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{{short description, Device by which motion picture film is advanced
An intermittent mechanism or intermittent movement is a device or movement which regularly advances an object,
The intermittent mechanism must be employed in concert with a rotating shutter which blocks light transmittance during the motion of the film and allows light through while the film is held in place usually by one or more registration pins. The intermittent mechanism can be accomplished in many ways, but most often, it is done with
Examples of camera movements
Mechanical synchronization
web
Web most often refers to:
* Spider web, a silken structure created by the animal
* World Wide Web or the Web, an Internet-based hypertext system
Web, WEB, or the Web may also refer to:
Computing
* WEB, a literate programming system created by ...
, or plastic film
Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces.
Plas ...
and then holds it in place. This process is commonly used in industry and manufacturing.
This motion is critical to the use of film
A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmospher ...
in a movie camera
A movie camera (also known as a film camera and cine-camera) is a type of photographic camera that rapidly takes a sequence of photographs, either on an image sensor or onto film stock, in order to produce a moving image to project onto a movie sc ...
or movie projector
A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Mod ...
. This is in contrast to a continuous mechanism, whereby the film is constantly in motion and the image is held steady by optical or electronic methods. The reason the intermittent mechanism "works" for the viewer is because of a phenomenon called persistence of vision
Persistence of vision traditionally refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye.
The illusion has also been d ...
.
History
Intermittent mechanisms were first used insewing machines
A sewing machine is a machine used to sew fabric and materials together with thread. Sewing machines were invented during the first Industrial Revolution to decrease the amount of manual sewing work performed in clothing companies. Since the in ...
, in order for the fabric to be fed through correctly - ensuring it is stationary as each stitch is made, while moving the required distance between stitches.
Methods used
The intermittent mechanism must be employed in concert with a rotating shutter which blocks light transmittance during the motion of the film and allows light through while the film is held in place usually by one or more registration pins. The intermittent mechanism can be accomplished in many ways, but most often, it is done with sprocket
A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain pas ...
wheels, claws, or pins coupled to the camera or projector drive mechanism.
In movie theater projectors, the intermittent movement is often produced by a Geneva drive (Maltese cross
The Maltese cross is a cross symbol, consisting of four " V" or arrowhead shaped concave quadrilaterals converging at a central vertex at right angles, two tips pointing outward symmetrically.
It is a heraldic cross variant which develope ...
mechanism).
However, in a movie camera, it is done through a process by which a shutter opens exposing the film negative
In photography, a negative is an image, usually on a strip or sheet of transparent plastic film, in which the lightest areas of the photographed subject appear darkest and the darkest areas appear lightest. This reversed order occurs because th ...
to light for a split second, then the shutter closes blocking light from reaching the negative. Once the shutter is completely closed, a claw pulls down the next film frame
In filmmaking, video production, animation, and related fields, a frame is one of the many '' still images'' which compose the complete '' moving picture''. The term is derived from the historical development of film stock, in which the sequenti ...
of negative film by the sprocket holes into the film gate The film gate is the rectangular opening in the front of a motion picture camera where the film is exposed to light. The film gate can be seen by removing the lens and rotating the shutter out of the way. The film is held on a uniform plane at a c ...
and the process begins again. A movie projector works in a similar way.Ascher, Steven, and Edward Pincus. ''The Filmmaker's Handbook: A Comprehensive Guide for the Digital Age''. New York: Plume, 1999.
The standard exposure period for regular motion in North America is 1/48 of a second, which corresponds to 180 degrees, but shutters with 200 degrees were popular back when the then-available color negative film had an ASA of 50; today's color negative film is available with an ASA of 500.
See also
* Dwell mechanism *Fast motion
Time-lapse photography is a technique in which the frequency at which film frames are captured (the frame rate) is much lower than the frequency used to view the sequence. When played at normal speed, time appears to be moving faster and thus ...
*Slow motion
Slow motion (commonly abbreviated as slo-mo or slow-mo) is an effect in film-making whereby time appears to be slowed down. It was invented by the Austrian priest August Musger in the early 20th century. This can be accomplished through the use ...
References
External links
Examples of camera movements
Mechanical synchronization