The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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500, no lens for general or pictorial work should be employed which would include a greater angle than 500, the wide-angle lens being reserved for obtaining representations of objects not obtainable without it, as high buildings in narrow streets. Practically a lens includes a wide angle, or a large amount of subject, only when its focus is short as compared to the plate with which it is used. The diagram (fig. 3) may make this clear. Let us assume that l is the optical centre of a lens, which will cover a half-plate, cc'. The same lens will also cover a quarter-plate, dd' ; it may also cover a whole plate, bb' ; and a 10 by 8; and a 12 by 10. Therefore with the quarter-plate it would be a narrow angle or long focus, with the half-plate an ordinary angle, on a whole-plate a mid-angle, on a 10 by 8 a wide-angle, on a 12 by 10 a wider angle.
Anglol. Under this name was introduced an English manu-factured Eikonogen (q.v.).
Angular Aperture is a relation borne by the working diameter of a lens to its focal length; that is to say, the angle which the aperture of the lens subtends at a distance equal to the equivalent focal length. The wider the angular aperture the less the depth of focus and covering power of the lens. This is well seen in a portrait lens.
Anhydrous, Anhydride. Anhydrous means free from water, as in the terms anhydrous alcohol, or anhydrous ether. By anhydride is understood what was formerly understood by an anhydrous acid - a body derived from an acid by the removal of the elements of water, and now recognised not to be an acid in the true sense of the term.
Aniline, Aniline Colours. Aniline is an oily liquid; strongly basic, and forming salts with acids. Solubility: 3 in 100 of cold water ; very soluble in alcohol, ether, and benzine. It is used in the aniline process (q.v.), and also as a base from which numerous colouring matters used in orthochromatic photography are derived. With aniline as a starting-point numerous colouring matters have been obtained ; but the term aniline colours is now very generally but loosely applied to all colouring matters derived from coal-tar products. Aniline colours are now largely used as