Distortion Correcting Printing Process
This article first appeared in
The 70mm Newsletter
Issue 42 - December 1995
The diagram shows why a distortion correcting
process, one of the features of the Todd-AO system, was felt to be
required. This printing method will counter balance the distortion
inherent in projection on a deeply curved screen from steep projection
angles. 1A, 1B, 2A and 2B indicate portions of the image striking the
four corners of the screen. The lines at bottom must travel further and
will therefore spread more than the lines at the top, causing the familiar keystone distortion. Observing line 3 will show that this
distortion is even further compounded by the fact that portions of the
image striking the center of the screen will always hit lover than
portions striking the edge. By means of simple test patterns, an
accompanying diagram show how this distortion looks on the screen and
how the Todd-AO people plan to correct it.
The distortion-correcting printing process was
initially meant to be an integrated part of the Todd-AO system. It was
originally designed to eliminate three types of distortion, keystone
distortion, distortion resulting from using a deeply- curved screen,
plus correcting the distortion arising from use of the extremely
wide-angle lenses, in both photography and projection.
Mark III Printer Principle
in the Todd-AO Mark III Printer
Who is Grant Lobban?
The drawing shows how straight horizontal and vertical
lines are distorted by keystone and screen curvature.
Two classes of print were to be produced, one to cover
projection angles from 10 to 15 degrees and another for even higher
angles. In theory, it was an workable idea, but each type of print was
required to cover a range of circumstances. For a perfect system, it
would really need to be infinitely variable, producing a print exactly matching each individual theatre. Also, if it was intended to
counter-balance the effect of the wide-angle lenses, this part of the
correction process would have to be made "switch able", in or
out, as the "bug- eyed" lenses were normally only used
occasionally throughout the early Todd-AO productions.
Distorting a print in processing so that vertical and
horizontal lines would take the shape shown in the film strip at center
could counter balance this distortion and provide straight lines on the
screen shown at bottom even though that screen be curved. These diagrams
are not meant to be an exact description of the Todd-AO corrective
printing process. Their purpose is to explain in simple language how it
works. In addition to the two types of distortion mentioned above, the
Todd-AO method also corrects a print for distortion caused by the use of
extreme wide-angle lenses in photography.
The reason for developing this special printing method
was largely financial. After his experiences with the high cost of
installing Cinerama, part of Michael Todd's brief to the American Optical
Company was to avoid the need for major structural alterations and loss
of seating, by using a theatres normal projection room, even if this was
in its traditional position high up at back of the balcony.
The American Optical Company continued to pursue the idea, right up to
the opening of "Oklahoma!". However, the use of an unsuitable print at
the premiere did spoil the screen image, judging by these extracts from
contemporary reviews from the New York papers.
In fact, further development was abandoned and future Todd-AO installations
followed the same pattern of having a new lower projection room constructed,
if the rake at the chosen theatre was too steep.
It must be remembered that, at the beginning, Todd-AO was regarded as just
another process, one among the many system which was constantly being
announced. It was the commercial success of
up by the even greater hits,
"Around the World in 80
"South Pacific" which lead to Todd-AO's acceptance and 70mm
projection becoming the cinemas premiere presentation process.
TRIBUNE, William K. Zinsser:
"......Fortunately, the movie
is true to the original.....and Todd-AO takes the moviegoer out of his
cramped theatre seat and into rolling farmland......The effect is not
completely three-dimensional, but there is a good illusion of depth.....The
figures on the screen are tremendous, and the close-ups are so sharp in
detail that the texture of skin and clothing, the sheen of a girls hair, are
almost real to touch. The colours are vivid, and the movie has many striking
landscapes......But Todd-AO is best in close-ups."
WORLD TELEGRAM, Altan Cook:
""Oklahoma!" seems likely to
become as much a box office milestone in movies as it was in stage annals.
The glamour of the title and music should keep the picture in the newly
refurbished Rivoli for months......News about Todd-AO is less
cheery......Level settings run downhill toward the edge of the screen, an
effect that is particularly disconcerting in dance numbers."
This mixed reaction from film critics, together with the general
disappointment with the screen image from the first Todd-AO print shown to
the public, prompted this report, which appeared in the International
Todd-AO corrective printing process.
"What puzzled some observers was that the picture shown at the
Theatre had a great many white scratches and distorted horizontal lines.
Another print shown privately on the West Coast sometimes earlier was
unscratched an nobody had reported distortion. The difference between the
New York showing and the earlier test in Hollywood is attributed to the
failure of the American Optical Company to produce a good
distortion-corrected print in time for the opening. The AO factory in
Southbridge, Mass., was badly damaged by flood in August and could not bring
the final model of its newly designed printer into use quickly enough. The
opening date at the Rivoli could not be postponed. The print used for the
premiere, according to Todd-AO president Henry Woodbridge, was a trial
product of a crude early version of the printer. It was never meant for
exhibition to the public.
Since the opening, projection methods at the
have been changed.
Instead of using the theatres regular projection room in the rear of the
theatre, which has a very steep angle of throw, an additional booth, built
in front of the mezzanine, was put into use. This booth has little or no
projection angle, so the corrective print was not required. A contact print,
similar to the one shown earlier in Hollywood, was used, and a much better
picture resulted. The
process, developed by Dr O`Brien of the American Optical Company, has
not really been tested publicly. This will have to wait until the Company
delivers a perfected product"