This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
By J. C. MOORE
The hand camera suitable for this work is the kind commonly known as the reversible back, which is a detachable part that carries a ground glass for focusing and a place to insert the plate holders. When this part is removed, it will be seen that the back of the camera is mortised to prevent light from entering. Construct a frame to take the place of the back, but make it about 5/8 in. larger all around, and make one surface to fit the mortise of the camera box.
A back is now made and attached to the frame, to carry the ground-glass reversible back, so that it can be shifted over the center of focus for each small portion of the plate on which the picture is to be made. Measure the outside of the plate holder and, doubling the dimensions both ways, lay out a diagram on a piece of paper. Lay the plate holder on the paper and move it to the extreme left, then to the right, to see if the center of the plate will coincide with the cen- ter of the back. In the same manner locate the center in a vertical position. If the center lines do not coincide, increase the dimensions until this occurs. Mark, in the exact center, an opening the size of the plate and cut out the wood. It is best to use a three-ply wood for making the back, but if this cannot be obtained, procure a dry piece of wood and mortise and glue strips to the ends to keep the wood from warping. Glue the frame to this back, over the opening, and make attachments to hold it to the camera in the same manner as the reversible back was attached.
Ill: The Attachment as It is Fitted to the Camera and the Reversible Back in the Frame
Ill: Manner of Laying Out the Pattern for the Back and Locating the Exact Center
If pictures of two or three different sizes are to be made, the opening in the new back should be fitted with as many new pieces as there are sizes of pictures, each to have an opening of corresponding size. For a 5 by 7-in. plate, 1 1/8 by 1 1/4-in. pictures is a good size, as there will be room for 24 pictures on the plate with a small margin left for notes. The piece to fill the opening should be made of the same material as the back so that a smooth joint will result. As a board cannot be made smooth enough for a perfectly light-tight joint, the surface on the new back, over which the reversible back travels, must be covered with cloth - a piece of black velvet is suitable - to exclude all light as the plate holder is shifted over the back.
A frame is now made to carry the reversible back of the camera, the size of which will depend on the size of the other parts, as well as on the size of the camera to be used. This frame