The solar camera for direct enlargement carries a mirror and large condensing lens. The mirror is designed to transmit the solar rays through the condenser, which in turn illuminates the negative to be enlarged. The method by which the enlarged image is obtained is a counterpart of what takes place in the magic lantern, with this difference, that the source of light in the camera is the sun. The limelight lantern has, indeed, to some extent taken the place of the solar camera in mo dern practice.
Micro-photographic cam era.—The principle em bodied in the micro-photo graphic camera is the same as that involved in the fore going apparatus. It is shown in Fig. 1088 : e, micro scope ; b, reflecting mirror ; 0, camera.
Photo-miorographic camera.—The photo-micrographic camera is a diminishing apparatus, and may be set down as the micro-photographic camera reversed. Reduced photographs of official despatches, obtained by this instrument, were largely used during the Franco-Prussian war for transmission by pigeon-post.
Kinnear's portable landscape camera is shown in Figs. 1089 and 1090.
Instantaneous shutters.—With the advent of what are termed " gelatine-emulsion " plates, came the necessity of rapid exposures, exposures too rapid for the handwork of uncapping and capping the lens. This necessity has been met by shutters made to fit the front of the objective.
Some of these are pierced with an aperture, which drops over the front of the lens at the moment of exposure. Others open and close instantaneously, by means of electricity or pneu matic pressure. But Dr. Vogel's shutter is perhaps the simplest of all. It consists of a black velvet sleeve A (Fig. 1091), fixed to the front of the camera B. At the end of the sleeve, is a light wooden board C, pierced with an oblong hole D. When the plate is ready for exposure, the board, which has been laid back on the top of the 'camera, is lifted, and dropped vertically in front of the lens. The passage of the aperture D across the field effects a momentary exposure of the plate.
In addition to the instruments described, there are many others used in photography, too complex to admit of anything beyond passing notice in the present article. The simplest of these are actino meters, for determining the actinic power of light. There are instruments for registering barometric
and thermometric changes, the vibrations of the magnetic needle, and the phenomena of the inter ference of the rays of the spectrutn. De La Rue, Rutherford, Grubb, and Huggans, are names inti mately associated with astronomical photography. Specially-constructed telescopes, made to follow the movements of our globe and of the planets, have been constructed. By means of these, the moon has been photographed, and, more wonderful still, the spectra of planets and of stars.
The Dark Room.—It is most essential in all photographic processes to employ what is termed a " dark room " in all operations connected with preparing and developing the sensitive plate. This dark room is not without light, hut its light is of a quality such as in no way affects the plate. It should be lighted from a small window covered with one or two thicknesses of orange paper, and furnished with a blind of Turkey red. When this blind is drawn down, sufficient light should pass through to enable the operator to see what he is about, and yet the light is so inactinic as to be harmless to the most sensitive plate during preparation and de velopment. Beneath the window, there should be a water-tap and leaden sink for washing purposes.
Rows of shelves right and left should also be fixed within reach.
These are handy for storing bottles.
Au ample deal bench, flush with the top of the sink, and made to slide over it, facilitates opera tions.
The Studio.—The "studio " pertains to professional photography, and is worthy of special notice. It is simply a well-lighted apartment in close proximity to the dark room. It used to be con structed almost entirely of glass, but that has become unnecessary, since a photograph can be taken in a fraction of a second. It is indeed advisable to dispense with much of the light of the old studio, so as to secure more artistic effect in portraiture. The apartment should recall a well-appointed drawing-room rather than a photographic atudio. In the construction of a studio, it should be borne in mind that a steady north light is the best to work by, and that, by an arrangement of blinds, the light may be so manipulated as to suit any subject.