3D - Workshop
How do we see in 3D?
The capacity to perceive our world dimensionally is primarily due to the way our two eyes are placed parallel to one another. This arrangement is different from many animals and birds. Their eyes are placed on either side of their heads. This provides them with a very broad viewing angle. Our eyes provide our brains with two nearly identical views of the same scene. The only difference between these two "flat" views is in the slight difference in viewing angle. And this slight difference is sufficient to provide our brains with the information necessary to construct a spatial 3D image. This capacity becomes evident in humans within the first few months of life. Not everyone learns to use this capacity. About 5% of the population base their perception of space on the fact that when the head is moved from side to side, objects which are near seem to move faster than those which are farther away. This is the way that the previously mentioned birds and humans with only one eye intact can perceive spatially. This can only be done with scenes that are in motion. Viewing 3D photographs is, unfortunately, not possible for this group of people.
How do we make 3D photos?
The least expensive method of producing three dimensional photographs is by using a device which produces two photographs, one after the other, taken from locations that are approximately 2 1/2 inches (6.5 cm) apart. The distance between our eyes is approximately 2 1/2 inches. A movable camera mount on a tripod is best. It is very important to insure that there is no difference in height between the two locations. This would prevent our eyes from blending the two images and could cause headaches. The main advantage of this method is lack of expense. However, this method can only be used for scenes that are absolutely static. A landscape with moving clouds, a tree with windblown leaves or even a person are definitely not suitable subjects. Substantially better results can be obtained with an arrangement that employs two cameras with synchronized shutters. The cameras must be mounted so that the horizontal distance between the lenses is the same as the distance between our eyes and they must be precisely adjusted. The difficulty here is in obtaining this distance of 2 1/2 inches (6.5 cm). I do not know of any mini-cameras that are small enough to permit them being mounted so closely, next to one another. You can get fairly close. I use two Minox GT cameras, offset slightly, one behind the other. Both cameras are attached to an extruded aluminum fixture with screws. By this means, I can achieve an acceptable horizontal distance between the lenses of slightly less than 3 inches (7.5 cm). A greater distance than this has the effect of making objects in the 3D pictures look like toys. The explanation for this is simple. Picture a small cube (a die) on a table in front of you. Because of its size, you can easily see the top surface and two sides. Now imagine that the cube is 3 feet (1 meter) on a side. Naturally, you would only be able to see the top surface. If your eyes were placed a corresponding distance of 59 inches (1 1/2 meters), you would again be able to see the three surfaces. The brain cannot accept such a dimensional exaggeration . It would assume that the cube was small. If, for example, landscape photographs are made with the distance between the lenses extremely large (about 3 feet, 1 meter), the resulting image would appear to the viewer as if it were for a model train. This effect can be used to produce very convincing trick photographs. For realistic photographs, the distance between the lenses should be as close as possible to the distance between the eyes.
Let's get back to the 3D photography setup. To synchronize the shutter action, I have modified the cameras by breaking the current supply lines and bringing the ends of the wires to the outside. A common pushbutton switch and a timer trips both shutters at the same time. Before each picture is taken, set both cameras and press both shutter releases. The advantage of using the Minox cameras lies in their electromagnetically driven shutter. The shutter does not trip and the film is not exposed until the current is connected by the common switch . If it happens that the two pictures are differently exposed, an adjustment can be made to the DIN/ASA exposure setting to compensate. Some remaining problems involve the two,separate focus and f-stop settings as well as the offset between the cameras. Because of the offset,this arrangement cannot be used satisfactorily to photograph obects that are nearer to the cameras than about 6 feet (2 meters). The best solution is, naturally, a real stereo camera. They are not widely available and, for the most part, are too expensive. These cameras employ a single film on which both images are simultaneously exposed. The lenses are mechanically coupled so that every adjustment affects both of them. Unfortunately, these cameras also present minor problems. The picture format on most models does not conform to the standard (24 x 36 mm). This standard is based on the optimum distance between the lenses of 2 1/2 inches (6.5 cm). The spacing of the images on the film is too far apart for two pictures next to one another. You waste a lot of film. The spacing is inadequate for three images in the standard format. The image size is reduced to a non-standard, 24 x 30 mm format. It can happen that the development of the film will be extremely disappointing. Your beautiful pictures may be split down the middle ( I speak from experience ). The selection of commercially available slide frames for the non-standard format is not exactly large. I use frames manufactured by BONUM. These frames can accomodate the lateral displacement. However, they cost nearly twice as much as the standard frames.
One more tip for 3D photos: Be sure to provide a sufficient depth of field. The observer must be able to focus on all points within the image.
How can we view 3D Photographs?
As we discussed earlier, two pictures are taken from viewpoints separated by a distance approximately the same as the distance between the eyes. If the left eye receives the left image and the right eye receives the right image, the illusion will be complete. Our brain will be able to process the information into a realistic, spatial image. Some objects appear to be three feet (1 meter) behind the picture plane, others jut forward, appearing to loom in front of the picture plane. How can we insure that the images get to the correct eyes? Truly avid 3D fans can do this without any assistance. They can view two pictures which are next to one another in a way which causes them to meld into a 3D image. This requires some practice. A better way involves using slides. You can use two, inexpensive, commercially available slide viewers glued together, about 2 1/2 inches (6.5 cm) apart. This produces a suitable 3D viewer. Extreme care must be taken when placing the slides in their frames. There can be no appreciable vertical displacement between the slides. The slides must be squarely aligned. The lateral displacement of the slides affects the apparent depth plane of the 3D image. This displacement can be used to determine whether the objects appear to thrust out of the plane or to be behind the plane, viewed as if through an imaginary window. The farther apart the slides are placed, the further behind the picture plane the objects appear to be. It is already evident that framing the slides correctly is crucial to the 3D experience. I use a small light table with a sheet of translucent, 1 mm quadrille (graph paper) stretched on it. Positions for the slide frames are drawn on it. This is sufficient for the necessary degree of accuracy. I use QUICKPOINT glue dots.
Over the long haul, the simple 3D viewer may wane in appeal because it is not possible to present you masterpieces to more than one person at a time. The answer to this problem is also the most satisfying viewing mode: projection.
However, this requires additional preparation and, more importantly, higher cost. You must use two slide projectors. Okay, two projectors. How do we insure that the left eye receives the left slide image and the right eye, the right image? There are two different procedures. The most common is the, so called, red-green process. Color filters are placed in front of the projectors, one red and one green. The projectors are positioned so that the two projected images are effectively superimposed. If the viewer wears glasses with a red filter on one side and a green filter on the other, the "green picture" is masked out by the green filter and the "red picture" is masked out by the red filter. This insures that each eye receives the corresponding image. Using colors this way unfortunately limits the procedure to black and white pictures, because the colors red and green are used to separate the left and right images. Do not confuse this process with the one used some time ago on television that requires different 3D glasses. This is an entirely different technique which you can experiment with yourself if you have a video camera.
The best quality 3D projection procedure employs polarization filters which can be purchased at a photography supply shop. Replace the color filters on the projectors and the glasses with the polarizing filters. The direction of polarization for one image is set at 90 degrees to the direction for the other image. Provided that the directon of polarization for the projectors corresponds to that of the glasses, the viewer perceives a clean separation of the right and left images with no loss of color. The last remaining problem is the screen. The common, commercially available screen is unsuitable because it diffuses and diminishes the polarization of the projected images. Some manufacturers offer a professional 3D projection screen at a steep price. By experimentation, I have found that a smooth wood surface, spray painted with "Eckhard-Silver" and several coats of buffed lacquer, provides acceptable results at a fraction of the cost of the professional screen. How does the polarization work? The simplest way to comprehend it is: A polarizing filter works like a sieve with elongated openings. These slits will only permit light waves with the same direction to pass through. Light polarized at 90 degrees to the direction of the filter cannot get through but it can get through a filter with slits at the same 90 degree angle.
Printed color images, like those in my 3D Gallery are done with the red-blue process. It is not of the highest quality but it is very practical. Scan each image separately into an image manipulation program and convert them to gray scale and then back to RGB images. The end result is two black and white pictures with color separations for each of the basic colors (red, green and blue). To effect the 3D image, recombine the RGB elements using the red portion of the left image and the green and blue portions of the right image. The resulting picture can be viewed with red and blue glasses (red-left). The program that I use is COREL-PhotoPaint, however, there are many other programs with these capabilities.
Certainly, there is a plethora of other techniques for viewing 3D pictures. I will leave it at this. You will see that it is not so terribly difficult to create your own 3D pictures. Be careful! It can become an obsession.
This text was translated from German into English by John Clark from Eaton, Ohio.
Thank you John, it was very kind of you.