| optical sectioning | <microscopy> The use of high numerical aperture objective and condenser lenses on a microscope to achieve a shallow depth of field. With a very shallow depth of field, objects above and below focus contribute little to the in-focus image, so that a clean optical section is obtained. See: depth of field. (05 Aug 1998) |
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| optical storage devices | A computer disk read by a laser beam, containing data prerecorded by a vendor. The buyer cannot enter or modify data in any way but the advantages lie in the speed of accessibility, relative immunity to damage, and relatively low cost of purchase. (12 Dec 1998) |
| optical transfer function | <microscopy> The relationship between the image produced by an optical instrument and the amplitude and phase of a periodic specimen, measured at various spatial frequencies. The optical transfer function curve, which shows how well contrast is maintained for finer specimen details, is a complex function, of which the real term gives the ratio of amplitudes, and the imaginary term the phase relationships. When the brightness of the periodic specimen varies as a sine wave, the modulus or absolute value of the optical transfer function becomes the modulation transfer function, when the brightness varies as a square wave, the modulation transfer function is known as a contrast transfer function. Acronym: OTF (26 Mar 1998) |
| optical tubelength | <microscopy> The distance from the second principal focal plane of the objective to the front focal plane of the ocular. This distance is about 180 mm for high-power objectives, less for those of low power. (05 Aug 1998) |
| electron optical axis | <physics> The path of an electron through an electron optical system along which it suffers no deflection due to lens fields. This axis does not necessarily coincide with the mechanical axis of the system. (05 Aug 1998) |
| electron optical system | <apparatus> A combination of parts capable of producing and controlling a beam of electrons to produce an image of an object. (05 Aug 1998) |
| tubelength optical | <microscopy> This distance is measured from the upper focal plane of the objective to the image formed by the objective alone upon removal of the eyepiece. A light microscope so arranged that the specimen, usually a solid-liquid colloid or suspension, is illuminated by a strong pencil of light at right angles to the microscope axis. The visibility is limited by the intensity of the light source. A laser can be used as the source. It is used to detect the presence of light-ultramicroscopic particles within the range of about 0.005,um to 0.2 ~m. Not to be confused with an electron microscope. (05 Aug 1998) |