Page:EB1911 - Volume 21.djvu/532

Rh camera, the front of it formed of light-proof cloth and the back by the curved flexible carriers. The lens is fitted on a vertical axis, so that the nodal point of emergence remains motionless, and is revolved round it by means of a handle worked by hand and carrying a view meter. he illumination of the image is regulated by an adjustable vertical slit in a tube attached to the lens inside the box, and by altering the rate at which the lens is revolved. The pictures taken embrace less than 180°. The apparatus folds together and is quite portable; it is fully described in Moessard's Le Cylzndrographe (Paris, 1889). The “Al-Vista” (1901) and the “Panoram Kodak” (1900) are on the same principle, but arranged as roll-holder hand cameras, in two sizes, carrying film for several exposures, 7 in. ✕ 2 in. or 4 in. ✕ 12 in. They work instantaneously, and by means of a clock-spring the lens rotates rapidly over a half-circle when released. The angle of view is about 120°

. 12.—“Al-Vista” Panoramic Camera, closed. (figs. 11 and 12). The views taken with this kind of camera are sometimes disappointing, on account of the development of cylindrical perspective on a plane surface causing apparent distortion. This distortion is avoided in Carl Zeiss's “Palmos Panoram” camera for plates 6 in. ✕ 3 in., fitted with “Tessar” lens and focal plane shutter, and other similar cameras which can be used for stereoscopic or single pictures. Other more elaborate instruments driven by clockwork have been made for making a complete tour of the horizon. Among them C. Damoizeau's “Cyclographe,” which can be used with lenses of different foci and takes the pictures on a roll-film, which is unrolled as the instrument revolves on its axis, the lens also rotating on its nodal point of emergence; and thus the image always remains sharp (Bull. Soc. Franc. d. Phot., 1891, p. 183). Commandant A. Daubresse has improved on Moessard's apparatus, by placing the lens vertically between two right-angled prisms, the upper of which receives the image and projects it through the lens on to the lower prism, from which. by rotation of the system on the vertical axis, it is projected on to a cylindrical film through an angle of 360° (Ibid. 1906, p. 430; E. Jb., 1907, p. 91). The “Periphote” and Ernemann's “Rundblick” camera are improved forms (E. Jb., 1908, p. 322).

Many early forms of panoramic cameras are described in B. J. A. 1892, p 517. Colonel R. W. Stewart’s “Panoram” (1893), A. Chevalier's “Photographic Plane Table,” J. Bridges Lee's “Photo-Theodolite” (1894). and similar cameras fitted with telescopes, levels and divided circles, are instruments of precision suitable for photographic surveying. Improved instruments for topographical surveying with stereo-photographic apparatus, on the principle worked out by Dr C. Pulfrich, of Messrs Zeiss & Co., in his stereo-comparator (1903), are being practically developed, and much information regarding them will be found in papers by E. Dolezal and others in J. M. Eder’s Jahrbücher, 1903 to 1908; also a paper by Lieut. F. V. Thompson in Geographical Journal, 1908, xxxi. 534.

Cameras for Three-Colour Photography.—Many forms of camera have been constructed for making the three negatives required

. 13—Diagram of Camera for Three-colour Photography. for trichromatic photography. They fall into two types: (1) those with a repeating back fitted with three colour-screens or filters—red, green and violet-through which the colour impressions are made successively with one lens upon a single colour-sensitive plate, as in the Sanger-Shepherd system. The colour-screens are placed immediately in front of the sensitive plate in the repeating back, which is moved on for each exposure. In a more recent form, by the same maker, the three images are taken on the sensitive plate with one exposure. The camera is divided into three compartments, and fitted with a special diaphragm which can be regulated for the varying sensitiveness of different batches of plates. he central image is impressed directly on the plate; the other two by reflection from prisms arranged so as to equalize the sizes in each case through a suitable colour-filter—red, green and blue-violet—somewhat on the principle of F. E. Ives’ camera of 1900 (fig. 13). It is convenient and successful in working. (2) Cameras made on the reflecting principle of L. Ducos du Hauron (1876), elaborated by F. E. Ives (1894) in his photo-chromoscope, in which three images are taken through three colour-screens on separate plates with one lens, the respective

exposures being regulated by reflection of the light coming from the lens by pane mirrors on to the sensitive plates, and its filtration through the colour-screens in front of them. Many variations of this method have been proposed, in which reflecting prisms replace the mirrors. The different systems have been discussed by W. Gamble (Ph. Jour. 1905, xlv. 150), the latter also by E. T. Butler (Ibid. p. 199). Sir W. de W. Abney has described three-colour cameras for landscape work in ''Ph. Jour.'' 1904, xliv. 81, and 1908, xlviii. 331.

Enlarging Cameras.—These cameras vary in form, according to the nature of the illumination, but ordinarily consist of a double or triple extension bellows camera, with a holder for the negative or transparency at one end, and for the sensitive plate or paper at the other, the lens being placed on a fixed partition between the two. Some recent forms of “daylight enlargers ” can be used as an ordinary camera. Other cheaper ones are on the fixed focus principle. Enlargers for use with artificial light are made like a magic lantern, with a condenser, projecting an enlarged image on to a sensitive plate or paper fixed on an easel or screen. A simple arrangement for daylight enlarging is to fix a suitable camera on to a larger one by a siding front, and mount the two on a studio stand tilted so that the image may be illuminated by the open sky.

Cinematographs.—Many special cameras and lenses have been introduced for taking on a long flexible sensitive film an extended series of small photographs of the successive phases of movements, and again projecting them on a screen so as to reproduce the scene, with an illusion of motion, in what are known as “living pictures,” biographs, &c. As each photograph requires a certain minimum time or exposure and must be kept in true position in sequence with the rest, some means of regulating the intermittent exposures and keeping the film in position have to be adopted; and there are many different ways of doing it, either by a continuous or intermittent motion and exposure of the film while it is being unwound from one roller on to another. The films used are similar to the ordinary celluloid films, but in narrow bands from 1 in. to 2 in. in width, the length varying with the number of exposures required, at the rate of 16 to 20 per second. They are perforated on both sides, so that they may run true and have the necessary intermittent motion, the perforations fitting on to studs on a s rocket wheel in connexion with the driving wheel and crank handle. Special lenses of short focus, from 1 in. to 3 in., with good covering power and large apertures f/4 to f/2, are required both for photographing and projecting; several such are noted below. Absolute rigidity in the camera is essential. Special stands are made for the purpose, but if a tripod stand is used it should be well braced. Special apparatus is required for developing and fixing the exposed films. hey are wound on large rollers supported over troughs containing the necessary solutions (see ). The mechanical arrangements are treated in H. V. Hopwood, Living Pictures (1899); F. P. Liesegang, Handbuch der praktischen Kinematographie (1907); K. W. Wolf-Czapek, Die Kinematographie (1908); G. Lindsay Johnson, Photographic Optics (1909); Eder's Jahrbücher.

A method of cinematography in colour was introduced by G. A. Smith and C. Urban in 1908, the main features of it being the use of a film sensitive to all colour waves to the furthest red; superimposing the colour records by persistence of vision; the use of two-colour records instead of three, in order to reduce the interval between the successive presentations; adaptation to existing cinematography machinery and films. These conditions are fulfilled by the use, in place of the ordinary revolving sector shutter in front of the lens passing intermittent white light, of a special, more rapidly revolving shutter divided into four sectors, one fitted with orange-red glass, another with bluish-green glass and two intermediate opaque sectors, so that at every revolution of the shutter an exposure is made through the red and green glasses alternately. The former passes white and yellow, and then orange, scarlet to deepest red; whilst the latter also passes white and yellow, green, blue-green, blue, all in proportion according to the red and green sensitiveness of the special y sensitized panchromatic emulsion on the film. The same shutter and colour screens are used for projection, some supplementary blue rays being added. The results are satisfactory and the method promises to be of great practical value (see Jour. Roy. Soc. Arts, 1908, 57, No. 2926).

Special cameras are made for various branches of scientific research in photo-micrograph, photo-spectroscopy, astronomical photography, &c.

Tripod Stands.—Field cameras are usually supported on wooden tripod stands, folding in two or more sections, the head being separate or fixed in the base-board of the camera. The legs should be capable of extension to about 5 ft. and adjustable in length for use on uneven round. A tripod stand may be light, but must be firm and rigid when set up. To prevent slipping, shoes of india-rubber or cork may be fitted to the points of the legs, and in some cases it may be desirable to strengthen the tripod by a folding adjustable brace. W. Butler's “Swirlcam” camera stand is made to enable the camera to be securely fixed in awkward positions, and has man valuable special features, eat extension, swivel points to the feet, &c. For hand cameras tire very light, portable metal folding and walking-stick stands are convenient. 