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Thread: Tupac "hologram" used last night at Coachella

  1. #21
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    Jun 2009
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    Neat display, but nothing compared to a real hologram.

  2. #22
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    Mar 2006
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    Quote Originally Posted by mixedgas View Post
    Its just ole "Pepper's Ghost" done with a new, specialized, coated, stretched plastic film or films and good quality video projectors.
    Awesome. 'They' (whoever they are) say the old ones are always the best. I first learned of Pepper's Ghost in a small book when I was a small kid. It looked like a neat idea, and not at all mysterious. I guess what gets people every time in cases like this is the scale of it. One thing about that always puzzled me: Assuming some of the earliest Pepper's Ghosts in theatres were also intended to amaze people, how did they get such huge sheets of glass, before anyone else seemed to get it? Multiple panels with cunningly hidden joins? Seems to me a strange use of expensive large sheets in times when I imagine far more demanding uses would be grabbing all of it that they could get. To put it another way, if such large sheets were commonplace in shop windows, no-one would have been very mystified by Pepper's Ghost in a theatre. Or would they? Cos it seems to still be working, even now. Maybe Barnum was right. Except 'they' say it wasn't Barnum who said it! Pepper's Ghost seems to apply beyond optics.....

  3. #23
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    Mar 2006
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    About the focussing thing, I don't know how it's done, but it may be that more than one beam is used, scanned independently to converge on a point in space. The SSY1 rangefinder laser can make sparks in air if the Q-switch is used. Peak power is very high to ionize air. The lens might not have to take huge power but making a lens that can change focal length that fast seems to imply that it's not a mass with refractive index changing at all, but some field in something vaguely like an AOM. But it may be easier to use two or three beams, all below threshold on their own, but wherever they meet, and if at that moment the lasers are pulsed (I don't think any of this is CW), the result is enough ionization to be visible. That's maybe what the air based one is doing, but the water based one looks as green as the lasers that excite it, so I'm not sure what that means. Although maybe tiny bursts of vapour in microscopic bubbles, so could just be rayleigh scattering.

    In all cases, it's huge amounts of energy, so I bet it won't be appearing in weird new domestic TV's.

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