Multiplex Hologram

jag2x · Post by **jag2x** » Mon Oct 12, 2009 7:40 am

Hi all,

I'm new to holograms here and would like to get a better understanding on how Multiplex/Stereogram Holograms are made.

I've seen examples on the web but unsure of the full projection of each image?
Say I have 3 images of an object, a left photograph, a centre photograph and a right photograph, each image is 6cm x 6cm. I've seen a laser output via a LCD panelof each photograph hit a hologram plate, which there is a slit or mask that doesnt expose the whole plate but part of it. There would be 3 slits revealing each part of the plate.
Though what confuses me is the projection, if each image is 6cm x 6cm from the LCD, and your slit is only 2cm wide, then the only thing that would registered on the plate is 2cm of the outputted 6cm x 6cm image? Is this correct? You'd then do the rest of the 2 images with the corresponding slits.
I dont really see how this would result in a 3D image?
I know I'd need to use more images than 3 to get a full on 3D image!

OR
you need to get EACH of your 6cmx6cm image NARROW enough to fit the slit????
I might be complicating the WHOLE THING now

Cheers
jag2x

holo_cyware · Post by **holo_cyware** » Mon Oct 12, 2009 8:25 am

Welcome on board !

You are right about the slits projections: only the corresponding part (2 cm) of the image is projected onto the plate.

How it works: just think about the "lens cards" (called "3d post cards"), but with a resolution as high as you can afford slits.

Are you from Europe?

jag2x · Post by **jag2x** » Mon Oct 12, 2009 12:38 pm

Hi Holo_cyware,
I'm located in Australia. Over here lasers over a certain class /mw range are regarded as a firearm!? Though I'm going to do a bit of digging on the type of law and what certain class of laser and mw I can get.

Thanks for the explanation.
Then I'm guessing the best way not to even have a slit, is just use a laser to beam, exactly 2cm width 6cm long projected from the lcd to the plate? Not sure if it can be done...
Cheers
Jag2x

BobH · Post by **BobH** » Mon Oct 12, 2009 2:35 pm

The three images in your example wouldn't be projected onto the recording plate, they would be projected onto a diffusing screen. The first image is projected onto the screen, the light scatters off the screen and illuminates the recording plate placed some distance away from it. If you mask the recording plate to allow only a portion of it (let's say the left third)to "see" the light from the whole screen, that portion of the recording plate will "see" the whole image on the screen.

So you project the left side image onto the screen, and the recording plate "sees" that whole image but only records in the left third slice. You change the image to show the center view, you move the mask to reveal the central third of the recording plate, and record the center slice. Same with the right view. When you look through the final hologram, your left eye sees through the left slice and sees the left side view of the screen/image. At the same time, your right eye sees through the right slice of the hologram,seeing the right side view of the screen/image.

holo_cyware · Post by **holo_cyware** » Mon Oct 12, 2009 2:47 pm

You can't project a laser beam as a slit would do; the optics would be extremly expensive.

As you know, the laserbeam is spread to a circle; the plate should be evenly covered by the laser light. The slit (it may be as tight as 1 mm) will get just a fraction of the total laser power. In an ideal world, one would use an optical system capable to spread the laser into a narrow line rather then a circle, thus concentrating the power with no loses. It may be done with a HOE, much like in the attached image. Maybe someone with more knowledge could help on this...

As about the needed laser, I'm sure someone from Oz could help you.

A good read: http://www.bobdbob.com/~protius/multiplex/

Ed Wesly · Post by **Ed Wesly** » Mon Oct 12, 2009 3:43 pm

Ye Olde Multiplex Company used a glycerine or mineral oil filled test tube to diverge the beam in only one dimension to provide a slit of a reference beam for their cylinders in addition to their oil-filled filed lenses.