SHOWSCAN - How It Works
My knowledge of and interest in SHOWSCAN actually began in the early to mid '70's when was spending a good deal of time with Doug Trumbull. I had made a documentary on Doug's feature film, "Silent Running", and we had become friends. At the time, Doug had a company called Future General, which was a subsidiary of Paramount Pictures and a major force in modern special effects techniques. While Doug and his then protege, John Dykstra were doing some innovative work with multi-pass, in-camera compositing techniques (early Motion Control), Doug was also experimenting with the idea which ultimately became SHOWSCAN.
Doug, John and I had a common interest in scuba diving and I spent some time with them testing a VISTAVISION underwater housing off Catalina Island. On one of those trips Doug told me of his ideas for SHOWSCAN and showed me his early prototype 35mm system. The basic idea, like many good ideas, was deceptively simple. If you increase the "system speed" of a recording process, you increase the "fidelity" or "definition" of that process. That is the heart of SHOWSCAN. Doug ultimately took it a step further by doing it in the 65/70mm format, but it will work in 8mm, 16mm or 35mm; it works in audio recording and even in video; although it is a little more complicated to make video run faster. However, the basic idea is that moving the tape or film faster will increase the bandwidth of the process and thereby allow you to increase the definition or fidelity proportionately. By speeding up the process you are just sampling and delivering more information in the same amount of time. In addition, the beauty of doing it on film is that you don't have to invent new hardware. The standards are all the same as normal motion pictures of the same format. You just have to make existing hardware go faster.
There are, of course, practical limits to how fast you can go, so Doug did many tests in 35mm. They shot a control scene at the normal 24 frames per second and then a series of identical scenes at ever increasing frame rates. They then brought in test audiences and showed these scenes while measuring audience response in several objective parameters, i.e., Galvanic skin response, heart rate, brain waves, etc. What they found was that audiences responded more actively to scenes as the frame rate increased. However, this increase in response seemed to reach a plateau at about 72 frames per second. So Doug decided to standardize at 60 fps because of its compatibility with the 60-cycle AC electrical standard and because of the 30 frame, 60 field NTSC television standard.
Doug could never get his FUTURE GENERAL'S parent company, Paramount, to back this new idea in any significant way. Paramount ultimately passed on the idea completely and Doug was able to form a new company, which ultimately became Showscan Film Corporation. By 1984, they had produced two spectacular demonstration films, NEW MAGIC and BIG BALL.
As with any technology, SHOWSCAN has advantages and disadvantages. On the screen, SHOWSCAN is all advantages. However, putting it "in the can" presents a few challenges to the Cinematographer. On the positive side, the higher frame rate gives a perception of sharper, more realistic images, because they are in fact sharper due to the faster shutter speed of 1/125 sec. This is a by-product of running a 180-degree shutter at 60 frames per second. Images also appear less grainy. Since the viewer is seeing 2.5 times as many frames per second. That, combined with image retention in human vision prevents the viewer from loosing the image of one frame before receiving another 1.5 frames, each with a different grain pattern. The result is a masking of grain, so that it seems to have gone away. Because Showscan is a flat (non-anamorphic) wide screen system, it uses spherical lenses, which present fewer problems than anamorphics. Finally, because of the increased frame rate and shorter exposure time, lateral (cross screen) motion or panning rates are greatly increased in SHOWSCAN. In fact, a look at the fourth edition of the AMERICAN CINEMATOGRAPHER MANUAL 35mm panning speed recommendations gives a clue to the SHOWSCAN advantage in this area. The text that accompanies the panning speed charts describes the physiological reasons for the "skipping" or "strobing" which results from panning too fast or allowing a too rapid motion across the screen. In addition, the last paragraph of the text mentions how, "early wide screen productions shot in 65/70mm, were shot at 30 frames per second, to smooth panning shots and cross-screen action". It goes on to say that this adverse skipping effect is related to screen brightness, lens focal length, frame rate and shutter opening. What it doesn't mention is that the projected image size, relative to the viewer, is also very important. This was another reason why the 65/70mm format films had more of a "strobing" problem, because they were projected bigger, wider! The 35mm panning speed recommendations were based on a standard screen size. When they exceeded that with larger format, wide screen processes, a higher frame rate solved the problem. Therefore, it is easy to see that at 60 frames per second, SHOWSCAN can handle lateral motion very well.
On the downside of the equation, the increased frame-rate takes light away from the negative. One and one quarter stops to be exact. Also in 65mm there is the approximate doubling of the focal length of the lenses, with the attendant shorter depth of field, for any given shot. This, coupled with the exposure loss can be troublesome, since you end up working at longer focal lengths with larger apertures than you might in 35mm. However, with the new, fast, fine-grained films you do get a little bit back. Finally, there is the rate at which SHOWSCAN uses film. In 65mm there are 12.8 frames per foot. At SHOWSCAN speeds, you're using 4.68 feet per second or 281 feet per minute.