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Resources / Glossary / B


Back Flange Distance

The distance from the front of the camera's lens mounting flange to the sensor plane (image distance).

  See also CS-Mount , C-Mount

Back Focal Length (BFL)

A mechanical measurement given as the distance between the last surface of an optical lens to its image plane.

Back Light Compensation

An automatic function in cameras that gives higher photometric weight to objects in the center of the field of view than to those in the periphery. It increases local contrast to help avoid silhouetting.


The amount of play (lost motion) between a set of moveable parts when changing the direction of travel.

Ball Bearing Slide

A type of positioning component comprised of a stationary base with a mobile carriage riding on top. Two rows of hardened steel balls on both sides of the base provide the smooth, accurate, low friction sliding motion between the stationary base and the top slide.

Ball Bearing Stage

A type of positioning component comprised of a precision linear ball slide which serves as a linear bearing and guide, and a drive mechanism which accurately moves and positions the slide top along the linear axis. They provide controlled, precise point-to-point positioning along a linear axis.

Ball Lens

A perfectly spherical optical component often used for improving signal coupling between fibers, emitters and detectors.

  See also Optical Fiber , Sphericity


Also referred to as passband or bandpass, a wavelength range used to denote a specific part of the spectrum that passes incident energy through a filter. The first order is always at the design wavelength of the filter.

Bayer Filter

Color filter array on an imaging sensor that allows for production of color images when deciphered by an algorithm.

BBAR Coating

Broad Band Anti-Reflection coating. Optical coating that reduces reflections over a wide range of wavelengths.

Beam Diameter

The calculated distance between two exactly opposed points on a beam at a chosen fraction of peak power (typically 1/e2). It is also defined as the diameter of a circular aperture that will pass a specified percentage (usually 90%) of the total beam energy.

Beam Divergence

The increase in cross-sectional area of a propagating beam of light that is not perfectly collimated.

Beam Expander

A component commonly used with lasers to increase the beam diameter. One advantage is that expanding a beam will decrease divergence by the expansion factor. The decreased divergence is a major advantage for long distance applications despite the initial increase in beam diameter. For example, a 1mm laser beam expanded 10X will be 10mm in diameter and will have one tenth the divergence of the original beam.

Beam Width

The angular width of a beam. With respect to a conical beam of light, it is the vertex angle of the cone. The beam width is a measure of the rate of divergence or convergence of a light beam.


An optical component designed to separate collimated light into a specific ratio of transmissions. Examples include a variety of cube beamsplitters and plate beamsplitters.

Bend Radius

In an optical fiber, the minimum radius the fiber can be bent before introducing damages to either the core or the cladding.

  See also Optical Fiber , Cladding


A slanted edge (chamfer) ground into the side of a lens, mirror, prism, or window; it is used to prevent chipping or sharp edges.


A rim designed to hold a lens or other component. Many lasers and laser diode modules have an optional mounting bezel to allow them to accept 1"-32 TPI components such as line generators or beam expanders. Mounting Bezels can also adapt the laser for use with C-Mount Integrated Mounting Components.


The physical summing of signals from adjacent pixels on an image sensor into one larger effective pixel, resulting in increased sensitivity but lower resolution.

  See also Pixel


The phenomenon of double refraction in crystalline materials. Birefringent materials have slightly different indices of refraction for light that is polarized in different orientations. They will separate incident unpolarized light into its parallel and orthogonal components.

Blaze Angle

The angle between the longer leg of the sawtooth profile of a grating and the plane of its surface (as if it were polished flat). The wavelength of peak efficiency is generally referred to as the blaze wavelength. The efficiency of a grating into a desired order can be maximized by altering the blaze angle.

Blaze Wavelength

The wavelength of peak grating efficiency based upon the blaze angle. The maximum efficiency occurs when the incident angle from the blaze normal and diffracted rays from the blaze normal are equal (Littrow configuration). Using the grating equation, it is easy to determine the appropriate blaze angle for a specific peak efficiency (blaze wavelength) or determine the blaze wavelength from the blaze angle.


The amount of light that is rejected, not passed, by a filter outside the passband. Expressed as the ratio of total energy transmitted outside the passband to the total energy transmitted within the passband. Blocking values are given over a specified wavelength range.

Blocking Range

Also referred to as stopband, a wavelength interval used to denote a spectral region of energy that is not transmitted by a filter. It is typically specified in terms of Optical Density (OD).


Spill-over of charge from an over-saturated pixel to adjacent pixel sites in a CCD, causing large bright spots and/or streaks to be visible in the image. Reducing exposure time and/or illumination levels prevents blooming.

Board-Level Camera

A type of camera consisting of a sensor mounted on a PC board, not connected to a particular terminations. Intended for integration by the user.

Bolt Circle (BC)

The circular line containing the center of holes about a common center in mechanical components such as bases and mounts.

Bore Sighting

Beam alignment for a laser is a mechanical specification that measures how well the optical axis coincides with the mechanical axis of the laser (usually expressed as an angle). It is often critical to know the alignment of the beam output to the mechanical housing of a laser for alignment or sighting applications.


A optical device, typically a long, narrow tube, allowing for the internal inspection of voids or hard-to-reach mechanical parts.

  See also Fiberscope

Breakdown Voltage (BDV)

The point at which the detector begins to behave as a conductor. Operating a photodiode at or above its breakdown voltage will damage the device.

  See also Photodiode , Amplifiers

Brightfield Illumination

An illumination technique which has most of the light bouncing off the object and collected by the lens. Surface defects then appear as high-contrast dark spots.

Buffer Material

In reference to optical fibers, extra material to protect the core and cladding material within the component.

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