0HV20 Mather Chapter 6 | Quizlet

Refraction

The change in direction of a light ray as it passes from one

transmitting medium to another, caused by a change in the velocity

of propagation.

Interference pattern

The pattern formed when two sets of waves overlap, producing

mutual reinforcement at some locations and cancellation at others.

Diffraction

The scattering or bending of a wave as it passes around an obstacle

or through a narrow opening.

Electromagnetic spectrum

The full range of frequencies that characterizes electromagnetic

radiation, only a tiny portion of it is visible as light.

Quantum

The smallest discrete unit of energy in which radiation may be

emitted or absorbed.

Refractive index

The ratio of the velocity of propagation of an electromagnetic wave

in a vacuum to its velocity in a given transmitting medium

Focal length

The distance from the center of a lens to its focal plane (the plane

in which parallel light rays are brought into sharp focus).

Radiometry

The measurement of electromagnetic radiation.

Photometry

The measurement of visible electromagnetic radiation.

Luminance

A photometric measure of the energy emitted or reflected by an

extended light source, in candelas per square meter of surface (cd/m2).

Reflectance

The proportion of incident light reflected from a surface.

Contrast

A measure of the difference between the highest luminance and

the lowest luminance emitted or reflected from a surface.

Spectral reflectance function

The proportion of light reflected from a surface as a function of the

wavelength of the incident light.

Cornea

The transparent membrane through which light enters a singlechambered eye.

Pupil

The circular aperture formed by a muscular diaphragm in the eye,

through which light passes after entering the cornea.

Visual angle

The angle an object subtends at the center of a lens: it is used to

measure the size of an object as a stimulus for vision.

Diopter

A measure of the refractive power of a lens, it corresponds to (1/f)

where f is its focal length in meters.

Accommodation

The process by which the shape of the eye's lens is changed to

alter its focal length.

Presbyopia

The age-related change in accommodative range, resulting from

loss of flexibility in the lens.

Myopia

A condition in which the refractive power of the eye's lens is too

great, causing the image of distant objects to be de-focused.

Hyperopia

A condition in which the refractive power of the eye's lens is too

weak, causing the image of near objects to be defocused.

Rod

A type of photoreceptor that is specialized to respond at low light

levels

Cone

A type of photoreceptor that is specialized to respond at high light

levels.

Grating

A pattern of alternating light and dark bars, widely used in vision

research.

Magnification

The size of the image produced by a lens: it depends on the focal

length of the lens.

Interreceptor angle

The visual angle between two neighboring photoreceptors, it

determines the resolving power of the eye.

Photon noise

The inherent natural variation in the rate at which photons strike a

receiving surface such as the retina.

Chromatic aberration

The property of an optical system that causes light rays at different

wavelengths to be focused in different planes, so degrading the

image.

Spherical aberration

The failure of light rays striking all parts of a lens to converge in the

same focal plane, so degrading the image.

Saccade

The rapid, jerky eye movement used to shift gaze direction.

Motion blur

Smearing in an image caused by movement of an object relative to

the imaging surface.

Airy disk

The image of a point light source created by an optical system: it

contains a bright central spot surrounded by several faint rings.

Linespread function The image (or a mathematical function describing the image) of a

very thin line created by an optical system.

Photopic vision

Vision a thigh illumination levels (above approximately 4 cd/m2),

mediated by cone photoreceptors.

Scotopic vision

Vision at low illumination levels (below approximately 1 cd/m2),

mediated by rod photoreceptors.

Troland

A photometric unit specifying retinal illuminance, which takes into

account pupil diameter.

Stiles-Crawford effect

The variation in the sensitivity of the retina with the place of entry

of light rays at the pupil.