Very good photographs indeed can be taken without the use of a lens by means of a pinhole, and Earp says that, with respect to the opening, it will be found that a fine needle heated to redness, and just pressed through a piece of thin, hard cardboard, will pierce a hole of suitable size, any little burr being removed by burning it off with the side of the hot needle, the point of which, being again gently inserted in the opening, will make it clear and round. If it be convenient, the better plan is, of course, to get a watch-maker to drill a hole in a thin piece of sheet metal, which, being blackened, as must be the cardboard, is ready for use. It may be attached to one of the lens stops by strips of thin gummed paper, or, if preferred, a piece of metal, cut to the pattern of the stop, may be pierced centrally and used in its place.
The lenses being removed from the mount, the latter is placed on the camera, the focusing glass is pushed forward to within 6 in. of the pinhole, and the image observed for sharpness. By turning the camera towards the sun, and getting his image as sharply defined as possible, especially if it can be observed through the branches of a tree, the approximately best position for the focusing glass, is obtained. In finding absolutely the best position, the side-swing is useful, as, by setting a plate at an angle and exposing, the resulting negative will be a guide in enabling the experimenter to get the best possible results. .
It must be borne in mind that as a rule the pinhole should be as small as possible, for if the opening be too large a pleasantly sharp image cannot result.
The time of exposure for an Ilford ordinary plate may be 4 minutes for a tolerably open view on a fine day, and up to 10 minutes, or even more, for the view of a shady lane. It is not easy to over-expose sufficiently to spoil the negative, as the very weak light does not readily pass through the film. Developing should be started with a minimum of alkali, and should be carried on tentatively, as the shadows suffer if any more than the absolutely necessary proportion of alkali has been present.
If a finder is attached to a camera, it will be useful for centring the view, as unless exceedingly well illuminated, it is difficult to dispense with some such contrivance. The only difficulty in the operation is in the focusing with the small amount of light available, and the chief things to avoid are placing the focusing glass too far from the opening and under-exposing.