Not all bugs in ArmA are unrealistic....

[opteryx 1562]

Apparently...

LINK

[Espectro (DayZ) 0]

Either fake, or a very nice controlled Aliasing

Nyquist theorem all the way

[Colossus 2]

I do know that the Hind has fixed-wings and can "glide", but was a bit too weird.

[-ZG-BUZZARD 0]

If this is real then the engines must have taken heavy abuse...

But my money is it's a fake somehow... an excellently made fake... Wonder how it was done...

[karantan 0]

Of course it's a fake.

[fardwark 0]

It's not a fake, the refresh-rate of the camera just happens to be perfectly synced with the rotation of the rotor. The blades are in the same-ish locations each time the shutter opens so it appears to the camera that they are not moving (eventhough they are spinning at full speed).

[karantan 0]

It's not a fake, the refresh-rate of the camera just happens to be perfectly synced with the rotation of the rotor. The blades are in the same-ish locations each time the shutter opens so it appears to the camera that they are not moving (eventhough they are spinning at full speed).

Means it's a fake. Or the illusion if you want. The point is that the blades ARE TURNING, there's no other way that the chopper get airborn yes? How it's done that it's appearing that the blades don't turning is just a question of technicality.

[-ZG-BUZZARD 0]

It's not a fake, the refresh-rate of the camera just happens to be perfectly synced with the rotation of the rotor. The blades are in the same-ish locations each time the shutter opens so it appears to the camera that they are not moving (eventhough they are spinning at full speed).

Means it's a fake. Or the illusion if you want. The point is that the blades ARE TURNING, there's no other way that the chopper get airborn yes? How it's done that it's appearing that the blades don't turning is just a question of technicality.

There's a big difference between a fake and an illusion. A fake means something was artificially made up for you to believe something that isn't real. An illusion is just a coincidental thing that makes you think something is happening in a way that it is wrong, while in reality it is happening in a "right" way.

And, for the record, said technicalities is what I'd be very interested to know, WHAT is happening and HOW this video got to be the way we see it.

[karantan 0]

BUZZARD @ May 17 2007,18:48)]An illusion is just a coincidental thing that makes you think something is happening in a way that it is wrong, while in reality it is happening in a "right" way.

Tell this to David Coperfield not me.

[da12thMonkey 1943]

BUZZARD @ May 17 2007,17:48)]And, for the record, said technicalities is what I'd be very interested to know,  WHAT is happening and HOW this video got to be the way we see it.

It's basically exactly as fardwark explained, the frequency at which the camera shutters operates, or the frame-rate of the video itself, are synced with the rotational frequency of the main rotor on the Hind.

The camera opens its shutter to take an image , let's say 20 times every second, in other words it operates at 20Hz.

Similarly, the rotor do a fixed number of rotations per second. To make the rotors appear to stop, they have to rotate 20, 40, 60 or some other multiple of 20, times per second, such that the rotors have returned to the same orientation relative to the rest of the chopper, by the time the shutter has opened again to take another image. If you want to be technical, the camera is in-phase with the rotation of the blades, or 2*pi*k radians out of phase, where k is an integer, and pi is the number 3.14.....etc.

This means that every frame the camera takes has the rotors at the same orientation, therefore when the video is played back, the rotors don't appear to rotate.

You can do all sorts of things with varying the frequency of the shutter speeds or light strobeing to produce strange effects on the image of objects with periodic or harmonic motion. It's possible to make them appear to stop like has happened here, make their rotation or oscillation look like it's slowed down or sped up, or that they're running backwards.

Your eyes operate at somewhere in the region of 20-30Hz (can't remember exactly what it is), but your brain blurs the motion within images it receives together so that these phase effects aren't visible. If you happen to have a cooling fan that operates at around 50, 100, 150Hz etc, you can make it appear to stop moving by placing it in front of a TV set (typically these refresh around 50 or 60Hz) and looking through it.

[Daniel 0]

Bit like the stroboscopic effect where workshop machinery and lights are set up on the same phase. Can make it look as though drills and lathes are switched off, when in fact they are spinning fast enough to make a mess of your finger.

But cool vid!

[Kirby 2]

Sounds like that could be nasty if you had earphones on to block out noise, Dan

[Albert Schweitzer 10]

Maybe the chopper was lifted and carried by transport helicopter? Would that be possible? In that case the back rotor spinning would make sense for the sake of balance.

[fardwark 0]

The answer has already been provided, the rotor and the camera are in phase with eachother making it seem like the rotor is stationary while it is infact spinning in full speed.

[abs 2]

Wouldn't there be blur if the camera was synced? The only way blur wouldn't be there is if the camera had a faster framerate than the spinning of the blades.

Abs

Edit: Typo.

[chipper 0]

HELLO!!

You guys ever heard of a RC scale model?

[blackdog~ 0]

HELLO!!

You guys ever heard of a RC scale model?

Damn, you beat me to it...

[abs 2]

No, what's that? I live in Canada.

Abs

[4 IN 1 0]

LOL, i acturally didnt think that this topic would go this far

put it simple, its the same theory of a movie, only this time its doing the opposite thing

[Espectro (DayZ) 0]

As already pointed out, they are just in phase with each other.

Another simple example, is looking at the wheels of a car. Sometime they appear to be rotating very slowly. This is because the framerate of your eyes simply sees the wheels at different rotations - very close to each other.

This is also why you have to sample a signal with atleast twice the frequency than the highest frequency of the signals bandwith. Or else you won't be able to determine what goes where. That is called aliasing.

[Dark_vityaz 0]

Thought Stalker is very clever game. Every bug can be accepted as an anomaly.

[da12thMonkey 1943]

Wouldn't there be blur if the camera was synced? The only way blur wouldn't be there is if the camera had a faster framerate than the spinning of the blades.

Abs

Edit: Typo.

That depends on the exposure time of the camera. However on many film cameras the shutter mechanism does depend on the frequency with which the shutters close. So yes, the camera is possibly operating with a higher frequency which due to the symmetry of the rotors means a rotor is in the same place whenever the shutter opens. But this depends on the type of shutter mechanism being used.

Exposure times on rotating shutter film cameras are E = (F*2pi)/S, where F is the frequency of the shutters, and S is the angle of aperture on the shutter disc.

If the camera has a fast exposure time (shutter speed) the images blur less because there is less time for the motion to smudge across the photo-diode. However if the shutter angle is too small on rotating-shutter cameras, you get noticeable periods where the wider motion in the scene is missed, making the video appear like stop-motion.

If the shutter motion is linear, which I suspect it is on hand-held cameras (rotating shutters require a big bulge around where the lense is for the shutter disc to rotate in) the shutter speed can just be really quick as it doesn't depend on the freqency of the camera, it just has to be in sync such that it opens whenever the camera takes an image.

[barcode6 0]

I had something here, but to understate, the above is much more informed.

Cool vid and nice description of the effect.

[-ZG-BUZZARD 0]

Thanks for the info, da12thMonkey!

I must say the result of it is really amazing... what luck that cameraman had that the rotors of that chopper were exactly in sync with his camera's shutters...

[Average Joe 0]

Hahah, nope it isnt fake its the camera sync, and to people who questioned whether it was really doing that Id recommend wikipedia and finding out how a helicopter works