much higher 1/1500 to 1/2000. Because the video is shot during a bright mid day sun the shutter speed is fast providing a sharp image of the rotors. In a coincidence the slow rotor head speed of the helicopter is perfectly matched with the frame rate and appears as if it is not moving at all...
Check out this YouTube video
Polish hind MI-24 in strange maneuver!!!
Its actually a combination of two things. First is frame RATE. The rate at which frames are recorded in terms of time between each one. If the rotational time of the blades coincides with the frame rate of the camera then the shutter opens at the same time rate as the props rotate. Given thats a 5 blade chopper. I suspect the frame rate is 1/5th the rotation of the chopper's blades. I would almost bet that if one blade were a different color you would see it rotating around to each of the 5 points but would appear stationary as a whole.
The second aspect it shutter speed, or the time that the shutter is actually open when its time to take a frame. The frame rate times when the shutter opens, the shutter speed controls how long its open at that time. So to stop those blades, I would guess the shutter speed was rather fast, probably 1/250 or higher.
Slowing the shutter speed (longer interval) would keep the props stationary but begin to blur them. Keeping the shutter speed the same and varying the frame rate would make the props begin to rotate but still remain crisp.
Often people confuse shutter speed and frame rate. They are independent things but one requirement is that the shutter speed MUST be faster or the same as the frame rate. For example you can shoot 30fps at 1/60th. But you can't shoot 60fps at 1/30th. A 1/30th of a second is longer in time than the time between frames spaced at 60 per second. Therefore the shutter would still be open from frame 1 when it was time to take frame two.
Framerate controls how many times per second you take a picture. Shutter speed controls how long that picture is taken for.
At least the phantom, but I presume the Inspire as well, have rolling shutters. Its the reason why if you see props or other fast moving straight objects in the scene, they will often appear as curves. Many videos you see on youtube of drones have this. Look at the props, they look like boomerangs rather than straight props. This is caused by a rolling shutter in electronic shutter systems. Basically, the sensor is turned on and off in a sweep from top to bottom. If the shutter speed is slow enough, the whole sensor is on all at once and the off line then progresses down the sensor. So its turned on flowing down, then the whole sensor is on, then its turned off going down. If the shutter speed is fast enough, the off edge begins at the top moving down before the on band reaches the bottom. In this scenario, the whole sensor is never on, only a band. Thats commonly when you see the boomerang props. As the prop rotates and the band flows down the sensor, it forms a curve or hook on the sensor. Then when assembled into one frame, a curved prop appears to be there when in reality it was straight.
Here is a good video on rolling shutters.
Since there doesn't appear any artifacts of rolling shutter in that video, I would guess it was not taken by a camera with a rolling shutter and likely shot using a CCD type camera..
The second aspect it shutter speed, or the time that the shutter is actually open when its time to take a frame. The frame rate times when the shutter opens, the shutter speed controls how long its open at that time. So to stop those blades, I would guess the shutter speed was rather fast, probably 1/250 or higher.
Slowing the shutter speed (longer interval) would keep the props stationary but begin to blur them. Keeping the shutter speed the same and varying the frame rate would make the props begin to rotate but still remain crisp.
Often people confuse shutter speed and frame rate. They are independent things but one requirement is that the shutter speed MUST be faster or the same as the frame rate. For example you can shoot 30fps at 1/60th. But you can't shoot 60fps at 1/30th. A 1/30th of a second is longer in time than the time between frames spaced at 60 per second. Therefore the shutter would still be open from frame 1 when it was time to take frame two.
Framerate controls how many times per second you take a picture. Shutter speed controls how long that picture is taken for.
At least the phantom, but I presume the Inspire as well, have rolling shutters. Its the reason why if you see props or other fast moving straight objects in the scene, they will often appear as curves. Many videos you see on youtube of drones have this. Look at the props, they look like boomerangs rather than straight props. This is caused by a rolling shutter in electronic shutter systems. Basically, the sensor is turned on and off in a sweep from top to bottom. If the shutter speed is slow enough, the whole sensor is on all at once and the off line then progresses down the sensor. So its turned on flowing down, then the whole sensor is on, then its turned off going down. If the shutter speed is fast enough, the off edge begins at the top moving down before the on band reaches the bottom. In this scenario, the whole sensor is never on, only a band. Thats commonly when you see the boomerang props. As the prop rotates and the band flows down the sensor, it forms a curve or hook on the sensor. Then when assembled into one frame, a curved prop appears to be there when in reality it was straight.
Here is a good video on rolling shutters.
Since there doesn't appear any artifacts of rolling shutter in that video, I would guess it was not taken by a camera with a rolling shutter and likely shot using a CCD type camera..
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