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 ?
A spherical lenses are relatively more expensive yet usually designed to obtain short effective focal lengths. The quality of the Gaussian beam that is produced by this type of lenses is acceptable fo rmost OCT applications.
The 8-inch, however, offers another 255 mm of effective focal length and very good star images even in the corners of an APS-C frame.
The NP 101 has an effective focal length of 540 mm (f/5.4), which is shorter than the 26-inch (660-mm) length of the tube would suggest.
The current design calls for a compound optical system with a maximum effective focal length of nearly 18 meters (f/50) on a three-axis mount.
The effective focal lengths for both components (camera lens and the used lens) are computed by using the following formula [10, 11].
Digital sensors are currently smaller than the area of a 35mm image, so the effective focal lengths of lenses are increased by about 50% when attached to a digital camera.
The parabolic mirrors have diameters of either 25.4 mm or 50.8 mm and effective focal lengths ranging from about 25 mm to over 150 mm.
The system is fully motorised with microprocessor control, and the lens offers parfocal selection of five effective focal lengths, four selectable filters and a four-line backlit display of focal length, filter position, focus range and operating status.

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