A film plane is the surface of an image recording device such as a camera, upon which the
lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
creates the
focused image. In cameras from different manufacturers, the film plane varies in distance from the lens. Thus each lens used has to be chosen carefully to assure that the image is focused on the exact place where the individual frame 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 ...
or
digital sensor
A digital sensor is an electronic or electrochemical sensor, where data is digitally converted and transmitted. Sensors are often used for analytical measurements, e.g. the measurement of chemical and physical properties of liquids. Examples of me ...
is positioned during
exposure. It is sometimes marked on a camera body with the 'Φ' symbol where the vertical bar represents the exact location.
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 ...
s often also have small focus hooks where the
focus puller
A focus puller or first assistant camera (1st AC) is a member of a film crew's camera department whose primary responsibility is to maintain the camera lens's optical focus on whatever subject or action is being filmed.
"Pulling focus" refers t ...
can attach one side of a
tape measure
A tape measure or measuring tape is a long, flexible ruler used to measure length or distance. It usually consists of a ribbon of cloth, plastic, fibreglass, or metal (usually - hard steel alloy) strip with linear measurement markings.
Types
Ta ...
to quickly gauge the distance to objects that the operator intends to bring into focus on the film.
The measurement is taken from the film plane to the subject and effectively the film plane is the point in the camera where the film sits in the gate.
Light measurements can also be taken at the film plane.
Due to
Petzval field curvature, the film plane upon which a lens focuses may not be a literal plane. Cameras may bend the film stock or even
plate stock slightly to compensate, improving the area of
critical focus and sharpness. Nevertheless, the general concept of a focal plane is understood to refer to this position in the camera sensor relative to the lens.
See also
*
Cardinal point (optics)
In Gaussian optics, the cardinal points consist of three pairs of Point (geometry), points located on the optical axis of a Rotational symmetry, rotationally symmetric, focal, optical system. These are the ''Focus (optics), focal points'', the p ...
*
Flange focal distance
For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), back focus or register, depending on the usage and source ...
References
Photography equipment
Planes (geometry)
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