MODULE FOUR: SHOOTING THE REFLECTION COPY
REFERENCE BEAM: 10 inches / 50 inches
50 inches from mirror to master plateholder
20 inches from large mirror to master plateholder
8 inches from master plateholder to copy plateholder
It is best to keep your object beam unspread, then place your master plate into the plateholder. Your unspread object beam should strike it right in the middle of the plate. Place a white card into the copy plateholder. Now flip the master plate in different orientations until you see an image appear on the white card. Make slight adjustments so that this image is centered on the white card. It is better to adjust several items (such as both the master plateholder AND the copy plateholder), rather than adjust just one or the other. Once you have your image centered, THEN remove the white card and move it forwards and backwards until the image is at its sharpest. This is the spot where your copy should be made. Reposition your copy plateholder in this spot. Return the white card to the plateholder and make sure that the image is now both centered and sharp. You may now spread the object beam with your lens or spatial filter. The image will now blur on the white card -- this is what is supposed to happen. No further adjustment is needed -- unless your beam distances have changed again.
Please note in the above illustration, how the relationship between the master plateholder and the reflection copy plateholder now mirrors the recording geometry between the ground glass and master plateholder in the laser transmission master recording. It's now just flipped around.
This is a rather unusual and unique recording geometry both in the mastering phase and in the copy phase. In fact, it would be unusual for even a regular H1 to H2 transfer. Usually, when mastering stereograms, the master plateholder faces the ground glass or LCD screen head-on, and the geometry between the two is that they are parallel to one another in the mastering set-up -- resulting in the master and copy plateholders being parallel during the H1 to H2 reflection copy process. You will note this in any articles or papers on recording stereograms. With the above geometry (both mastering and it's associated copy set-up, above), the two are at 45-degree angles to one another. One would think that this would not work, but remember that a hologram will "direct" light in whatever direction we tell it to. This is apparent in HOE's -- especially those that are used in greenhouses that show that the Sun is overhead regardless of where it is located in the sky during the day.
In our case here, it will direct whatever was recorded on the groundglass surface, to the hologram in the copy plateholder, regardless of the associated angle of said recording.
This serves several purposes, the most important being that when viewing the copy hologram while displayed on a wall, and the image being located right in the plane of the copy hologram, the slits are reconstructed approx. 8 inches in front of the hologram AND at a 45-degree angle. My puroses in this is:
1. Not having a parallel plane of slits that the eye could easily focus on between the viewer and the hologram. Having an ANGLED plane of slits eliminates this possibility to a great extent due to the fact that any point along the length of each slit area is located, and focused, at a different point in space relative to the viewer.
2. Due to the fact that the ground glass was located approx. 8 inches from the master plateholder, this projects the slit area far enough out from the plane of the hologram to allow quite a bit of "blurring" to the contact areas between slits. Since the master plateholder and ground glass were recorded at the 45-degree angle, this blurring is enhanced even further due to the angled nature of their reconstruction. Remember, with this method it is NOT the slits that are going to be recorded AT the copy hologram. Our IMAGE will be focused and recorded there. The slits are going to be recorded way out where the master plate is located AND on an angle (due to the angled relationship between the master and copy plateholders).
In a nutshell, the whole point is to eliminate any sense, on the viewers part, that they are looking through slits. Especially since these are not highly-accurate, mechanical or computer generated/controlled, slits to begin with. Even slight mistakes in spaces or overlaps with the slits can be effectively "smeared" out enough to lessened in their noticeability to the viewer, at a usual viewing distance to the hologram displayed.
Once your set up is ready to go, determine your exposure time by reading your reference beam intensity. Normally, you would take both a reference and object reading -- but this is difficult to do since there is no physical object, just focused light. If you are using a 50-50 beamsplitter you should be pretty close to being where you need to be as far as beam ratios. I often use a 60-40, with 60% going to the object beam, and 40% going to the reference.
If you already have experience with H1 to H2 transfers, you should be well versed in getting a real-image intensity reading already -- so, proceed as usual. The only difference with this technique is that you're taking a measurement of a flat plane of light -- rather than the real-image of a three-dimensional recorded object. Even though the person is three dimensional in the hologram, the wavefront that is reconstructed from the master plate is a flat plane of light. This flat plane is projected into the plane of the copy plate. This is why the resulting reflection hologram remains so sharp . . . because the "depth" that is perceived by the viewer doesn't actually project or receed into the hologram. The closer you are at nailing the exact plane of the projection, the sharper your resulting finished hologram will be.
Once you have your reference intensity reading, determine your exposure time for the recording media you are using. Make sure things are settled, expose, then process as usual for a reflection hologram.