Harper's indoor book for boys

by Joseph H. Adams

In order to adapt the focus of the lenses according to the distance the lantern is from the screen, a sliding front is necessary (see Fig. 5). Cut a base-block scant seven inches wide and six inches long, fastening to it, three and one-half inches from the front, an upright piece of wood high enough to be even with the top of the lantern-box. When the base is resting on the deck in front of the box two small angle-brackets will steady the upright and make it rigid (see Fig. 5). Cut a hole in this upright board so that the centre of the projector mounted in it lines exactly with the centre of the condensing-lenses. This is an important point; if the lenses are not carefully mounted opposite one another the picture will not be clear. Now fit a piece of wood one-fourth of an inch in front of the main box, fastening it at the top with a strip of tin. There must be a hole three inches square cut in this board, the middle of which must line with the centre of condensing-lens. In the opening between this board and the box slip a thin piece of board for the slides to rest on. Set a double-wick lamp or central-draught burner within the box at the proper height, so that the brightest part of the flame will be in direct line with the centre of the reflector and the condensing-lenses.

The principle of the magic lantern is the reflection of the light through the condensing-lenses, which pick up all the light possible and throw it through the slide, which is located directly in front of it. The light is then taken up by the projector, and the pencils of light are thrown onto the screen, at the same time magnifying the picture. This principle is shown by the dotted lines in Fig. 6, which show also the relative position of the lamp, lenses, and reflector.

To keep in the light that would escape through the top opening in the box, put a piece of common stove-pipe (small) over the lamp-chimney. Cut a cap from a piece of tin (Fig. 7 A), the ears extending down inside the chimney to hold the cap in place, when the cap-piece is bent in a half circle as shown at Fig. 7 B.

To cover the space between the lantern-top and the moving front board a piece of black cloth can be used. Or if you have an old camera-bellows it may be made fast to the back of the projector-lens board and to the front of the slide-board located close to the box. It is not necessary to have an absolutely light-tight bellows; indeed, a very good one can be made from some wire hoops with black cloth sewed to them.

In Fig. 8 the wire hoops are shown, and in Fig. 9 the finished bellows, with the cloth stitched in place, is ready to be attached to the boards with small tacks or staples.

When all the parts are assembled, and the lantern is complete (except the bellows, which has been omitted so that the working parts may be more clearly shown), the lantern will appear as in Fig. 10.

A Stereopticon

The cost of a good stereopticon will range from twenty-five to seventy-five dollars, and that sum places it beyond reach of the average boy. The following instructions and illustrations will enable any smart boy, who is handy with tools and light materials, to make a high-grade stereopticon with lamp and mechanism that is capable of doing really good work.

Fig. 8. Fig. 9. Fig. 10.