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Can Someone Explain This To Me?

  1. Jun 16, 2008 #1
    To some people this may seem like a very stupid question so I will let you know in advance that I am in no way, shape, or form studying physics and I would just like to see if anyone here can answer/explain this subject.

    Let me secondly attempt to explain this in a manner which will not confuse anyone and please let me know if I need to seek advice elsewhere. Ok. Here goes.

    Lets say I have a very large screen (50 feet X 50 feet) 10-75 feet in front of me. Light is being reflected off of this screen 200 feet away. Let's also say that I have a video camera that is capturing a live shot of the light on screen.

    Is there anyway to reverse the process? ex; instead of the camera picking up the light being reflected off of the screen, it will show darkness...or perhaps a variation of colors?

    Or could some form of contraption aimed in the general direction of the camera deflect the light entering the camera?

    Like I said...pretty dumb question, just would like to see if its possible and how?


  2. jcsd
  3. Jun 16, 2008 #2


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    It's not really possible to deflect the light - well it is but you would need to put a very large mass, like the sun, near the camera!
    Particles of light (photons) are very fast, have no mass and no electrical charge and so it is very difficult to effect their path.
  4. Jun 16, 2008 #3
    ok...maybe not deflect the light but somehow interfere with it so that the camera picks up nothing.

    ok..lets try this...is there anything that will make a camera NOT pick up a light source that is being projected in front of it....infrared beams, i dont know...isnt there something?
  5. Jun 16, 2008 #4
    If there was a specific phenomenon that you observed, could you give an account? I am a little confused as to what you are trying to describe.
  6. Jun 16, 2008 #5
    It depends on the type of camera. CCD cameras are very sensitive to infrared light. A lot of them have no real filters for it, especially security cameras, which makes them ideal for low-light levels.

    If you project a bright infrared beam at a CCD camera without an IR filter, it could wash out the image (not block it, just overpower it). However, IR light, being lower in wavelength is much less energetic than visible light, so it would have to be pretty bright, much brighter than the sun, which is going to be difficult to achieve. Maybe you could do it with a carefully designed IR laser system.
  7. Jun 17, 2008 #6
    Maybe there's some gas that visible light could pass through, excite an electron, and the electron emits a photon as it drops down to a different energy level that is below the visual range?

    Or you could make a screen that scatters light in any direction except the camera's. Then the light that passes through just continues, that which interacts with the screen is deflected away from the camera.
    Last edited: Jun 17, 2008
  8. Jun 17, 2008 #7


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    You could project the image onto the screen at an angle so it is polarised and then have a crossed polariser on the camera.
    Or project an image using only a specific color and have an interference filter on the camera - this used to be done in film making with sodium D lights before electronic blue screen.
    You could sync the projecter with the camera to only take an image between projector fields.
  9. Jun 17, 2008 #8
    thats very interesting. for those that are confused, i'm a consultant to the movie theater industry and we are just trying to gather some insight as to how we can deter piracy in theaters. if anyone else can shed more light on this subject it would be very helpful
  10. Jun 17, 2008 #9
    and also simplify the "physics" language :-) as i'm not a physicist :-) If a solution can be found you may be paid handsomely for your work
  11. Jun 17, 2008 #10


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    Ok if you had mentioned that in the first place!
    The problem is that you want the light to reach the customer's eyes but not the camera. You have a non-cooperative target, ie you can't ask the camera to be fitted with any special attachments.

    The most common solution is to use bright infrared 800-950nm lights that flash at random intervals. The camera is (slightly) sensitive to this and it affects the automatic brightness control.
  12. Jun 17, 2008 #11
    Yes, the infrared idea is probably the best, and it should work well in a movie theater, because there is so little ambient light.

    Essentially, infrared is light with a lower wavelength than the visible spectrum (that which humans can see). However, most CCD cameras (the most common type cameras today) can record infrared. Since humans cannot see infrared, but cameras can, you could flood a movie theater with pulses of infrared light, making it difficult to get a good recording, but completely unnoticeable to the human eye.

    EDIT: I should add, that there is really going to be no way to solve the problem. As long as there is a market for bad camera recordings of new films, eventually, the most hardcore pirates are going to figure out how to defeat a copy-protection scheme.

    For instance, the infrared pulses we have discussed will defeat a plain, off the shelf camera from Best Buy. But the pirates surely have some smart people who are going to spend the time and the money figuring out what kind of filters they need to use on their cameras to filter out the infrared pulses, it will be posted on the internet, and the knowledge will spread among people who do these sorts of things.
    Last edited: Jun 17, 2008
  13. Jun 17, 2008 #12
    Basically what you seem to be asking (although you've disguised it as a thought experiment involving a camera) is can you make a cloaking field. The answer for practical purposes is no (as was previously mentioned you could always but a massive celestial body like the sun (compressed small enough so that it wouldn't block the view whilst not becoming a black hole which would just eat the light) between you and the light source). However, they have developed metamaterials which can bend a single wavelength of light around itself and project it out the other side (i.e. a single wavelength is like a very very very very very specific colour). However, the metamaterial has to meticulously designed for just that PRECISE wavelength (and by wavelength one doesn't mean the color blue but like 75.342% blue, 21.312% red 11.313% yellow) and the design of these metamaterials can not be expanded to deflect more than one wavelength (at least in any obvious ways). So it seems highly unlikely that this technology will ever lead to a true cloaking field for the visible spectrum (i.e. in these contraptions one specific wavelength is deflected around by the rest reflect of it just like anything else).
    Last edited: Jun 17, 2008
  14. Jun 17, 2008 #13


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    Most pirate movies are from review copies of DVDs or leaked from production companies.
    Or projectionists who 'mislay' a film for a couple of hours and run it through a telecine.
    Confiscating cell phones from customers is more a 'being seen to be doing something' measure than a real solution.
  15. Jun 17, 2008 #14
    I have doubts about something as simple as including IR in the transmission because it wouldn't take pirates long to simply put a cheap filter over their cameras.
  16. Jun 17, 2008 #15
    Plus I imagine it would required every (digital and non) screen in the world to be replaced since I don't think digital screens can project IR and I doubt projection screens are designed to reflect IR.
  17. Jun 17, 2008 #16
    I think a more viable option would be to focus efforts on keeping cameras out of a theater. Or maybe scanning the theater with some night vision camera's to find anyone filming might be a more cost effective method.
  18. Jun 17, 2008 #17
    You could send out intense pulses of IR to wash out the picture the camera records, but like I wrote earlier, the savy ones are just going to add IR filters to their cameras.
  19. Jun 22, 2008 #18
    IR would probably the overall best option. But, as mgb said, theres no outsmarting the pirates.
    But yea again as mgb said, leaked screeners are the more favored method of piracy early now, especially since the industry started releasing DVDs early in Russia.
    But I gues, the theaters have to do their part to prevent the videocamera's.
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