Movie projector | Wikipedia audio article

Movie projector | Wikipedia audio article


A movie projector is an opto-mechanical device
for displaying motion picture film by projecting it onto a screen. Most of the optical and
mechanical elements, except for the illumination and sound devices, are present in movie cameras.==History==The first movie projector was the Zoopraxiscope,
invented by British photographer Eadweard Muybridge in 1879. The zoopraxiscope projected
images from rotating glass disks in rapid succession to give the impression of motion.
The stop-motion images were initially painted onto the glass, as silhouettes. A second series
of discs, made in 1892–94, used outline drawings printed onto the discs photographically,
then colored by hand.Kazimierz Prószyński (4 April 1875 – 13 March 1945), born in
Warsaw, Poland, was a Polish inventor active in the field of cinema. He patented his first
film camera, called Pleograph (in Polish spelling: Pleograf), before the Lumière brothers, and
later went on to improve the cinema projector for the Gaumont company, as well as invent
the widely used hand-held Aeroscope camera. A more sophisticated movie projector was invented
by Frenchman Louis Le Prince while working in Leeds. In 1888 Le Prince took out a patent
for a 16-lens device that combined a motion picture camera with a projector. In 1888,
he used an updated version of his camera to film the first ever motion picture, the Roundhay
Garden Scene. The pictures were privately exhibited in Hunslet.
The Lumière brothers invented the first successful movie projector. They made their first film,
Sortie de l’usine Lumière de Lyon, in 1894, which was publicly screened at L’Eden, La
Ciotat a year later. The first commercial, public screening of cinematographic films
happened in Paris on 28 December 1895. The cinematograph was also exhibited at the Paris
Exhibition of 1900. At the Exhibition, films made by the Lumière Brothers were projected
onto a large screen measuring 16 by 21 meters (approximately 52.5 x 69 feet).===Decline of film projectors===
In 1999, digital cinema projectors were being tried out in some movie theatres. These early
projectors played the movie stored on a computer, and sent to the projector electronically.
Due to their relatively low resolution (usually only 2K) compared to later digital cinema
systems, the images at the time had visible pixels. By 2006, the advent of much higher
4K resolution digital projection reduced pixel visibility. The systems became more compact
over time. By 2009, movie theatres started replacing film projectors with digital projectors.
In 2013, it was estimated that 92% of movie theatres in the United States had converted
to digital, with 8% still playing film. In 2015, numerous popular filmmakers—including
Quentin Tarantino and Christopher Nolan—lobbied large studios to commit to purchase a minimum
amount of 35 mm film from Kodak. The decision ensured that Kodak’s 35mm film production
would continue for several years.Although usually more expensive than film projectors,
high-resolution digital projectors offer many advantages over traditional film units. For
example, digital projectors contain no moving parts except fans, can be operated remotely,
are relatively compact and have no film to break, scratch or change reels of. They also
allow for much easier, less expensive, and more reliable storage and distribution of
content. All-electronic distribution eliminates all physical media shipments. There is also
the ability to display live broadcasts in theaters equipped to do so.==Physiology==
In 1912 Max Wertheimer discovered beta movement and the phi phenomenon. In each the brain
constitutes an experience of apparent movement when presented with a sequence of near-identical
still images. This theory is said to account for the illusion of motion which results when
a series of film images is displayed in quick succession, rather than the perception of
the individual frames in the series. Persistence of vision should be compared with
the related phenomena of beta movement and phi movement. A critical part of understanding
these visual perception phenomena is that the eye is not a camera, i.e.: there is no
frame rate for the human eye or brain. Instead, the eye/brain system has a combination of
motion detectors, detail detectors and pattern detectors, the outputs of all of which are
combined to create the visual experience. The frequency at which flicker becomes invisible
is called the flicker fusion threshold, and is dependent on the level of illumination.
Generally, the frame rate of 16 frames per second (frame/s) is regarded as the lowest
frequency at which continuous motion is perceived by humans. This threshold varies across different
species; a higher proportion of rod cells in the retina will create a higher threshold
level. Because the eye and brain have no fixed capture rate, this is an elastic limit, so
different viewers can be more or less sensitive in perceiving frame rates.
It is possible to view the black space between frames and the passing of the shutter by rapidly
blinking ones eyes at a certain rate. If done fast enough, the viewer will be able to randomly
“trap” the image between frames, or during shutter motion. This will not work with (now
obsolete) cathode ray tube displays due to the persistence of the phosphors nor with
LCD or DLP light projectors because they refresh the image instantly with no blackout intervals
as with film projectors. Silent films usually were not projected at
constant speeds, but rather were varied throughout the show at the discretion of the projectionist,
often with some notes provided by the distributor. This was more a function of hand-cranked projectors
than the silence. When the electric motor supplanted hand cranking in both movie cameras
and projectors, a more uniform frame rate became possible. Speeds ranged from about
18 frame/s on up – sometimes even faster than modern sound film speed (24 frame/s).
16 frame/s – though sometimes used as a camera shooting speed – was inadvisable
for projection, due to the risk of the nitrate-base prints catching fire in the projector. (A
dramatic rendition of a nitrate print fire and its potentially devastating effects is
contained in Cinema Paradiso (1988), which revolves around the goings-on of a projectionist.)
Nitrate film stock was replaced by cellulose triacetate in 1948.
The birth of sound film created a need for a steady playback rate to prevent dialog and
music from changing pitch and distracting the audience. Virtually all film projectors
in commercial movie theaters project at a constant speed of 24 frame/s. This speed was
chosen for both financial and technical reasons. A higher frame rate produces a better looking
picture, but costs more as film stock is consumed faster. When Warner Bros. and Western Electric
were trying to find the ideal compromise projection speed for the new sound pictures, Western
Electric went to the Warner Theater in Los Angeles, and noted the average speed at which
films were projected there. They set that as the sound speed at which a satisfactory
reproduction and amplification of sound could be conducted.
There are some specialist formats (e.g. Showscan and Maxivision) which project at higher rates—60
frames/sec for Showscan and 48 for Maxivision. The Hobbit was shot at 48 frames/sec and projected
at the higher frame rate at specially equipped theaters. Each frame of regular 24 fps movies
are shown twice or more in a process called “double-shuttering” to reduce flicker.==Principles of operation=====
Projection elements===As in a slide projector there are essential
optical elements:====Light source====
Incandescent lighting and even limelight were the first light sources used in film projection.
In the early 1900s up until the late 1960s, carbon arc lamps were the source of light
in almost all theaters in the world. The Xenon arc lamp was introduced in Germany
in 1957 and in the US in 1963. After film platters became commonplace in the 1970s,
Xenon lamps became the most common light source, as they could stay lit for extended periods
of time, whereas a carbon rod used for a carbon arc could last for an hour at the most.
Most lamp houses in a professional theatrical setting produce sufficient heat to burn the
film should the film remain stationary for more than a fraction of a second. Because
of this,absolute care must be taken in inspecting a film so that it should not break in the
gate and be damaged, particularly if it is flammable cellulose nitrate film stock.====Reflector and condenser lens====
A curved reflector redirects light that would otherwise be wasted toward the condensing
lens. A positive curvature lens concentrates the
reflected and direct light toward the film gate.====Douser====
(Also spelled dowser.) A metal or asbestos blade which cuts off light
before it can get to the film. The douser is usually part of the lamphouse, and may
be manually or automatically operated. Some projectors have a second, electrically controlled
douser that is used for changeovers (sometimes called a “changeover douser” or “changeover
shutter”). Some projectors have a third, mechanically controlled douser that automatically closes
when the projector slows down (called a “fire shutter” or “fire douser”), to protect the
film if the projector stops while the first douser is still open. Dousers protect the
film when the lamp is on but the film is not moving, preventing the film from melting from
prolonged exposure to the direct heat of the lamp. It also prevents the lens from scarring
or cracking from excessive heat.====Film gate and frame advance====
If a roll of film is continuously passed between the light source and the lens of the projector,
only a continuous blurred series of images sliding from one edge to the other would be
visible on the screen. In order to see an apparently moving clear picture, the moving
film must be stopped and held still briefly while the shutter opens and closes.
The gate is where the film is held still prior to the opening of the shutter. This is the
case for both filming and projecting movies. A single image of the series of images comprising
the movie is positioned and held flat within the gate.
The gate also provides a slight amount of friction so that the film does not advance
or retreat except when driven to advance the film to the next image. The intermittent mechanism
advances the film within the gate to the next frame while the shutter is closed.
Registration pins prevent the film from advancing while the shutter is open. In most cases the
registration of the frame can be manually adjusted by the projectionist, and more sophisticated
projectors can maintain registration automatically.====Shutter====
It is the gate and shutter that gives the illusion of one full frame being replaced
exactly on top of another full frame. The gate holds the film still while the shutter
is open. A rotating petal or gated cylindrical shutter interrupts the emitted light during
the time the film is advanced to the next frame. The viewer does not see the transition,
thus tricking the brain into believing a moving image is on screen. Modern shutters are designed
with a flicker-rate of two times (48 Hz) or even sometimes three times (72 Hz) the frame
rate of the film, so as to reduce the perception of screen flickering. (See Frame rate and
Flicker fusion threshold.) Higher rate shutters are less light efficient, requiring more powerful
light sources for the same light on screen.====Imaging lens and aperture plate====A projection objective with multiple optical
elements directs the image of the film to a viewing screen. Projector lenses differ
in aperture and focal length to suit different needs. Different lenses are used for different
aspect ratios. One way that aspect ratios are set is with
the appropriate aperture plate, a piece of metal with a precisely cut rectangular hole
in the middle of equivalent aspect ratio. The aperture plate is placed just behind the
gate, and masks off any light from hitting the image outside of the area intended to
be shown. All films, even those in the standard Academy ratio, have extra image on the frame
that is meant to be masked off in the projection. Using an aperture plate to accomplish a wider
aspect ratio is inherently wasteful of film, as a portion of the standard frame is unused.
One solution that presents itself at certain aspect ratios is the “2-perf” pulldown, where
the film is advanced less than one full frame in order to reduce the unexposed area between
frames. This method requires a special intermittent mechanism in all film handling equipment throughout
the production process, from the camera to the projector. This is costly, and prohibitively
so for some theaters. The anamorphic format uses special optics to squeeze a high aspect
ratio image onto a standard Academy frame thus eliminating the need to change the costly
precision moving parts of the intermittent mechanisms. A special anamorphic lens is used
on the camera to compress the image, and a corresponding lens on the projector to expand
the image back to the intended aspect ratio.====Viewing screen====In most cases this is a reflective surface
which may be either aluminized (for high contrast in moderate ambient light) or a white surface
with small glass beads (for high brilliance under dark conditions). A switchable projection
screen can be switched between opaque and clear by a safe voltage under 36V AC and is
viewable from both sides. In a commercial theater, the screen also has millions of very
small, evenly spaced holes in order to allow the passage of sound from the speakers and
subwoofer which often are directly behind it.===Film transport elements=======
Film supply and takeup=========Two-reel system=====
In the two-reel system the projector has two reels–one is the feed reel, which holds
the part of the film that has not been shown, the other is the takeup reel, which winds
the film that has been shown. In a two-reel projector the feed reel has a slight drag
to maintain tension on the film, while the takeup reel is constantly driven with a mechanism
that has mechanical ‘slip,’ to allow the film to be wound under constant tension so the
film is wound in a smooth manner. The film being wound on the takeup reel is
being wound “head in, tails out.” This means that the beginning (or “head”) of the reel
is in the center, where it is inaccessible. As each reel is taken off of the projector,
it must be re-wound onto another empty reel. In a theater setting there is often a separate
machine for rewinding reels. For the 16 mm projectors that were often used in schools
and churches, the projector could be re-configured to rewind films.
The size of the reels can vary based on the projectors, but generally films are divided
and distributed in reels of up to 2,000 feet (610 metres), about 22 minutes at 24 frames/sec).
Some projectors can even accommodate up to 6,000 feet (1,800 metres), which minimizes
the number of changeovers (see below) in a showing. Certain countries also divide their
film reels up differently; Russian films, for example, often come on 1,000-foot (300
m) reels, although it’s likely that most projectionists working with changeovers would combine them
into longer reels of at least 2,000 feet (610 metres), to minimize changeovers and also
give sufficient time for threading and any possibly needed troubleshooting time.
Films are identified as “short subjects,” taking one reel or less of film, “two-reelers,”
requiring two reels of film (such as some of the early Laurel & Hardy, 3 Stooges, and
other comedies), and “features,” which can take any number of reels (although most are
limited to 1½ to 2 hours in length, enabling the theater to have multiple showings throughout
the day and evening, each showing with a feature, commercials, and intermission to allow the
audiences to change). In the “old days” (i.e., ca. 1930–1960), “going to the movies” meant
seeing a short subject (a newsreel, short documentary, a “2-reeler,” etc.), a cartoon,
and the feature. Some theaters would have movie-based commercials for local businesses,
and the state of New Jersey required showing a diagram of the theater showing all of the
exits.=====Changeover=====
Because a single film reel does not contain enough film to show an entire feature, the
film is distributed on multiple reels. To prevent having to interrupt the show when
one reel ends and the next is mounted, two projectors are used in what is known as a
“changeover system,” after the switching mechanism that operates between the end of one reel
on the first projector and the beginning of the next reel on the second projector. The
two-reel system was used almost universally for movie theaters before the advent of the
single-reel system in order to be able to show feature-length films. Although one-reel
long-play systems tend to be more popular with the newer multiplexes, the two-reel system
is still in significant use to this day. The projector operator operates two projectors,
starting the first reel of the show on projector “A.” While this reel is being shown, the projectionist
threads the second reel on projector “B.” As the reel being shown approaches its end,
the projectionist looks for cue marks at the upper-right corner of the picture. Usually
these are dots or circles, although they can also be slashes. Some older films occasionally
used squares or triangles, and sometimes positioned the cues in the middle of the right edge of
the picture. The first cue appears twelve feet (3.7 metres)
before the end of the program on the reel, equivalent to eight seconds at 24 frames/sec.
This cue signals the projectionist to start the motor of the projector containing the
next reel. After another ten and a half feet (3.2 m) of film is shown (seven seconds at
24 frames/sec), the changeover cue should appear, which signals the projectionist to
actually make the changeover. When this second cue appears, the projectionist has one and
a half feet (460 mm), or one second at 24 frame/s, to make the changeover. If it doesn’t
occur within one second, the tail leader of the reel coming to an end will be projected
on the screen. Twelve feet before the “first frame of action,”
Academy leaders have a “START” frame. The projectionist positions the “START” in the
gate of the projector. When the first cue is seen, the motor of the starting projector
is started. Seven seconds later the end of the leader and start of program material on
the new reel should just reach the gate of the projector when the changeover cue is seen.
On some projectors, the operator would be alerted to the time for a change by a bell
that operated when the feed reel rotation exceeded a certain speed (the feed reel rotates
faster as the film is exhausted), or based on the diameter of the remaining film (Premier
Changeover Indicator Pat. No. 411992), although many projectors do not have such an auditory
system. During the initial operation of a changeover,
the two projectors use an interconnected electrical control connected to the changeover button
so that as soon as the button is pressed, the changeover douser on the outgoing projector
is closed in sync with the changeover douser on the incoming projector opening. If done
properly, a changeover should be virtually unnoticeable to an audience. In older theaters,
there may be manually operated, sliding covers in front of the projection booth’s windows.
A changeover with this system is often clearly visible as a wipe on the screen.
Once the changeover has been made, the projectionist unloads the full takeup reel from projector
“A,” moves the now-empty reel (that used to hold the film just unloaded) from the feed
spindle to the takeup spindle, and loads reel #3 of the presentation on projector “A.” When
reel 2 on projector “B” is finished, the changeover switches the live show from projector “B”
back to projector “A,” and so on for the rest of the show.
When the projectionist removes a finished reel from the projector it is “tails out,”
and needs to be rewound before the next show. The projectionist usually uses a separate
rewind machine and a spare empty reel, and rewinds the film so it is “head out,” ready
to project again for the next show. One advantage of this system (at least for
the theatre management) was that if a programme was running a few minutes late for any reason,
the projectionist would simply omit one (or more) reels of film to recover the time.=====Single-reel system=====There are two largely used single-reel systems
(also known as long-play systems) today: the tower system (vertical feed and takeup) and
the platter system (non-rewinding; horizontal feed and takeup).
The tower system largely resembles the two-reel system, except in that the tower itself is
generally a separate piece of equipment used with a slightly modified standard projector.
The feed and takeup reels are held vertically on the axis, except behind the projector,
on oversized spools with 12,000-foot (3,700 m) capacity or about 133 minutes at 24 frame/s.
This large capacity alleviates the need for a changeover on an average-length feature;
all of the reels are spliced together into one giant one. The tower is designed with
four spools, two on each side, each with its own motor. This allows the whole spool to
be immediately rewound after a showing; the extra two spools on the other side allow for
a film to be shown while another is being rewound or even made up directly onto the
tower. Each spool requires its own motor in order to set proper tensioning for the film,
since it has to travel (relatively) much further between the projector film transport and the
spools. As each spool gains or loses film, the tension must be periodically checked and
adjusted so that the film can be transported on and off the spools without either sagging
or snapping. In a platter system the individual 20-minute
reels of film are also spliced together as one large reel, but the film is then wound
onto a horizontal rotating table called a platter. Three or more platters are stacked
together to create a platter system. Most of the platters in a platter system will be
occupied by film prints; whichever platter happens to be empty serves as the “take-up
reel” to receive the film that is playing from another platter.
The way the film is fed from the platter to the projector is not unlike an eight-track
audio cartridge. Film is unwound from the center of the platter through a mechanism
called a payout unit which controls the speed of the platter’s rotation so that it matches
the speed of the film as it is fed to the projector. The film winds through a series
of rollers from the platter stack to the projector, through the projector, through another series
of rollers back to the platter stack, and then onto the platter serving as the take-up
reel. This system makes it possible to project a
film multiple times without needing to rewind it. As the projectionist threads the projector
for each showing, the payout unit is transferred from the empty platter to the full platter
and the film then plays back onto the platter it came from. In the case of a double feature,
each film plays from a full platter onto an empty platter, swapping positions on the platter
stack throughout the day. The advantage of a platter is that the film
need not be rewound after each show, which can save labor. Rewinding risks rubbing the
film against itself, which can cause scratching of the film and smearing of the emulsion which
carries the pictures. The disadvantages of the platter system are that the film can acquire
diagonal scratches on it if proper care is not taken while threading film from platter
to projector, and the film has more opportunity to collect dust and dirt as long lengths of
film are exposed to the air. A clean projection booth kept at the proper humidity is of great
importance, as are cleaning devices that can remove dirt from the film print as it plays.=====Automation and the rise of the multiplex
=====The single reel system can allow for the complete
automation of the projection booth operations, given the proper auxiliary equipment. Since
films are still transported in multiple reels they must be joined together when placed on
the projector reel and taken apart when the film is to be returned to the distributor.
It is the complete automation of projection that has enabled the modern “multiplex” cinema
– a single site typically containing from 8 to 24 theaters with only a few projection
and sound technicians, rather than a platoon of projectionists. The multiplex also offers
a great amount of flexibility to a theater operator, enabling theaters to exhibit the
same popular production in more than one auditorium with staggered starting times. It is also
possible, with the proper equipment installed, to “interlock”, i.e. thread a single length
of film through multiple projectors. This is very useful when dealing with the mass
crowds that an extremely popular film may generate in the first few days of showing,
as it allows for a single print to serve more patrons.====Feed and extraction sprockets====
Smooth wheels with triangular pins called sprockets engage perforations punched into
one or both edges of the film stock. These serve to set the pace of film movement through
the projector and any associated sound playback system.====Film loop====
As with motion picture cameras, the intermittent motion of the gate requires that there be
loops above and below the gate in order to serve as a buffer between the constant speed
enforced by the sprockets above and below the gate and the intermittent motion enforced
at the gate. Some projectors also have a sensitive trip pin above the gate to guard against the
upper loop becoming too big. If the loop hits the pin, it will close the dousers and stop
the motor to prevent an excessively large loop from jamming the projector.====Film gate pressure plate====
A spring-loaded pressure plate functions to align the film in a consistent image plane,
both flat and perpendicular to the optical axis. It also provides sufficient drag to
prevent film motion during the frame display, while still allowing free motion under control
of the intermittent mechanism. The plate also has spring-loaded runners to help hold film
while in place and advance it during motion.====Intermittent mechanism====
The intermittent mechanism can be constructed in different ways. For smaller gauge projectors
(8 mm and 16 mm), a pawl mechanism engages the film’s sprocket hole one side, or holes
on each side. This pawl advances only when the film is to be moved to the next image.
As the pawl retreats for the next cycle it is drawn back and does not engage the film.
This is similar to the claw mechanism in a motion picture camera.
In 35 mm and 70 mm projectors, there usually is a special sprocket immediately underneath
the pressure plate, known as the intermittent sprocket. Unlike all the other sprockets in
the projector, which run continuously, the intermittent sprocket operates in tandem with
the shutter, and only moves while the shutter is blocking the lamp, so that the motion of
the film cannot be seen. It also moves in a discrete amount at a time, equal to the
number of perforations that make up a frame (4 for 35 mm, 5 for 70 mm). The intermittent
movement in these projectors is usually provided by a Geneva drive, also known as the Maltese
Cross mechanism. IMAX projectors use what is known as the rolling
loop method, in which each frame is sucked into the gate by a vacuum, and positioned
by registration pins in the perforations corresponding to that frame.==Types==
Projectors are classified by the size of the film used, i.e. the film format. Typical film
sizes:===8 mm===Long used for home movies before the video
camera, this uses double sprocketed 16 mm film, which is run through the camera, exposing
one side, then removed from the camera, the takeup and feed reels are switched, and the
film run through a second time, exposing the other side. The 16 mm film is then split lengthwise
into two 8 mm pieces that are spliced to make a single projectable film with sprockets holes
on one side.===Super 8===Developed by Kodak, this film stock uses very
small sprocket holes close to the edge that allow more of the film stock to be used for
the images. This increases the quality of the image. The unexposed film is supplied
in the 8 mm width, not split during processing as is the earlier 8 mm. Magnetic stripes could
be added to carry encoded sound to be added after film development. Film could also be
pre-striped for direct sound recording in suitably equipped cameras for later projection.===9.5 mm===Film format introduced by Pathé Frères in
1922 as part of the Pathé Baby amateur film system. It was conceived initially as an inexpensive
format to provide copies of commercially made films to home users. The format uses a single,
central perforation (sprocket hole) between each pair of frames, as opposed to 8 mm film
which has perforations along one edge, and most other film formats which have perforations
on each side of the image. It became very popular in Europe over the
next few decades and is still used by a small number of enthusiasts today. Over 300,000
projectors were produced and sold mainly in France and England, and many commercial features
were available in the format. In the sixties the last projectors of this format were being
produced. The gauge is still alive today. 16mm projectors are converted to 9,5mm and
it is still possible to buy film stock (from the French Color City company).===16 mm===This was a popular format for audio-visual
use in schools and as a high-end home entertainment system before the advent of broadcast television.
In broadcast television news, 16mm film was used before the advent of electronic news-gathering.
The most popular home content were comedic shorts (typically less than 20 minutes in
length in the original release) and bundles of cartoons previously seen in movie theaters.
16 mm enjoys widespread use today as a format for short films, independent features and
music videos, being a relatively economical alternative to 35mm. 16mm film was a popular
format used for the production of TV shows well into the HDTV era.===35 mm===The most common film size for theatrical productions
during the 20th century. In fact, the common 35 mm camera, developed by Leica, was designed
to use this film stock and was originally intended to be used for test shots by movie
directors and cinematographers. 35 mm film is typically run vertically through
the camera and projector. In the mid-1950s the VistaVision system presented wide screen
movies in which the film moved horizontally, allowing much more film to be used for the
image as this avoided the anamorphic reduction of the image to fit the frame width. As this
required specific projectors it was largely unsuccessful as a presentation method while
remaining attractive as filming, intermediate, and source for production printing and as
an intermediate step in special effects to avoid film granularity, although the latter
is now supplanted by digital methods.===70 mm===High-end movie productions were often produced
in this film gauge in the 1950s and 1960s and many very large screen theaters are still
capable of projecting it in the 21st century. It is often referred to as 65/70, as the camera
uses film 65 mm wide, but the projection prints are 70 mm wide. The extra five millimeters
of film accommodated the soundtrack, usually a six track magnetic stripe. The most common
theater installation would use dual gauge 35/70mm projectors.
70 mm film is also used in both the flat and domed IMAX projection system. In IMAX the
film is transported horizontally in the film gate, similar to VistaVision.
Some productions intended for 35 mm anamorphic release were also released using 70 mm film
stock. A 70 mm print made from a 35 mm negative is significantly better in appearance than
an all-35 mm process, and allowed for a release with 6 track magnetic audio.
The advent of 35 mm prints with digital soundtracks in the 1990s largely supplanted the widespread
release of the more expensive 70 mm prints.==Sound==
Regardless of the sound format, any sound represented on the film image itself will
not be the sound for the particular frame it occupies. In the gate of the projector
head, there is no space for a reader, and the film is not travelling smoothly at the
gate position. Consequently, all optical sound formats must be offset from the image because
the sound reader is usually located above (for magnetic readers and most digital optical
readers) or below (for analog optical readers and a few digital optical) the projector head. See the 35 mm film article for more information
on both digital and analog methods.===Analog optical sound===
Optical sound constitutes the recording and reading of amplitude based on the amount of
light that is projected through a soundtrack area on a film using an illuminating light
or laser and a photocell or photodiode. As the photocell picks up the light in varying
intensities, the electricity produced is intensified by an amplifier, which in turn powers a loudspeaker,
where the electrical impulses are turned into air vibrations and thus, sound waves. In 16
mm, this optical soundtrack is a single mono track placed on the right side of the projected
image, and the sound head is 26 frames after the gate. In 35 mm, this can be mono or stereo,
on the left side of the projected image, with the sound head 21 frames after the gate.The
first form of optical sound was represented by horizontal bands of clear (white) and solid
(black) area. The space between solid points represented amplitude and was picked up by
the photo-electric cell on the other side of a steady, thin beam of light being shined
through it. This variable density form of sound was eventually phased out because of
its incompatibility with color stocks. The alternative and ultimately the successor of
variable density has been the variable area track, in which a clear, vertical waveform
against black represents the sound, and the width of the waveform is equivalent to the
amplitude. Variable area does have slightly less frequency response than variable density,
but because of the grain and variable infrared absorption of various film stocks, variable
density has a lower signal-to-noise ratio. Optical stereo is recorded and read through
a bilateral variable area track. Dolby MP matrix encoding is used to add extra channels
beyond the stereo pair. Left, center, right and surround channels are matrix-encoded into
the two optical tracks, and decoded using licensed equipment.
In the 1970s and early 1980s, optical sound Super-8 mm copies were produced mainly for
airline in-flight movies. Even though this technology was soon made obsolete by video
equipment, the majority of small-gauge films used magnetic sound rather than optical sound
for a higher frequency range.===Magnetic sound===
Magnetic sound is no longer used in commercial cinema, but between 1952 and the early 1990s
(when optical digital movie sound rendered it obsolete) it provided the highest fidelity
sound from film because of its wider frequency range and superior signal to noise ratio compared
to optical sound. There are two forms of magnetic sound in conjunction with projection: double-head
and striped. The first form of magnetic sound was the double-head
system, in which the movie projector was interlocked with a dubber playing a 35 mm reel of a full-coat,
or film completely coated with magnetic iron-oxide. This was introduced in 1952 with Cinerama,
holding six tracks of stereophonic sound. Stereophonic releases throughout 1953 also
used an interlocked full-coat for three-channel stereophonic sound.
In interlock, since the sound is on a separate reel, it does not need to be offset from the
image. Today, this system is usually used only for very low-budget or student productions,
or for screening rough cuts of films before the creation of a final married print. Sync
between the two reels is checked with SMPTE leader, also known as countdown leader. If
the two reels are synced, there should be one frame of “beep” sound exactly on the “2”
frame of the countdown – 2 seconds or 48 frames before the picture start.
Striped magnetic film is motion picture film in which ‘stripes’ of magnetic oxide are placed
on the film between the sprocket holes and the edge of the film, and sometimes also between
the sprocket holes and the image. Each of these stripes has one channel of the audio
recorded on it. This technique was first introduced in September, 1953 by Hazard E. Reeves for
Cinemascope. Four tracks are present on the film: Left, Center, Right and Surround. This
35mm four-track magnetic sound format was used from 1954 through 1982 for “roadshow”
screenings of big-budget feature films. 70 mm, which had no optical sound, used the
5 millimeters gained between the 65 mm negative and the final release print to place three
magnetic tracks outside of the perforations on each side of the film for a total of six
tracks. Until the introduction of digital sound, it was fairly common for 35 mm films
to be blown up to 70 mm often just to take advantage of the greater number of sound tracks
and the fidelity of the audio. Although magnetic audio was of excellent quality
it also had significant disadvantages. Magnetic sound prints were expensive, 35mm magnetic
prints cost roughly twice as much as optical sound prints, whilst 70mm prints could cost
up to 15 times as much as 35mm prints. Furthermore, the oxide layer wore out faster than the film
itself, and magnetic tracks were prone to damage and accidental erasure. Because of
the high cost of installing magnetic sound reproduction equipment only a minority of
movie theaters ever installed it and the magnetic soundheads needed considerable maintenance
to keep their performance up to standard. As a consequence the use of the Cinemascope
35mm four-track magnetic sound format decreased significantly during the course of the 1960s
and received stiff competition from the Dolby SVA optical encoding format. However, 70mm
film continued to be used for prestigious “roadshow” screenings until the introduction
of digital sound on 35mm film in the early 1990s removed one of the major justifications
for using this expensive format. On certain stocks of Super 8 and 16 mm an
iron-oxide sound recording strip was added for the direct synchronous recording of sound
which could then be played by projectors with a magnetic sound head. It has since been discontinued
by Kodak on both gauges.===Digital===
Modern theatrical systems use optical representations of digitally encoded multi-channel sound.
An advantage of digital systems is that the offset between the sound and picture heads
can be varied and then set with the digital processors. Digital sound heads are usually
above the gate. All digital sound systems currently in use have the ability to instantly
and gracefully fall back to the analog optical sound system should the digital data be corrupt
or the whole system fail.====Cinema Digital Sound (CDS)====Created by Kodak and ORC (Optical Radiation
Corporation), Cinema Digital Sound was the first attempt to bring multi-channel digital
sound to first-run theaters. CDS was available on both 35 mm and 70 mm films. Film prints
equipped with CDS did not have the conventional analog optical or magnetic soundtracks to
serve as a back-up in case the digital sound was unreadable. Another disadvantage of not
having an analog back-up track is that CDS required extra film prints be made for the
theaters equipped to play CDS. The three formats that followed, Dolby Digital, DTS and SDDS,
can co-exist with each other and the analog optical soundtrack on a single version of
the film print. This means that a film print carrying all three of these formats (and the
analog optical format, usually Dolby SR) can be played in whichever format the theater
is equipped to handle. CDS did not achieve widespread use and ultimately failed. It premiered
with the film Dick Tracy and was used with several other films, such as Days of Thunder
and Terminator 2: Judgement Day.====Sony Dynamic Digital Sound (SDDS)====SDDS runs on the outside of 35 mm film, between
the perforations and the edges, on both edges of the film. It was the first digital system
that could handle up to eight channels of sound. The additional two tracks are for an
extra pair of screen channels (Left Center and Right Center) located between the 3 regular
screen channels (Left, Center and Right). A pair of CCDs located in a unit above the
projector reads the two SDDS tracks. The information is decoded and decompressed before being passed
along to the cinema sound processor. By default, SDDS units use an onboard Sony Cinema Sound
Processor, and when the system is set up in this manner, the theatre’s entire sound system
can be equalized in the digital domain. The audio data in an SDDS track is compressed
in the 20-bit ATRAC2 compression scheme at a ratio of about 4.5:1. SDDS premiered with
the film Last Action Hero. SDDS was the least commercially successful of the three competing
digital sound systems for 35mm film. Sony ceased the sale of SDDS processors in 2001–2002.====Dolby Digital====Dolby Digital data is printed in the spaces
between the perforations on the soundtrack side of the film, 26 frames before the picture.
Release prints with Dolby Digital always include an analog Dolby Stereo soundtrack with Dolby
SR noise reduction, thus these prints are known as Dolby SR-D prints. Dolby Digital
produces 6 discrete channels. In a variant called SR-D EX, the left and right surround
channels can be dematrixed into left, right, and back surround, using a matrix system similar
to Dolby Pro Logic. The audio data in a Dolby Digital track is compressed in the 16-bit
AC-3 compression scheme at a ratio of about 12:1. The images between each perforation
are read by a CCD located either above the projector or in the regular analog sound head
below the film gate, a digital delay within the processor allowing correct lip-sync to
be achieved regardless of the position of the reader relative to the picture gate. The
information is then decoded, decompressed and converted to analog; this can happen either
in a separate Dolby Digital processor that feeds signals to the cinema sound processor,
or digital decoding can be built into the cinema processor.One disadvantage of this
system is if the digital printing is not entirely within the space between the sprocket holes;
if the track was off a bit on either the top or the bottom, the sound track would be unplayable,
and a replacement reel would have to be ordered. In 2006, Dolby discontinued the sale of their
external SR-D processor (the DA20), but included Dolby Digital decoding in their CP500 and
later CP650 cinema processors. A consumer version of Dolby Digital is also
used on most DVDs, often at higher data rates than the original film. A bit for bit version
is used on Blu-ray Discs and HD DVDs called Dolby TrueHD. Dolby Digital officially premiered
with the film Batman Returns, but it was earlier tested at some screenings of Star Trek VI:
The Undiscovered Country.====Digital Theater Systems (DTS)====DTS actually stores the sound information
on separate CD-ROMs supplied with the film. The CDs are fed into a special, modified computer
which syncs up with the film through the use of DTS time code, decompresses the sound,
and passes it through to a standard cinema processor. The time code is placed between
the optical sound tracks and the actual picture, and is read by an optical LED ahead of the
gate. The time code is actually the only sound system which is not offset within the film
from the picture, but still needs to be physically set offset ahead of the gate in order to maintain
continuous motion. Each disc can hold slightly over 90 minutes of sound, so longer films
require a second disc. Three types of DTS sound exist: DTS-ES (Extended Surround), an
8 channel digital system; DTS-6, a 6 track digital system, and a now-obsolete 4 channel
system. DTS-ES derives a back surround channel from the left surround and right surround
channels using Dolby Pro Logic. The audio data in a DTS track is compressed in the 20-bit
APTX-100 compression scheme at a ratio of 4:1.
Of the three digital formats currently in use, DTS is the only one that has been used
with 70 mm presentations. DTS was premiered on Jurassic Park. Datasat Digital Entertainment,
purchaser of DTS’s cinema division in May 2008, now distributes Datasat Digital Sound
to professional cinemas worldwide. A consumer version of DTS is available on
some DVDs, and was used to broadcast stereo TV prior to DTV. A bit for bit version of
the DTS soundtrack is on Blu-ray Discs and HD DVDs called DTS-HD MA (DTS-HD Master Audio).==Leaders==
Academy leader is placed at the head of release prints containing information for the projectionist
and featuring numbers which are black on a clear background, counting from 11 to 3 at
16 frame intervals (16 frames in 35 mm film=1 ft). At −12 feet there is a START frame.
SMPTE leader is placed at the head of release prints or video masters containing information
for the projectionist or video playback tech. The numbers count down in seconds from 8 to
2 at 24 frame intervals ending at the first frame of the “2” followed by 47 frames of
black. Usually there’s an audio POP that play 48
frames (2 seconds at 24 frame per second) before first frame of action (FFOA) that helps
to sync audio and video during printing processes or postproduction.==Types of lenses and screens=====Spherical===
Most motion picture lenses are of the spherical variety. Spherical lenses do not distort the
image intentionally. Used alone for standard and cropped wide screen projection, and in
conjunction with an anamorphic adapter for anamorphic wide screen projection, the spherical
lens is the most common and versatile projection lens type.===Anamorphic===Anamorphic filming uses only special lenses,
and requires no other modifications to the camera, projector and intermediate gear. The
intended wide screen image is compressed optically, using additional cylindrical elements within
the lens so that when the compressed image strikes the film, it matches the standard
frame size of the camera. At the projector a corresponding lens restores the wide aspect
ratio to be seen on the screen. The anamorphic element can be an attachment to existing spherical
lenses. Some anamorphic formats utilized a more squarish
aspect ratio (1.18:1, vs. the Academy 1.375:1 ratio) on-film in order to accommodate more
magnetic and/or optical tracks. Various anamorphic implementations have been marketed under several
brand names, including CinemaScope, Panavision and Superscope, with Technirama implementing
a slightly different anamorphic technique using vertical expansion to the film rather
than horizontal compression. Large format anamorphic processes included Ultra Panavision
and MGM Camera 65 (which was renamed Ultra Panavision 70 in the early 60s). Anamorphic
is sometimes called “scope” in theater projection parlance, presumably in reference to CinemaScope.===Fish eye with dome===
The IMAX dome projection method (called “OMNIMAX”) uses 70 mm film running sideways through the
projector to maximize the image area and extreme wide angle lenses to obtain an almost hemispherical
image. The field of view is tilted, as is the projection hemisphere, so one may view
a portion of the ground in the foreground. Owing to the great area covered by the picture
it is not as bright as seen with flat screen projection, but the immersive qualities are
quite convincing. While there are not many theaters capable of displaying this format
there are regular productions in the fields of nature, travel, science, and history, and
productions may be viewed in most large urban regions. These dome theaters are mostly located
in large and prosperous science and technology museums.===Wide and deep flat screen===
The IMAX flat screen system uses large format film, a wide and deep screen, and close and
quite steep “stadium” seating. The effect is to fill the visual field to a greater degree
than is possible with conventional wide screen systems. Like the IMAX dome, this is found
in major urban areas, but unlike the dome system it is practical to reformat existing
movie releases to this method. Also, the geometry of the theater and screen are more amenable
to inclusion within a newly constructed but otherwise conventional multiple theater complex
than is the dome style theater.===Multiple cameras and projectors===
One wide screen development during the 1950s used non-anamorphic projection, but used three
side by side synchronised projectors. Called Cinerama, the images were projected onto an
extremely wide, curved screen. Some seams were said to be visible between the images
but the almost complete filling of the visual field made up for this. This showed some commercial
success as a limited location (only in major cities) exhibition of the technology in This
is Cinerama, but the only memorable story-telling film made for this technology was How the
West Was Won, widely seen only in its Cinemascope re-release.
While neither a technical nor a commercial success, the business model survives as implemented
by the documentary production, limited release locations, and long running exhibitions of
IMAX dome movies.==Three-dimensional==
For techniques used to display pictures with a three-dimensional appearance, see the 3-D
film article for some movie history and the stereoscopy article for technical information.==See also==
Film format List of film formats
Projector (disambiguation) for a directory of projector types
Projectionist Movietone sound system
Sound follower

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