[52] With this kind of a camera you can see the object you are photographing up to the very instant you snap the shutter.
Every good camera has what is called a rectilinear lens, that is, a compound lens formed of two achromatic lenses, which means that each acromatic lens is made up again of two lenses one of which is of crown glass and the other is of flint glass, and these two latter lenses are cemented together with Canada balsam.[53]
[53] This is a clear gum that is obtained from a tree called the Canada balsam.
Now whereas a common convex lens will produce all the colors of the rainbow around its edges when a ray of light passes through it, an acromatic lens lets through only the white light and while a single convex lens makes the straight lines of a building curved in the picture, an acromatic lens keeps all the lines straight, or rectilinear, and hence its name.
These little cameras are filled with mechanical snap shutters and they use roll films, that is the sensitive silver and gelatine emulsion is spread on a thin celluloid film instead of on glass plates. These roll films come on spools in lengths of ¹⁄₂ and 1 dozen each and they can be loaded into the camera in daylight. The same kind of developing and fixing solutions are used for films that are used for dry-plates.
How to Make an Enlarging Apparatus.
—To make an enlarged picture of a small negative take out the back of your camera and get two perfectly clear sheets of glass to fit the opening.
Make a box of ¹⁄₄ inch thick wood, 6 inches wide, 6 inches long and 7 inches high and have the top of it separate so that it can be lifted off and put on the box. In the middle of the top near one edge cut a hole 1¹⁄₄ inches in diameter and put an electric light socket—to which a cord and plug is fixed—in it as far as it will go and then screw in a nitrogen 100 watt electric lamp[54] which gives about 75 candle power, as shown at [A in Fig. 58].
[54] The Delco Light Co., 52 Park Place, New York, sells these lamps and all other electrical supplies.
