A movie projector is an opto Optics 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. Because light is an electromagnetic wave, other forms of electromagnetic radiation-mechanical Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment. The discipline has its roots in several ancient civilizations (see History of classical mechanics and Timeline of classical mechanics). During the early modern device for displaying moving pictures A film, also called a movie or motion picture, is a story conveyed with moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects. The process of filmmaking has developed into an art form and industry by projecting them on a projection screen A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed as in a movie theater, painted on the wall , semi-permanent or mobile, as in a conference room or other non-dedicated viewing space. Uniformly. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras The 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; "frame". This is accomplished through an intermittent mechanism. The frames are later played back in a.

Contents 1 Physiology 2 Principles of operation 2.1 Projection elements 2.1.1 Light source 2.1.2 Reflector and condenser lens 2.1.3 Douser 2.1.4 Film gate and single image 2.1.5 Shutter 2.1.6 Imaging lens and aperture plate 2.1.7 Viewing screen 2.2 Film transport elements 2.2.1 Film supply and takeup 2.2.1.1 Two reel system 2.2.1.2 Single reel system 2.2.1.3 Automation and the rise of the multiplex 2.2.2 Feed and extraction sprockets 2.2.3 Film loop 2.2.4 Film gate pressure plate 2.2.5 Intermittent mechanism 3 Types of projectors 3.1 8 mm 3.2 Super 8 3.3 9.5 mm 3.4 16 mm 3.5 35 mm 3.6 70 mm 4 Sound 4.1 Optical 4.2 Magnetic sound 4.3 Digital 4.3.1 Cinema Digital Sound (CDS) 4.3.2 Sony Dynamic Digital Sound (SDDS) 4.3.3 Dolby Digital 4.3.4 Digital Theater Systems (DTS) 5 Leaders 6 Types of lenses and screens 6.1 Orthographic 6.2 Anamorphic 6.3 Fish eye with dome 6.4 Wide and deep flat screen 6.5 Multiple cameras and projectors 7 Three-dimensional 8 See also 9 References 10 External links

Physiology

According to the theory of persistence of vision The myth of persistence of vision is the mistaken belief that human perception of motion is the result of persistence of vision (eye centred). The myth was debunked in 1912 by Wertheimer but persists in many citations in many classic and modern film-theory texts. A more plausible theory to explain motion perception (at least on a descriptive level), the perceptual processes of the brain The 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. In vertebrates, the brain is located in the head, protected by the skull and close to the primary and the retina The 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 events that ultimately trigger nerve impulses. These of the human Humans, known taxonomically as Homo sapiens , are the only living species in the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo eye Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms complex neural pathways exist that connect the eye, via the optic nerve to the visual cortex and other areas of the brain. Complex optical systems with resolving 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 film A film, also called a movie or motion picture, is a story conveyed with moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects. The process of filmmaking has developed into an art form and industry 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 Beta 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. This is often erroneously referred to as the phi phenomenon, which is a different, related illusion and phi movement The 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. In discussions of the perception of film and video it is often confused with beta movement, but it is a distinct phenomenon not. A critical part of understanding these visual perception Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision . The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in phenomena is that the eye is not a camera, ie: there is no "frame rate Frame rate, or frame frequency, is 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. Frame rate is most often expressed in frames per second (FPS) and in progressive scan monitors as hertz (Hz)" 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 threshold The 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 (this article centers around human observers). Flicker fusion threshold is related to persistence of vision, 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 Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On average, there is approximately 92 million rod cells in 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 A liquid crystal display is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly or DLP light projectors due to the continuity of image, although certain color artifacts may appear with some digital projection A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. Video projectors are widely used for conference room technologies.

Silent films A silent film is a film with no synchronized recorded sound, especially spoken dialogue. In entertainment silent films the acting and dialogue is commuted through muted gestures, pantomime and title cards. The idea of combining motion pictures with recorded sound is nearly as old as film itself, but because of the technical challenges involved, 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 Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton-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 Nuovo 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.)

Since the birth of sound film A 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 sound motion pictures were made commercially practical. Reliable synchronization was difficult to, 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 seed at which a satisfactory reproduction and amplification of sound could be conducted. There are some specialist formats (eg Showscan Showscan is a cinematic process developed by Douglas Trumbull. Like some other wide-screen processes, it uses 70 mm film, but photographs and projects it at 60 frames per second—2.5 times faster than standard movie film. It renders a picture that is not only extremely high in definition, but is dramatically smoother and more realistic in its and Maxivision Maxivision 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. The format can run either at the standard 24 frames per second, or at 48 frames per second, which reduces strobing effects and increases) which project at higher rates, often 48 frame/s.

Principles of operation

35 mm 35 mm film is the basic film gauge most commonly used for chemical 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 35 millimeters (about 1 3/8 inches) wide—hence the Kinoton FP30ST movie projector, with parts labeled. (Click thumbnail for larger text.)

Projection elements

As in a slide projector A flat piece of heat absorbing glass is often placed in the light path between the condensing lens and the slide, to avoid damaging the latter. This glass transmits visible wavelengths but absorbs infrared. Light passes through the transparent slide and lens, and the resulting image is enlarged and projected onto a perpendicular flat screen so the there are essential optical elements:

Light source

Incandescent lighting The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric light that works by incandescence . An electric current passes through a thin filament, heating it until it produces light. The enclosing glass bulb prevents the oxygen in air from reaching the hot filament, which otherwise would be destroyed rapidly and even limelight Limelight 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 quicklime , which can be heated to 2572 °C before melting. The light is produced by a combination of incandescence and candoluminescence. Although it has long since been replaced by were the first light sources used in film projection. In the early 1900s up until the late 1960s, carbon arc lamps "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, krypton, sodium, metal halide, were the source of light in the almost all theaters in the world.

The Xenon arc lamp A 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 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 lens A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element. A compound lens is an array of simple lenses with a common axis; the use of multiple elements allows more optical aberrations to be corrected than is 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 rate Frame rate, or frame frequency, is 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. Frame rate is most often expressed in frames per second (FPS) and in progressive scan monitors as hertz (Hz) and Flicker fusion threshold The 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 (this article centers around human observers). Flicker fusion threshold is related to persistence of vision.) 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.

Imaging lens and aperture plate

Imaging lens Diastar of an Askania 35mm movie projector (focal length The focal length of an optical system is a measure of how strongly the system converges or diverges (defocuses) light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the: 400 mm)

A projection objective In optics, an objective is the lens or mirror in a microscope, telescope, camera or other optical instrument that gathers the light coming from the object being observed, and focuses the rays to produce a real image. The objective is also called the object lens, object glass, and objective glass with multiple optical elements directs the image of the film to a viewing screen (imaging lens). Imaging lenses also differ in aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at and focal length The focal length of an optical system is a measure of how strongly the system converges or diverges (defocuses) light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the. 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

Main article: Projection screen A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed as in a movie theater, painted on the wall, semi-permanent or mobile, as in a conference room or other non-dedicated viewing space. Uniformly white

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.

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