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SB Transmission



SB Reflection

MB Transmission

MB Reflection



Recording and Processing

This sub-section should be read through completely before implementing. After reading this sub-section, it would be a good idea to review the sub-section on Exposure Calculation Techniques and Processing Steps before implementing this sub-section.

Now that you have your single-beam transmission arrangement set up, you are ready to make your first hologram and measure its density. Each bullet listed is a step in the recording and processing procedure and should be followed in the sequence listed.

The Recording and Exposure

Note: Wear power-free surgical gloves when practicing. Remove the gloves once you're through practicing. You can reuse gloves if you know that you haven't touched anything that would leave fingerprints on your plate or glass plates like touching your skin, eating food, drilling holes, those sorts of things. After processing, throw the gloves away.
Note: Practice leaning this against the front of the laser to cover the aperture, then tilting the board away from the laser, then gently lifting the board while still blocking the laser beam, then waiting about 60 seconds, then lifting the board higher so the beam can expose the photographic plate, then lower the board to block the beam again after the appropriate exposure time, and finally rest the board on the table and lean the board against the laser again. When you're through practicing, remove the shutter.
Note: It's important to know which side of the plate the emulsion is on. As you face the plate box, make sure the Integraf label is right side up so you can read it from where you are standing. If their plates are loaded in the box consistently in the same direction, then the emulsion will face to your left. Remember this side of the plate as you remove it from the box and place it in the plate holder. The emulsion should be facing the object scene. With film, you can tell which side the emulsion is on because the film curves slightly towards the emulsion side.

During the washing phase of the development process, you can determine the emulsion side of the plate or film. Lift the plate out of the washing tray water. The water will flow off the plate slower on the emulsion side than on the glass side. The emulsion side is also duller (less reflective) than the glass side. Both of these properties are also true for the film. We assumed that the emulsion was on the left side of the plate as it sat in the plate box and you've kept this side up while processing. If the up side shows the slower water flow, then our assumption was correct. You can now place an arrow on the outside of the plate box facing to the left with a black marker. If our assumption was incorrect, then the arrow should face to the right. You will find that all the plates' emulsions will face in the same direction inside the plate box.
Note: The box has sliders on the right and left sides of the box and once the sliders are in place, the lid is sealed tightly. You want to do this at this time because later on you will be turning the room lights on and you want to make sure the box is closed and sealed tightly. Additionally, when I'm through with the plate box for the day, I run a piece of 1/2 inch wide black masking tape along the seam where the lid seals with the lower part of the box just to insure no room lighting can leak in over time.


Density Check

Note: As I mentioned a little earlier, while you're doing the first wash, check to see if the side of the plate you've been keeping up is the emulsion. If it is, our assumption about plate placement in its box was correct - the emulsion side of the plate faces to the left in the box. If it turns out that the emulsion is actually facing down, then in the next paragraph where you view the hologram, the glass side of the plate will need to face the object scene. With you now knowing which side of the plate has the emulsion, all future exposures should have the emulsion facing the object scene.

Viewing Your First Hologram

You are now ready to view your first hologram. Take a piece of black mounting board and place it in front of the object scene facing the plate holder so you can't see the object scene from the plate holder's perspective. Remove the shutter. Since you now know what side of the plate the emulsion is on, hold the plate behind the plate holder in the reference beam with the side of the plate that faced the object scene during the exposure. If you see the image of your object scene as shown in Figure 75, you can now place the plate in its holder and view it for hours. If you don't see an image, you need to rotate the plate 180 degrees around it's vertical axis to see the image. If you still don't see an image, you may have misjudged which side of the plate was facing the object scene. Rotate the plate 180 degrees around its horizontal axis and look for the image again. If it's still not there, rotate the plate 180 degrees around it's vertical axis and see if the image is there. If it's still not there, then vibrations and/or movement occurred during the exposure and you'll need to try again. But with this setup, I'm very confident you'll have an image.

Figure 75 shows an illustration of what you should see (your object scene will be slightly off to the right as shown in Figure 72). The holographic image in Figure 72 is located in the same position as your original object scene. This image is called a virtual image like the image you see of yourself in a mirror.

Viewing virtual image
                   Figure 75: Transmission hologram virtual image.

Now take the hologram out of the plate holder and rotate it 180 degrees about the Z axis (vertical axis) so that axes X and X- switch positions and Y and Y- switch positions. Figure 76 shows what the image will look like now. You will see the image floating in space between the plate and yourself. This is called a real image because it is actually being focused into space and can be seen on a screen. Using a piece of white mounting board as a screen, you can focus different parts of the image on the card by moving the card through the focused 3D image.

Viewing real image
            Figure 76: Projected transmission hologram real image.

You may notice something unusual about this real image while viewing it floating in space between you and the plate. If you move left to right to view parallax in the image, the image moves with you and its parallax cannot be observed. Also, the foreground of the original image has become the background and the background has become the foreground. Left and right parts of the original image have also switched positions. This type of image is called a pseudoscopic real image and is the inverse image of the original scene and the virtual (orthoscopic) holographic image.

You will use this real image to produce a multi-beam white light reflection display hologram in which the image will revert back to its normal orientation (called orthoscopic). You will also notice that the pseudoscopic real image is greatly magnified. This magnification is caused by the fact that you used a diverging beam during this recording. When you produce a multi-beam hologram, you will use a collimated (the leading edge of the beam is flat instead of curved) reference beam which will keep the virtual and real images at a 1:1 (1 to 1) magnification.

Transmission holograms have to be reconstructed with laser light. If you tried to reconstruct the image with the sun or a 100 watt clear envelope light bulb, your image would be a rainbow of colors and blurry. Transmission holograms take the full visual spectrum of the sun or light bulb and creates an image for every color in the visual spectrum therefore creating overlapping images that produce a rainbow blur.

Note: Why do we have the reference beam incident on the recording plate at an angle to the plate's normal? In addition to the advantages of Brewster's angle as previously mentioned, when the hologram image is reconstructed with the original reference beam, the beam would be visible as part of the holographic image if it wasn't incident at an angle to the plate's normal and you don't want that. The angle is "off-axis" enough so you don't see the reconstructing beam in the image. Your final white light multi-beam reflection display hologram will be illuminated (reconstructed) using a white light lamp and you certainly don't want to see that lamp as part of your fantastic image!