# True or false?



## Grampa (Dec 12, 2012)

Here's a clip of something that you have to judge if this is true or false by your self.


_View: https://www.youtube.com/watch?v=M5POy9iKtPA_


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## FLYBOYJ (Dec 12, 2012)

The main rotor is really spinning, optical illusion from the camera


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## meatloaf109 (Dec 12, 2012)

Either that, or photoshop.
I believe very little of what I see on You-tube.


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## Njaco (Dec 12, 2012)

Agree with Joe.


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## tyrodtom (Dec 12, 2012)

Haven't you noticed in films of aircraft shutting down their engines they appear to go slowly in one direction, stop, then go in the other direction. That's because the prop rpm is close to number of frames per second shot by the camera. That's how some crappy shows have the pictures of birds and insects that appear to have tandem wings.
In that helicopter video the main rotor's rpm is sychronized with the video camera's frames per second.


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## stona (Dec 12, 2012)

FLYBOYJ said:


> The main rotor is really spinning, optical illusion from the camera



I thought that too but I can see a stationary shadow from a rotor blade a couple of times. I don't know whether that is part of the illusion.

Steve


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## FLYBOYJ (Dec 12, 2012)

tyrodtom said:


> Haven't you noticed in films of aircraft shutting down their engines they appear to go slowly in one direction, stop, then go in the other direction. That's because the prop rpm is close to number of frames per second shot by the camera. That's how some crappy shows have the pictures of birds and insects that appear to have tandem wings.
> In that helicopter video the main rotor's rpm is sychronized with the video camera's frames per second.


Sums it up right there.........


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## Capt. Vick (Dec 12, 2012)

stona said:


> I thought that too but I can see a stationary shadow from a rotor blade a couple of times. I don't know whether that is part of the illusion.
> 
> Steve



Which you would as a film is made up of a number of frames, with each frame capturing and instant of time. The shadow would be stationary (or appear to be) just as the blades are stationary (or appear to be). Obviously a shadow would exactly mimic the relative movement of whatever is casting it.


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## N4521U (Dec 12, 2012)

Oh so true.........
But, oh so cool.


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## mikewint (Dec 12, 2012)

stroboscopic effect. You can do the same thing at home using the TV. Spread your fingers apart and wave then back and forth in front of the screen or use a fan spinning in front of the screen. Wheels of a car speeding up or slowing down move forward, slow, stop, then reverse over and over


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## tyrodtom (Dec 12, 2012)

I get the same effect when I use a timing light to set the spark timing on a car.


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## A4K (Dec 13, 2012)

For same reason neon lights are forbidden in RNZAF workshops. A spinning lathe (etc) can appear stationary ...not good for the fingers.


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## GrauGeist (Dec 13, 2012)

And sometimes, depending on the video camera, a propellor on an aircraft will appear as vertical bars if filmed from the cockpit...
Also, I've taken many shots from the office of aircraft and the prop appears to be radiused depending on aperature shutter speed


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## stona (Dec 13, 2012)

Capt. Vick said:


> Obviously a shadow would exactly mimic the relative movement of whatever is casting it.



Good point 

Steve


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## evangilder (Dec 13, 2012)

Yep, frame rate and spinning propellers cause some interesting effects. If you look at some of my flying videos, the props look like they are hardly spinning at all, or they get distorted. The normal video camera is 30 fps, makes it difficult to capture spinning objects.


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## N4521U (Dec 13, 2012)

Been thinkin about this.

My dream plane would be a Cessna 206C, STOL kit, tundra tires, gap seals.
I could carry All the camping gear, And the beer! 
Any where I want!


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## GrauGeist (Dec 14, 2012)

Here's a real quick example of what I was talking about, regarding the odd effects that a camera can produce when photographing objects like propellors, spoked wheels and the like...

This shot was taken with a Pentax K100D DSLR camera during a flight in an Ercoupe several years ago, which has a two-bladed prop. The blades are definately straight and yet in this shot it's hard to tell if they're soft rubber or a new style shaped like a Scimitar (which would look badass, but highly impractical)...


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## Airframes (Dec 14, 2012)

It's an effect more noticeable with electronic imaging (video/digital) than film cameras. A traditional cine camera normally shoots at 24 fps, compared to the 30 fps of a video camera, with each frame recording a separate, silver (photographic) image. A video camera is recording the _equivalent_ of 30 FPS, but as an electronic 'signal'. The faster frame rate, and immediate 'capture', are similar to using a fast shutter speed, with a high ASA (ISO) film rating in a traditional 'still' film camera, where the faster the shutter speed, the more likelihood of 'freezing' a prop (or a spoked wheel, for example).
You've probably noticed, in videos taken from the cockpit, that a prop might also seem erratic, turning fast, then slow, then stopping totally, then jerkily, and so on.
In a traditional film cine camera, prop movement, depending on exposure conditions, is more likely to be shown as the human eye would normally see it, as a spinning disc.


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## stona (Dec 14, 2012)

Check these out!


_View: https://www.youtube.com/watch?v=ltMPMz37VPk_


_View: https://www.youtube.com/watch?v=Y9Px9EAhyss_


_View: https://www.youtube.com/watch?v=Y1OUZf9jxoQ_


_View: https://www.youtube.com/watch?v=Um3bGnSqLRY_

I'm sure there are many more.

Steve


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## N4521U (Dec 14, 2012)

Personally I think the photo above proves the theory that as soon as a prop starts turning, it starts bending!


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## Capt. Vick (Dec 15, 2012)

Another well known "effect" produced by the camera is it’s unflattering ability to add 10 pounds to anyone being photographed. That being said, I often wonder while looking at pictures of myself: “Exactly how many camera’s are pointing at me?”


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