Photonics Dictionary

The maximum distance at which the eye can perceive and evaluate objects.

1. An instrument used to determine the visual range in an environment. 2. A type of photometer that artificially reduces an object's visibility to threshold limits and records the quantity of...

That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to 750 nm in wavelength.

That term pertaining to the spectral region that can be perceived by the eye.

An instrument that uses an erbium:glass laser to determine cloud height from the ground.

The processes in which luminous energy incident on the eye is perceived and evaluated.

The numerical definition of the ability of an observer to perceive fine detail. The average value may be taken as one minute, or 6.7 cycles/mm, at 250 mm (normal viewing distance).

The angle subtended by an object at the point of observation.

An imaginary line between the object, through the nodal point of the eye, and the fovea, or point of finest retinal acuity.

A pair of stars (double star) that can be seen separately with a telescope, generally by setting a filar micrometer for the separation and position angle. Observation of visual binaries improves with...

A device that enables visual tracing of a fiber optic cable to check for breaks and defects by coupling visible light into the cable. Also called fiber tracer.

The angular field of view that is seen by the eyes when fixed on a point straight ahead. The normal binocular visual field is approximately 130° in diameter.

A photometer that permits visual comparison of the luminance of two surfaces.

The value of the expanse of b-particles in an absorber, evaluated by visual examination of breaks in the absorption curve.

An electron tube that stores and visually displays information by means of a cathode-ray-beam-scanning and charge-storage mechanism.

A series of high contrast block letters or similar objects arranged to permit the evaluation of eyesight in humans.

A visual system including a tiny television tube and imaging optics, all contained in a helmet to be worn by pilots in flight simulator training.

A television format with enhanced vertical resolution (400 lines as compared with the standard 330) that, unlike high-definition television, can operate on existing bandwidths and with existing...

The angle subtended by an object, determined by the size of the object and its distance from the viewer.

Concerned with the transmission and reception of both sight and sound. An audiovisual system communicates pictorial images and audio signals.

In astronomy, the method of deliberately viewing objects with peripheral vision to take advantage of the eye's greater sensitivity to faint light a few degrees from the optical center.

The ability of the two eyes to see an object from two slightly different points of view. This difference allows an individual to perceive the depth and dimension of the object in view.

A television system that does not broadcast television signals but transmits them over a closed circuit.

A television system that is capable of producing an image whose colors approximate the colors of the original, by the use of additive color mixing of the three primary colors.

Aspect of vision permitting the observer to distinguish among stimuli by their hue, saturation, and brightness or lightness.

Situation in which the observer requires fewer than three independent stimuli to make color matches. Dichromats require only two stimuli and are classified as protanopes and deuteranopes (both...

Computer vision enables computers to interpret and make decisions based on visual data, such as images and videos. It involves the development of algorithms, techniques, and systems that enable...

A small handheld instrument consisting of a slit and collimator that feeds light into a small direct-vision dispersing prism. The eye is placed behind the prism to observe the spectrum of a colored...

An assembly of multiple prisms that disperses incident light into its spectral components without deviating light at the central wavelength.

The near-point distance of the normal eye. The value of 10 in. or 25 cm is normal. This value is used in evaluating the designated magnification of a simple magnifier or eyepiece.

A defect of a binocular instrument causing two images to be seen separately instead of being fused. It is caused when the optical axes of the two telescopes are not parallel. In minor cases, the eyes...

Embedded vision refers to the integration of computer vision technologies into various embedded systems, devices, or machines. Computer vision involves teaching machines to interpret and understand...

The object distance at which the eye is focused with the eye lens in a neutral or relaxed state.

A satellite-borne remote sensing device capable of transmitting images at 10 and 20 m resolution from an altitude of 830 km, each sensor covering a ground area of 60 km, by means of a folded...

A filter that transmits infrared and ultraviolet but is opaque to visible radiation.

The perception of visual stimuli at the left and right outer boundaries of the visual field.

A machine vision lens is a specialized optical lens designed for use in machine vision systems, which are used for automated inspection, measurement, and quality control in industrial applications....

Machine vision lighting refers to the use of specific lighting techniques and equipment in the field of machine vision, which is a technology that enables machines to capture and interpret visual...

A machine vision system is an integrated combination of hardware and software components designed to capture, process, and analyze images to perform automated inspection, measurement, and quality...

Machine vision, also known as computer vision or computer sight, refers to the technology that enables machines, typically computers, to interpret and understand visual information from the world,...

Vision at intermediate levels of luminance between photopic and scotopic vision, where both retinal cones and retinal rods are stimulated for visual use in dim, low light situations. See also...

The smallest area of uniform brightness that can be seen by the eye. It is measured in terms of the solid angle subtended by that area from the eye.