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# Focal length

The focal length of an optical system is a measure of how strongly the system converges or diverges light. [1]

Addison-Wesley is a publisher of textbooks and computer literature.

## Angle of view

In photography, angle of view (AOV) describes the angular extent of a given scene that is imaged by a camera.

## Camera lens

A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

## Cardinal point (optics)

In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system.

## Collimated light

Collimated light is light whose rays are parallel, and therefore will spread minimally as it propagates.

## Crop factor

In digital photography, the crop factor, format factor or focal length multiplier of an image sensor format is the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference.

## Curved mirror

A curved mirror is a mirror with a curved reflecting surface.

## Depth of field

In optics, particularly as it relates to film and photography, the optical phenomenon known as depth of field (DOF), is the distance about the Plane of Focus (POF) where objects appear acceptably sharp in an image.

## Digital camera

A digital camera or digicam is a camera that captures photographs in digital memory.

## Dioptre

A dioptre (British spelling) or diopter (American spelling) is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres.

## Distortion (optics)

In geometric optics, distortion is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image.

## F-number

The f-number of an optical system (such as a camera lens) is the ratio of the system's focal length to the diameter of the entrance pupil.

## Field of view

The field of view is the extent of the observable world that is seen at any given moment.

## Film format

A film format is a technical definition of a set of standard characteristics regarding image capture on photographic film, for either stills or filmmaking.

## Focal Press

Focal Press is a publisher of media technology books and it is an imprint of Taylor & Francis.

## Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.

## Full-frame digital SLR

The term full frame or ff is used by users of digital single-lens reflex cameras (DSLRs) as a shorthand for an image sensor format which is the same size as 35mm format film.

## Image

An image (from imago) is an artifact that depicts visual perception, for example, a photo or a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person, thus providing a depiction of it.

## Lens (optics)

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.

## Light

Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.

## Magnification

Magnification is the process of enlarging the appearance, not physical size, of something.

## Microscopy

Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye).

## Mirror

A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection.

## Normal lens

In photography and cinematography, a normal lens is a lens that reproduces a field of view that appears "natural" to a human observer.

## Optical power

Optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light.

## Optics

Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

## Photography

Photography is the science, art, application and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film.

## Pinhole camera

A pinhole camera is a simple camera without a lens but with a tiny aperture, a pinhole – effectively a light-proof box with a small hole in one side.

## Pinhole camera model

The pinhole camera model describes the mathematical relationship between the coordinates of a point in three-dimensional space and its projection onto the image plane of an ideal pinhole camera, where the camera aperture is described as a point and no lenses are used to focus light.

Radius of curvature (ROC) has specific meaning and sign convention in optical design.

## Ray (optics)

In optics a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow.

## Rectilinear lens

In photography, a rectilinear lens is a photographic lens that yields images where straight features, such as the walls of buildings, appear with straight lines, as opposed to being curved.

## Refractive index

In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium.

## Sign convention

In physics, a sign convention is a choice of the physical significance of signs (plus or minus) for a set of quantities, in a case where the choice of sign is arbitrary.

## Sphere

A sphere (from Greek σφαῖρα — sphaira, "globe, ball") is a perfectly round geometrical object in three-dimensional space that is the surface of a completely round ball (viz., analogous to the circular objects in two dimensions, where a "circle" circumscribes its "disk").

## Telephoto lens

In photography and cinematography, a telephoto lens is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length.

## Telescope

A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).

## Thin lens

In optics, a thin lens is a lens with a thickness (distance along the optical axis between the two surfaces of the lens) that is negligible compared to the radii of curvature of the lens surfaces.

## Wide-angle lens

In photography and cinematography, a wide-angle lens refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane.

## 135 film

135 is photographic film in a film format used for still photography.

## 35 mm equivalent focal length

In photography, the 35 mm equivalent focal length is a measure that indicates the angle of view of a particular combination of a camera lens and film or sensor size.

## 35 mm film

35 mm film (millimeter) is the film gauge most commonly used for motion pictures and chemical still photography (see 135 film).

## References

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