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Introduction

Overview

Optical Table

Environment

Laser

Beamsplitter

Mirrors/Lenses

Table Mounts

Optic Mounts

Plate Holder

Objects/Scenes

Hardcopy

Resources

Plate ⁄ Film Holder

This system utilizes a 4 inch x 5 inch hologram plate holder as shown in Figures 12a & 12b. The plate holder is made up of numerous parts as shown in Figures 12c and 12d. These parts include three aluminum bars, two 1/4-20 short rods and two 1/4-20 nuts, two acrylic plastic pressure plates, four sets of 3/4 inch long round head 8-32 bolts, nuts, & compression springs, two Velcro strips, and four 1/2 inch long round head 8-32 bolts. Figure 12c shows the parts without labeling for clarity.

plate holder front view image
Figure 12a: Finished plate holder showing front side.

plate holder back view image
Figure 12b: Finished plate holder showing back side.

plate holder parts image
Figure 12c: Plate holder parts and holes without labels for clarity.

plate holder parts labeled image
Figure 12d: Plate holder parts and holes with labels.

Three aluminum bars need to be cut for this holder and are available from hardware stores. The horizontal bar is 7-3/4 inches long x 1.0 inch wide x 1/4 inch thick. The length of this bar is critical for upcoming measurements, so cut this length as accurately as you can. The two vertical bars are 5 inches long x 3/4 inches wide x 1/8 inch thick .

With a pencil or fine/medium point permanent marker, mark one side of the horizontal bar as the "top" (or "F" for front) and do the same with the two vertical bars as shown in Figure 12c. The "top" side of all the bars is the front of the plate holder. You should also mark which vertical bar is the left bar and which one is the right bar and also which side of the horizontal bar is left and which is right when the "top" is facing up. Later on, you will be placing the vertical bars on top of the horizontal bar and you will need to make sure all the "top" sides are facing up and the left/right positions are in the right place. I've suggested a permanent marker so the markings are not accidentally erased. If you make a mistake in placing your markings, you can use lacquer thinner and paper towel to remove them. You'll be painting all these bars with enamel flat black paint so you don't have to remove these markings before you paint.

Before you attach the vertical bars to the horizontal bar, you need to drill some holes in all three bars. Figures 12c and 12d show the locations of these holes and are numbered. Drill a hole (hole #1) on each end of the horizontal bar using a 1/4 inch bit to accommodate a short rod with a 1/4-20 bolt and nut for mounting to a table mount with a connector. These holes should be drilled 3/8 inches from each end of the horizontal bar and centered 1/2 inch on its width as shown in Figure 12e. The plate holder uses two table mounts, one on each side, to provide good stability. Next, you will drill several holes in the vertical bars before you drill the holes in the horizontal bar for attaching the vertical bars.

hole measurements diagram
Figure 12e: Positions and measurements of holes.

The photographic plate is held tight to the vertical bars with plastic pressure plates held to the vertical bars with 8-32 bolts and nuts and #9 compression springs. Two holes are drilled in each vertical bar with a 5/32 inch bit for inserting 8-32 bolts and nuts that hold the pressure plates and compression springs. One hole (hole #2) is drilled a distance of 1-1/4 inch from the end of the vertical bar furthest from the horizontal bar (Figure 12d & 12e). This will be the top end. A second hole (hole #3) is drilled a distance of 1-7/8 inches from the end of the vertical bar closes to the horizontal bar (Figure 12d & 12e) and the end that will be attached to the horizontal bar. Both holes should be centered in the middle of the width of the vertical bar.

Note: since the pressure plates apply pressure to the edges of the photographic plate and press the edges of the photographic plate against the vertical bars to hold it secure and stable, these holes are drilled in these positions to provide the best uniform pressure across the photographic plate. This will become important later on when you use photographic film instead of a photographic plate.

Next, using again a 5/32 inch bit, drill two holes (holes #4) in each vertical bar 5/8 inches from the bottom end of each vertical bar (measure from the center of each hole to the bottom edge) as shown in Figure 12e. The center of these holes should be 3/8 inches apart from each other to accommodate the round heads on the 8-32 bolts you will use to screw the vertical bars to the horizontal bar.

Now you are going to place the vertical bars on top of the horizontal bar and use the two holes on the bottom of each vertical bar to mark drill holes on the horizontal bar. This whole process should be as accurate as you can make it when marking the holes to be drilled, their positions, and drilling the holes. So take your time and measure often.

Using Figures 12d & 12e as visual guides, lay the horizontal bar on a table top and then lay both vertical bars with their bottom ends (the ends with the two drilled holes #4) on top of the horizontal bar with "top" facing up for all the bars. Take an extra piece of 1/4 inch thick bar long enough to place under the top ends of the two vertical bars. This will keep the vertical bars parallel with the table top and make marking the drill holes on the horizontal bar more accurate. Once you get the all the bars in position as shown in Figure 12e, tape down both 1/4 inch thick bars with duct tape. You don't want these to move while you're positioning the vertical bars.

Let's start with the right vertical bar first, so remove the left vertical bar. Adjust the position of the right vertical bar on top of the horizontal bar so the vertical bar is perpendicularly to the horizontal bar (a small plastic right angle is useful here). Position the right edge of the right vertical bar 3/4 inches from the horizontal bar's right end as shown in Figure 12e. The bottom of the vertical bar should be a 1/4 inch above the bottom of the horizontal bar as shown in Figure 12e. Double check your measurements and perpendicular alignment. Tape the right vertical bar in place so it doesn't move. Stick a pencil or fine/medium point permanent marker into the two holes (holes #4) in the vertical bar to place marks on the horizontal bar. These marks will be where you will drill holes in the horizontal bar for attaching the vertical bar to the horizontal bar.

Do the same procedure with the left side vertical bar in relation to the horizontal bar's left end. Keep the two 1/4 inch thick bars and the right side vertical bar in their taped positions while completing the left vertical bar.

Before you drill out these four marks on the horizontal bar and with all the bars taped down, you need to check that the vertical bars are positioned where they should be as shown in Figure 12e. Here's the bottom line: the distance between the inside edges of the vertical bars should be 4-3/4 inches from top to bottom. If they are not, then you need to adjust both vertical bars equally on the horizontal bar to obtain this distance between them. If you've already placed permanent marks for each vertical bar, remove them and remark them once you've got the spacing right. This distance is critical so that the photographic plate will seat itself properly behind the pressure plates and against the vertical bars.

Here's the math:

You can now see why it was important to accurately cut the horizontal bar to its correct length since the distance between the vertical bars is based on the distance of the vertical bars from the ends of the horizontal bar. If you need to adjust the vertical bars to achieve the correct distance between them, you do have a bit of space to move the vertical bars more towards the ends of the horizontal bar or towards each other.

Since the length of a 4 inch x 5 inch photographic plate is 5 inches, the distance of 4-3/4 inches between the inside edges of the vertical bars allows 1/8 inch of each side of the photographic plate to rest against the flat surface of each vertical bar and be held in place by the pressure plates.

Once you've achieved the distance between the two vertical bars and have marked their holes on the horizontal bar, remove all the duct tape and separate the parts. You are now ready to drill out the four holes in the horizontal bar (holes #5). Drill out the holes using a 1/8 inch bit. Thread the holes using an 8-32 tap. Now attach the vertical bars to the horizontal bar using 1/2 inch long 8-32 bolts. The vertical bars should be attached on the back side of the horizontal bar (the side without the "top" written on it) and the 8-32 bolts inserted from the back side and screwed into the tapped holes on the horizontal bar. See Figure 12b. As a reminder, the "top" side of the bars is the front of the plate holder.

Next, attach the two short 3 inches short rods with 1/4-20 bolts to each side of the horizontal bar with 4-20 nuts and lock washers (Figure 12a, b). These rods should be on the back side of the horizontal bar where the vertical bars are attached.

The final part to make are the pressure plates. Cut two pieces of acrylic plastic with the dimensions of 4 inch x 1.0 inch x 1/4 inch thick. File the cut edges as smooth as you can. You need to cut or file one 4 inch side of each piece to about a 25 degree angle as shown in Figure 12f. A small band saw works well for this delicate cut. The reason for this will be explained shortly. Again, file the edges as smooth as you can. This angular edge of the pressure plate will face the photographic plate and vertical bars as shown in Figure 12g.

pressure plate angle diagram
Figure 12f: End view of a pressure plate with 25 degree angle.

close-up view pressure plate
Figure 12g: Close-up top view of pressure plate attached to vertical bar.

Next, you will mark the location for drilling holes in the pressure plates for attaching the plates to the vertical bars. With the plate holder front facing you, take one of the pressure plates and position it in front of the right vertical bar with the angle cut facing towards the inward side of the vertical bar, the angle facing away from the front of the plate holder, and the pressure plate resting on the top of the thickness of the horizontal bar as shown in Figure 12h. Label this pressure plate "R" for right and "F" for front. Now move the pressure plate so its left side is 1/16 inch to the right of the inward side of the vertical bar. Once it is in position, hold the pressure plate firmly in place (or you may want to tape the pressure plate to the vertical bar) and reach back behind the vertical bar and stick a permanent marker in holes #2 and #3 to mark the drill holes on the pressure plate. Repeat this procedure for the pressure plate on the left vertical bar. Drill holes in the pressure plates where you've marked them using a 5/32 inch bit.

pressure plate positioning image
Figure 12h: Pressure plate position for
marking drilling holes.

Next, drill perpendicular holes where the markings are on the pressure plates using a 5/32 inch bit. Cut two Velcro strips 1/8 inch wide and 4 inches long using the soft part of the Velcro. Place these strips on the front side of the two vertical bars as shown in Figure 12d with the adhesive side of the strip pressed against the bars.

You will now attach each pressure plate to their respective vertical bars using the 8-32 bolt and nut. Insert the 8-32 bolt from the front into the top right pressure plate hole #2 and through the right vertical bar hole #2. On the back side of the vertical bar, place a #8 washer on the bolt, then a #9 compression spring, then another #8 washer, and finally screw on a 8-32 nut to the end of the bolt. Repeat this procedure for hole #3 in both the right pressure plate and right vertical bar. Now repeat both of the above procedures for the left pressure plate and left vertical bar. You may have to cut the length of the compression springs with wire cutters if the original length is too long to get the nut screwed on.

compression in springs image
Figure 12i: Showing how much
compression in the springs.

Look at Figure 12i to get an idea of how compressed the spring should be after the nut is screwed on and flush with the end of the bolt. There should be a small amount of compressibility left in the spring so you can pull the pressure plate away from the vertical bar a distance of at least 1/16 inch. This facilitates the insertion of the photographic plate into the plate holder. Figures 12j and 12k show the finished, unpainted plate holder with the photographic plate inserted.

finished unpainted plate holder image
Figure 12j: Front view of unpainted finished plate holder.

finished unpainted plate holder image
Figure 12k: Back view of unpainted finished plate holder.

The plate holder in Figures 12j and 12k was photographed before I made some modifications to the plate holder described in the above text. So just ignore the fact that in the front view above, the pressure plate is not shown resting on the surface of the horizontal bar. If there is a small space between the pressure plate bottom and horizontal bar, this is fine. Also in the back view above, a #8 washer is missing between the vertical bar and compression springs.

When you start making your first holograms, I recommend you use photographic plates instead of film to enhance your success in making a good hologram (except when making density test exposures). Later on you can switch to using photographic film which is less expensive than the plates. Film is more difficult to use because it is flexible and must be sandwiched between glass plates, which are then inserted into the plate holder. The ability to pull the pressure plates away from the vertical bars is a great help in inserting these two glass plates since they are twice the thickness of one photographic plate. When I first started making 4 inch x 5 inch holograms with plates, some of them didn't come out well, so I saved at least two of these plates to use for sandwiching film. You can remove the emulsion from these photographic plates by soaking them in a solution of 50% bleach and 50% hot (110°-120° F [43°-49° C] ) water for about 30 minutes. Most of the emulsion should just slide off but if some of the emulsion is still present, you can use a new single edged razor blade to remove it. You can use a plastic film development tray for the soaking part. Once all the emulsion is gone, you can further clean the plates using a window cleaner.

Once you have the plate/film holder built, you should disassemble it and paint all the pieces with enamel flat black paint. Once thoroughly dry, you can reassemble the holder. Spray paint the springs just lightly. Otherwise, over time, the paint may chip off from the springs expanding and contracting. As shown in Figure 12d, add a strip of Velcro 1/8 inch wide, running the length of the inside front edge of each vertical bar. Use the hook side of the Velcro, not the fuzzy side. This helps to cushion the plate edge against the metal of the vertical bars.

Note: You may have noticed in Figure 12a that the top surface of the vertical bars are white. These are actually small strips of "glow-in-the-dark" phosphorescent plastic from a solar system wall kit. The strips are attached to the top surface with 5 minute epoxy. These strips help you locate the top area of the plate holder for inserting the photographic plate or sandwiched film when room lighting is under certain safe light conditions or non-existent. This strips will glow but not expose the recording emulsion.

 

Revised 5/2/2017