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Thermal current produced in an operating photodetector device when no optical radiation impinges on the detector.
See also Threshold Current
Refers to light that enters a transparent or translucent object through the edge perpendicular to the lens.
A logarithmic measure of relative power levels. It is used to specify the amount of attenuation in optical fibers.
The ability of a lens to maintain a desired amount of image quality as the object being viewed moves in and out of focus. It is defined with an associated resolution and contrast, as both suffer when an object is placed closer or farther from the optimal working distance.
In an imaging system, the range in image space over which the system delivers an acceptably sharp image. This is the amount that the image surface could be moved while maintaining acceptable focus. In a nonimaging system, the range in image space over which the focused spot diameter remains below an arbitrary limit.
A measure of the detecting ability or sensitivity of a photodiode. The reciprocal of noise equivalent power (NEP).
A type of plate beamsplitter that splits incident light based on wavelength.
A filter or mirror coating that transmits or reflects light depending on wavelength rather than polarization. The color varies with angle of incidence and thickness of deposition material. Metallic coatings tend to be more spectrally flat.
A type of filter coated with thinfilms to achieve a desired transmission and reflection percentage across a given spectrum. It is often used as a color filter (both additive and subtractive). A dichroic filter is slightly angle sensitive but is much more forgiving than an interference filter.
See also Filter
A type of coating consisting of materials that are electrical insulators. The reflective coatings consist of alternating layers of higher and lower index materials (compared to the substrate) in order to achieve a certain reflectivity over a certain wavelength region.
When light is obstructed by an object and the wavefront is changed, interference occurs between components of the altered wavefront. The pattern formed by interference is called the diffraction pattern. Many components are designed to yield very specific diffraction effects (e.g. diffractive optics, gratings, etc).
See also Diffraction Grating
An optical component used to disperse light into its individual wavelengths. As incident light strikes a transmission grating's groove spacing, it is dispersed on the opposite side of the grating at a fixed angle. As incident light strikes a reflective grating's groove spacing, it is reflected and dispersed on the same side of the grating at a fixed angle.
A theoretical limiting factor governing the resolution of an optical or imaging system.
See also Modulation Transfer Function (MTF)
Diffuse, even light from an extended source.
The effect of light scattering over a large solid angle. Light is diffused by reflecting from or transmitting through an irregular (rough) surface. Typically, precautions are taken to remove diffusion in applications; however, diffusers can be utilized to introduce a specific amount of diffusion in order to create a desired effect (i.e. minimizing glare, homogenating a beam, removing speckle in a laser application, etc).
A signal that changes in regular steps. The signal level at each step is represented by a number.
Found often in high-end industrial cameras, it involves analog-to-digital conversion of all or part of a standard video signal to enhance/change the resulting signal recovered upon digital-to-analog conversion. Enhancements usually pertain to RGB balancing for more accurate color reproduction.
An industry standard for the design of microscope objectives and eyepieces. DIN standard microscopes have a 160mm tube length.
Unit of optical measurement of a lens that equals the inverse of the focal length of the lens in meters.
Point source illumination from single or multiple sources.
A measure of how much the index of refraction of a material changes with respect to wavelength. It also determines the separation of wavelengths known as chromatic aberration. Quantitatively, dispersion is inversely given by the Abbe number.
Nonlinear geometrical aberration in which magnification changes with field height (i.e. no distortion at center), defined at maximum field. If imaging a square grid, positive distortion gives a pincushion effect while negative distortion yields a barrel effect.
A term that describes the degree to which a light source expands as the distance from the laser increases. Divergence is generally specified as a full angle and can be used to predict spot sizes at a given distance through tangent calculation. Beam divergence can be reduced for long distance uses by expanding the diameter of the beam.
An imaging lens design that employs low f/# imaging lenses that provide superior overall correction and produce less distortion than standard fixed focal length lenses. However, this design can be subject to residual oblique spherical aberration. Two Gauss lenses, each comprised of a negative doublet and a positive singlet, are situated symmetrically in the design. Double Gauss lenses are commonly used in machine vision applications.
A type of singlet lens with two inward, equally curved surfaces and a negative focal length. Optimized for infinite/ infinite conjugates and ideal for image reduction and to spread light.
A type of singlet lens with two outward, equally curved surfaces and a positive focal length. Optimized for finite/ finite conjugate imaging and ideal for electronic imaging, relay systems and image projection.
Also known as a doubler, an imaging lens adapter that consists of a negative focal length achromatic lens that doubles the magnification for a specified working distance by giving half the field of view.
A lens with two optical components such as an achromatic lens.
A type of prism that inverts an image by rotating it by twice the prism rotation angle. It is available in two versions: uncoated and coated. An uncoated dove prism is used for image rotation. A coated dove prism retroreflects an image.
See also Retroreflector
In motorized stages, the ratio of motor revolutions per leadscrew revolution.
The difference between the lowest detectable light level and the highest detectable light level. Physically, this is determined by the saturation capacity of each pixel, the dark current or dark noise, the ADC circuits, and gain settings.
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