PINHOLE PHOTOGRAPHY. —It is a well-known fact that, although the lens is the most important part of the graphic apparatus, pictures can be made entirely without its use Very passable negatives can be made by means of a small hole in a rectangular light-tight box, and a plate fixed at the other end, or the lens can be moved from the camera front and a piece of tinfoil in which a small hole has been made can be substituted It is usually stated that no focusing is required—the larger the plate the wider the angle, and the greater the distance the larger the image—but ing to Professor Pickering 12 inches is the maximum for sharp work. He found that the shorter the distance the better the, definition, and, further, that the size of the hole is regulated by the distance. At tz inches the best results are obtainable with a hole -4, in. in diameter. If it be made any smaller than this the image will suffer by diffraction, and if any larger it also becomes blurred and indistinct. A general rule may be laid down that with short foci the aperture should in no case exceed in,, or be less than in. The hole itself requires to be very carefully made to get the best effects. There must be no burr. This must be removed. A very simple method of avoiding its formation is to burn the hole in a piece of black paper with a red-hot needle. The accompanying illustrations were made by Liesegang.
PINHOLES.—Tiny transparent spots visible in the negative.
In the collodion process they are caused by the silver solution, which is added to the developer, dissolving out the iodide from the film. Unless the preservative be well filtered the same defect may also occur.
In the gelatine dry-plate process, pinholes may be due tiny air bubbles in the emulsion, or from dust in the dark slide settling on the plate previous to exposure. In the former case the pinholes will be represented by clear glass, and in the latter by transparent emulsion. To pre vent air-bubbles in the emulsion, it should be allowed to settle for some time, and the top skimmed off before using.
Before laying the plates in the dark slide they should be dusted over with a broad camel-hairbrush. Abney further recommends rubbing the interior of the dark slide with a minute trace of glycerine, which acts as a trap for the dust and prevents it from settling on to the plate.
PINS. —Pins are used in photography for hanging up papers to dry, or for pinning the corners to a board. For pinning up silver sensitized paper, pins silver plated or coated with enamel should be used, otherwise the metal when in contact with the silver chloride will cause it to turn black at those parts.