focal length

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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
= r/2Syn. focal distance. See principal focus; mirror; cardinal points; principal points; equivalent power; refractive power; sign convention.


1. limited to a small area or volume.
2. pertaining to or emanating from focus.

focal distance
see focal-film distance.
focal length
the distance between the lens and an object from which all rays of light are brought to a focus.
focal liver disease
widely disseminated micro-abscesses or abscesses, migration paths of helminth larvae.
focal macular melanosis
dark colored spots on the skin, not elevated above the skin surface but apt to be confused with melanosis.
focal myelitis-encephalitis
widely disseminated inflammatory lesions, usually the result of blood-borne infection, in brain and spinal cord.
focal symmetrical encephalomalacia
see focal symmetrical encephalomalacia.
focal symmetrical spinal poliomalacia
see focal symmetrical spinal poliomalacia.
focal ulcerative dermatitis
manifest by ulcers in the unfeathered anterior breast skin of 4 to 5 months old male turkeys. The incidence is influenced by litter type. Called also breast buttons.
focal zone
in ultrasound, the area of the transducer where the sound beam is most sharply focussed and where the area under examination will give the best image.
References in periodicals archive ?
The camera is able to shoot in 4K and includes autofocus and optical image stabilization.
Price, "Dynamic autofocus for continuous-scanning time-delay-and-integration image acquisition in automated microscopy," Journal ofBiomedical Optics, vol.
The addition of Autofocus and specific mode of Macro mode Autofocus algorithms make this camera to be most suitable for desktop magnifier applications such as growth monitoring, article inspection, defect detection etc.
The new ASMT-FJ70 and ASMT-FG70 devices are available in one of the market's thinnest, smallest-footprint packages for LEDs with the brightness needed for autofocus functionality in dark settings.
7 MP sensor, an electronic viewfinder, an articulated LCD screen and incredibly fast autofocus.
The webcam's fold-and-go design, coupled with autofocus capabilities and a 360-degree swivel rotation, expand the possibilities of capturing in HD video anytime, anywhere.
Although numerous image-based autofocus methods have been proposed and some found their ways into commercial products, they all suffer from limited applicability when either the observation of specific objects is wanted or when objects in different optical layers need to be in focus.
Coleshill car crash support firm Accident Exchange launched legal action in September 2009 against Suffolk-based car consultancy Autofocus after uncovering what it claimed was evidence of thousands of cases of "incorrect or dishonest" information being used in insurance claims.
The Olympus IX81-ZDC2 Zero Drift motorized inverted microscope system features a comprehensive, integrated autofocus solution for investigators doing time-lapse experiments.
Two new 1D bar code scanners are offered: the CLV650 with autofocus technology and the CLV640 with dynamic focus.
Image acquisition is optimized by using a monochrome camera and advanced illumination, autoexposure, and autofocus techniques.
Autofocus sensors that detect a specific object in the surgical field and adjust the optics quickly to ensure a clear 3D image at the working distance.