" Spirit" Photography Stamp Photographs, Camera for
can be introduced at will, giving the so-called diffusion of focus. Spherical aberration may be detected in a lens by very simple tests, and its effect is to render the image upon the focussing screen indistinct, so that it is impossible to focus accurately either the centre or the margins. An easy test is: To a window affix two small circles of opaque paper so as just to touch each other, and having focussed these on the centre of the screen, insert a diaphragm by the aid of a focussing magnifier, and see whether the images gain in sharpness. If they do, spherical aberration has not been totally eliminated. Another method is to cut a piece of opaque paper the exact size of the lens, and then cut the centre of this circle out, so as to leave a ring about one-seventh the diameter. Then lightly affix this ring to the front of the lens, and focus a sheet of newspaper, or the two circles of paper mentioned above; then remove the ring and affix the central circle to the lens, and again focus. There should be no alteration of focus if there is spherical aberration present.
" Spirit" Photography. The general scene having been arranged, together with any persons to whom the " spirit" is to manifest itself, about two-thirds of the exposure is given-The lens is now capped, and, while all others are still, the "spirit" steps into its place, and the.remainder of the exposure is given. Sometimes it is more convenient to include the " spirit " in the first exposure, which should then be short. The lens being covered, the "spirit" walks away, and the exposure is completed. The conventional white sheet is generally most appreciated as a garment. For instructions how to produce a photograph depicting an interview between a person and his own ghost, see Polypose. Also see Portraiture.
Squeegee. A strip of india-rubber mounted in a wooden holder. When drawn or pushed over wet paper it not only skins the excess of fluid off, but also drives out the excess of water from under the sheet. The squeegee is chiefly used for establishing good contact between wet sheets of paper, or paper and glass in carbon printing.
Stamp Photographs, Camera for. See Multiplying Camera.