Optics Dictionary

Sometimes reading a scientific explanation is as difficult as reading Parseltongue. This section features definitions and etymology for the terms and phrases you will encounter as you explore the science of light. Etymology is the study of the history of words — when they entered a language, from what source, and how their form and meaning have changed over time. Ever wonder how the word optics got its meaning? OK — probably not but now you can find out!

Object

General Terms

1) A material thing that can be observed. 2) The figure seen through or imaged by an optical system.

Object space

General Terms

The space between the object being viewed and the system entrance pupil of an optical system.

Objective

General Terms

The optical element that receives light from the object and forms the first or primary image in telescopes and microscopes.

1620, originally in the philosophical sense of "considered in relation to its object" (opposite of subjective), formed on pattern of M.L. objectivus, from objectum "object." The lens or lens system in a microscope or other optical instrument that first receives light rays from the object and forms the image.

Ocular

General Terms

Related to the eye or its vision.

Ocular prism

General Terms

The prism used in a rangefinder to bend the lines of sight through the instruments into the eyepieces.

Offset prism

General Terms

A prism or prism assembly that serves to displace the instrument's optical axis.

Optics

General Terms


A branch of physics that studies electromagnetic radiation (for example, light and infrared radiation), its interactions with matter, and instruments used to gather information due to these interactions. Optics includes the study of sight.

1541, from M.Fr. optique, obtique (c.1300), from M.L. opticus "of sight or seeing," from Gk. optikos "of or having to do with sight," from optos "seen, visible," from op-, root of opsesthai "be going to see," related to ops "eye," from PIE *oqw- "eye/see" (see eye). Optics "science of sight and light" is from 1579; optician is first attested 1687, after Fr. opticien.

Optical activity (optical rotation)

General Terms

The ability of a substance to rotate the plane of linearly polarized light about the direction the light is traveling in, as the light travels through the substance. It often occurs in substances with molecules that have a mirror image structure, rotated crystal planes, and gases that have their molecular spins polarized (aligned in a particular direction).

Optical axis

General Terms

The line passing through both the centers of curvature of the optical surfaces of a lens.

Optical Coherence Testing (OCT scan)

General Terms

An interfermotetric technique used to create three-dimensional images. Often infrared light is used and scattered off of biological tissue to image the tissue with a resolution of up to a millionth of a meter. Better resolution can be achieved through proper selection of the light source. Interferometric techniques are ones that use the combination of light waves to obtain information about the light waves.

Optical distance or optical path length (OPL)

General Terms

The product of the geometrical distance and the refractive index, in a medium of constant index of refraction that the light travels through.

Optical fiber

General Terms

A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index of refraction to promote internal reflection.

Optical path length (OPL)

General Terms

The product of the geometrical distance and the refractive index, in a medium of constant index of refraction that the light travels through.

Optical rotation (optical activity)

General Terms

The ability of a substance to rotate the plane of linearly polarized light about the direction the light is traveling in, as the light travels through the substance. It often occurs in substances with molecules that have a mirror image structure, rotated crystal planes, and gases that have their molecular spins polarized (aligned in a particular direction).

Orthoscopy, orthoscopic

General Terms

Normal, undistorted view.

Oscillation

General Terms

A repetitive motion, usually in time, about a central value. A vibration.

1658, from Fr. oscillation, from L. oscillationem (nom. oscillatio), pp. of oscillare "to swing," supposed to be from oscillum "little face," lit. "little mouth," a mask of open-mouthed Bacchus hung up in vineyards to swing in the breeze.

Oscilloscope (scope)

General Terms

A system used to observe the variation in voltages as a function of time. Many signals can be converted to voltages and viewed this way. They are often used to observe the shape of an electrical signal.

Otoscope or auriscope

General Terms

A medical device consisting of a light source and magnifying lens used to image and inspect the inner ear.

Overhead projector

General Terms

A projector used to project transparencies. This type of projector usually consists of a large box with bright lamps and a fan, above which is a Fresnel lens that acts to collimate the light and acts as a platform for placing the transparencies. The transparencies can be written and projected onto a wall by utilizing a 45° mirror and lens system above that turns the vertical beam from the lamps below into a horizontal direction. The image is usually projected onto a screen. This allows a speaker to face the audience and utilize normal writing on the transparency, and an erect and magnified image appears on the screen for the audience.