Wilson's quarter century in photography : a collection of hints on practical photography which form a complete text-book of the art . the time of exposure ofthe margins of an objective is almost too short to count at all. As in consequence of theintroduction of highly sensitive plates instantaneous shutters come more and more intouse, these indications are of special interest for practical men.—Dr. H. W. Vogel. Lenses, such as are used for instantaneous landscape work, are almost all fitted withdiaphragms, which slide into the body of the tube between the two lenses. I believe thissystem is kn
Wilson's quarter century in photography : a collection of hints on practical photography which form a complete text-book of the art . the time of exposure ofthe margins of an objective is almost too short to count at all. As in consequence of theintroduction of highly sensitive plates instantaneous shutters come more and more intouse, these indications are of special interest for practical men.—Dr. H. W. Vogel. Lenses, such as are used for instantaneous landscape work, are almost all fitted withdiaphragms, which slide into the body of the tube between the two lenses. I believe thissystem is known as the Waterhouse diaphragm (see Fig. 222, 1 and 2). A similar slit ismade in the under portion of the tube, and a long, thin piece of steel, with a hole in thecentre, replaces the ordinary diaphragm (Fig. 223). After having focussed, the steelslide is placed into the slit and held in an upright manner by means of a catch or springunder the lens; when this is pressed the steel slide slips rapidly down through thegrooves, and the image is thrown but for an instant upon the sensitized surface in the ^23. Fig. 224. Fig. regulated by having two or three slides with different openings (Figs. 224 and 225). Ifmore rapidity be required, a small weight can be attached to the slide by means of astrong silken thread (Fig. 225, A). If this is insufficient, a number of small metal disksor quoits can be made to lay on the top of the weight (Fig. 5, B). No shaking of thewhole apparatus, as with the old system, need be feared, for the steel slide slips throughits brass guides in an easy and uniform manner, and, when the shock arrives, the im-pression has been already obtained. The shock itself can be softened by lining theflange at the top of the slide with India-rubber, or by some mechanical contrivance, suchas a spring, etc.—Prof. E. Stebbing. I have no intention of recommending any particular shutter; let the reader exercisehis own judgment in making his selection; but I would
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