There are many different types of motion picture cameras of varying sizes that serve a variety of purposes, but all cameras have the same basic structure. The basic components of a camera are photosensitive film, a light-proof body, a mechanism to move the film, a lens, and a shutter. Most cameras have a number of other features, ranging from viewfinders to detachable magazines to video assists, but the basic elements are the same in all cameras (save for those of the digital variety).

The film used in modern motion picture cameras is very much the same as the film that was developed in the 1880s and 1890s. It consists of an emulsion bound to a flexible, transparent base. Until 1951, the base was made of cellulose nitrate, a highly unstable substance that was prone to fire and decay. Since the 1950s, films have used a nonflammable safety base, usually of cellulose triacetate (acetate) or a thinner and more durable synthetic polyester base. Along with the emulsion, the filmstrip contains perforations on one or both sides, used to pull the film into place in front of the lens, and sound film has a strip along the edge containing the soundtrack.

The film is housed in the magazine (A), a detachable, light-tight unit that attaches to the camera. Unexposed film starts out on the supply reel (B), and after winding through the camera the now-exposed film ends up on the take-up reel (C) in a separate compartment of the magazine. There are different types of magazines for motion picture cameras. In the most common type, the displacement magazine, the supply reel sits directly in front of the take-up reel in an oval-shaped compartment on top of the camera. Coaxial magazines mount on the back of the camera and situate the two reels parallel to one another. Coaxial magazines are less widely used than the displacement type, but can be useful because their lower profile makes it possible to shoot in smaller spaces. Quick-change magazines contain parts of the camera mechanism in the magazine itself, making the magazine heavier and more expensive, but allowing for faster film changes. These magazines are generally the rear-mounted coaxial design. Magazines hold different amounts of film, depending on their size. Magazines for 35mm cameras most often hold 400-foot reels (four minutes at twenty-four frames per second [fps]), 1,000-foot reels (ten minutes) or 2,000-foot reels (twenty minutes). The standard reel size for 16mm cameras is 400 feet (eleven minutes at twenty-four fps), but other sizes are available.

A drive mechanism, or motor, pulls the film from the supply reel in the magazine and feeds it past the lens and aperture. With the exception of Edison's Kinetograph, which used a battery-operated motor, early cameras were cranked by hand. This practice resulted in irregular film speeds and potentially inconsistent exposure times, as frames were stopped in front of the lens for varying amounts of time. The introduction of electric motor drives meant that film could run through the camera at a consistent pace of twenty-four frames per second. Motor drives on modern cameras can also provide

Cutaway view of a reflex movie camera.
variations in speed, useful for producing the effects of fast motion (by reducing the film speed) or slow motion (by speeding up the film).

Just before the film reaches the area in front of the lens it makes a small loop, known as a Latham loop (D). The Latham loop was developed by the Latham family (Woodville Latham [1837–1911] and his sons Gray and Otway) around 1895 as a way to prevent film from breaking as it worked its way through the camera. By placing a loop above and below the lens, stress on the film is redistributed, allowing for longer films with less breakage. Once the film passes the Latham loop, it is pulled into place in the film gate by the claw. The claw advances the film using intermittent motion, and holds it in the film gate while the frame is exposed to light. The film gate (E) consists of two plates that help hold the film during exposure. The front plate, which has a rectangle cut into it to allow light onto the film, is called the aperture plate. The edges of the rectangle, called the aperture (F), form the border of the film. The rear plate, which holds the film flat, is called the pressure plate.

For the fraction of a second that the film is stopped in the film gate, the shutter opens to allow light to pass through the lens (G) and aperture and onto the film. The purpose of the lens is to focus the light rays from the scene in front of the camera onto the film. There are two basic kinds of lenses: prime lenses, which have a fixed focal length, and zoom lenses, which can change focal lengths. The focal length refers to the size of the lens, and affects how the image will appear on film. Lenses with focal lengths of less than 25mm, called wide-angle lenses, take in a wider area than telephoto lenses (lenses longer than 50mm), which can shoot objects at greater distances but provide a narrower shot. Camera lenses are also classified according to how much light they let in, also known as the lens speed. Lens speed is described in terms of f-stop or t-stop ("t" for "true" or "transmission"), with the smaller number f-stop or t-stop letting in the greatest amount of light, and therefore signifying faster lenses. The lens is attached to the camera on the lens mount; some older cameras use turret mounts, which feature three or four prime lenses of varying focal lengths that can be rotated into place.

Thomas Edison's studio, the Black Maria in West Orange, New Jersey.

While the film is stopped in front of the lens, the shutter (H) opens to allow light to enter through the aperture. After the film has been exposed to light, the shutter closes and the film advances to the next frame. If the shutter is not completely closed before the film starts moving, the image will be blurred. The most basic shutter is in the form of a rotating disc, and the standard shutter speed, or exposure time, when shooting at 24 fps is 1/50 second. Some shutters are variable, and can be adjusted to allow longer or shorter exposure times. Once the shutter closes, the exposed film advances, continuing past another loop beneath the film gate, and finally ending up on the take-up reel in the magazine.

The camera operator is able to see what is being recorded by looking through the camera's viewfinder. Most cameras today use a reflex viewfinder, which allows the operator to see through the camera's lens, also known as the taking lens. Older cameras employed a nonreflex viewfinder, which used a separate lens and was therefore less accurate. Viewfinders work by using a series of mirrors to divert light from the lens to a viewing screen, which displays information crucial to the camera operator, such as the outline of the frame. An alternative to the viewfinder is the video assist, or video tap, a device that allows more than one person to view the image from the camera. The video assist is similar to the viewfinder in that it diverts light from the taking lens and sends the picture to a screen, in this case a video monitor that can be set up near the camera. The quality of the images and color on the video assist monitor are inferior to what is actually being recorded by the camera, and therefore the video assist is not used to gauge what the final product will look like. Because it is not attached to the camera, an important use of the video assist is for crane or Steadicam shots, or any other shots for which the camera operator is unable to look through the viewfinder.

While all cameras operate in essentially the same way, the size of the filmstrip varies depending on the camera type, which affects the size and shape of the projected image. There are four film gauges, or widths, that are standard worldwide: 8mm, 16mm, 35mm, and 70mm (the numbers refer to the actual width of the filmstrip, in millimeters). These gauges are used for different purposes and yield different image types and quality. The larger film widths provide better quality images because they offer larger frame sizes that afford more room for detail. However, as film formats increase in size, they become progressively more expensive to use, and the equipment becomes heavier and more cumbersome. The standard professional film gauge, used in most feature films, commercials, and television movies, is 35mm. This is approximately the size that was used in Edison's Kinetograph and the Lumière brothers' Cinématographe, and it has been the most commonly used size throughout cinema's history. In most movie theaters projectors require 35mm film.

In the 1920s 16mm film was introduced, with the goal of providing a less expensive alternative to 35mm film. Because the size of the frame of 16mm film is about a quarter the size of 35mm film, the image is not as sharp. However, 16mm cameras are significantly smaller and lighter than 35mm cameras, and their portability makes them ideal for documentary filmmakers, news reporting, and amateur filmmaking. The 16mm camera is also frequently used by avant-garde and experimental filmmakers, who appreciate the format's portability, low cost, and overall flexibility. The size and weight of 16mm and 8mm cameras allow freedom of camera movement and eliminate many of the constraints involved with 35mm shooting, and the grainy quality of 16mm and 8mm film stocks can be manipulated by experimental filmmakers to create interesting effects. Because of their versatility and ease of use, then, both the 16mm and 8mm formats have long been favored by filmmakers working outside the mainstream.

Long popular with amateur filmmakers, 8mm film was originally introduced in 1932. Because it was created from 16mm film split down the middle, 8mm film has sprocket holes along only one side of the filmstrip. Super 8 film was created by Kodak in 1965, and, like the Super 16 film developed in the 1970s, is able to record a larger image on each frame. Due to their low cost and easy to operate handheld cameras, 8mm and Super 8 were, for many years, the formats most commonly used in home Cine and amateur movies, although their popularity has since been eclipsed by video and digital video.

The largest gauge in use is 70mm, which offers beautiful details and clarity, but is extremely expensive to shoot. Film that is described as 70mm uses 65mm for the image and perforations and 5mm for the soundtrack. Frequently, films that are projected in 70mm today are shot using anamorphic lenses, which compress the image to fit on 35mm film, and then decompress the image during projection to restore it to its original size. The 70mm format can increasingly be found in amusement parks, as part of 3-D attractions such as Walt Disney World's Honey, I Shrunk the Audience or rides such as Disneyland's Star Tours . IMAX films, the largest format in use today, make use of 65mm film, but position the frames horizontally on the filmstrip, rather than vertically.

A wide variety of cameras are available to filmmakers, depending on their needs. Bolex offers student, independent, and amateur filmmakers low-cost, high-quality 16mm and Super 16 cameras known for their versatility. In 1937, Arri introduced the first 35mm camera with a reflex mirror shutter, which allowed the camera operator to focus and frame a shot using the viewfinder. Arri produced a professional 16mm camera with the same reflex mirror shutter in 1952, and Arri cameras have since become the industry standard for 16mm filmmaking. The French Éclair 16mm camera is quiet enough to allow for synchronous audio recording, and light enough to allow for easy handheld operation; it was used frequently by cinéma vérité and New Wave filmmakers in the 1950s and 1960s. Mitchell cameras, introduced in the 1910s, were known for their steadiness and reliability, as well as their special effects abilities. Mitchell cameras were also used extensively in 65/70mm widescreen production. Panavision provides 16mm, 35mm, 65/70mm and digital cameras and lenses that have been widely used in Hollywood feature filmmaking since the 1950s.

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