MA KING THE Boss.
The operation of making a satisfactory pinhole is not such a simple matter as, at first sight, it would appear, for certain conditions should be observed which are by no means easy. In the first place, the hole must be circular, with perfectly clean edges, and it should have no thickness, that is to say, the thickness of the material should be at the edges of the hole less than the diameter of the hole itself. The necessity of this will be obvious when one thinks how small the holes are, and that any appreciable thickness at the edge would give precisely the same effect as photographing through a tube. As an ex aggerated example, supposing we take an aperture of of an inch, made in a sheet of metal a sixteenth of an inch thick, we should have precisely the same result as though we used an aperture of one inch and a tube four inches long; that is to say, the angle of view, or amount of sub ject included, would be limited. Besides this, there are other considerations, such as reflections from the interior of such a tube, which play an important part when dealing with such minute apertures. The
most satisfactory material for making pin holes would be tinfoil, were it only strong enough to stand any handling. Very thin sheet brass or copper is most serviceable, though if one has a small Archimedean metal up to one sixteenth of an inch or more may be used, because one can countersink it and drive the hole through the middle. If thin brass, such as used for stencil plates, be used, it is advisable to make first a small boss in the centre by hearing heavily, or lightly tapping with a hammer, on some round pointed stick. A good-sized penholder is a capital thing, though an ordinary lead pencil may he em ployed first to make a fairly large boss, and then a. more pointed instrument used in the centre of this. The metal should be supported on something yielding ; a dozen sheets of good thick blotting-paper is an excellent thing.