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Posted: Tue Jun 08, 2004 8:11 am
Ok, so if I take a 6 by 6 inch shallow box and fill it with plaster and let it set up half way, then take a mirror and break it by pushing in the center how will this effect be portrayed by a hologram. I would like the center, the point of pressure and breakage to be recessed about an inch or so. Then in that center I want to place a 1/2 steel ball bearing. I will be shooting in the 488 with emulsion away from object and fabricating and processing for broadband. How close I get to a "silver" mirror hologram will depend on many things.

So here are my thought provokers;
How will polarization be a factor with the mirror being broken and every piece at a slightly different angle for reflection?
How will the light from one piece of the mirror act as it will be reflected to other pieces of mirror?
How will this hologram look if it is viewed from the back side (pseudoscopic)? The mirror will look projected but will the ball look to funny to be realistic? Do I have to use the inside of a half ball or because the ball is reflective - parallax may be deceived?
Should I use a diffuser of some sort? If so how diffused and where should it be placed? Between the plate and the broken mirror?
How will the hologram look if it is nicely broadband and efficient? Should a person be able to see their broken reflection in it?

Feel free to comment or suggest but I am really excited about making this hologram which will purposely be made to view pseudoscopically.

Peace!

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Posted: Tue Jun 08, 2004 8:13 am
1/2 inch diameter steel ball bearing.- in first paragraph.

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Posted: Tue Jun 08, 2004 10:52 am
First, if the mirror is broken randomly light will reflect in all sorts of directions whereas the reference beam is coming in from only one direction. This means the Bragg planes will "point" in all sorts of directions and from any one angle you'll see the dazzle of gratings where the mirror happened to reflect light in that direction. The ball bearing will be a source of divergent light and so there will be an overall grating which will be bright at the center and dimming at the edges. This overall grating will be superimposed on all the "sub-gratings" caused by the mirror which will be much brighter. Most of this will be due to the surface profile caused by the gratings.

There will be also be volume gratings which will give the effect of holographic mirrors, ie the hologarm will appear with a surface sheen of a particular color. The color of the sheen will depend on the angle between the reference and mirror freflection so it will vary according to the viewing position. If you use this as a mirror, ie look at reflected light from the hologram say by reflecting sunlight onto a white wall, you'll see a patchwork of different colors reflecting onto the wall. As a reflecting HOE, the ball bearing will have no effect, apart from robbing the reconstructed HOE light.

"How will polarization be a factor with the mirror being broken and every piece at a slightly different angle for reflection?"
Depends. If you're shooting with 's' polarisation, the mirror will maintain 's' and so the grating strength will be at a maximum. You'll get strong diffraction but woodgrain. If you're using 'p', the mirror will retain 'p' and the grating strength will vary as the cosine of the angle between object and reference - the larger that angle, the weaker the diffraction until at 90 degrees cos(90) = 0 and you get nothing! However, there's no woodgrain. This is all assuming the same plane. If your beam goes up or down slightly, then 's' and 'p' polarisation may create angular weakening of the grating due to azimuthal angle changes. The angle "twists' up-and-down as well as side-to-side.

"How will the light from one piece of the mirror act as it will be reflected to other pieces of mirror?"
Exactly as if it had come from the second mirror but weaker. The second mirror will alter the angle it makes with the reference and weaken the light due to the reflection. This causes a lower beam ratio and so the grating (color 'flash') may be stronger than the HOE mirror.

"How will this hologram look if it is viewed from the back side (pseudoscopic)?"
Pretty much the same. An abstract light field as in a HOE or grating does not have parallax so visually there would not be much different between pseudoscopic and orthoscopic. These terms refer to the parallax along the z axis of an object in the visual field. The grating colors will probably be backwards, but without calculation this is only a gut feeling.

"Should I use a diffuser of some sort? If so how diffused and where should it be placed? Between the plate and the broken mirror?"
I think a diffuser will weaken the color 'flash' of the grating and so the HOE mirror will dominate, ie the sheen of color on the surface. However, if you want to use a diffuser, that'd be the place to put it.

Should a person be able to see their broken reflection in it?
Not unless the face was there when you shot the hologram. A hologram of a mirror is not a mirror holoogram. To get that effect, you'd have to make a uniform reflection HOE and then crack the hologram itself. I wish I had a link to Adrian Lines' "Mirror Man" because he does have a face and a reflection of it with the hologram itself seeming to be the mirror.

If you want a suggestion, use the same system you described with the diffuser between plate and mirror(s), but crack or score the diffusion glass.

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Posted: Tue Jun 08, 2004 11:24 am
Ah, that's one I had not thought of. I was going to try a white painted mirror but the effect would not be the same. I like the idea of using a diffused piece of glass instead of mirror.

So I may try the broken mirror, broken mirror with diffuser and broken diffuser possibly with a white ball instead of silver.

Thanks, peace!

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Posted: Tue Jun 08, 2004 2:06 pm
with (Armour Etch) on a reg mirror

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Posted: Tue Jun 08, 2004 2:12 pm
Excellent, where do I get it? Any local Depots carry it?

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Posted: Tue Jun 08, 2004 4:13 pm
"There will be also be volume gratings which will give the effect of holographic mirrors, ie the hologarm will appear with a surface sheen of a particular color. The color of the sheen will depend on the angle between the reference and mirror reflection so it will vary according to the viewing position."

I find that many of my holograms have a "sheen" when viewed from a specific angle. I have always assumed that it is from a specular reflection somewhere but I can never seem to find it. I also have assumed that it causes some loss if efficiency. Can you give me some clues on what is causing this and how to stop it?

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Posted: Tue Jun 08, 2004 4:18 pm
or try the net, i use it for my glass defusers..for object light..just like have a miny photo studio with fill, main, key, and backgrown lighting

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Posted: Tue Jun 08, 2004 6:31 pm
Assuming it's what I think it is, it's caused by too strong a reference beam. The reference beam hits the front of the plate, goes through, hits the back of the plate and returns to interfere with the incoming reference creating a holographic mirror. Let's call this "the mirror effect". If the sheen appears at the reference angle, it may well be a mirror.

Ideally during the recording process, the reference beam is interacting with the object beam as it goes through the volume of the hologram. By the time the reference beam gets to the back of the recording plate, it should be weak compared to the object and so the reflected reference beam does not have enough relative power to record fringes with the incoming reference beam. However, if the reference beam is too strong, relative to the object beam, then it's back-reflection records significantly compared to the ref beam-obj beam interaction. This then causes a "mirror effect"

This could be caused by a weak ratio (ref beam too strong) or it could be caused by low coherence - the object beam does not have enough coherence to interact with the reference beam.