Newb(?) question about perceived depth

[NuZenith]

If this has been covered already, 45 minutes of surfing couldn't answer my question. Maybe I'm not searching for the right terms, maybe I'm barking up the wrong tree, but I basically joined to ask it.

Question:
Is there a type of hologram that could display an image as if it were far off in the distance?

That is to say the hologram surface would represent a "window" to the viewer, and the subject matter could be a landscape, large room, cityscape, etc.

Thoughts:

♦To the viewer, the subject matter would remain relatively the same size regardless to the distance from which the viewer stands away from the hologram surface. Rather, as the viewer walks closer, more of the image comes into view.

♦The subject matter wouldn't necessarily have the quality of depth within it, but rather be at a depth. By this, I mean holograms play off the fact that a subject looks slightly different as it rotates about a focal point/plane, but if the subject were far away, the ratio of the distance between points within the image/subject matter compared to the distance from which they are being viewed causes the effect of rotation about the hologram acts more as a panning move rather than a shift of parallax.

♦Probably computer generated

♦This might not be a "Hologram" at all. This might concern a whole other process from Holography, I'm just not sure.

♦And I think I realize that there are variables and factors that might come into play here, making this sort of question either hard to answer, or easy with a "duh".

So I've done the best I can to describe my question without creating drawings or researching unfamiliar terminology. I'm interested to hear some thoughts.

[Din]

Is there a type of hologram that could display an image as if it were far off in the distance?

Yes, with reservations. The reconstruction of any hologram is presumed to be illuminated with a point source. That is, the reconstruction source must be as narrow as the laser itself. The photons used to reconstruct must only come from one point. Practically, this means that any light source must emit light from a very, very small, almost zero, aperture. In an incandescent or halogen bulb with a filament, the light source is the filament, which has a certain size. The halogen bulb has a smaller filament, but still has a finite filament size. An led emits from a very narrow aperture (the pn junction, if you're interested), so the source size is pretty small, much smaller than an incandescent or halogen bulb, but still has a finite size. A laser is pretty much infinitely small, so, in practice, has no size at all. Now, when you illuminate a hologram with a source of any aperture size, the source emits photons from every point in the aperture. So, in the case of a halogen, with a filament size of, say, 1mm, you have a source of photons all along the 1 mm length. Every one of these photons creates it's own image. So, if there are N photons coming off the source (along the 1mm length of the filament in the previous example), you're generating N images from the hologram. These several images all originate from the point at which the image is "focused" (ie where the image "is"). So, if the image is an inch behind the holographic plate, then these N images originate from an inch behind the hologram and all float towards your eyes. As these images travel from the point of origin to your eyes, they separate out laterally. You can see that the further away from the hologram the image is, the further will the N images separate out laterally. Therefore, you will effectively see a blur, whose size depends on the illumination source. So, given a specific illumination source, say a halogen lamp, it has a particular source size (the filament length). This source size produces a number of images, depending on the size. Each of these images starts at the point of origin of the image sails towards your eyes while separating out laterally. Therefore you see a blur. If the point of origin of the image is fairly near the hologram plate, then the lateral separation is not too bad, and you won't notice the blur. As the image source is further and further from the hologram plate, the lateral separation is greater and greater and the blur increases.If/when the blur is unacceptable, you need to illuminate with a smaller and smaller aperture for your reconstruction.

Practically, for a deep hologram,, the blur size goes as the following:
incandescent bulb up to about an inch or so
halogen bulb up to about 2 or three inches
the sun, up to about 6, maybe 7 inches
A laser is theoretically infinite, but no laser has a zero source size. In practice, a laser can go several feet.

To the viewer, the subject matter would remain relatively the same size regardless to the distance from which the viewer stands away from the hologram surface. Rather, as the viewer walks closer, more of the image comes into view.

The relative size of objects in the scene remains constant, but the scene as a whole will increase as you approach; just as if you were approaching a real window from a distance.

The subject matter wouldn't necessarily have the quality of depth within it, but rather be at a depth. By this, I mean holograms play off the fact that a subject looks slightly different as it rotates about a focal point/plane, but if the subject were far away, the ratio of the distance between points within the image/subject matter compared to the distance from which they are being viewed causes the effect of rotation about the hologram acts more as a panning move rather than a shift of parallax.

The image size would have to be larger (much larger!) than the hologram size. It's do-able, but tricky.

Probably computer generated

The processing time of a computer generated hologram is relatively large. This is why most CGHs are relatively small. If you have a powerful enough computer, the processing time may be manageable. By the way, the term "computer generated hologram" has become vague. The method of creating a hologram just by calculating the Fraunhofer pattern is what's now called "CGH". There is also a method of recording a conventional hologram but using computer generated imagery. This is called, variously, lenticular or multiplexed (There is a religious fervour amongst holographers in these naming methods! Some go ape-shit if you use the "incorrect" term!). There is also a computerised holographic technique called the "Zebra method", which is probably what you're looking for. In this case, contact Zebra ( http://www.zebraimaging.com/ ).

We have a holographic technique where we show a view throughout 360 degrees of a computer generated object (the teapot was made in Blender): https://www.youtube.com/watch?v=1Nq4ri2t-HI. This is a technique originated by Craig Newswanger (now head of Zebra), but we altered the geometry slightly.

[Wells_C]

I think transmission holograms of room scenes would be the closest thing to what you describe.

Check out this video of the work of Paula Dawson, the bit where they look at the reflection of the car in the mirror (at 2:11) in the opposite room is particularly striking.

https://www.youtube.com/watch?v=RrGR-f1VNHI

Wells

[Ed Wesly]

Good YouTube find!

Thinking of a hologram as a window with its view a dimension frozen in time is a good analogy to what a hologram is. Here is another example similar to Paula’s, shot when I worked at Fermi National Accelerator Lab.

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We did our best to change the Laser Room into an alley, complete with garbage can. You can see the wooden wall in the background, dirt on the floor, however when you look up into the holo you see the ceiling, not the top of any buildings.

This image is 30 by 40 cm, shot with a large pulsed ruby laser, as opposed to Paula’s, which was all the more remarkable as it was shot with a continuous wave laser, and a full meter plate. But there are no people in hers.

This image is for sale, PM me c/o this forum if interested. Or if interested in seeing it in person, as there will be a big party at my Home + Studio, in honor of the guy who pushed the Fire Button while I was sitting on the motorcycle. http://edweslystudio.com/HnEPortfolio/Hansfest2016.html So if you by any chance live near Chicago, please so come! (It would be nice to fill in where you are from on your profile.)

I was pushing the Fire Button for this set of images similar to the motorcycle: http://edweslystudio.com/HoloArt/RPSaOD/index.htm
And yes, I do have the firepower to holograph a room full of people in my studio.

[lobaz]

Is there a type of hologram that could display an image as if it were far off in the distance?

I would try much simpler technology for that: a simple lens. If you take a convex lens e.g. f = 50 cm (i.e. 2 diopters) and put a flat image to distance O < f from the lens, the image will be magnified and shifted backwards to the distance I = (f O) / (f - O). For instance, if you put your image to O = 49 cm from the lens, it will be shifted to the distance I = (0.5 * 0.49) / (0.5 - 0.49) = 24.5 m.
If the original image was 10 cm wide, the image seem through the lens will be I / O = 24.5 / 0.49 = 50x larger, i.e. it will be 5 m wide.

It would be the easiest to try it with a lens for prescription glasses. They come in diameter about 60 mm and are cheap.

Of course, it would be hard if not impossible to get a big lens with minimal aberrations. However, making large hologram is not easy too.