Scott Marshall, publisher of Widegauge Film and Video Monthly was kind enough to provide the following transcription of a document published by Cinerama, Inc. in 1963. The document had been posted in the newsgroup REC.ARTS.MOVIES.TECH by John Schmuhl, and we gratefully acknowledge his sharing this with the world.
Single Lens Cinerama was a pitifully poor replacement for the three strip original. It did make it much more convenient to exhibit story telling films, produced conventionally, in a giant curved screen process but the impact was lost and most of the films were rather forgettable. But Cinerama, Inc. had been sold to Pacific Theatres, and single lens Cinerama exhibition was far less costly to operate than the real thing. The benefits outlined in this document are largely vapor. Inasmuch as I can pretty well do whatever I want on this web site I am going to interject comments and corrections throughout this text in order to clarify information for those people that may not have seen both, or either, of the Cinerama formats. My comments will appear in yellow text, to match the color of my journalism.
CINERAMA SINGLE LENS PROCESS
Cinerama has been seen and appreciated by millions. One naturally wonders what could possibly be done to improve a motion-picture process that has become part of the American heritage. It is true that a few technical defects were apparent to the observer who momentarily lost touch with the drama of the presentation and became aware of technical problems. These problems consisted essentially of the difficulty of matching the three separate images projected on the gigantic cylindrical screen. It was difficult to match the edges of the images so that there was no relative movement or "jitter" observable, and it was difficult to match the illumination from the three projectors so that there was uniform brightness across the picture area. Sometimes there was also a slight problem connected with the inability of the three lens Cinerama camera to relate objects appearing near the border between pictures to a common point. This resulted in the projection of double images of some objects.
The problem with interpanel "jitters" was often mentioned in the early days of the three strip system. By the time that the MGM / Cinerama co-productions were released, there was virtually rock solid stability between the panels. Thirty year old Cinerama three strip prints currently being run in Bradford, UK and Dayton, OH attest to that fact.
The Cinerama single lens process was devised in order to make possible a motion-picture presentation equivalent in all respects to the quality of the existing Cinerama presentation, but without its acknowledged technical defects. The process is basically a single lens process--that is, the camera has only one lens and the theatre requires in principle only a single projector, although for convenience two projectors are provided for changeover. Quality of both sound and picture is maintained through use of a wide 70 mm release print. This is equivalent in picture area to the three separate images taken with the three lens Cinerama camera. The print has directly recorded six individual magnetic sound tracks which are essentially equivalent to the seven tracks past employed.
The above paragraph could have been summed up by saying that Cinerama now was standard 70mm, but that would make it seem less glamorous. It is interesting to note that the author states that the six track sound is essentially the same as Cinerama's seven track and yet he says the 70mm picture area is equivalent to the three separate images. In fact the 70mm frame is only about 52% of the area of the three strip version.
The new Cinerama process employs a special optical printer and a special projection lens in order to present a picture on the standard Cinerama screen equivalent in all respects to the old Cinerama presentations, but without the slight technical flaws alluded to. In addition, the process is more flexible because the single-lens 65 mm camera used for taking the negative may be fitted with any one of a large range of focal length lenses. The new process offers the imaginative motion-picture director a more versatile tool than he had available in the old three-lens Cinerama camera which had, after all, only one focal length lens available. The problem that had to be solved in the creation of the new Cinerama process was that of projecting a picture taken with a standard lens, with or without an anamorphic or "squeeze" attachment, onto the deeply curved Cinerama screen without grotesquely distorting the picture or losing a large portion of the image spilled over the top and bottom center of the screen.
The Cinerama screen as seen by the projection lens looks like a huge butterfly with straight sides and deeply curved top and bottom lines narrowed to a waist at the center which in some theatres appears to be less than two-thirds the height of the sides of the screen. Obviously, rectangular image projected on this apparently butterfly shaped screen would largely spill-over the center top and bottom edges of the screen. The screen does not actually have a butterfly shape of course, for it is a section of a cylinder of equal height at all points. It merely appears that way because the center of the screen is about twenty-four feet further from the projection lens than are the extreme edges.
A special Cinerama projection lens was designed with a large amount of so-called "pin cushion" distortion such that the shape of the projected rectangular image approximates the projected shape of the screen. The amount of pin-cushion distortion provided is proportionate to the focal length of the projection lens required for any particular theatre. Thus, the longer houses or those with smaller screens, require longer focal length lenses with less pin-cushion distortion. By thus approximating the shape of the projected image to the shape of the screen, very little spill-over and loss of picture area occurs. However, this results in an accompanying difficulty in that the images of objects near the center of the screen are reduced in size in proportion to the amount of pin-cushion distortion. Consequently a special lens and a special optical printer have been designed which introduce a compensating degree of enlargement in the center images when the release prints are printed from the negative. This is done by introducing what is known as "barrel" distortion in the printer lens. Since the barrel distortion of the printer lens and the pin-cushion distortion of the projection lens compensate each other, the resulting projected picture appears normal because the size of the images at the center and at the edges of the screen is correct.
In addition to compensating for the apparent butterfly shape of the screen, the special Cinerama optical system is responsible for another function. The curved Cinerama screen distorts the width of the images projected onto it from the flat film plane of a single lens projector in varying degrees. This is because an element of image width projected onto the deeply curved sides of the screen is spread out over a wider area than a similar element of the image projected head-on to the center of the screen. Consequently a figure projected near the edge of the screen appears to be much stouter than when it is projected onto the center of the screen, where it is rendered realistically. It is therefore, necessary to compensate for this optically before projection. This is done in the special printer optics, in addition to introducing barrel distortion as previously described. In effect, the printer optics imparts an increasing amount of "squeeze" to the image as the edge of the screen is approached. This has been called a "non- linear squeeze". A result of this correction is that images at the center of the screen are printed normally, but images near the edges of the screen are printed so that they look much thinner but upon projection are seen correctly because of their apparent increase in width as seen on the screen.
Optical corrections in making the print and in the projection lenses still did not properly fill the screens in most Cinerama theatres. A special projector aperture plate with a "butterfly" or "bow-tie" shape was used to crop the center of the projected image to prevent it from spilling onto the ceiling and floor. In some theatres there was not adequate pin-cushion effect to make the sides of the image expand to fully cover the height of the screen sides and maskings were used that had a curvature in reverse to the butterfly shape. These maskings created a screen that was larger in the center than on the sides and reduced the impression that the screen was curved at all.
In order to utilize negatives taken with ordinary spherical lenses as well as those taken with "squeeze" lenses such as in the Panavision process, the special Cinerama printer optics is provided alternatively with an additional "unsqueeze" lens whose linear horizontal magnification is superimposed onto the non-linear squeeze just described. Thus a print is obtained which is directly projectable without the use of an anamorphic projection lens such as would ordinarily be required to project Panavision prints. Because it is forseen that a only a few pictures will be printed from original Panavision negatives, the Cinerama printer equipped to print from Panavision negatives is referred to as an interim printer. Subsequent Cinerama pictures will be photographed with special lenses which do not require unsqueezing. Only the non-linear squeeze will be introduced in the printer optics.
The Panavision process referred to is actually Ultra Panavision 70. The 1.25x squeeze used in Ultra Panavision was removed as per the description above.
Because it is not convenient to introduce the entire amount of barrel distortion into the printer lens that is required to compensate for the pin-cushion distortion of the projection lens, it is desirable and convenient to accept a small amount of barrel distortion in the spherical taking lenses which will be used for shooting Cinerama pictures. The dramatic effect of the Cinerama process is in many cases due to the use of very short focal length taking lenses, which tend to be naturally afflicted with a certain amount of barrel distortion. This tendency is taken advantage of to secure the additional compensating barrel distortion referred to.
The above two paragraphs state clearly that the anamorphic photography used in Ultra Panavision 70 was a temporary expedient and that special non-anamorphic lenses would be used on future productions. In fact the third single film presentation, THE GREATEST STORY EVER TOLD, was also photographed in Ultra Panavision 70, (though it was originally planned to be a genuine three strip project), and no special lenses were used. The second single film presentation, CIRCUS WORLD was photographed in standard Technirama, (aka Super Technirama 70), and, again, no wide angle lenses were available for that process. Not until GRAND PRIX and, to a lesser extent, 2001: A SPACE ODYSSEY were true wide angle optics, with the barrel distortion mentioned, used. Apparently the disdain of directors and photographers for such wide angle optics on flat screens prevented their use in films slated for initial release as single film Cinerama. Despite what might have been good intentions on the part of the Cinerama people, the majority of single film productions were done in Ultra Panavision 70. From information currently available, the special "rectified" Cinerama print may have been used only on the Ultra Panavision 70 prints and not on films made in Technirama, Super Panavision, or Todd-AO.
No motion-picture projection appears equally good to all observers in the theatre. It is characteristic that there is only one position in the house from which the viewer receives an impression of naturally perfect perspective or at least the best rendition of which the system is capable. In other seating locations the viewer is exposed to a more or less distorted representation of what the camera lens originally saw. This is true in ordinary single-lens motion-picture projection onto a flat screen if the observer has a seat at the front or side of the house. It is expected however, that as a result of the many optical and perspective compensations that have been built into the optics of the new Cinerama process, that more people than ever, over a larger range of seats, will enjoy a presentation more favorable than that given by the old Cinerama process. In addition to this, the absence of the mosaic effect of the old Cinerama process contributes appreciably to the unimpaired enjoyment of Cinerama presentations.
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