Tuesday, March 20, 2007

Movie camera

From Wikipedia, the free encyclopedia

Jump to: navigation, search
The Arricam ST, a popular 35 mm film camera currently used on major productions.
The Arricam ST, a popular 35 mm film camera currently used on major productions.
This article is about motion picture film cameras. See video camera for cameras which record images electronically.

The movie camera is a type of photographic camera which takes a rapid sequence of photographs on strips of film; once developed this film can be projected as a motion picture. In contrast to a still camera which captures a single snapshot at a time, the movie camera takes a series of images, each called a "frame". This is accomplished through an intermittent mechanism. The frames are later played back in a movie projector at a specific speed, called the "frame rate" (number of frames per second) to give the illusion of motion. Human eyes and brain merge the separate pictures together to generate the illusion, a phenomenon called the "persistence of vision".



[edit] Technical details

Basic operation: when the shutter is open, the film is illuminated. When it is completely covering the film gate, the film is being moved one frame further by one or two claws which advance the film by engaging and pulling it through the perforations.
Basic operation: when the shutter is open, the film is illuminated. When it is completely covering the film gate, the film is being moved one frame further by one or two claws which advance the film by engaging and pulling it through the perforations.

Most of the optical and mechanical elements of a movie camera are present in the movie projector. The camera will not have an illumination source and will maintain its film stock in a light-tight enclosure. A camera will also have exposure control via an iris aperture located on the lens. Also, there is a rotating, sometimes mirrored shutter behind the lens, which alternately passes the light from the lens to the film, or reflects it into the viewfinder. Otherwise, the requirements for film tensioning, take-up, intermittent motion, loops, and rack positioning are almost identical. See the movie projector article for these details and for the various film formats used. The righthand side of the camera is often referred to by camera assistants as "the dumb side" because it usually lacks indicators or readouts and access to the film threading, as well as lens markings on many lens models. More recent equipment often has done much to minimize these shortcomings, although access to the film movement block by both sides is precluded by basic motor and electronic design necessities.

A spring-wound Bolex 16 mm camera
A spring-wound Bolex 16 mm camera

The standardized frame rate for commercial sound film is 24 frames per second. The standard commercial, i. e. movie theater film width is 35 millimeters, while many other film formats exist. The standard aspect ratios are 1.66, 1.85, and 2.39 (anamorphic widescreen). NTSC video (common in the U. S. and Japan) plays at 29.97 frames/s; PAL (common in most other countries) plays at 25 frames/s. These two television and video systems also have different resolutions and color encodings. Many of the technical difficulties involving film and video concern translation between the different formats. Video aspect ratios, always measured as whole numbers, are 4:3 for full screen and 16:9 for widescreen.

[edit] Multiple cameras

Multiple cameras to take surround images (1909 Cinéorama system, for modern version see Circle-Vision 360°
Multiple cameras to take surround images (1909 Cinéorama system, for modern version see Circle-Vision 360°

Multiple synchronised cameras may be used and the films then projected simultaneousy, either on a single three-image screen (Cinerama) or upon multiple screens forming a complete circle, with gaps between screens through which the projectors iluminate an opposite screen. (See Circle-Vision 360°.)

[edit] Sound synchronisation

One of continuing problems in film is synchronizing a sound recording with the film. Most film cameras do not record sound internally; instead, the sound is captured separately by a precision audio device. This is called double-system. The exceptions to this are the single-system news film cameras, which had either an optical --or later-- magnetic recording head inside the camera. For optical recording, the film only had a single perforation and the area where the other set of perforations would have been was exposed to a controlled bright light that would burn a waveform image that would later regulate the passage of light and playback the sound. For magnetic recording, that same area of the single perf 16 mm film that was prestriped with a magnetic stripe. A smaller balance stripe existed between the perforations and the edge to compensate the thickness of the recording stripe to keep the film wound evenly.

The clapper board which typically starts a take is used as a reference point for the editor to sync the picture to the sound (provided the scene and take are also called out so that the editor knows which picture take goes with any given sound take). It also permits scene and take numbers and other essential information to be seen on the film itself. Aaton cameras have a system called AatonCode that can "jam sync" with a timecode-based audio recorder and prints a digital timecode directly on the edge of the film itself. However, the most commonly used system at the moment is unique identifier numbers exposed on the edge of the film by the film stock manufacturer (KeyKode is the name for Kodak's system). These are then logged (usually by a computer editing system, but sometimes by hand) and recorded along with audio timecode during editing. In the case of no better alternative, a handclap can work if done clearly and properly, but often a quick tap on the microphone (provided it is in frame for this gesture) is preferred.

Some cameras have low-accuracy ("non-sync" or MOS) film-advance systems. One of the most common uses of these cameras in commercial films are the spring-wound cameras used in hazardous special effects, known as "crash cams". Scenes shot with these have to be kept short, or resynchronized manually with the sound. MOS cameras are also often used for second-unit work or anything involving variable or non-standard speed filming. Due to their non-sync nature, some designs forgo traditional low-noise considerations for a studio camera and thus are quite noisy.

The most popular 35 mm cameras in use today are Arriflex, Moviecam (now owned by the Arri Group), and Panavision models. For very high speed filming, PhotoSonics are used.

[edit] Home movie cameras

Various German Agfa Movex Standard 8 home movie cameras.
Various German Agfa Movex Standard 8 home movie cameras.

Movie cameras, although available before the Second World War, had an upsurge in popularity in the immediate post-war period giving rise to the creation of home movies. Compared to the pre-war models, these cameras were small, light, fairly sophisticated and affordable. Whilst a basic model might have a single fixed aperture/focus lens, a better version might have three or four lenses of differing apertures and focal lengths on a rotating turret. A good quality camera might come with a variety of interchangeable, focusable lenses or possibly a single zoom lens. The viewfinder was normally a parallel sight within or on top of the camera body. In the 1950s and for much of the 1960s these cameras were powered by clockwork motors, again with variations of quality. A simple mechanism might only power the camera for some 30 seconds, whilst a geared drive camera might work for as long as 75 - 90 seconds (at standard speeds). Even today there is a market among collectors for these types of camera, as the engineering and materials were of a very high standard. Whilst film stock and the ability to process it exists, these cameras can still be used.

The common film used for these cameras was termed Standard 8, which was a strip of 16 millimetre wide film which was only exposed down one half during shooting. The film had twice the number of perforations as film for 16mm cameras and so the frames were half as high and half as wide as 16mm frames. The film was removed and placed back in the camera to expose the frames on the other side once the first half had been exposed Once the film was developed it was spliced down the middle and the ends attached, giving 50 foot of Standard 8 film from a spool of 25 foot of 16 mm film. 16 mm cameras, mechanically similar to the smaller format models, were also used in home movie making but were more usually the tools of semi professional film and news film makers.

In the 1960s a new film format, Super8, coincided with the advent of battery operated electric movie cameras. The new film, with a larger frame print on the same width of film stock, came in a cassette which simplified changeover and developing. Another advantage of the new system is that they had the capacity to record sound, albeit of indifferent quality. Camera bodies, and sometimes lenses, were increasing made in plastic rather than the metals of the earlier types. As the costs of mass production came down, so did the price and these cameras became very popular. This type of format and camera was more quickly superseded for amateurs by the advent of video cameras, although some professionals continued to make use of its visual characteristics alongside larger format film and video cameras.

[edit] See also

No comments: