A
movie projector is an
optoOptics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
-
mechanicalMechanics is the branch of physics concerned with the behaviour of physical bodies when subjected to forces or displacements, and the subsequent effect of the bodies on their environment....
device for displaying
moving picturesFilm encompasses individual motion pictures, the field of film as an art form, and the motion picture industry. Films are produced by recording images from the world with cameras, or by creating images using animation techniques or visual effects....
by projecting them on a projection screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in
movie cameraThe movie camera is a type of photographic camera which takes a rapid sequence of photographs on strips of film. In contrast to a still camera, which captures a single snapshot at a time, the movie camera takes a series of images, each called a "frame". This is accomplished through an intermittent...
s.
Physiology
According to the theory of
persistence of visionPersistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina....
, the perceptual processes of the
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
and the
retinaThe vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
of the
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
eyeEyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system...
retains an image for a brief moment of time. This theory is said to account for the illusion of motion which results when a series of
filmFilm encompasses individual motion pictures, the field of film as an art form, and the motion picture industry. Films are produced by recording images from the world with cameras, or by creating images using animation techniques or visual effects....
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 movementBeta movement is a perceptual illusion, described by Max Wertheimer in his 1912 Experimental Studies on the Seeing of Motion, whereby two or more still images are combined by the brain into surmised motion...
and
phi movementThe phi phenomenon is a perceptual illusion described by Max Wertheimer in his 1912 Experimental Studies on the Seeing of Motion, in which a disembodied perception of motion is produced by a succession of still images...
. A critical part of understanding these
visual perceptionVisual perception is the ability to interpret information and surroundings from visible light reaching the eye. The resulting perception is also known as eyesight, sight or vision...
phenomena is that the eye
is not a camera, ie: there is no "
frame rateFrame rate, or frame frequency, is the measurement of the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
" or "
scan rate" in the eye. 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 thresholdThe flicker fusion threshold is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer...
, 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. (Interestingly this threshold varies across different species; a higher proportion of rod cells in the retina will create a higher threshold level.)
It is possible to view the black space between frames and the passing of the shutter by the following technique:
Close your eyelids, then periodically rapidly blink open and closed. If done fast enough you will be able to randomly "trap" the image between frames, or during shutter motion. This will not work with television due to the persistence of the phosphors nor with LCD or
DLPDigital Light Processing is a trademark owned by Texas Instruments, representing a technology used in projectors and video projectors. It was originally developed in 1987 by Dr...
light projectors due to the continuity of image, although certain color artifacts may appear with some digital projection technologies.
Since the birth of
sound filmA sound film is a motion picture with synchronized sound, or sound technologically coupled to image, as opposed to a silent film. The first known public exhibition of projected sound films took place in Paris in 1900, but decades would pass before reliable synchronization was made commercially...
, virtually all film projectors in commercial movie theaters project at a constant speed of 24 frame/s. This speed was chosen for financial and technical reasons. When Warner Bros. and Western Electric were trying to find the proper projection speed for the new sound pictures, Western Electric went to the Warner Theater in LA and noted the AVERAGE speed at which films were projected there. They set that as the sound seed at which a satisfactory reproduction and amplification of sound could be conducted. There are some specialist formats (eg
ShowscanShowscan is a cinema process developed by Douglas Trumbull. Like some other spectacular wide-screen processes, it uses 70 mm film, but Showscan films and projects at a frame rate of 60 frame/s, 2.5 times as fast as standard cinema...
and
MaxivisionMaxivision 24 and Maxivision 48 are 35 mm motion picture film formats, created by Dean Goodhill in 1999. The system uses normal 35 mm motion picture film, capturing images on 3 perforations of film per frame...
) which project at higher rates, often 48 frame/s.
Silent films usually were not projected at constant speeds
http://www.cinemaweb.com/silentfilm/bookshelf/18_car_1.htm but rather were varied throughout the show at the discretion of the projectionist, often with some notes provided by the distributor. Speeds ranged from about 18 frame/s on up - sometimes even faster than modern sound film speed (24 frame/s). Contrary to received opinion, 16 frame/s - though sometimes used as a camera shooting speed - was dangerously inadvisable for projection, due to the high risk of the
nitrateNitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent...
-base prints catching fire in the projector. (A dramatic rendition of a nitrate print fire and its potentially devastating effects is famously found in
Nuovo Cinema ParadisoNuovo Cinema Paradiso is a 1988 Italian film written and directed by Giuseppe Tornatore. It was internationally released as Cinema Paradiso in France, Spain, the UK and the U.S....
, which revolves around the goings-on of a projectionist.)
Principles of operation
Light source
Incandescent lighting and even
limelightLimelight is a type of stage lighting once used in theatres and music halls. An intense illumination is created when an oxyhydrogen flame is directed at a cylinder of lime , which can be raised to 2572°C before melting. The light is produced by a combination of incandescence and candoluminescence...
were the first light sources used in film projection. In the early 1900s up until the late 1960s,
carbon arc lampsAn arc lamp or arc light is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, typically made of tungsten, which are separated by a gas. The type of lamp is often named by the gas contained in the bulb; including neon, argon, xenon,...
were the source of light in the almost all theaters in the world.
The
Xenon arc lampA xenon arc lamp is an artificial light source. Powered by electricity, it uses ionized xenon gas to produce a bright white light that closely mimics natural daylight.Xenon arc lamps can be roughly divided into three categories:...
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, care must be taken in inspecting a film so that it should not break in the gate and be damaged, particularly inflammable 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
lensA lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens is a lens consisting of a single optical element...
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 single image
A single image of the series of images comprising the movie is positioned and held flat within an aperture called 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.
Shutter
A commonly-held misconception is that film projection is simply a series of individual frames dragged very quickly past the projector's intense light source; this is not the case. If a roll of film were merely passed between the light source and the lens of the projector, all that would be visible on screen would be a continuous blurred series of images sliding from one edge to the other. It is the shutter that gives the illusion of one full frame being replaced exactly on top of another full frame. 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 rateFrame rate, or frame frequency, is the measurement of the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
and
Flicker fusion thresholdThe flicker fusion threshold is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer...
.) Higher rate shutters are less light efficient, requiring more powerful light sources for the same light on screen.
Imaging lens and aperture plate
A
lens systemA lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens is a lens consisting of a single optical element...
with multiple optical elements directs the image of the film to a viewing screen. Different lenses are used for different aspect ratios.
Aspect ratios are controlled by the lens 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.
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). 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.
Two reel system
The two reel system is also known as a changeover system, after the switching mechanism that operates between the end of one reel and the beginning of the next. In a two reel system the feed reel has a slight drag to maintain tensioning in the film, while the takeup reel is driven with a constant tension by a mechanism that is allowed to slip.
The two reel system was almost universally used before the advent of the single reel system for movie theaters 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, threading one with the next reel while the other projector plays the current reel. As the outgoing reel approaches its end, the projectionist looks for
cue markA cue mark, also known as a cue dot, a changeover cue or simply a cue is a visual indicator used with motion picture film prints, usually placed on the right-hand upper corner of a frame of the film....
s, at the upper right corner of the picture. Usually these are dots or circles, although they can also be slashes. (Some older films have occasionally been known to have used squares or triangles, and even positioned the cues in the middle of the right edge of the picture.) The first cue appears twelve feet (3.7 m) or eight seconds at 24 frame/s before the end of the reel, and signals the projectionist to start the motor of the projector containing the incoming reel. After another ten and a half feet (3.2 m) or seven seconds at 24 frame/s, 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 (457 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 outgoing reel will be projected on the screen. On some projectors, the operator would be alerted to the change by a bell that operated when the feed reel rotation exceeded a certain speed (that reel rotates faster as the film is exhausted), or based on the diameter of the remaining film (Premier Changeover Indicator Pat.411992), although many projectors do not have such an auditory system.
During the actual 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. 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.
The size of the reels can vary based on the projectors, but generally films are divided and distributed in reels of up to 2000 feet (610 m, about 22 minutes at 24 frame/s). Some projectors can even accommodate up to 6000 feet (1,830 m), which minimizes the number of changeovers in a showing. Certain countries also divide their film reels up differently; Russian films, for example, often come on 1000 foot (305 m) reels, although it's likely that most projectionists working with changeovers would combine them into longer reels of at least 2000 feet (610 m), to minimize changeovers and also give sufficient time for threading and any possibly needed troubleshooting 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 (3,660 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-trackStereo 8, commonly known as the eight-track cartridge, eight-track tape, or eight-track, is a magnetic tape sound recording technology, popular from the mid-1960s to the early 1980s. Stereo 8 was created in 1964 by a consortium led by Bill Lear of Lear Jet Corporation, along with Ampex, Ford Motor...
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, he transfers the payout unit 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
automationAutomation is the use of control systems , in concert with other applications of information technology , to control industrial machinery and processes, reducing the need for human intervention...
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 "
multiplexA movie theater, movie theatre, picture theatre, film theater or cinema is a venue, usually a building, for viewing motion pictures ....
" 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 mechanismThe intermittent mechanism or intermittent movement is the device by which film is regularly advanced and then held in place for a brief duration of time in a movie camera or movie projector. This is in contrast to a continuous mechanism, whereby the film is constantly in motion and the image is...
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 Maltese Cross mechanism (also known as the Geneva 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 of projectors
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 twice. The 16 mm film is then split lengthwise into two 8 mm pieces that are spliced to make a single projectable film with sprockets 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.
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. They are now collectors' items.
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. 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 35 mm.
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 1950's the
VistaVisionVistaVision is a higher resolution, widescreen variant of the 35 mm motion picture film format which was created by engineers at Paramount Pictures in 1954....
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
IMAXIMAX is a motion picture film format and projection standard created by Canada's IMAX Corporation. The traditional version of IMAX has the capacity to record and display images of far greater size and resolution than conventional film systems...
projection system. In IMAX the film is transported horizontally in the film gate, similar to
VistaVisionVistaVision is a higher resolution, widescreen variant of the 35 mm motion picture film format which was created by engineers at Paramount Pictures in 1954....
.
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. Consequently, all optical sound formats must be offset from the image because the sound reader is usually located above (for magnetic readers) or below (for optical readers) the projector head.
- See the 35 mm film article
35 mm film is the basic film gauge most commonly used for both still photography and motion pictures, and remains relatively unchanged since its introduction in 1892 by William Dickson and Thomas Edison, using film stock supplied by George Eastman. The photographic film is cut into strips...
for more information on both digital and analog methods.
Optical
Optical sound constitutes the recording and reading of
amplitudeAmplitude is the magnitude of change in the oscillating variable, with each oscillation, within an oscillating system. For instance, sound waves are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
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
photodiodeA photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.Photodiodes are similar to regular semiconductor diodes except that they may be either exposed or packaged with a window or optical fiber connection to allow...
. As the photocell picks up the light in varying intensities, the electricity produced is intensified by an
amplifierGenerally, an amplifier or simply amp, is any device that changes, usually increases, the amplitude of a signal. The relationship of the input to the output of an amplifier—usually expressed as a function of the input frequency—is called the transfer function of the amplifier, and the magnitude of...
, which in turn powers a
loudspeakerA loudspeaker is an electroacoustic transducer that converts an electrical signal into sound. The speaker pulses in accordance with the variations of an electrical signal and causes sound waves to propagate through a medium such as air or water.Loudspeakers are the most variable elements in a...
, where the electrical impulses are turned into air vibrations and thus, sound waves. In 16 mm, this optical soundtrack is a single mono track places 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 20 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 had a lower
signal-to-noise ratioSignal-to-noise ratio is an electrical engineering measurement, also used in other fields , defined as the ratio of a signal power to the noise power corrupting the signal...
.
Optical stereo is recorded and read through a bilateral variable area track, recorded using
Dolby StereoDolby Stereo,Dolby A was the original analog optical technology developed by Dolby Laboratories for 70mm film and 35mm film prints in 1976. The Dolby mix was first used on the movie Logan's Run. The brand of Dolby Stereo became a world leader, and synonymous with high quality sound in thousands...
matrix encoding and Dolby noise reduction. Left, center, right and surround channels are matrix-encoded into these two tracks.
In the 1970s and early 1980s, optical sound Super-8 mm copies were produced mainly for airline in-flight movies. Even though 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
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 on each side of the perforations, for a total of six tracks. Unlike all other non-double head magnetic sound, 70 mm magnetic heads are located before the gate. 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.
35 mm four-track magnetic sound was used from the 1950s through the mid 1970s for big-budget feature prints. It was of excellent quality, although somewhat prone to damage and erasure over time. As analog optical stereo gained popularity (it was also more durable and far less expensive to include on a film print), 35 mm four-track magnetic sound was increasingly only used for special road show screenings, and the development of digital sound systems made it completely obsolete.
35 mm and 16 mm each are sometimes run in sync with a separate reel of magnetic sound (known as double head projection because two reels are running on one projector in sync); the image goes through a gate while the magnetic reel passes over a sound head. Since the sound is on a separate reel, it does not need to be offset from the image. 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.
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 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 wide-spread 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 sound runs on the outside of 35 mm film, between the perforations and the edges, on both edges of the film. SDDS 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
CCDA charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
s located in a unit above the projector read 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. In contrast, both DTS and Dolby Digital soundtracks must be passed through to standard analog cinema sound processors - which are also used for analog optical sound, so equalization of the sound remains in the analog 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 HeroLast Action Hero is a 1993 action comedy cult film directed by John McTiernan. The film is a satire of the action genre and its clichés. The film includes within it several parodies of action films, in the form of films within the film....
. Sony ceased the sale of SDDS processors in 2001-2002.
Dolby Digital
Also known as Spectral Recording Digital or "SR•D." Sound is printed between the perforations and is 26 frames before the picture (the offset can be varied based on processing presets). 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
Dolby Pro LogicDolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround. Dolby Surround Stereo was originally developed by Dolby in 1976 for analog cinema sound systems...
. 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
CCDA charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
located either above the projector or in the regular analog sound head below the film gate. The information is then decoded, decompressed, and converted to analog; this can happen either in a separate SR-D processor that feeds signals to the cinema sound processor, or SR-D decoding can be built-in to the cinema processor.
As of 2006, Dolby has discontinued sale of their external SR-D processor (the DA20), so, aside from the used market, purchasing a Dolby processor with integrated SR-D is the only way to purchase an SR-D decoder.
A consumer version of Dolby Digital is also used on most
DVDDVD, also known as Digital Versatile Disc or Digital Video Disc,is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage...
s, often at higher data rates than the original film. Dolby Digital officially premiered with the film
Batman ReturnsBatman Returns is a 1992 superhero film directed by Tim Burton. Based on the DC Comics character Batman, the film is a sequel to 1989's Batman, with Michael Keaton reprising the lead role. Batman Returns tells the story of a corrupt businessman and the grotesque Penguin plotting to take control...
, but it was earlier tested at some screenings of
Star Trek: 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 will 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 LogicDolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround. Dolby Surround Stereo was originally developed by Dolby in 1976 for analog cinema sound systems...
. The audio data in a DTS track is compressed in the 20-bit APTX-100 compression scheme at a ratio of about 4.5:1. 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 ParkJurassic Park is a 1993 science fiction thriller film directed by Steven Spielberg and based on the novel of the same name by Michael Crichton. The film centers on the fictional island of Isla Nublar, where scientists have created an amusement park of cloned dinosaurs...
. A consumer version of DTS is available on some
DVDDVD, also known as Digital Versatile Disc or Digital Video Disc,is an optical disc storage media format, and was founded in 1995. Its main uses are video and data storage...
s.
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.
Orthographic
Before the advent of certain wide screen technologies, lenses always reproduced the exact proportions of the film image onto the screen. Such lenses are relatively simple to design and manufacture. Prior to modern wide screen, the industry standard image ratio of width to height was 1.37:1.
35 mm
VistaVisionVistaVision is a higher resolution, widescreen variant of the 35 mm motion picture film format which was created by engineers at Paramount Pictures in 1954....
was a wide screen orthographic system. The wide image was obtained by running the film horizontally across the gate so that the width limitation of the film was transformed to a height limitation. See the
VistaVision articleVistaVision is a higher resolution, widescreen variant of the 35 mm motion picture film format which was created by engineers at Paramount Pictures in 1954....
for more information.
Anamorphic
1953 saw the development of
wide screenA widescreen image is a film, computer or television image with a wider and shorter aspect ratio than the standard Academy frame developed during the classical Hollywood cinema era. Silent film was projected at a ratio of four units wide to three units tall, often expressed as 4:3 or 1.33:1...
films using special lenses for filming and projection. The images on these films utilized a more squarish aspect ratio (1.18:1) in order to accommodate both magnetic and optical tracks. The wide image is compressed horizontally in half onto the film in the camera using additional cylindrical elements within the lens, with a corresponding lens used in the projector to expand the image to the wide screen. This technique is called anamorphic projection and various implementations have been marketed under several brand names, including
CinemaScopeCinemaScope was an anamorphic lens series used from 1953 to 1967 for shooting widescreen movies created by the president of 20th Century Fox from 1953, and marked the beginning of the modern anamorphic format in both principal photography and movie projection...
,
PanavisionPanavision is a motion picture equipment company specializing in cameras and lenses, based in Woodland Hills, California. Formed by Robert Gottschalk as a small partnership to create anamorphic projection lenses during the widescreen boom in the 1950s, Panavision expanded its product lines to meet...
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 and Ultra Panavision and Camera 65 (which was renamed Ultra panavision in the early 60s).
Fish eye with dome
The
IMAXIMAX is a motion picture film format and projection standard created by Canada's IMAX Corporation. The traditional version of IMAX has the capacity to record and display images of far greater size and resolution than conventional film systems...
dome projection method (called "OMNIMAX") uses 70 mm film oriented 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 U.S. large urban regions. These dome theaters are mostly located in large and prosperous science and technology museums.
Wide and deep flat screen
The
IMAXIMAX is a motion picture film format and projection standard created by Canada's IMAX Corporation. The traditional version of IMAX has the capacity to record and display images of far greater size and resolution than conventional film systems...
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
CineramaCinerama is the trademarked name for a widescreen process which works by simultaneously projecting images from three synchronized 35 mm projectors onto a huge, deeply-curved screen, subtending 146° of arc. It is also the trademarked name for the corporation which was formed to market it...
, 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 CineramaThis is Cinerama is a 1952 full-length film designed to introduce the then-new widescreen process Cinerama, which broadens the aspect ratio so the viewer's peripheral vision is involved...
, but the only memorable story-telling film of two made for this technology was
How the West Was WonHow the West Was Won is a 1962 epic Western film which follows four generations of a family as they move ever westward, from western New York state to the Pacific Ocean. Filmed in the Cinerama curving widescreen process, the movie is set between 1839 and 1889.The all-star cast includes Carroll...
, widely seen only in its Cinemascope re-release.
While neither a technical nor a commercial success, the
business modelA business model is a framework for creating economic, social, and/or other forms of value. The term business model is thus used for a broad range of informal and formal descriptions to represent core aspects of a business, including purpose, offerings, strategies, infrastructure, organizational...
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 filmIn film, the term 3-D is used to describe any visual presentation system that attempts to maintain or recreate moving images of the third dimension, the illusion of depth as seen by the viewer....
article for some movie history and the
stereoscopyStereoscopy, stereoscopic imaging or 3-D imaging is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image. The illusion of depth in a photograph, movie, or other two-dimensional image is created by presenting a slightly different...
article for technical information.
See also
- Film format
A film format is a technical definition of a set of standard characteristics regarding image capture on photographic film, for either stills or movies. It can also apply to projected film, either slides or movies. The primary characteristic of a film format is its size and shape.In the case of...
- List of film formats
- Projector
Projector may refer to:* Video projector, a device that projects a video signal from computer, home theater system etc.* Movie projector, a device that projects moving pictures from a filmstrip...
for a directory of projector types
- Projectionist
A Projectionist is a person whose profession entails the operating of a movie projector.In some movie theater chains, but not all, booth work is done only by the management. The level of automation also varies by chain. Some companies feel that shows should be started manually to ensure that...
External links