focal length


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length

 [length]
an expression of the longest dimension of an object, or of the measurement between its two ends.
crown-heel length (CHL) the distance from the crown of the head to the heel in embryos, fetuses, and infants; the equivalent of standing height in older persons.
Measuring an infant's crown-heel length. From Lammon et al., 1996.
crown-rump length (CRL) the distance from the crown of the head to the breech in embryos, fetuses, and infants; the equivalent of sitting height in older subjects.
cycle length in cardiac pacing terminology, the time interval in milliseconds from one event to the next; it is the inverse of the intrinsic rate (beats per minute) or the paced rate (pulses per minute).
focal length the distance between a lens and an object from which all rays of light are brought to a focus.

focal length

In optics, the length from the lens to the point of focus of light rays passing through the lens.
See also: length

length, focal

The linear distance separating the principal focal point (or focus) of an optical system from a point of reference (e.g. vertex, principal point, nodal point). The first (anterior) focal length is the distance from the lens (or first principal point) to the first principal focus. The second (posterior) focal length is the distance from the lens (or second principal point) to the second principal focus. Symbol: f.In a spherical mirror the focal length f, i.e. the distance between the focal point and the pole of the mirror, is equal to half its radius of curvature r
f
= r/2Syn. focal distance. See principal focus; mirror; cardinal points; principal points; equivalent power; refractive power; sign convention.
References in periodicals archive ?
Longer focal lengths such as the 70mm end of a 24-70mm zoom or Nikon's purposely-designed 85mm f/1.4 are better choices for this, but even the 17in (42cm) nearest focusing distance of a 50mm will deliver a close-up portrait capable of revealing every facial detail.
To have the option of taking wide-angle and telephoto pictures, you needed other lenses of fixed focal lengths. That meant extra expense and more weight to carry around.
They generally have longer focal lengths than reflectors but suffer no blockage.
Remote camera set-ups such as this are always fitted with shorter focal length lenses because the combination of a wide view and great depth of field ensures an image of enormous detail and sharpness.
What makes 200 mm the optimal focal length? The longer the focal length of the tube lens, the fewer distortions are created by high-angle light passing through intermediate components, as the cone-shaped pattern of the light rays widens more gradually in a longer tube than in a short one.
Despite the move to full-frame (35mm) format In recent digital SLR cameras, many macro specialists prefer to use a cropped sensor (APS-C) camera because it extends the focal length of any full-frame lens by a factor of approximately 1.5x and utilises only the central area of the lens for optimum image definition.
Also it's not the focal ratio of a fast refractor that permits "wide-field views of the Sun" but rather its focal length. This is why the 480-mm Pronto or TV-76 scopes, used with the Quark's amplifying optics and 21-mm back filter, permit a full-disk solar view.
Manufacturer Celestron Model C8-S Price (US$) $1,059 Mount included Optics type Schmidt-Cassegrain Aperture 203 mm Focal length f/ratio 2,032 mm f/10 Finder 6x 30 Mount type German equatorial Motor drive optional Computerized "Go To" no Also available: C8-SGT "Go To" system for $1,359.
This produces a rounded lens with a small focal length, so the drop can focus light only to a point near itself.
of Englewood Cliffs, New Jersey, provides a focal length of 7.5 mm to 75 mm for 3/2" CCTV cameras and a reach of 10 to 100 mm when used on a 1/3" camera.
Computar offers an extended family of larger format, C-mount, fixed focal length lenses as well as a complete family of CS and M12 mount lenses.
It has a 30x zoom lens which in terms of focal length is 4.3mm to 129mm (35mm film equivalent of 24-720mm).