Photonics Dictionary: A

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aperture

An opening or hole through which radiation or matter may pass.

aperture card

A combination 80-column computer card containing a 35-mm microfilm frame. Reference data can be punched onto the card to facilitate retrieval of it on film.

aperture diaphragm

The second adjustable iris diaphragm in an optical system. In the common microscope condenser system, it usually is located beneath the substage condenser on a transmitted light microscope. When the...

aperture distortion

A loss of resolution or detail in a television signal caused by the size of the electron scanning beam.

aperture illumination

The amplitude, polarization and phase contained in the field distribution over the aperture.

aperture imaging

The formation of an image by a pinhole aperture that transmits radiation, such as gamma radiation.

aperture mask

Also known as a shadow mask, a perforated plate placed between the focusing and accelerating electrodes, and the tricolor phosphor screen in a color-television tube.

aperture ratio

The ratio of the lens aperture to its focal length (1/f/#).

aperture stop

A physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.

angular aperture

The angle between the most divergent rays that can pass through the lens to form an image. In a birefringent crystal light modulator or Pockels cell, the maximum angle in the incident light rays that...

accessible radiation

Electromagnetic radiation present upon the open aperture of the source within an operating environment.

angular spectrum approach

The angular spectrum approach is a mathematical and computational technique used in the field of optics to analyze and simulate the propagation of optical waves, particularly in the context of wave...

apertometer

An instrument designed to measure the numerical aperture of an objective.

apodization

The use of a variable transmission filter at the aperture stop of a lens to modify its diffraction pattern. Reduced transmission at the center of the aperture will favor performance at high...

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area concentration

The ratio of aperture area over receiving area for a specific lens. Also called geometric concentration.

astronomical mirror

An astronomical mirror, also known as a telescope mirror or primary mirror, is a key component of a reflecting telescope. It serves as the primary optical element responsible for gathering and...

astronomical telescope

An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial objects for observation and analysis. It typically consists of two main optical...

auto-iris lens

A device for automatic exposure control in which a motor-driven diaphragm adjusts the aperture in response to a signal from a photocell detecting ambient light.

Photonics DictionaryA

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