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Also known as Abbe constant, it inversely quantifies the amount of dispersion in an optical medium. It is given by a function of the refractive index of a material at the f (486.1nm), d (587.6nm), and c (656.3nm) wavelengths. A material with a high Abbe number means that different wavelengths will have nearly the same index of refraction in that medium, yielding less separation between wavelengths of light.
Imperfections in a transmitted image compared with that predicted by paraxial limits. Types of aberrations include chromatic, tilt, defocus, spherical, coma, astigmatism, field curvature and distortion.
Regarding diffraction gratings, it is the actual percentage of incident monochromatic light diffracted into a specific order. Also referred to as grating efficiency or relative efficiency.
See also Diffraction Grating
Light energy lost through transformation to another form, such as heat, while passing through a material.
The maximum angle within which an optical fiber, electro-optic detector, or other component can collect light.
Also known as an achromatic doublet, it consists of two optical elements, usually one of crown glass and the other of flint glass, cemented together. It corrects for chromatic aberrations.
A type of microscope objective that has a flat field in approximately 65% of the center of the image, compared to the 80% of a Semi-Plan objective and the 95% of a Plan objective. They correct for chromatic aberration in the red and blue wavelengths and spherical aberration in the green wavelength.
Also known as a right angle roof prism, it inverts the image and changes the line of sight by 90°, still having left to right correct. It is essentially a right angle prism with a roof.
See also Prism
An electro-optical device for increasing the incident signal from a photodiode, photmultiplier, or similar current/voltage source.
See also Photodiode
A signal that continuously changes over time with respect to a reference level or standard. Analog-to-digital signal conversion involves sampling an analog signal at high frequency and representing each sample level by a number, stored as binary data. Analog cameras output analog video signals unlike digital cameras, in which case the analog-to-digital conversion takes place in the camera rather than in a computer.
The angle formed between a ray of light and the normal point of incidence to the surface it approaches.
The angle formed between a ray of light and the normal point of incidence to the surface it leaves.
See also Angle of Incidence
The maximum angle between surfaces measured using an autocollimator assembly.
The chemical oxidation of the surface of aluminum components to prevent corrosion and increase abrasion resistance. Black anodizing is not only cosmetically appealing, but also does not reflect light in optical, imaging and photonics systems.
A type of coating applied to optics designed to minimize back reflection and maximize throughput. AR coatings are available in single wavelength, laser-line, and broadband options.
Also denoted by f-number (or f/#) and f-stop. In optics, it refers to the ratio of the focal length to diameter; whereas, in imaging, it refers to the ratio of the focal length to exit pupil of the system. A low f/# (fast lens) has high light collecting ability while a high f/# (slow lens) has low light light collecting ability.
The limiting aperture that defines how much light is allowed through an optical system. It can be an optical lens surface or an iris, but it is always a physical surface.
A type of gas laser that uses argon ions as the amplification (lasing) medium. Although argon-ion lasers are generally larger and less efficient than Helium Neon (HeNe) lasers, they can be used to produce a wider variety of wavelengths.
The ratio of width to height in a video device. NTSC, PAL, EIA, and CCIR video signals use a 4:3 aspect ratio.
A type of lens that is not spherical in construction. Its non-spherical geometric shape allows it to correct for spherical aberrations, inherently present in spherical optics.
See also Hybrid Molding
The loss of average optical power, usually given as decibels (dB) per unit distance.
See also Decibel (dB)
A single instrument combining the functions of a telescope and a collimator to detect small angular displacement of an optical flat by means of its own generated collimated light.
Used in cameras to maintain a constant video signal output when light levels become very low, especially below minimum sensitivity. Applying gain to a signal lowers the signal-to-noise ratio by intensifying noise as well as the signal.
See also Gain
When two polarizers are placed in front of a light source with transmission axes at 90 degrees to each other, the theoretical transmission should reach zero percent of the input. Because real polarizers will not reach this limit, average extinction is cited as a measure of how closely polarizers approach the theoretical limit.
Also known as diffuse axial illumination. Refers to light that strikes an object along the optical axis, generally accomplished by using a beamsplitter.
For rotary stages, this is the amount of vertical motion of the stage as it rotates, measured with respect to the center of rotation.
A conical prism, defined by its alpha and apex angles, that focuses a light source to a line consisting of multiple points along the optical axis. A beam generated by an axicon crosses the optical axis and forms a ring of increasing diameter over distance while maintaining a constant ring thickness.
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