The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more st...
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http://en.wikipedia.org/wiki/Focal_length
Distance from a lens or mirror to the point it draws light to a focus.
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http://planetfacts.org/space-terms/
(from the article `photoreception`) ...suggests that resolution is sacrificed for light-gathering power (see Figure 2). The mouse lens, for example, is so large that it almost touches ... ...to as a lens and may have one or more components. The physical shape of the components may be convex, concave, or plane-parallel. Figure 2 ... ....
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http://www.britannica.com/eb/a-z/f/41
The distance between a mirror or a lens and its focal point. The focal length of a compound optical system, given as if it were a single optical element, is called the equivalent focal length. The focal length at which an optical system seems to be working in a given situation is known as the effect...
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http://www.daviddarling.info/encyclopedia/F/focal_length.html
The distance between a lens or mirror and the point where it brings light to a focus.
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http://www.encyclo.co.uk/local/20448
(Digital cameras and photo printers) The distance between the centre of the lens system and the film or CCD sensor, i.e. where the image is in focus. Normal focal length gives an image impression roughly corresponding to that of the human eye (about 50 mm in conventional film cameras and about 7 mm in digital cameras with a 1/3� CCD).
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http://www.encyclo.co.uk/local/20472
<microscopy> The distance from the optical centre of the lens to the focal point<microscopy> The focal length of an objective and its working distance are directly proportional. ... (05 Aug 1998) ...
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http://www.encyclo.co.uk/local/20973
The distance, usually given in millimeters, between the optical center of a lens and the point at which rays of light from objects at infinity are brought to focus. In general, the greater the focal length, the smaller and more magnified the part of the scene, it includes in the picture frame
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http://www.encyclo.co.uk/local/21048
The distance from the rear model plane of a lens to the focus when the lens is focused at the infinity position.
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http://www.encyclo.co.uk/local/21469
The focal length of a lens is the distance from the lens to the place at which light from a distant object is brought to a focus. The focal length of a lens is decided by the curvature of its glass surfaces - the more curved the surfaces, the shorter the focal length
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http://www.irpoyser.co.uk/glossary.php
The distance between the film and the optical center of the lens when the lens is focused on infinity. The focal length of the lens on most adjustable cameras is marked in millimetres on the lens mount. The distance from the principal point to the focal point. In 35mm-format cameras, lenses with a focal length of approx. 50mm are called normal or s...
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http://www.rodsmith.org.uk/photographic%20glossary/rods%20photographic%20gl
The distance, usually given in millimeters, between the optical center of a lens and the point at which rays of light from objects at infinity are brought to focus. In general, the greater the focal length, the smaller and more magnified the part of the scene, it includes in the picture frame.
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http://www.rodsmith.org.uk/photographic%20glossary/rods%20photographic%20gl
The distance (usually expressed in millimeters) from a mirror or lens to the image that it forms. In most telescopes the focal length is roughly equal to the length of the tube. Some telescopes use extra lenses and/or mirrors to create a long effective focal length in a short tube.
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http://www.skyandtelescope.com/astronomy-terms/
The focal length of a lens is the distance along the optical axis from the lens' second principal point to the CCD plane when the lens is focused at infinity.
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http://www.sony.co.uk/glossary/ShowGlossary.action?site=odw_en_GB§ionty
The focal length of lens is measured in metres. It is the distance from the centre of the lens to the point at which rays passing through the lens meet (i.e. focus). It is related to lens power
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http://www.users.zetnet.co.uk/computing/MainPage/SecDepts/Physics/Resources
The distance between the optical centre of a lens and the principal convergent focus point.
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http://www.zoo.co.uk/~z0001325/Glossary.html
the distance from the lens to the image point when the object is at a definite distance from the lens (this is also the distance to the focal point)
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https://courses.lumenlearning.com/microbiology/chapter/glossary/
The distance between the film plane and the focal point (optical centre of the lens) when the lens is focused at infinity. The focal length of the lens is marked in millimetres on the lens mount. The principal focal point is the position of best focus for infinity. There are two principal focal points, if a lens is turned around a second focus is o...
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https://www.encyclo.co.uk/local/20176
The distance from a mirror or the centre of a lens to its focal point.
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https://www.encyclo.co.uk/local/20687
Is the distance between the central point of a lens and the point where the beams are bundled (focal point). The bigger the focal length the closer targeted objects appear to be on the image
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https://www.encyclo.co.uk/local/20955
Simply put, how wide or narrow a view the lens will provide, smaller numbers being wider and larger numbers being narrower
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https://www.encyclo.co.uk/local/21112
Distance from the centre of a lens or curved mirror to the focal point. For a concave mirror or convex lens, it is the distance at which rays of light parallel to the principal axis of the mirror or lens are brought to a focus (for a mirror, this is half the radius of curvature). For a convex mirror ...
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https://www.encyclo.co.uk/local/21221
A lens' angle of view. Such as Wide angle, standard or telephoto.
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https://www.encyclo.co.uk/local/22122
The distance from the lens' optical center to its focal point, usually measured in millimeters. Ther
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https://www.encyclo.co.uk/local/22375
the distance from a focal point of a lens or mirror to the corresponding principal plane. Symbol: f · the distance between an object lens and its corresponding focal plane in a telescope. Also called
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https://www.infoplease.com/dictionary/focal-length
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