Volltext Seite (XML)
JANUARY 2, 1885.] THE PHOTOGRAPHIC NEWS. 5 limpid. For soft limestones, a soaking of two or three days will be sufficient, but a piece of boiler incrustation will require to be left in the solution for at least a fort night. When the rock is thoroughly impregnated with the hardening solation, take it out, and put it to dry in a warm place until the solvent has evaporated, leaving the balsam or shellac iu the pores quite hard. Sections of rocks which contain organisms—such as foraminifera, should not be ground very thin, or most of the fossils will be ground away, leaving the section quite useless as a specimen. Most thin rock sections photograph better by polarised light, as the structure is thus much better shown. Sedi mentary rocks, even white limestones, stop a great deal of light, and will reqnire a long exposure. Such sections are always much improved by a few days’ soaking in balsam and benzol, to render them more transparent. TAKING PHOTOGRAPHS BY ARTIFICIAL LIGHT. BY EUGEN HIMLY. In many countries, especially in the larger cities, there has been for a long time a desire for sources of artificial light, so as to be independent of the time of day and the weather in taking photographs. Of course, many photographers may say that since the introduction of dry plates the want is not so pressing ; but to those I answer that it is almost impossible iu dark foggy weather to make good negatives ; also that, in some countries—as, for instance, Russia, Sweden, Norway, Denmark, England, Canada, &c.—it is for most of the time very cloudy and foggy, and, iu conse quence, almost impossible to make good exposures; further, in the larger cities, it is inconvenient for the public and for the artist to have the studios on the ground-floor. In the year 1887, Mr. Vander Weyde opened in London his studio illuminated by electric light, and used at first for illumination a system of Fresnel lenses, behind which a white-washed reflector was placed. The Fresnel lenses send parallel rays, but without giving really diffused light, so that a part of the shades is very dark, while, on the other side, the light of the electrical arc is so bright and dazzling as to be disagreeable to the eye. With the electrical apparatus thus arranged, it is only possible to afford front and top light (in which case the negative is flat), or side and top light, when that side of the face which is nearest to the light is very brightly illuminated, and the other side too dark in the shades. The sensitive plates take at first the impressions of the high-lights, and later the shades, so that it generally happens that the high lights are over-expose 1 when the shades begin to make impression on the sensitive plate. Vander Weyde, of London, and Liebert, in Paris, altered the arrangement, and put the Fresnel lenses aside, and took a spherical hollow reflector, pliced the electric lamp and arc in the centre, which they blended off by means of opaque or ground glass, to hide the bright flame of the arc. The reflector was then painted inside dull white. The faults of this system are the sune as above mentioned—the shades are too deep, and have t>0 much contrast with tho high lights ; besides, the electric arc shines so brightly that it is almost impossible for many persons to look into it with out injuring the eyes. In the year 1878, whenl experimented a good deal, Iliad the idea to use, for instance, five electric lamps, and to place three in front, which should give front and top light, and two sidewards, which should give side and top light; but, at that time, it was necessary to have one dynamo electric machine for each lamp ; the division of the electric current was not discovered, the differeatial lamp of Siemens and Halske not invented, and such an arrangement would have been too costly. I tried my best to succeed with two limps, but in vain. Mr. Kurtz, of New York, has now his studio illuminated with seven or nine arclamps; he places the larger part in front of the sitting person, and a few to give side light. To ward off the extreme dazzling light, he shades it off by means of Joseph paper. My experience of long years’ standing is, that all kinds of blending off of the arc is bad, because every uneven place in the paper, or even in the ground or opaque glass, shows itself enlarged on the background. Kurtz uses besides a kind of platform, on which the camera and the sitting person are placed, and this is turned during the exposure at an angle of about 80 deg. ; through this movement he succeeds in equalizing the seven or nine shades which his lamps make, for each lamp must absolutely have its distinct shadow. In the spring of 1821, I commenced to experiment upon an entirely new idea, and invented an apparatus, which is well tried, so that I can safely say my system of artificial illumination for studios is at present the best. I will try to give a short description of it below. The best artificial light would always be that which is diffuse, and equal to diffuse daylight, and my aim was to invent a reflector (diffusor, I will call it), which really spends diffuse light. I constructed a diffusor in which the sources of the artificial light were hidden in cornices on the sides of it, so that the direct rays of the lights cannot come out, but are compelled to cross themselves on the hollow inside of the diffusor. This diffusor I can mount either on a crane which is movable, or I fasten a L-rail, bent into a semicircle of two meters radius, under the ceiling, on which I place a small carriage which carries the diffusor ; the arrangement being shown by the cut. The carriage can be moved in the circle by means of a small steel wire cord. The movement can be made by a lever, pulley movement. The diffusor spends a beautiful light which is agreeable to the eye, and really diffuse, so that it is a good imitation of diffuse daylight. When I place the diffusor in front of the sitter, I have front and top light; when I slowly move the same to the side at an angle of about 30 degrees, I have side and top light. I commence, when I expose, with the diffusor in front, and move now during the exposure the same sidewards ; by this manner I have illuminated the deepest shadows, and have more light on that side of the face to which the crane with the diffusor was swung. The result is a picture pro duced by front, top, and side light. As an auxiliary, I make use of a funnel shaped side screen, made of tin, which is mounted on a solid iron stand (like head-rests generally have), and by means of ball- and-socket joint, the screen can be fastened and kept in any position. This screen can also be used in daylight exposures ; it can be made of bright tin or pasteboard lined with tinfoil or white paper, and I can well recom mend the same, for its reflection power is astonishing. The sources of artificial light which can be used are the following:—!. Electric light, which is costly when no steam or other power is at command. 2. Gas light, with the powerful regenerator burners of Mr. Fredr. Siemens, of Dresden. Mr. Law, of Newcastle-on-Tyne, and others, have taken photographs by gas light since 1880, and since the introduction of the most sensitive dry plates, I can safely say that this light will be made very much use of for reason of cheapness and easy management.