Holograms: How Do They Do It?

[billfish678]

Oh, one thing though. The smaller your hologram, the less “accurately” such “depth of field 3D” information would be encoded. At few millimeters across, it might be hard to tell the one inches away from the one 20 feet away based on trying to focus on one vs the other. So, I guess in that regard as your hologram gets smaller you could say things look flatter (but it is not because you have restricted yourself to one fixed point of view).

Then again, as your hologram gets smaller, it is also going to get worse at recreating what the object looks like in general, so you are losing both forms of your 3D information.

[Mangetout]

@billfish678

I don’t think that is true. Lets just make the hologram pretty darn small so it still works.

Lets say the hologram was made in this fashion. One chess piece was 2 inches behind the sheet of holographic film. Another one was 20 feet back. Expose film to laser light, process film, “replay” hologram.

Now, I take the hologram and cover it all up except a hole a few millimeters across. When I place my eye a few inches from that hole and peer through it, my eye will be able to tell that the close chess piece is just a few inches from my eye and the far one is 20 feet because I won’t be able to focus on both at the same time.

Or in other words, depth of field/focus considerations will still exist. So there is still 3 D information encoded even though for all practical purposes you have eliminated all but one perspective/point of view.

You’re probably right on the depth of field - I hadn’t really considered that - do you know for sure that it is in fact possible to focus on individual items at different ‘depths’ inside a hologram? I can see why it ought to be, but I can also see why maybe it wouldn’t.

In any case, I think we’re in agreement on the way the loss of image information works - you don’t lose the fidelity of any particular view, you just get fewer of them.

[cmyk]

@billfish678

I don’t think that is true. Lets just make the hologram pretty darn small so it still works.

Lets say the hologram was made in this fashion. One chess piece was 2 inches behind the sheet of holographic film. Another one was 20 feet back. Expose film to laser light, process film, “replay” hologram.

Now, I take the hologram and cover it all up except a hole a few millimeters across. When I place my eye a few inches from that hole and peer through it, my eye will be able to tell that the close chess piece is just a few inches from my eye and the far one is 20 feet because I won’t be able to focus on both at the same time.

Or in other words, depth of field/focus considerations will still exist. So there is still 3 D information encoded even though for all practical purposes you have eliminated all but one perspective/point of view.

I shall default to your knowledge on the matter of no loss of fidelity. But yeh, the loss freedom in how much range in degrees your vantage has is because you’re eliminating the bits that of the hologram that has those angles recorded. The depth and field of view should remain.

[Chronos]

Your eyes focusing on things at different depths is just another manifestation of the “looking around from different vantage points” effect. The left edge of your pupil is seeing things from a slightly different vantage point than the right edge of your pupil. Shrink the hologram below the size of your pupil, and you’ll start losing the focus information, too.

[Mangetout]

@Chronos

Your eyes focusing on things at different depths is just another manifestation of the “looking around from different vantage points” effect. The left edge of your pupil is seeing things from a slightly different vantage point than the right edge of your pupil. Shrink the hologram below the size of your pupil, and you’ll start losing the focus information, too.

Good point - the hologram-window becomes a pinhole - and pinhole cameras have infinite depth of field.

[billfish678]

@Chronos

Your eyes focusing on things at different depths is just another manifestation of the “looking around from different vantage points” effect. The left edge of your pupil is seeing things from a slightly different vantage point than the right edge of your pupil. Shrink the hologram below the size of your pupil, and you’ll start losing the focus information, too.

Yes. And sorta no in that you can maintain a given “depth of field” fidelity yet have it from a very point of view if you wish (one small corner of the hologram vs the opposite one for example).

Or in other words, it goes down but it doesn’t dissappear till the hologram becomes so small it can’t recreate anything in the first place., so thats not particularly surprising.

Yes, me thinking about pinholes is what made me make my other comment about losing depth of field fidelity.

Lets take a stab at what goes down as you make your hologram smaller.

opps, gotta run. more later.

[Jamicat]

I made a hologram on a piece of clear plastic with a pair of pointed dividers using arcs.

This sums it up…

How to Make your own scratch holograms

Gives you an idea what the lasers are doing without all that scratchy stuff.

[ZenBeam]

@Jamicat

I made a hologram on a piece of clear plastic with a pair of pointed dividers using arcs.

I like that. I’m going to go do that to my wife’s windshield, as a surprise for her next time she’s driving at night.

Merry Christmas Honey!

[Jinx]

Wow, you have all given me some food for thought. Now, to digest! Mangetout, I appreciate your explanation about viewing an apple from one viewpoint. That has helped me better understand what is happening. I’ll keep mulling over this thread until the light dawns. If I could only make my own holograms, it would probably help me understand by hands-on learning.