An intermittent mechanism or intermittent movement is a device or movement which regularly advances an object,

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. Plast ...

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 known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

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 onto film stock or an image sensor, in order to produce a moving image to display on a screen. In c ...

movie projector A movie projector (or film projector) is an optics, opto-mechanics, mechanical device for displaying Film, motion picture film by projecting it onto a movie screen, screen. Most of the optical and mechanical elements, except for the illuminat ...

. 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 is the optical illusion that occurs when the visual perception of an object does not cease for some time after the Light ray, rays of light proceeding from it have ceased to enter the eye. The illusion has also been descr ...

History

Intermittent mechanisms were first used in sewing machines, 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 pin A registration pin is a device intended to hold a piece of film, paper or other material in place during photographic exposure, copying or drawing. Registration pins are used in offset printing and cartography, to accurately position the different ...

s. 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 A wheel is a rotating component (typically circular in shape) that is intended to turn on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the whe ...

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 The Geneva drive or Geneva mechanism is a gear mechanism that translates a continuous rotation movement into intermittent rotary motion. The ''rotating drive'' wheel is usually equipped with a pin that reaches into a slot located in the other ...

(

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 sequentia ...

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 (or an opening for showing the film with a projector). The film gate holds the film during exposure through the aperture formed by t ...

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.

References

External links

*{{Commonscatinline, Intermittent mechanism
Examples of camera movements
Mechanical synchronization

History

Methods used

See also

References

External links