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from where I come from ,they taught us in high school that it is possible to project holograms in thin air simply by illuminating the hologram with the "correct light" , and having a semi transparent medium in the path of the reflecting light "e.g. Water vapor or smoke" resulting in something like this image enter image description here

-is this true & if not is there any technology that can project such 3dImages in thin air ?

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mahos
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    Holography can make such images appear in total vacuum. But you need a screen of some sort to make it happen. If there is a kind of gas or smoke around to project an image, then it is not an hologram, just light projection onto some material. Which one are you talking about? – fffred Jan 03 '14 at 05:55
  • @fffred what they taught us seems to be the second case you are talking about "smoke" , but they told us that the projection appears 3d ,with different views for people looking from different angels. – mahos Jan 03 '14 at 06:50
  • One TV development back in 1930's had a screen less viewer that appeared to float in space. Like viewing an image reflected on a rotating fan blade. Mechanically it would work better in a vacuum. "Google Images" may help explain "Mirror Screw tv". In the 1930's there were limitations on turning a light on/off. LED's would not have that problem. – Optionparty Jan 03 '14 at 16:57
  • This may help http://www.televisionexperimenters.com/mirscrws.html – Optionparty Jan 03 '14 at 17:11
  • @fffred , both ideas are compatible, and there are differences between typical lens projections and holographic projections. Read my answer below. – Andrestand Sep 14 '14 at 09:13

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The car in the picture seems to be projected with the projector in the top (2D projection). A similar 3D static car image could be accomplished with a cylindrical hologram. Any hologram can be illuminated in an appropriate way ("the correct light") to build a real image besides a virtual one.

Then, if you put a screen inside it, you are going to see a low contrast (due to light converging in other planes) picture (a view) of the 3D holographed object. The point or difference with lens imaging, like the one due to a standard projector, is that this allows to project in many planes (one at each time, or at the same time with dust/fog), as there is 3D information.

If you use dust you may project a 3D image, also low contrast, because your 3D distribution of point-like sources of light has a background due to light focusing in other points and that pass through. You'll also see your object is transparent, as you are watching light coming from every point.

In 2D lens image projections, light focusing in other planes produce blur (points become discs).

Andrestand
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