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IEC Laser Class

A laser class standard administered by the Commission Electrotechnique Internationale, which publishes international standards for electronic components. It is an an alternative to the CDRH laser class standard used throughout North America.

See also CDRH Laser Class, CE Certified

Image Capture Board (Frame Grabber)

A computer card that samples and digitizes analog video signals so that the information may be processed, stored, or operated on by the computer. Ideal for analog cameras because they have no computational software or digital cameras to maximize bandwith by transmitting data from large sensors at high frame rates.

See also Analog Signal, Digital Signal

Image Circle

The diameter of the maximum usable image produced by an imaging lens.

Index of Refraction (n)

The ratio of the speed of light in a vacuum (c) to the speed of light in a refractive material (v). The index of refraction of a given medium varies with wavelength because the speed of light varies with wavelength. Common indices of refraction include nd (the yellow helium line at 587.6nm), nf (the blue hydrogen line at 486.1nm) and nc (the red hydrogen line at 656.3nm).

See also Abbe-Number, Birefringence, Angle of Incidence , Glass Code, Angle of Reflection, Dispersion, Refraction, Gradient Index, Cladding

Infinite/Finite Conjugate

A conjugate distance relationship that combines two processes by focusing a source placed at infinity down to a spot. In terms of imaging, the object is placed at infinity (defined as the distance at which light rays can be considered collimated) in relation to the optical elements and imaged a finite distance onto a sensor or other image plane.

See also Plano-Convex (PCX) Lens, Meniscus Lens, Conjugate Distance

Infinite/Infinite Conjugate

A conjugate distance relationship that takes collimated light, changes the beam diameter according to the magnification, and emits collimated light. In terms of imaging, the object is placed at infinity (defined as the distance at which light rays can be considered collimated) in relation to the optical elements and relayed an infinite distance. No image is formed, but can be with the introduction of a secondary infinite/ finite conjugate design system.

See also Conjugate Distance, Double-Concave (DCV) Lens, Plano-Concave (PCV) Lens

Infrared (IR) Spectrum

The wavelength interval of the electromagnetic spectrum that corresponds to infrared light (light that is beyond the visible red range). IR radiation is often divided into three smaller regions: 0.750 - 3μm, 3 - 30μm, and 30 - 1000μm – defined as near-infrared (NIR), mid-wave infrared (MWIR), and far-infrared (FIR), respectively.

See also Visible Spectrum, Ultraviolet (UV) Spectrum

Integration Time

In an imaging device, the length of time during which the sensing elements are collecting charge between transfers to the transport registers. Also known as exposure time.

Interference Filter

A type of filter made up of several metallic or dielectric layers of material, typically composing a three-cavity design. The correct combination yields high spectral transmittance over very narrow wavelength ranges due to interference effects between layers.

See also Filter, Cavity, Dielectric Coating

Interference Fringe

Alternating light and dark bands in an intensity pattern due to the wave nature of light. The phase difference remains constant along one fringe. When using an optical flat, straight, parallel, and evenly spaced interference fringes indicate that the work surface flatness is equal to or higher than that of the reference surface.

See also Power, Irregularity, Interferometry, Optical Flat


A family of techniques that utilizes the interference of waves of light for precise determinations of, wavelength, flatness, or other attributes.

See also Power, Irregularity, Optical Flat, Interference Fringe

Interlaced Scan

Interlaced imaging devices produce images by scanning and reading out odd-numbered lines in the first pass, then even-numbered lines in the second pass, and so on. Two fields are assembled into one full frame.

See also Frame, Field, Progressive Scan

Interline Transfer

Also referred to as 2:1 interlaced video, it combines two fields to make up each video. If each field is scanned at 60Hz, the frame rate is necessarily 30Hz.

See also Frame, Field

Inverted Load Capacity

The reverse, or inverse, or normal load capacity whereby the load or force applied to a mechanical component is directed upward.

See also Normal Load Capacity

Ion-Beam Sputtering (IBS)

A physical vapor depostition technique to increase the density of thin-film coatings, thus creating "hard coated" filters. The thin film is deposited by sputtering (ejecting) material from a target by ion bombardment which is then deposited onto the filter substrate.

Iris Diaphragm

A mechanical aperture designed to smoothly change the aperture size. It can be used to control the amount of light entering an optical system if used as the aperture stop.

See also Aperture (f/#), Aperture Stop


Denoted by E, it is the incident power per unit area, measured in W/m2. Also known as radiant flux density.


A type of surface accuracy specification that describes how the shape of a surface deviates from the shape of a reference surface. Regularity refers to the sphericity of the circular fringes that are formed from the comparison of the test surface to the reference surface. When the power of a surface is more than 5 fringes, it is difficult to detect small irregularities of less than 1 fringe. So surfaces are specified with a ratio of power to irregularity of approximately 5:1.

See also Power, Interferometry, Optical Flat, Interference Fringe