Movie projector

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This article is concerned with technical aspects of moving film projection. For non-film movie projection, see digital cinema. For historical aspects, see the article history of cinema.
35 mm movie projector in operation.



The cinématographe Lumière in projection mode.
Simulation of a spinning zoopraxiscope

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.[1]

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.[2] The cinematograph was also exhibited at the Paris Exhibition of 1900. At the Exhibition, films made by the Lumière Brothers were projected unto a large screen measuring 16 by 21 meters (approximately 52.5 x 69 feet).[3]


According to the theory of persistence of vision, the perceptual processes of the brain and the retina of the human eye retain 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 film images is displayed in quick succession, rather than the perception of the individual frames in the series.


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. (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 DLP light projectors due to the continuity of image, although certain color artifacts may appear with some digital projection technologies.

Silent films usually were not projected at constant speeds [1] 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 nitrate-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 Paradiso, which revolves around the goings-on of a projectionist.)

Since the birth of sound film, 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. 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 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.

Principles of operation[edit]

35 mm Kinoton FP30ST movie projector, with parts labeled. (Click thumbnail for larger text.)

Projection elements[edit]

As in a slide projector there are essential optical elements:

Light source[edit]



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 if it is flammable cellulose nitrate film stock.

Reflector and condenser lens[edit]




(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[edit]

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.


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 rate and Flicker fusion threshold.) Higher rate shutters are less light efficient, requiring more powerful light sources for the same light on screen.

Mechanical sequence when image is shown twice and then advanced.
Outer sprockets rotate continuously while the frame advance sprockets are controlled by the mechanism shown - a Geneva drive.

Imaging lens and aperture plate[edit]

Imaging lens Diastar of an Askania 35mm movie projector (focal length: 400 mm)

A projection objective with multiple optical elements directs the image of the film to a viewing screen (imaging lens). Imaging lenses also differ in aperture and focal length. Different lenses are used for different aspect ratios.


Viewing screen[edit]

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.

Film transport elements[edit]

Film supply and takeup[edit]

Two-reel system[edit]



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 frames/sec). Some projectors can even accommodate up to 6000 feet (1,830 m), 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 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.

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.





The first cue appears twelve feet (3.7 m) 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 (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 reel coming to an end will be projected on the screen.


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.


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.


Single reel system[edit]
Christie AW3 platter, BIG SKY Industries console, and Century SA projector.

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).




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.

nonrewind in Royal - Malmo, Sweden.


Automation and the rise of the multiplex[edit]


Feed and extraction sprockets[edit]


Film loop[edit]


Film gate pressure plate[edit]


Intermittent mechanism[edit]

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.


Types of projectors[edit]


8 mm[edit]

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[edit]


9.5 mm[edit]

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[edit]

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[edit]


A diagram of the VistaVision format


70 mm[edit]






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) or below (for optical readers) the projector head.

See the 35 mm film article for more information on both digital and analog methods.

Analog Optical Sound[edit]



Optical stereo is recorded and read through a bilateral variable area track, recorded using Dolby Stereo matrix encoding and Dolby noise reduction. Left, center, right and surround channels are matrix-encoded into these two tracks.


Magnetic sound[edit]






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. Furthermore they wore out faster and were also prone to damage and erasure over time. 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 effectively ended with the success of the Dolby Stereo optical stereo format in the late 1970s. 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.




Cinema Digital Sound (CDS)[edit]


Sony Dynamic Digital Sound (SDDS)[edit]


Dolby Digital[edit]


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.


Digital Theater Systems (dts)[edit]

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 Logic. 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 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. 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).


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[edit]


Before the advent of certain wide screen technologies, lenses always reproduced the exact proportions of the film image onto the screen. Such lenses (known as a "flat" lens in theater projection parlance) 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 VistaVision 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 article for more information.


Simulated wide screen image with 1.96 to 1 ratio as it would be seen in a camera viewfinder or on a theater screen
Simulated anamorphed image with 1.33 to 1 ratio (4:3) as it would appear on a frame of film

1953 saw the development of wide screen 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 (known as "scope" in theater projection parlance), 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 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).

Fish eye with dome[edit]


Wide and deep flat screen[edit]


Multiple cameras and projectors[edit]

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 of two made for this technology was How the West Was Won, widely seen only in its Cinemascope re-release.




See also[edit]


  1. ^ "Motion Picture Pioneer: Eadweard Muybridge and the Zoopraxiscope". Retrieved 2012-12-17. 
  4. ^ Nowell-Smith, Geoffrey (ed.) The Oxford History of World Cinema, pp. 446–449. Oxford University Press: Oxford, 1996.
  5. ^ Kodak Film Notes Issue # H-50-03: Projection practices and techniques - see Manuals at

External links[edit]