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Compugraphic Corporation, commonly called cg, was an American producer of typesetting systems and phototypesetting equipment, based in Wilmington, Massachusetts, just a few miles from where it was founded.
An achromatic doublet brings red and blue light to the same focus, and is the earliest example of an achromatic lens. In an achromatic lens, two wavelengths are brought into the same focus, here red and blue. An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses ...
The achromatic number ψ(G) of a graph G is the maximum number of colors possible in any complete coloring of G. A complete coloring is the opposite of a harmonious coloring , which requires every pair of colors to appear on at most one pair of adjacent vertices.
Pure achromatic colors include black, white, all grays and beiges; near neutrals include browns, tans, pastels, and darker colors. Near neutrals can be of any hue or lightness. For example, the "Achromatic" use of a white background with black text is an example of a basic and commonly default color scheme in web design.
For instance, a purple of medium lightness and fairly saturated would be 5P 5/10 with 5P meaning the color in the middle of the purple hue band, 5/ meaning medium value (lightness), and a chroma of 10 (see swatch). An achromatic color is specified by the syntax N V/. For example, a medium grey is specified by "N 5/".
Chester Moore Hall (9 December 1703, Leigh, Essex, England – 17 March 1771, Sutton) was a British lawyer and inventor who produced the first achromatic lenses in 1729 or 1733 (accounts differ). He used the achromatic lens to build the first achromatic telescope , a refracting telescope free from chromatic aberration (colour distortion).
This was a simple plano-convex or bi-convex lens, or sometimes a combination of lenses. With the development of the modern achromatic objective in 1829, by Joseph Jackson Lister, the need for better condensers became increasingly apparent. By 1837, the use of the achromatic condenser was introduced in France, by Felix Dujardin, and Chevalier.
An achromatic doublet An old Carl Zeiss Tessar camera lens with four elements, comprising two doublets. The front doublet is air-gapped and divergent ; the rear doublet is glued and convergent. This arrangement was better at correcting spherical and chromatic aberrations and astigmatism than previous lens designs.