Photonics Dictionary

1. The focal point. 2. To adjust the eyepiece or objective of a telescope so that the image is clearly seen by the observer. 3. To adjust the camera lens, plate, or film holder so that the image is...

1. A mechanism that permits the focusing of an optical system.2. A means of obtaining the sharpest image from a cathode-ray tube display by adjusting the size of the spot where it reaches the screen.

An incandescent or carbon arc lamp designed with a stable and compact arc or filament that permits it to be used as a light source to be focused by a lens system.

A single-particle scattering technique in which an incident laser beam is tightly focused by means of lenses to yield a focal spot in the scattering material with a diameter on the order of the...

One of the electrodes used to focus the electron beam of a cathode-ray tube. As the electrode's voltage is changed, its electrical field is changed, resulting in a change of the electron beam's spot...

A coil used to focus an electron beam by the generation of a magnetic field parallel to the beam.

A retroreflector that can focus a beam of light, with one planar reflective surface, one spherical and a third that is either planar or convex cylindrical.

A scale on an optical instrument that indicates the condition of focus. May indicate the distance to the object or diopter output, or from infinity focus.

That point in the electromagnetic spectrum at which an optical system focuses the most chemically effective rays.

A means of adjusting the sharpness of an image automatically, with a sensor for estimating distance or contrast and a drive mechanism to adjust the lens. Active systems generate a light source to...

A system that determines whether an image is in or out of focus by means of a source of illumination at the conjugate focal point, which reflects off the target; the return beam is mediated by masks...

A high-quality focuser that uses rollers rather than gears and offers smooth, precise motion while reducing or eliminating image shift and backlash.

The progressive defocusing of a cathode-ray tube display image that occurs when the deflected electron beam impinges on the cathode-ray tube screen at a slant.

The range of image distances that corresponds to the range of object distances covered by the depth of field.

In a camera, the focusing of an image on the screen located at the camera's film plane. Once the image is in complete focus, the recording medium is inserted in place of the screen.

A mass spectrometer utilizing both radial electrostatic and magnetic field analyzers to improve the focusing and increase resolution.

The use of an applied electrical field to focus a cathode-ray tube's electron beam.

An image intensifier that uses electrostatics to amplify and focus the electronic image.

Describes devices that are not provided with a means of focusing.

A method of focusing an optical system by moving the front component (the lens closest to the subject) to change the distances between components. Also known as front-element focusing.

In a camera, the movement of one or more lenses behind the front lens, rather than of the front lens itself, to bring the subject into focus. Because internal focusing does not require the front lens...

Also known as gas focusing. The introduction of an inert gas into a cathode-ray tube for the concentration of the electron beam. The gas molecules are ionized by the electrons, producing a core of...

A vacuum tube in which a magnetic field is superimposed onto the tube's electrical field. When the two fields are aligned, electrons from the photocathode are accelerated through the tube in a spiral...

Focus derived from paraxial data.

The focusing of an electron beam by a magnetic field that permanently retains the majority of its magnetic properties.

A device used in solar systems to direct mirror-reflected sunlight to a heat absorber and heat-driven engine, which turns a generator to produce electricity.

A planar photocathode and a planar phosphor screen mounted in a close-spaced parallel configuration in an evacuated enclosure so that the ensemble of photoelectrons emitted from each photocathode...

A type of internal focusing in which only the lens elements closest to the rear of the lens barrel are moved.

Also known as reversed telephoto lens. A lens consisting of an ordinary objective with a negative component near its front focal point. Thus, the back focus is large, relative to its focal length....

A filter that creates spherical aberration resulting in an image with a soft outline.

A lens that exhibits spherical aberration when used at large aperture settings, and that forms an image with a slightly blurred outline.

An Abbe condenser in which the upper lens element is fixed. The lower lens may focus the illumination between the elements so that it emerges from the fixed lens as a large-diameter parallel bundle....

A lens assembly containing several movable elements to permit changing of the effective focal length (EFL). Unlike a zoom lens, a variable-focus lens may require refocusing with each change of EFL....

Derived from "self-focusing,'' Nippon Sheet Glass Co. (NSG) of Japan's trade name for graded-index fiber rods with parabolic index profile, suitable for use as cylindrical microlenses.

A two-lens arrangement intended to image light into a microscope slide sample. The primary aberrations present are red and blue rings observed around the image focus.

The value of the distance of distinct vision, minimum focusing distance or near point, divided by the focal length of the lens. Magnification is produced when the optic is placed at its focal...

An achromat, in the context of optics, refers to a type of lens or lens system designed to reduce chromatic aberration. Chromatic aberration is an optical phenomenon where different colors of light...

Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of atmospheric distortions. The Earth's atmosphere can cause light passing through it...