There have been several inventions from time to time with the object of taking on a single plate a picture of much wider angle than can be included by the lens. Some, like Damoiseau's Cyclograph, and Moissard's Cylindrograph, include a very wide angle - upwards of 1800. The best known for the ordinary flat glass plate is that of Johnson and Harrison, originally invented by the former gentleman about 1870, but improved very greatly during later years. The lens moves on a vertical axis in front of a casing with vertical slot, and the motion of the plate is geared harmoniously; so that the portion under the action of the lens at any one time is always in sufficiently true position on the circumference of the circle described by the slit, which need only be about a 1/4 in. wide. In the Panoram Kodak, a much simpler but sufficiently accurate instrument for ordinary purposes, the lens swings on a pivot during exposure, and the shutter is so adjusted as to give even illumination throughout. The larger size will take views embracing an angle of 142°, and is adapted for high waterfalls, mountain peaks, and lofty towers, as well as for broad stretches of landscape.
The Panoram Kodak.
An instrument called a duplicator is frequently used in order to enable the subject (one or more persons) to appear twice in the same picture in different or contradictory attitudes - e.g. a man playing a game of chess, or fighting in a duel with his own double. It consists of an ordinary lens hood, either of cardboard or metal, from which a small segment of the plane disk is cut away on one side by a straight, true line. The hood is first placed on the lens to the left, the subject posed on that side immediately opposite the aperture, and the exposure made (rather more than three times the usual period); after which the cap is reversed, and a fresh exposure made with the subject in his new position on the right side of the picture. If the aperture is of the proper size (about 1/5 measured across the diameter) the two exposures will blend accurately into one. Double pictures, without the duplicator, are often made for other purposes. Thus "ghost" pictures of a very startling character may be created by previously exposing a plate on the person who is to represent the ghost, and then photographing the landscape or apartment which is to form the scene of his untimely wanderings. The first must obviously be an under-exposure to secure proper effects.
For a more legitimate use of the double photograph we are indebted to a well-known American engineer, Mr. C. Francis Jenkins. He was requested to ascertain, approximately, the thrust of a bridge, in going over which the brakes of a railway train were applied to stop it at a station a few hundred yards beyond. The quickest and most convincing way that occurred to him was to take a double exposure of the bridge on the same plate, first before the train reached the bridge, and then again while crossing. The developed negative showed conclusively that the bridge had moved several inches during the passing of the train.
Some developers are readily kept in dry form, the simplest way being to enclose in small, well-corked bottles a sufficient quantity to make up 4 oz. in water. Marking-ink bottles, cleared of all traces of silver by means of potassium cyanide, will sometimes serve for the purpose. A good dry developer, which will keep for some considerable time if preserved from damp and air, is composed of -
Sodium Sulphite (anhydrous) . . . . . 60 „
Another one-solution developer, which may be kept without danger of spoiling for several months in the dry state, is -
Sodium Sulphite (anhydrous) . . . . . 30 „ Sodium Carbonate (anhydrous) . . . . 95 „
Of two-solution developers one of the simplest is pyrocatechin, but for nearly all it will be necessary to mix the developer with anhydrous sodium sulphite in one bottle, and to keep the alkali, also anhydrous, in a separate receptacle.
Gun Cotton (soluble) . . . . . . 25 gr.
Sulphuric Ether ...... 2 oz.
Alcohol......... 2 „
Ordinary celluloid varnish, made by digesting old celluloid films in amyl-acetate or acetone, is as good as anything, being preservative and pliable for either leather or cloth bellows.
A dead-black varnish for coating any surface may be prepared with lamp-black mixed with a solution of sandarac in alcohol; fine lamp-black as used by artists is preferable. For camera bellows celluloid dissolved in amyl-acetate may be substituted for the sandarac.
Plates which have accidentally been exposed to light may have their sensitiveness restored by the following solution :
A. Potassium Bichromate . . . . . 10 gr. Water . . . . . . . 1 oz.
B. Potassium Bromide . . . . . . 10 gr.
Water........ 1 oz.
Soak the plate in a mixture of A and B, equal parts, and then wash in three or four changes of water. A weak solution of potassium bichromate, acidulated with hydrochloric acid, will also have a similar effect, but the chromate salt must be completely eliminated from the plate, which will be considerably less sensitive than it was originally.
It is important that the backing should not only be in optical contact with the glass and absorb the actinic light which reaches it, but that it contain nothing injurious to the sensitive film. Nor should it chip or scratch off easily, so as to cause dust. Collodion mixed with some actinic dye answers fairly well, but is difficult to remove after development. The best for general use seems to be a composition with caramel, the usual proportions being -