zoom lens


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zoom lens

a lens system that allows the focal length of a camera lens to be varied continuously without altering the sharpness of the image
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Zoom Lens

 

a combination of a telescopic attachment and an objective lens, forming an optical system with a variable focal length. The mechanical motions of the individual elements of the telescopic attachment ensure that the image scale of an object varies smoothly within a specified range. The focal length of a zoom lens is varied, but the sharpness of focus of the objective and the relative aperture remain unchanged.

Zoom lenses are used most often on motion-picture cameras for creating the illusion that the camera is approaching or receding in cases where it is not desirable to move the camera relative to the object being filmed. Because the aberrations of the telescopic attachment and the objective lens are usually calculated separately, the same attachment may be used with different objective lenses.

L. A. RIVKIN

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

zoom lens

[′züm ¦lenz]
(optics)
A system of lenses in which two or more parts are moved with respect to each other to obtain a continuously variable focal length and hence magnification, while the image is kept in the same image plane. Also known as variable-focal-length lens; varifocal lens.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

digital zoom

Simulating a longer focal length in a digital camera via software. The digital zoom is accomplished via image enhancement software within the camera itself rather than the inherent mechanics of the physical zoom lens. For more details, see optical zoom.

field of view

The observable view through a camera lens and the scene that winds up in the photo. A wide angle lens (short focal length) delivers a wide field of view (FOV). A telephoto lens (long focal length) yields a narrow one. See focal length and optical zoom.


The Field of View
These photos were taken with an 18-70mm zoom lens on a digital SLR (see DSLR). At 18mm (top), the field of view is the greatest (wide angle). At 70mm (bottom), the scene is the narrowest (telephoto). This lens is equivalent to a 27-105mm lens on a 35mm SLR camera (see crop factor).


The Field of View
These photos were taken with an 18-70mm zoom lens on a digital SLR (see DSLR). At 18mm (top), the field of view is the greatest (wide angle). At 70mm (bottom), the scene is the narrowest (telephoto). This lens is equivalent to a 27-105mm lens on a 35mm SLR camera (see crop factor).

optical zoom

Changing the focal length of a camera by adjusting the physical zoom lens. All zoom lenses in film cameras and digital single lens reflex (DSLR) cameras are optical zoom. Digital point-and-shoot cameras as well as consumer and prosumer video camcorders have optical zoom, but they also have digital zoom.

Digital Is Software Zoom
At the telephoto side of the camera, the computer takes over and interpolates the results. For example, a still camera may have 3x optical zoom in the lens, but can process the image with its internal computer to 10x. Depending on the camera and subject matter, the software-created digital zoom can be quite acceptable or mediocre.

The Higher the Optical, the Better
The higher the optical zoom, the better the results. In a still camera, an optical zoom of 10x or more is called a "superzoom" lens. Note that if a still camera is advertised with "10x zoom," that does not necessarily mean optical zoom only. In many cases, the optical is 3x with the additional 7x being digital.

With camcorders, the optical zoom typically ranges from 10x to 64x, while the digital zoom can go from 100x to 1000x. See digital camera.
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For my second example (opposite, top left), I used a telephoto zoom lens set at about 200mm to flatten perspective in this photograph of a row of tombs in a Buddhist cemetery in Pakxe, Laos.