Movie projector
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. The unexposed film is supplied in the 8 mm width, not split during processing as is the earlier 8 mm.The tower is designed with four spools, two on each side, each with its own motor. 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.
When Warner Bros. 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.
Large format anamorphic processes included and Ultra Panavision and Camera 65 (which was renamed Ultra panavision in the early 60s). The IMAX 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. Typical film sizes: Long used for home movies before the video camera, this uses double sprocketed 16 mm film, which is run through the camera twice.
(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. In the mid 1950 s 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 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. 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.
A movie projector is an opto-mechanical device for displaying moving pictures by projecting them on a projection screen. thread a single length of film through multiple projectors.
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. It also provides sufficient drag to prevent film motion during the frame display, while still allowing free motion under control of the intermittent mechanism.
Sync between the two reels is checked with SMPTE leader, also known as countdown leader. 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.
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. Usually these are dots or circles, although they can also be slashes.
Some projectors have a second, electrically-controlled douser that is used for changeovers (sometimes called a changeover douser or changeover shutter ). 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.
These dome theaters are mostly located in large and prosperous science and technology museums. The IMAX flat screen system uses large format film, a wide and deep screen, and close and quite steep stadium seating. 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. 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.
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 Logic. 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. One wide screen development during the 1950s used non-anamorphic projection, but used three side by side synchronised projectors.
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. Projectors are classified by the size of the film used, i.e. 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.
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. 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. 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.
Called Cinerama, the images were projected onto an extremely wide, curved screen. Each disc can hold slightly over 90 minutes of sound, so longer films will require a second disc.
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. 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. A rotating petal or gated cylindrical shutter interrupts the emitted light during the time the film is advanced to the next frame.
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. This technique is called anamorphic projection and various 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 urban regions. The audio data in an SDDS track is compressed in the 20-bit ATRAC2 compression scheme at a ratio of about 4.5:1.
Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. According to the theory of persistence of vision, the perceptual processes of the brain and the retina of the human eye retains an image for a brief moment of time. Magnetic stripes could be added to carry encoded sound to be added after film development. 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 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 DVDs, often at higher data rates than the original film.
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. 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. A spring loaded pressure plate functions to align the film in a consistent image plane, both flat and perpendicular to the optical axis.
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. 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. CDS was available on both 35 mm and 70 mm films.
In the sixties the last projectors of this format were being produced. 35 mm four-track magnetic sound was used from the 1950s through the mid 1970s for big-budget feature prints.
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.
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. 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 viewer does not see the transition, thus tricking the brain into believing a moving image is on screen. 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. The single reel system can allow for the complete automation of the projection booth operations, given the proper auxiliary equipment.
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. 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).
If done properly, a changeover should be virtually unnoticeable to an audience. 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.
It was of excellent quality, although somewhat prone to damage and erasure over time. The douser is usually part of the lamphouse, and may be manually or automatically operated.
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. 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.
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. 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.
Such lenses are relatively simple to design and manufacture. 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.
Of the three digital formats currently in use, DTS is the only one that has been used with 70 mm presentations. (A dramatic rendition of a nitrate print fire and its potentially devastating effects is famously found in Nuovo Cinema Paradiso, which revolves around the goings-on of a projectionist.) As in a slide projector there are essential optical elements: Incandescent lighting and even limelight were the first light sources used in film projection.
In older theaters, there may be manually operated, sliding covers in front of the projection booth s windows. Some projectors can even accommodate up to 6000 feet (1,830 m), which minimizes the number of changeovers in a showing.
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. 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.
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. 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.
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 of two 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. 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. . 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.
There are some specialist formats (eg Showscan and Maxivision) which project at higher rates, often 48 frame/s. 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. (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. A lens system with multiple optical elements directs the image of the film to a viewing screen.
It is also possible, with the proper equipment installed, to interlock , i.e. 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. Smooth wheels with triangular pins called sprockets engage perforations punched into one or both edges of the film stock.
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. 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. 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.
DTS was premiered on Jurassic Park. As the pawl retreats for the next cycle it is drawn back and does not engage the film.
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. 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.
A consumer version of DTS is available on some DVDs. 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). They set that as the sound seed at which a satisfactory reproduction and amplification of sound could be conducted.
The plate also has spring-loaded runners to help hold film while in place and advance it during motion. The intermittent mechanism can be constructed in different ways. 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.
Since the sound is on a separate reel, it does not need to be offset from the image. 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.
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. 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 time code is placed between the optical sound tracks and the actual picture, and is read by an optical LED ahead of the gate. 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.
The effect is to fill the visual field to a greater degree than is possible with conventional wide screen systems. 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.
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. 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. This increases the quality of the image.
See the VistaVision article for more information. 1953 saw the development of wide screen films using special lenses for filming and projection. 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. 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. (Also spelled dowser.) A metal or asbestos blade which cuts off light before it can get to the film.
The field of view is tilted, as is the projection hemisphere, so one may view a portion of the ground in the foreground. 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.
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. (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.
They are now collectors items. 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. SDDS was the first digital system that could handle up to eight channels of sound.
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. 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). Over 300,000 projectors were produced and sold mainly in France and England, and many commercial features were available in the format.
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. Before the advent of certain wide screen technologies, lenses always reproduced the exact proportions of the film image onto the screen. 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.
It became very popular in Europe over the next few decades and is still used by a small number of enthusiasts today. 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.
It is the shutter that gives the illusion of one full frame being replaced exactly on top of another full frame. DTS-ES derives a back surround channel from the left surround and right surround channels using Dolby Pro Logic.
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. CDS did not achieve wide-spread use and ultimately failed.
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 nitrate-base prints catching fire in the projector. 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.
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 audio data in a Dolby Digital track is compressed in the 16-bit AC-3 compression scheme at a ratio of about 12:1.
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. Dolby Digital officially premiered with the film Batman Returns, but it was earlier tested at some screenings of Star Trek: The Undiscovered Country. DTS actually stores the sound information on separate CD-ROMs supplied with the film.
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. Switchable projection screen can be switched between opaque and clear by a safe voltage under 36V AC and is viewable from both sides.
In the early 1900s up until the late 1960s, carbon arc lamps were the source of light in the almost all theaters in the world. The Xenon arc lamp was introduced in Germany in 1957 and in the US in 1963. Speeds ranged from about 18 frame/s on up - sometimes even faster than modern sound film speed (24 frame/s).
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. Three or more platters are stacked together to create a platter system.
This will not work with television due to the persistence of the phosphors nor with LCD or DLP light projectors due to the continuity of image, although certain color artifacts may appear with some digital projection technologies. Since the birth of sound film, virtually all film projectors in commercial movie theaters project at a constant speed of 24 frame/s. 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.
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. These serve to set the pace of film movement through the projector and any associated sound playback system. 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.
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. 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.
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. 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.
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. Dolby Digital produces 6 discrete channels.
Prior to modern wide screen, the industry standard image ratio of width to height was 1.37:1. 35 mm VistaVision was a wide screen orthographic system. It also prevents the lens from scarring or cracking from excessive heat. A single image of the series of images comprising the movie is positioned and held flat within an aperture called the gate.
Digital sound heads are usually above the gate. 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.
Some projectors also have a sensitive trip pin above the gate to guard against the upper loop becoming too big. The projector operator operates two projectors, threading one with the next reel while the other projector plays the current reel.
In the gate of the projector head, there is no space for a reader. 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.
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 ratio. Optical stereo is recorded and read through a bilateral variable area track, recorded using Dolby Stereo matrix encoding and Dolby noise reduction. Rewinding risks rubbing the film against itself, which can cause scratching of the film and smearing of the emulsion which carries the pictures.
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. 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.
If done fast enough you will be able to randomly trap the image between frames, or during shutter motion. The extra five millimeters of film accommodated the soundtrack, usually a six track magnetic stripe.
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. This variable density form of sound was eventually phased out because of its incompatibility with color stocks.
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. 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.
A critical part of understanding these visual perception phenomena is that the eye is not a camera, ie: there is no frame rate or scan rate in the eye. 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).
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. This speed was chosen for financial and technical reasons.
As the outgoing reel approaches its end, the projectionist looks for cue marks, at the upper right corner of the picture. 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.
This pawl advances only when the film is to be moved to the next image. It has since been discontinued by Kodak on both gauges. Modern theatrical systems use optical representations of digitally encoded multi-channel sound.
The images on these films utilized a more squarish aspect ratio (1.18:1) in order to accommodate both magnetic and optical tracks. It premiered with the film Dick Tracy and was used with several other films, such as Days of Thunder and Terminator 2: Judgement Day. SDDS sound runs on the outside of 35 mm film, between the perforations and the edges, on both edges of the film.
The information is decoded and decompressed before being passed along to the cinema sound processor. Unlike all other non-double head magnetic sound, 70 mm magnetic heads are located before the gate.
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. The most common film size for theatrical productions during the 20th century. 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.
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. 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.
the film format. A pair of CCDs located in a unit above the projector read the two SDDS tracks.
It is often referred to as 65/70, as the camera uses film 65 mm wide, but the projection prints are 70 mm wide. Sony ceased the sale of SDDS processors in 2001-2002. 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).
Some seams were said to be visible between the images but the almost complete filling of the visual field made up for this. SDDS premiered with the film Last Action Hero.
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). 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. Regardless of the sound format, any sound represented on the film image itself will not be the sound for the particular frame it occupies.
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. 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. 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. 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.
