Camera Knights’ Experiments
It has been presumed in commencing these notes that most would-be experimenters already possess a camera, or will at least shortly do so. Thus the greater number of experiments are such as would interest a camera fiend more deeply than the ordinary reader, although the latter might still derive much enjoyment from conducting them so far as the lack of a “dark box” will allow him.
It will perhaps be as well to spend a paragraph at the outset in describing simply and noting a few peculiarities about the commonplace camera. Photography means drawing by the agency of light. Now light is reflected from an illuminated object in straight lines or rays, of which a proportion may be collected by a lens and thrown in points upon a surface behind. (See [Fig. 1], A, illuminated object; B, lens; C, surface behind lens; D, rays of light thrown upon surface C.)
Fig. 1.—Rays of light collected by lens and thrown upon surface behind.
The front of a camera contains the lens, and is provided with a movable shutter, so that light may be only allowed to enter the dark box when a picture is to be taken on one of the sensitive plates inside. According to [Fig. 2]—which represents a camera in position to photograph the object A—the light is reflected in rays, which are collected in myriads of groups and cast pointed upon the surface of the sensitized plate B. Such ray groups—being parallel when they leave the object and pointed after passing the lens—are termed pencils of light, a most applicable name when they are employed in “sketching” a portrait on the photographic plate.
Fig. 2.—Camera in position to photograph object A.
It will be seen that the action of the lens causes the base of the object to be registered upon the top of the plate, and vice versa—i.e. the picture is taken upside down. Another noticeable feature about the magazine box camera, which does not, however, apply to the focussing camera with bellows, is that it may not be placed nearer than a certain distance (usually 10 feet or thereabouts) to the object photographed, or else the picture obtained will be blurred. The remembrance of this simple fact will save the loss of many plates to the tyro.
Finally a last note remains to be taken of the “stops.” These are really various sized holes in a metal screen, any one of which may be placed at will before the lens, and by the use of which the sharpness or distinctness of the photograph may be improved. Thus a lens at full aperture will not give such a sharp picture as would be obtained if a small hole were used, but, as the amount of light permitted to pass in the latter case is much diminished, a longer exposure must be given. Consequently when a short-timed snapshot is being secured, the largest practicable aperture or stop should be employed, even though the sharpness of the picture be thereby to some extent sacrificed.
Having thus briefly reviewed the essential features of a camera, arrangements may be made for conducting our first experiment.