Transmission Rainbow DCG holograms

These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
JohnFP

Transmission Rainbow DCG holograms

Post by JohnFP »

Has anyone tried to make a transmission rainbow hologram in DCG and then use a foil reflective backing to view it as a reflection hologram? How did it turn out?
Dinesh

Transmission Rainbow DCG holograms

Post by Dinesh »

Colin and I made a transmission rainbow in DCG.
You can't transfer DCG transmissions to silver foil, but you can view them with a mirror (simulating the foil). They turn out exactly as if you'd see them in transmission since all you're doing is re-directing the reconstruction beam.
I mentioned I'd bring the transmission/reflection hologram I made a while back to Texas. I did bring it but never got the chance to show it. It was made both as a reflection and trnasmission simultaneously. When viewed in reflection mode with a mirror behind it, you saw both a colored image and a white image simultaneously (the transmsion was an achromat).
John Pecora

Transmission Rainbow DCG holograms

Post by John Pecora »

Was that a transmission set up with a mirror behind the plate in recording?
John Pecora

Transmission Rainbow DCG holograms

Post by John Pecora »

Now this was difficult to draw so just try to visualize what I am doing here, not the accuracy of the drawing. I could not get the Plate with slit mask at the correct angle but the idea is represented. I think this would work. Any comments? Am I dillusional? Hehe!




Michael Harrison

Transmission Rainbow DCG holograms

Post by Michael Harrison »

I haven't done it with DCG but I have done it with silver and the process would be the same.

I got some of the highly reflective silver foil from a local sign company and put it on the back of one of my rainbows. It was applied the same way that I use Oracal to back all my holograms. I can't see any reason why you couldn't use it for DCG and it would probably help protect the gel from moisture.

Here's a picture


Dinesh

Transmission Rainbow DCG holograms

Post by Dinesh »

So collimated light goes through the slit onto a mirror with a cylindrical lens embedded in it. The mirror reflects light onto the object. The reflcted object light then goes through the cylindrical lens and creates a real image at the film plane. Is this right?
If so, you'll lose a lot of object light. depending on polarisation, you could lose some 20% at the mirror. The incoming light will also refract through the lens and create either a focus at the plate or a pretty aberrated wavefront due to coma, depending on the fl of the lens. The reflected light is expanding outward from the object and so, in order to focus it at the image plane, the plane of the lens and the mirror may have to be varied. In either case, the lens will refract a small portion of the reflected object light. I suspect you'll get a strong grating and maybe a weak image.
One-step rainbows have been talked about a lot in the last few years. I don't see that many papers anymore (although I've not read "Applied Optics" in a while). Rummaging in my "paper drawer" I find this:
"Rainbow holography of 3D stationary objects with no slit"
- A. Beauregard and R. A. Lessard, Applied optics, vol. 23 No. 18 15 September 1984.
There was also a scheme of moving the slit since the FT of a moving slit simulated a gaussian and so countered the gaussian wavefront of the laser. This was the paper I thought of a while back when someone asked how to "straighten out" a Gaussian profile. I couldn't lay my hands on the paper and couldn't remember off-hand how the calculation went, which is why I said at the time there were "numerous methods' without going into details.
There are also schemes to use positive mirrors to create a real image of an object and so make a one-step image-planed reflection. I can't lay my hand on that paper either, but I recall it was sometime in late 80's, early 90's in Applied Optics.

Dinesh

Transmission Rainbow DCG holograms

Post by Dinesh »

"Was that a transmission set up with a mirror behind the plate in recording?"
No, the mirror was used to view. I should also mention that Jason Sappan used these "mixed holographic media" techniques a while back. When I visited him in the mid-90's he showed me a piece he'd done mixing rainbow with achromat and transfering to gold foil. I believe this was for a magazine cover. When I showed my mixed transmssion/reflection to Hans, he mentioned someone who'd also done something similar. I didn't quite catch the name and it was lunch time by then. At SPIE, this involves a lot load of wandering holographers saying, "So, where are we going?" "How about ..." this or that? Someone invariably says "Getting holographers together is liking herding cats" I always reply that I have no idea why one would want to herd cats.
Kaveh Bazargan

Transmission Rainbow DCG holograms

Post by Kaveh Bazargan »

The cylindrical lens won't form an image. You will need a conventional lens I think.

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The holographer's home page:
http://www.holographer.org/
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danny bruza

Transmission Rainbow DCG holograms

Post by danny bruza »

you should up load this to your PCG folder...with the text
Dinesh

Transmission Rainbow DCG holograms

Post by Dinesh »

It's pretty much the same. One fact of interest is that DCG rainbows are not that much better than Silver rainbows, assuming they're both done well. This sort of re-inforces Bob's statement that DCG reflections only appear bright because they're broadband. Since Silver rainbows are just as broadband as DCG rainows, it's a true test of the real 'brightness' of DCG's.
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