675. Making The Pin-Hole

Making The Pin-Hole. To make a pin-hole, take a piece of very thin brass, or other metal, or even tough black paper. Take a wire nail and place it in the center of the brass, and strike with a hammer. A depression will be made on one side. With a fine file rub on the raised portion until a very minute hole appears, and then push a needle through a little way. Withdraw the needle and file the rough edges. Again insert the needle and draw it back and forth, carefully, and upon removing it file until the edge of the hole is perfectly smooth. It is absolutely essential that the hole be perfectly round, thin and sharp. Especially is this necessary when extreme wide-angle pictures are to be made. The use of a magnifying glass will greatly assist in securing a perfectly formed, smooth-edged pin-hole. In order that the exposure may be determined exactly, it is essential that the needle fit the hole perfectly, not too tightly- so it will be possible to move the needle backward and forward without any side play.

676. Blackening The Brass

Blackening The Brass. All reflection must be avoided; therefore, it is necessary to blacken the brass. The portions that have been filed would render the pin-hole useless if left bright. The best method to employ is one that will not clog the hole, and this is accomplished by holding the brass in the fumes of burning rock sulphur.

677. Placing The Pin-Hole In Position

Placing The Pin-Hole In Position. The pin-hole is placed where the lens should be. An extra lens board may be employed. The pin-hole, whether of brass, paper, or other material, is fastened so that the hole will be in the center of the camera front. Care must be taken that no light enters the camera other than that coming through the pin-hole.

678. Size Of Needles

Size Of Needles. The most useful sizes of needles are numbers 8, 10, 11 and 12, which give a variation in the size of the hole from l-35th to l-75th of an inch. The number 8 is useful for 5 x 7 or larger plates, but will give too much diffusion for smaller sizes. With 4 x 5 negatives, the number 10 is the most useful for all-round work. The numbers 11 and 12 will give still sharper definition, but require a correspondingly greater amount of exposure.

Practice Work.

679. Composing The View On Ground-Glass

Composing The View On Ground-Glass. It is necessary to have some means of composing the picture on the ground-glass, but the amount of light passed through the holes, previously recommended, is too small to allow of the image being clearly seen. There are four methods of accomplishing this, any one of which will give satisfactory results. First, the image may be clearly seen on the ground-glass by constructing a larger aperture, about 1-16 of an inch in diameter.

680. The second method is to fix a pin in the lens board, directly over the pin-hole, and two pins at the edges of the ground-glass in the panel at the rear of the camera; then stretch an elastic band on these three pins. By looking along the line of the elastic from one of the back pins to the front pin, and on out into the view, all objects along this line will be included in the picture. Of course it is necessary to then look along the line formed by the other back pin and the front pin, in order to obtain the other boundary of the view - all objects between these two boundary lines will be included on the ground-glass.

681. Third, if the angle of view included by any lens, or combination of lenses, which you might have, is considered satisfactory, it is possible to overcome the difficulty of arranging the subject on the ground-glass by focusing with such a lens, and then substituting for it the pin-hole. The amount of view on the negative will be practically the same as that projected on the ground-glass by the lens. A pin-hole placed the same distance from the ground-glass as the focal length of a certain lens will give the same angle of view as that lens.

682. The fourth and simplest method of overcoming this difficulty is the use of a direct vision view-finder, as large as possible, and so arranged that any raising of the front also raises the wire frame of the finder, in order that the amount of rise may be automatically shown.