Opacity of holograms

Simple answers are here! For Theory look in General Holography.
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Jamesapp

Opacity of holograms

Post by Jamesapp »

Hello,

I am new to the forums and holography. I just got done reading two books from the library on holography. I am in the process of obtaining material and equipment I need.

I have a question on holograms. I have seen pictures and videos of holograms, some from the books I have read and others online. I have also fooled around with photography most recently 16mm. My question has to do with the opacity of the hologram. I don't know if that is the right term, but I want to make a hologram. And I would think the hologram I would make would be monochromatic. I have seen several images of holograms, and I kinda realize these are 2d renditions of something that should be seen in 3d to get the full effect.

So I am wondering, if I use a red laser, would my developed hologram appear red? And can you see through the hologram?like one picture I saw I believe was a hologram of dominoes. But I can't be certain from the picture and the caption of the picture if it was a holographic image? If it was a true picture of a hologram it was very impressive. Like I wouldn't be able to tell the difference between this picture of a hologram, if that is what it, and a picture of real dominoes.

I know I am justing beginning in holography, haven't even bought any equipment yet. I guess I am at the stage of trying to figure out what materials and equipment I need. And what would be most cost effective and allow me to grow as I learn about holography. And I have fooled around with photography cameras and film for years. I guess I am just wondering about opacity, like some pictures I see it seems like you can look through the image, but like with the dominoes the black part of the dominoes looks solid. Just wondering if anyone who has made holograms could explain the final developed image when it gets illuminated. I kinda wonder if the laser is red will the final image appear reddish in color? Does the type of film used have an effect? Any info would be appreciated.
BobH

Opacity of holograms

Post by BobH »

If you made the hologram on silver halide photographic film, the hologram will be gray to black (depending on the density it's developed to). The color of the image reconstructed by the hologram will be the same as the color of the laser used to illuminate the hologram after it's been developed. The hologram in this example is gray to black because the fringe pattern recorded in it is made of silver, exactly like a B&W photograph.

Other types of holograms will be clear or slightly tinted, depending on the material and/or the process used to "develop" the material. Slightly tinting a hologram green and illuminating it with red laser light to reconstruct a red image gives better contrast. Same with a red tinted hologram and a green image. The absence of tint is very important in full color holography. Control of tint is a trick that's been responsible for more than a few holographers' rise to "Mt. Holympus". :whistle: :whistle: :silenced: :shhh:
Tom B.

Opacity of holograms

Post by Tom B. »

When you view a hologram, the image only appears as seen within a window defined by the bounds of the film. If you make a hologram in a two stage (H1-H2) transfer process, you can make an object appear to be in front of the window, but it can only be seen within the bounds of the window as seen from your point of view. The image is not opaque - if you put a finger behind the apparent object image, the finger will not be hidden. The holographic image is a reconstructed light wavefront, not a solid object.
Jamesapp

Opacity of holograms

Post by Jamesapp »

Thanks for the replies. One thing I read about is white light transmission holograms. From what I have read. You use a H1 H2 process. And the finished hologram will be viewable with white light. I have heard the term rainbow holography also. I also read that the final hologram has limited vertical parallax. And also that the process makes the final hologram (anchromatic) which I believe means 'no color'. Have I got that right?

I think the pictures I saw were white light holograms. There is black and white film available for motion picture work that is panchromatic. I don't know a lot of the technical info behind it. But is this different than a black and white hologram? I also wondered what type of light source you would need to alluminate a white light transmission hologram? I heard you use a filtered light I think.

One article I read said that white light transmission holograms, being black and white can appear more realistic. And he said a laser ilumminated hologram can have a hue to it. I wondered what drawbacks there are to white light transmission holography, other than the limited vertical parralax.
Tom B.

Opacity of holograms

Post by Tom B. »

Jamesapp wrote:Thanks for the replies. One thing I read about is white light transmission holograms. From what I have read. You use a H1 H2 process. And the finished hologram will be viewable with white light. I have heard the term rainbow holography also. I also read that the final hologram has limited vertical parallax. And also that the process makes the final hologram (anchromatic) which I believe means 'no color'. Have I got that right?
Transmission holograms are viewable with white light but they have a vertical color gradient - red to blue, so they don't look very realistic. Achromatic transmission holograms use a clever optical scheme (invented by Steve Benton) to cancel the color dispersion, so they look less rainbowish. It's difficult to do this well.
Jamesapp wrote:I think the pictures I saw were white light holograms. There is black and white film available for motion picture work that is panchromatic. I don't know a lot of the technical info behind it. But is this different than a black and white hologram? I also wondered what type of light source you would need to illuminate a white light transmission hologram? I heard you use a filtered light I think.
Panchromatic film is sensitive to all colors of light. Normal black and white photographic film is panchromatic, but the grain size of the film is much too coarse to capture the detail needed for holography. Panchromatic film for holography is available, but to make a full color hologram requires at least three lasers, typically red, green and blue which is very expensive and difficult for amateurs to finance. But it has been done.
Jamesapp wrote:One article I read said that white light transmission holograms, being black and white can appear more realistic. And he said a laser illuminated hologram can have a hue to it. I wondered what drawbacks there are to white light transmission holography, other than the limited vertical parallax.
(1) Well - more realistic than a rainbow smear perhaps. (2) It's hard to avoid a hint of color with a single-wavelength laser illuminated hologram. (3) Not sure, but from the description in Graham Saxby's "Practical Holography" it looks tricky to do, and probably works well only for some some scenes "(fairly shallow images such as portraits)"
Jeffrey

Opacity of holograms

Post by Jeffrey »

James - Holograms are recorded on black and white film, just the little lightwave patterns, in high contrast. Color film has no place here. The recording creates a prismatic/diffractive device which bends a beam of light into the image. Generally the colors we expect in full color viewing are screwed up, separated, filtered out, leaving a rainbow image, a monochrome image, or when viewing in laser light, a laser colored image. Getting WHITE or the color you want is difficult and a little more advanced, leaving the world covered with simple green or rainbow holograms, yuk.
Transmission H2 images can be white if they are shallow. Reflection H2 images you can tune which rainbow color or colors you want, but if you try more than one color, aligning them is an additional trick, as they want to rainbow-smear.
The point being, you start with the finest grain black and white emulsion made, and create colors after that.
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