| Bertrand lens | <physics> A small, low-power lens, usually on a slide for insertion into the drawtube between analyser and ocular. It is used to observe the back focal plane of the objective so as to examine interference figures or as an aid in achieving interference figures. It is apt to be strongly astigmatic. It is used to image the lamp filament in setting up Kohler illumination as well as for centreing dispersion staining stops to the substage aperture diaphragm. (05 Aug 1998) |
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| biconcave lens | A lens that is concave on two opposing surfaces. Synonym: concavoconcave lens, double concave lens. (05 Mar 2000) |
| biconvex lens | A lens with both surfaces convex. Synonym: convexoconvex lens, double convex lens. (05 Mar 2000) |
| bifocal lens | A lens used in cases of presbyopia, in which one portion is suited for distant vision, the other for reading and close work in general; the reading addition may be cemented to the lens, fused to the front surface, or ground in one-piece form; other bifocal lens's are the flat-top Franklin type, or blended invisible. (05 Mar 2000) |
| Geneva lens measure | A device for measuring the radii of the curvature of a spectacle lens. Synonym: lens clock. Origin: Geneva, Switzerland (05 Mar 2000) |
| vergence of lens | The reciprocal of the principal focal distance used as a measure of the divergence or convergence of parallel rays. (05 Mar 2000) |
| cataract lens | Any lens prescribed for aphakia. (05 Mar 2000) |
| meniscus lens | A lens having a spherical concave curve on one side and a spherical convex curve on the other. Synonym: meniscus. (05 Mar 2000) |
| periscopic lens | A lens with 1.25 D base curve. (05 Mar 2000) |
| photochromic lens | A light-sensitive spectacle lens that reduces light transmission in sunlight and increases transmission in reduced light. (05 Mar 2000) |
| minus lens | A diverging minus power lens. Synonym: minus lens. (05 Mar 2000) |
| collimating lens | <physics> A lens used to produce a collimated beam from a light source. With a true point source on the axis the beam would be an axial tube of parallel rays With practical sources having real area the beam will be a diverging cone of parallel rays from each light point, this beam still has special properties and can be collected again by a good lens. (05 Aug 1998) |
| plan apochromatic objective lens | <physics> A modern, high-numerical aperture microscope objective lens designed with high degrees of corrections for various aberrations. It is corrected for spherical aberration in four wavelengths (dark blue, blue, green, and red), for chromatic aberration in more than these four wavelengths, and for flatness of field. A single Plan Apo objective may contain as many as 11 lens elements. (05 Aug 1998) |
| concave lens | A diverging minus power lens. Synonym: minus lens. (05 Mar 2000) |
| concavoconcave lens | A lens that is concave on two opposing surfaces. Synonym: concavoconcave lens, double concave lens. (05 Mar 2000) |