A BLACK AND WHITE STEREO PRINTING SYSTEM
By ROBERT J. VAUGHAN
It is simply amazing the extent of work we stereographers will go to in order to enjoy our hobby. Not being content with the mounting accuracy of commercial photo labs, many of us mount our own slides. Stereo projection can be as elaborate as one wants. We print makers meticulously cut and paste our stereo pairs onto cards for side by side viewing. About 15 years ago, I developed a system for printing black and white stereo pairs onto a single piece of photo paper to eliminate the cutting and pasting of stereo print pairs. While both L/R images are projected at the same time, the exposures are sequentially made. For stereo pairs made with stereo cameras, this system automatically sets the stereo window at about 6 feet. In order to make these printed stereographs, 3 custom items are required. 1, a special negative carrier, 2, a transposing easel, and 3, a fog mask.
While most of the 5-P cameras have a built-in stereo window, as that format seems to have been fairly well standardized, my 7-P Verascope does not offset the lenses to fix a stereo window. Neither does my 8-P RBT. This will affect the stereo negative carrier design. For Realists, Kodak's, and some other 5-P cameras with 70-mm base, the negative carrier design and measurements will probably serve for most cameras. For example, I can print from both Realist and Kodak negatives using the same negative carrier. However, for the 7-P and 8-P cameras, the negative carriers will have to be designed and made for the specific camera at hand. Cameras that form a small loop between frames have a stereo base smaller than the space between the L/R images. Negative carrier measurements for these cameras can only be derived from your measurement negatives.
In order for this system to work simply and accurately, the negatives must be left as complete uncut strips. This maintains perfect image alignment. For twinning I place both negative strips in parallel to each other so that the L/R film gates are placed next to each other along the Y-axis instead of in tandem along the X-axis as in the case of all stereo cameras.
Let’s first describe the negative carrier. It can be made from camera or film measurements as described below. All measurements as outlined should be accurate to .001". Accuracy at this level can be made with a machinists dial indicator and a good magnifier. Lesser accuracy can be had with a finely divided metal measuring rule found in hardware stores along with a good magnifier. Use the same measuring units for all measurements. When measuring camera parts, extreme care must be exercised around lens elements, camera surfaces, shutters, and film gates. Dial indicator jaws and high grade metal measuring rules have extremely sharp points and edges on them and will scratch or damage camera surfaces before you even know it. It also goes without saying that the test film will be scratched and damaged while measuring as in item I. below so don’t use film that must be archived. Although not quite as accurate, I would recommend using the film, not the camera as the measuring medium so as not to damage your camera. If you decide to use your camera to obtain the measurements, you must proceed at your own risk. I cannot and will not be responsible for any and all of your actions that might damage your camera and/or your lenses. While you can get more accurate camera based measurements for the crafting of your negative carrier, I would recommend using expendable film for obtaining your measurements.
1. Composed together within the same stereo negative pairs, make test shots of both near subject (6’ for stereo window calibration) and far subject (over 300’ to determine deviation). Test shots must be made in the camera to which the negative carrier will be matched and should be made with a medium focal length setting if camera is outfitted with zoom lenses. Setting the lenses to longer focal lengths will increase the deviation if desired.
2. After developing film, measure distance from left edge of leftmost image pair on film to right edge of rightmost image pair. (These images are transposed on film.) Subtract .020" to set outermost cut positions in negative carrier film gates. The reduction in measurement above is to create a small margin to eliminate the possibility of printing a slight bleed of clear space between frames. The negative carrier determines the print borders, not the easel nor fog mask.
3. Measure distance between images on film of close (window setting) subject.
4. Subtract measurement #3 from measurement #2. This gives you the widths of each L&R negative carrier film gate opening measured from the outermost cuts in measurement #2. As a measurement check, the middle space between film gates is measurement #2 (less the to .020" margin) minus 2 times the film gate widths.
5. If deviation information of camera is desired, deviation measurement is far subject measurement minus near subject measurement as performed in measurement #3 above.
6. Measure vertical distance on film of each image. They should be equal. If not, chose the measurement of the smallest image. Subtract .020" to set the top and bottom cuts of the film gates in negative carrier. If a slight vertical error from the camera is noticed, the L/R film gates can be offset by that amount thus automatically correcting any vertical error in your prints (but only for that particular camera).
II. USING CAMERA WITHOUT FILM AS MEASURING GUIDE (be extremely careful)
1. Measure distance from left side of left film gate in camera to right side of right film gate. Subtract .020" to set outermost cuts in negative carrier film gates. The reduction in measurement above is to create a small margin to eliminate the possibility of printing a slight bleed of clear space between frames. The negative carrier determines the print borders, not the easel nor fog mask.
2. Measure distance between L&R lens optical centers. An accurate method is to subtract the outside diameter of one of the lens barrels from the overall outside distance measurement of those similar barrel parts of L&R lenses. This determines the lens stereo base between lens optical centers.
3. Using the same measurement units, calculate the image deviation by dividing the product of the lens stereo base measurement of the #2 measurement times the focal length of the camera lenses into the window distance minus the lens focal length. The formula: deviation = (lens base X focal length) / (window distance – focal length)
4. Measure the camera film gate widths. Each should be equal in size. If not, chose the measurement of the smallest film gate.
5. Subtract image deviation of #3 calculation from film gate width measurement in #4. This gives you the widths of each L&R negative carrier film gate opening measured from the outermost cut positions determined in #1. above.
6. Measure the camera film gate heights. Each should be equal in size. If not, chose the measurement of the smallest film gate. Subtract .020" to set the top and bottom cuts of the film gates in the negative carrier.
With these measurements from either I or II above, the negative carrier can be constructed. I use .032" sheet aluminum for this purpose. Start by cutting the outer size of negative carrier equal in size to your other commercial negative carriers for your enlarger replicating all alignment details so as to properly fit your enlarger. My Omega DII has two 3/16" registration pins to position and align the negative carrier. This alignment detail is very helpful for accurate and consistent set-up. Round all corners and finish the edges to be free of sharp edges and burrs. With your measurements, scribe the two rectangles representing the film gates using an accurate square and sharp awl. Locate these rectangles symmetrically in line with the optical center of your enlarger. Drill a 3/8" hole inside of each rectangle. Use a nibbling tool to remove all material inside of the scribed rectangles. A nibbling tool can be found at Radio Shack which cuts small 1/16" X ¼" pieces making it easy to make accurate and straight cuts. Leave a little material for filing to exact size. Next, measure the film width. Take the bottom piece and mark, cut, and bend four 3/8" X ½" tabs 90° upwards. These two tabs on the left side and two on the right side of the bottom negative carrier piece are spaced the film width apart. These tabs position and hold the film in place. In the same positions, cut four slots out of the top negative carrier piece. These slots line up with the up-turned tabs and align both halves of the negative carrier together. Where the film exits out of the negative carrier, the edges of the aluminum should be slightly bent away from the film about 15° to prevent scratching negatives. Polish all surfaces touching the film. With both pieces mated together, accurately file and polish the film gate openings to correct size, as this will form your print stereo window border. Use the dial indicator to get the openings exactly to size. This must be very accurate as those openings form the image borders. With a black magic marker, darken the cut sides of the rectangular openings to prevent printed reflections on your prints.
With the aid of a special transposing easel, this negative carrier can be used in most any 4X5 enlarger and suitable lens to create B/W or color stereo pairs onto a single piece of photographic paper. I made my easel out of ¾" plywood painted white. It is 21" long and 4 ½" wide and has a ¼" tall parapet along the top and right side forming paper stops. For proper operation the easel must be clamped onto the enlarger work surface. This keeps everything aligned during the printing period. An easy way to do this is to elevate your enlarger onto a piece of ¾" plywood spacer that is about 3" narrower than your enlarger base leaving edge space underneath for clamps. The transposing easel can then be secured to the enlarger base with C clamps at the left end. The movable left paper stop can be located under the same clamps. Set-up calibration involves determining the magnification necessary to make proper sized images for the size of paper you want by raising the enlarger head as necessary. Then the easel position must be properly located relative to the images and clamped in place. Lastly, the left paper stop must be located and clamped to set the image spacing on the paper. That can be almost any small piece of wood. Mine is ¼" thick, 1" wide and 3" long. Once this juxtaposition is determined, for future set-ups, measure the height of the enlarger frame to the easel and the width of the space between the left paper stop and the right parapet of the easel. I cut a dowel to length between the easel surface and enlarger carrier frame as a gauge with the left paper stop measurement written on it. I have 5 different format sizes of stereo negative carriers, each size having its own set-up measurements.
The transposing easel is designed to position the left half of the paper under the rightmost projected image (left transposed image). The paper is positioned against the right paper stop. After the left image is exposed, the paper is then shifted over to the leftmost projected image (right transposed image) against another paper stop located at the left of the paper for its right exposure. A special fog mask made of 1/8" masonite with an image sized cutout is positioned over the paper covering the parts of the paper not being exposed at the time. The mask is designed so that it can be placed onto paper and flipped between the left and right exposures. It prevents fogging and also holds the paper flat. This mask does not form the image borders. Instead, it is made with the cutout just large enough to cover the edges of the paper plus the entire opposite image area. For twinning, the images are projected one above the other along the Y-axis thus requiring a different easel. Mine has an additional paper stop along the bottom edge. In order to get side by side prints, the paper movement is along both the Y-axis and X-axis between exposures. Aligning the closest item of the negative images to the carrier borders manually sets the stereo window for each image pair.
When properly set up and calibrated, printing stereo pairs is just as simple as printing single flat images. The only extra time involved is for shifting the paper and making the second exposure, which is on the order of 15 seconds or less per pair. Once designed, set-up time for a printing session can be done in less than ten minutes.
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