| achromatic aplanatic condenser | <microscopy> A well-corrected microscope condenser lens, corrected for chromatic and spherical aberrations and satisfying the sine condition. (05 Aug 1998) |
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| condenser or condenser lens | <physics> A term applied to lenses or mirrors designed to collect, control, and concentrate radiation in an illumination system. (05 Aug 1998) |
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| aplanatic | <microscopy> Corrected for spherical aberration and coma. (05 Aug 1998) |
| aplanatic lens | A lens designed to correct spherical aberration and coma (q.v.). Synonym: periscopic meniscus. (05 Mar 2000) |
| aplanatic points | <microscopy> The two conjugate points for which a completely spherical glass lens is aplanatic. They lie on the principal axis, both within the sphere. (05 Aug 1998) |
| achromatic | <microscopy> Literally, colour-free. A lens or prism is said to be achromatic when corrected for two colours. The remaining colour seen in an image formed by such a lens is said to be secondary chromatic aberration. A truly achromatic lens would transmit light without decomposing it spectrally and there would be no colour fringing in the image. A doublet, composed of a positive and negative lens element, can be made achromatic for two colours which much improves the performance for most of the others. (05 Aug 1998) |
| achromatic apparatus | The nonstaining asters and spindle fibres in a dividing cell. (05 Mar 2000) |
| achromatic lens | A compound lens made of two or more lens's having different indices of refraction, so correlated as to minimise chromatic aberration. (05 Mar 2000) |
| achromatic objective | <microscopy> An objective that is corrected chromatic for two colours, and spherically for one, usually in the yellow-green part of the spectrum. (05 Aug 1998) |
| achromatic threshold | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| achromatic vision | A severe congenital deficiency in colour perception, often associated with nystagmus and reduced visual acuity. Synonym: achromatic vision, monochromasia, monochromasy, monochromatism. Origin: G. A-priv. + chroma, colour, + opsis, vision (05 Mar 2000) |
| Abbe's condenser | A system of two or three wide-angle, achromatic, convex and planoconvex lenses that may be moved upward or downward beneath the stage of a microscope, thereby regulating the concentration of light (directly from a bulb or reflected from a mirror) that passes through the material to be examined on the stage. (05 Mar 2000) |
| automatic condenser | A mechanically or electrically activated device used to provide condensing pressure in the placement of amalgam or gold foil in a cavity preparation. Synonym: automatic condenser. (05 Mar 2000) |
| cardioid condenser | A type of dark-field condenser. (05 Mar 2000) |
| cardioid dark field condenser | <microscopy> A condenser designed with two reflecting surfaces, the first, a spherical surface which reflects the rays to a second, cardioid (heart-shaped) surface. The virtue in such an arrangement is that, if the cardioid surface is of true figure, the lens is both achromatic and aplanatic. It has a limiting numerical aperture of about 1.0. Thus objectives of a greater numerical aperture cannot be used successfully with it. A true cardioid figure is the trace of a point on the circumference of a circle rolling around an equal, fixed circle. (05 Aug 1998) |
| paraboloid condenser | A type of dark-field condenser. (05 Mar 2000) |