Here's one for you... explain why...

Discussion in 'Off-Topic Chat' started by Fishsta, Jan 16, 2004.

  1. Fishsta

    Fishsta Active Member

    OK, try the following:

    Take your digital camera or webcam, and put it in preview mode.

    Whilst watching the screen, point a remote control at the lens and press a button on it.

    Why does it light up so bright?

    Why will a digital camera pick up this in a way our eyes can see it when our eyes can't see it normally?

    You think that's good... you know those big security cameras with infra-red tracking for nightvision... look at one of them through it!!! It's like a floodlight!

    Explanation?
     
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  3. BottyBurp

    BottyBurp Member

    Could be wrong (probably am) but isn't it to do with a remote control using Infra Red which cameras (both digital and non) can pick up, but infra-red isn't within the light spectrum that the human eye can see?

    Anyway, more to the point, why are you pointing remote controls at a camera? You bored? :lol:
     
  4. Fishsta

    Fishsta Active Member

    Well, I thought that, but then why does a camera effectively change the wavelength of the light to be in our range?

    Is it something to do wth the reason the "Racing Blue" colour F1 cars sometimes use comes out as black on TV?
     
  5. Okiedokie of Oz

    Okiedokie of Oz Active Member

    Maybe I am on the wrong track, but could it have something to do with the light being reflected or refracted in the lens??

    you know how a triangular prism splits light into all the colours...maybe the lens redirects light into something more visible?
     
  6. BigHorn

    BigHorn Active Member

    Nothing to do with prisms. A Prism doesnt change or add to whats there, it just splits the component parts out at different angles due to internal refraction.
    I imagine the effect described is something to do with the electronic colour correction on the camera. Perhaps in preview mode the colour correction does not operate fully and the intensity of infra red is visible. When you take a photo the colour correction filters will kick in and strip out all the bad wavelengths to leave something that makes more sense to the human eye. Try taking an actual snap and see.
     
  7. MoominDave

    MoominDave Well-Known Member

    Just a suggestion, as I don't have a any good ideas or the equipment to test them, but could it be an aliassing effect? If it is a digital camera, it may be doing some little mathematical tricks inside, which may or may not include some sort of Fourier transformation, which could produce the effect that light not far outside the visible range would be represented inside the visible range.

    Disclaimer: I know nothing about digital cameras! Or maybe that's already obvious... :lol:

    Dave
     
  8. Daniel Sheard

    Daniel Sheard Member

    I'm guessing a bit, but here goes:

    The detector in your digital camera is intended to convert photons of all visible light to electrical signals. But, photons at the blue end of the visible spectrum are more energetic than those at the red end, so the detector and/or electronics probably has to amplify the red end of the spectrum to compensate and to get a decent strength signal. Infra-red transmitters such as remote controls aren't all that far infra-red visible, and the detector picks up the signal and interprets it as a red light which it then amplifies.

    Go on, shoot the argument down if it's not right!

    Daniel
     
  9. andyp

    andyp Active Member

    This is a mixture of what I know and educated guesswork, but.....

    Digital cameras use a CCD (charge coupled device) to detect light, it's kind of like a load of tiny photodetectors stuck together. This when scanned by the electronics in the camera converts light to an electrical signal, which is then either stored, or converted back (by the camera or your PC) to create the picture on screen.
    It sounds as though the CCD can detect infra-red (a lot of cameras use it for focussing), but the display can't re-emit it, so the camera converts it to visible light instead.
    It also means, if you can get an infra-red floodlight from somewhere, you should be able to take pictures in the dark!
     
  10. tewkeshorn

    tewkeshorn Account Suspended

    Yup, infrared light can be detected by video cameras, well anything that detects infrared really! And the reason we can see it on TV screens filmed by cameras is because obviously TV's don't display in infrared (would lead to some very boring TV shows as we couldnt see them!) They just display in coloured normal light (i know it's not called 'normal' light but I'm not sad enough to know what the actual name is!).

    I guess this is a similar principle on which they developed Night-Vision goggles...
     
  11. Kari Anson

    Kari Anson Member

    Where do I start - well I can only attempt to explain why we see the bits we see and answer a few of the questions that have arisen throughout the post. Note - doesn't actually answer the initial query!

    Firstly the correct term for 'normal colour' - the one that we actually see is hue. There is a relationship between the hue and the wavelength, which is measured in nanometres and usually ranges from approx 400 to 700.

    You need to understand about cones and rods before you understand any of the theories as to why we see the colours that we do. Cones and rods are cells distributed over the retina, the cones are low on the peripheral but increase towards the centre (fovea). In reverse, rods are plentiful on the peripheral but absent in the fovea. No rods or cones exist at the blind spot. It is the cones that are the colour receptors. For those of you that are totally colourblind this is because you only have rods in your retina.

    There are numerous theories in extistence such as the trichromatic or component theory (put forward by Thomas Young and later developed by Helmholtz) but the most applicable one is the opponent process theory developed by Ewald Hering in 1878.

    This theory proposed that there were two classes of cells for colour excitery and inhibitary and some were matched:
    Red-Green, the red is the excitery and green the inhibatory
    Blue- Yellow, the blue excitery and yellow inhibits
    Black - White, the black excites and white inhibits
    The firing potential of a neuron is effected by colours, for example, red excites so there's an increase of the base line from 50 to 75 but green inhibits so the base line reduces from 50 to 25 - so cancels it out. If you mix red and green light they cancel each other out. This also explains why you sometimes see another colour, once you've been staring at a colour for a while. If you were to look at a red object for a while and then have it taken away and are told to look at a white screen you will actually see green. The same goes for blue/yellow etc.

    Some really useless information for you all.
     
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