This method is a version of our dual monitor 3D viewer. |
THE TABLETOP MIRROR-VIEW 3D PRINT DISPLAY Prof. John Hart Program in Atmospheric and Oceanic Sciences University of Colorado Boulder, CO 80302 June 2001 nimbus.colorado.edu/hart/science.htm
Here is a simple, robust, stable and very effective way to view large stereo prints. The resolution is good, the 3D effect is easily comprehended, and the color saturation and lack of ghosts is excellent. This report describes how to build this inexpensive viewer and outlines the theory for it.
Figure 1. A typical print setup. Prints are mounted on a rigid and substantial substrate. We use 1/2 inch "paintable pine" plywood rather than the usual foam-board employed by frame shops. The weight keeps the alignment and the prints stay straight. The left print is mirrored (flipped horizontally). The viewer is a front surface mirror on a simple adjustable mount, described below.
Figure 2. Diagram of the setup. Parameters are (typically) Theta ~ 45 degrees, print width 20", D ~ 20 inches. The viewing location is very near the ortho-stereo point for an image made with a 40mm lens on a film 32mm wide (40mm being an average or typical focal length, somewhere between normal and wide angle). The observer looks straight at the right print.
Figure 3. Looking at the stereo pair. You look straight ahead at the right print. Head position is important but not critical. You don't have to touch the mirror, an inch or two clearance is fine. Design Goals: 1) High quality ghost free viewing of large (i.e. highly detailed) prints. 2) Inexpensive and easily acquired parts.. 3) Easy to setup and stable. The parts you need are: Two 2 foot square sheets of 1/2 inch plywood (preferably Birch or Pine), or other stiff mounting material. White PVC Vinyl tape. 2" Wide. 3M 77 contact cement spray. About 2 square feet of 3/4 inch particle board (good 'cause its heavy, other scrap wood will do). Some aluminum angle and a small amount of plastic sheet stock or masonite (optional). A front surface mirror, about 16.5" H by 12" wide by ~3/64 thick. Obtain from the stained glass warehouse ($37 per pair). NOTE: a 1/8" regular glass mirror from a glass shop will work well. It will be somewhat cheaper (maybe $6 each). Front surface has that extra little degree of clarity that is appreciated. A pair of prints, about 16x20, with a 3" white space in between (if printed all at once). The left print is mirrored (or reversed left to right). Some hardware. The Print Frame: The two pieces of plywood are taped together along the center vertical seam to form a hinge. A continuous print (44 inches wide for example) can then be glued down and the whole thing folded over. Metal hinges have an offset that would crimple the print.
Figure 4a. Vinyl Tape Hinge. If the prints are made on a continuous sheet (via a widebed printer, for example), carefully glue down the print at mid height on the plywood, with the 3" white stripe centered on the fold of the plywood. If there are individual prints make sure there is enough white border to just meet up at the center line. See figure 1. To use the 3M 77 spray, if found it best to tape down the lower edge of the image using white vinyl tape. Fold the print back and spay its reverse side lightly. Carefully roll it back, avoiding air bubbles. More than one person might be good for this. In the end, the full double-picture print should be centered on the plywood. Most importantly it should be parallel to the bottom. The Mirror Stand: The mirror stand is made of two wood bases. The sub-base allows for support and rough positioning, while the upper base allows for fine positioning and tilt adjustment. Pictures are more efficient than words:
Fig. 4b. The sub-base is a 10" to 12" square piece of 3/4 particle board. A 2.5" 10-32 screw is countersunk into the bottom and sticks upright, held in place with a nut.
Fig. 4c. The mirror mount. An aluminum bracket is screwed to a piece of plexiglass. The latter is glued to the mirror with silicone rubber. Alternatively a wood piece can be glued perpendicular to the upper base and then the mirror glued to it. The mirror is thin (less than 1/16") and should not just be attached at the bottom. The front-surface faces away in this image.
Fig 4d. The upper base is 6" on a side (not critical). A 1 inch hole is drilled in the middle. The tilt adjustment screw (1/4-20) is seen at the front. The upper base sits over the sub-bases attachment screw.
Fig. 4e. Here is the underside of the upperbase. A 1/4-20 nut is hammered into a shallow 15/32" hole on the right. The nut provides the threads for the adjustment screw. On the left, 1/4 (or so) thick piece of material (wood, aluminum, plastic...) is glued to the base. This enables the tilt adjustment to go both ways off of vertical.
Fig. 4f. The assembled mirror stand with locking wing-nut.
Fig. 4g. A thin piece of plexiglass or masonite is glued onto the leading edge of the mirror to protect it, and the viewer.
Fig. 4h.
Fig. 4i. In order to achieve the alignment illustrated in figure 2 set the device up as shown (upper base square on lower base, mirror lined up with the fold as in blue line). Looking straight at the right print, slide and twist the unit until the right edges of both images overlay each other and have the same height. The green arrow shows how to slide to decrease the relative height of the left image. There may be a vertical shift, which is corrected by adjusting the tilt screw while the locking nut is loose. Once the right edges line up and the heights are the same, scan across the top of the pictures and make sure the tops are coincident all the way across. If they are not, adjust tilt until they are and reposition the mirror left to right so that the images have the same height. What you want, simply, is for the left image to overlay the right one so that all the edges are coincident. When good alignment is attained the 3D effect should be immediately evident and easy to fuse. Now is a good time to mark the table (tape or pencil). You may want to attach the sub-base with double sided sticky mounts or something if you want to leave the setup insensitive to bumps. The one inch hole gives enough room for fine adjustments later. Moving the mirror closer gives a wider angle of view. This is good, but eventually the mirror will not be wide enough to cover the view.
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