SPECTRAL PHOTOGRAPHY
Reprint from "Scientific American" - December 27, 1902
by George M. Hopkins

Exhibits in the Haunted Museum are based on the work of Troy Taylor from his book, Ghosts by Gaslight!


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Probably the oldest method of taking a spectral photograph is to expose the plate for a brief period, in the camera, with a skeleton, or person in ghostly apparel, some hideous monster, or even a large bunch of flowers as a subject, afterward using the same plate again in the camera, upon the subject to be taken, with the spectral images, and then developing the whole plate, in one operation.

Another method of producing spectral photographs is to make a very thin positive image on glass, of the same size as the plate to be used in producing the spectral photograph, then placing the plate in the holder, as usual, with the weak positive superimposed, and making the exposure through the positive, thereby giving on the negative plate, along with the person, a ghostly image of any prearranged subject. This is a very good way of producing a ghost picture; but it is liable to detection if the same weak positive is used a second time.

Another method of producing such images is to paint an outline on the background the figure desired, but using a solution of quinine sulphate. The image when dry is invisible to the eye, but it capable of producing an image on a sensitive plate.

In some recent experiments still another method of producing spectral photographs was discovered. This method, together with a specimen, is illustrated in the accompanying engravings. It consists of supporting a mirror in front of the photographic lens, which is smaller in diameter than the lens, so as to cause an image of the object, at one side of and at right-angles to the axis of the lends, to be reflected in the camera, and produce and image simultaneously with the image of the person or object, the same being formed by marginal rays, which pass to the photographic lens, around the edges of the mirror. The mirror being entirely out of focus does not appear on the photographic plate. By this very simple contrivance images of various objects may be made upon the same plate.

The amount of light reflected into the camera by the mirror is regulated by the distance of the latter from the lends, and the marginal rays which enter the lens may be regulated by the diaphragm. The apparatus required for this experiment is very simple indeed. It consists simply of an apetured plate, slipped over the lens, and clamped between the lens and the collar. The plate is bent at right angles and the horizontal arms is slotted. In the slot is placed a screw, having a shoulder which is clamped against the plate by a milled nut. The head of the screw is slotted, and provided with a clamping screw, for holding a downwardly projecting wire, to which is attached a small mirror by means of beeswax. The wire should be provided with a  coat of dead black varnish, to prevent it from showing on the plate. The mirror should be varied in size to suit the lens to which it is applied. In the present case it consists of a silvered microscope slide-cover 5/8 inch in diameter, and about 1-200 of an inch thick. Thin glass is used for this purpose to avoid the forming of a double image of the specter. The simplest way to silver the slide cover is to scrape the amalgam from a small piece of looking-glass, leaving a disk the size of the glass to be silvered. By placing a minute drop of mercury on the disk and allowing it to remain for a few hours and then varnished with a shellac varnish. If too much mercury has been used, the surplus can be taken up by means of a thin piece of tinfoil applied to the back of the mirror, which is allowed to remain.



Fig. 1 - Mirror for Producing Spectral Images



Fig. 2 - Arrangement of Specter, Mirror and Subject



Fig. 3 - A Ghost Story

By a little practice in the adjustment of the mirror and shutter, the proportionate amount of light for the specter and for the subject may be regulated. The object representing the specter is mounted on black cloth, preferably black velvet, so that no other object than the specter will be represented by reflection.

A screen may be placed between the sitter and the specter, so that the delusion may be made complete. By folding the screen over the specter when it is not in use, the litter will be concealed, so that by careful manipulation, the trick will not be discovered by the sitter.

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