PORTABLE APPARATUS.—A term given to light, compact photograph apparatus, suit able for tourists or out-door photography.
PORTRAITURE.—Portrait photography is one of the most difficult branches of the art, and requires considerable experience and artistic culture. Amateur photographers, as a rule, fail in their attempt at this class of work owing to want of experience, and also to want of suit able appliances. Although by judicious management, fairly good portraits can be made in the open air, or in a well-lighted room, yet the best results are only obtainable in a properly con structed portrait studio. The advantage of the glass house or studio lies, not only in the fact that a large quantity of light is admitted, but principally in the additional arrangement by means of which the quality and quantity of the light can be regulated and adjusted at the will of the operator. An artist could not easily depict a round ball without suitable shading. A portrait taken in the open usually has this defect, namely the lighting is the same all over the face, caus ing it to appear flat and pasty in the picture. In the studio, however, the light is thrown more on some portions of the face than on others, so as to give a delicate shading and roundness to the image.
Considerable artistic skill and ability is required in posing the sitter in a natural and pleas ing position. There are few photographs in which the sitter does not appear to be aware that he is being photographed, and a most constrained and unnatural effect is the result.
Fairly good portraits may often be made in a well-lighted room having large windows pre ferably facing the N.N.W. or N.E. To avoid too black and white results, a reflector or white screen should be used to light up the side of sitter away from the window.
With regard to the lens most suitable for portrait work, this will be found treated upon under Lens.
Rapid plates are the best for this purpose, as the shorter the exposure the less chance the sitter has to move. For very restless subjects ahead-rest should be used, but only when absolutely necessary.
• Avoid elaborate backgrounds and accessories. With a plain or graduated background the best effects are obtainable. If accessories or scenic backgrounds are to be used they should be in harmony with the subject. No further information upon the subject of lighting and posing can be given, experience and natural ability are required. Several books (notably those by H. P. Robinson) have been published on the subject, which the student would do well to follow.
Artificial light is now being employed in portrait photography. Electric light, magnesium light, flashlight and gaslight have all been employed. Electric light is perhaps the most suitable, although the most difficult and expensive to obtain.
The light is usually fixed in the center of a large parabolic reflector, and thus thrown down on the sitter ; various other reflectors are used to light up the darker parts and prevent too great contrasts. The sitter's eyes must be carefully guarded from the light, otherwise an unnatural expression will be given.
POSITIVE.—The image of an object in which the lights and shades are represented as seen in nature. It is the opposite to a negative.
Positives may be obtained directly in the camera, or from the negative, by a great variety of processes.
In the Daguerreotype and ferrotype processes the images made in the camera appear as positives owing to the dark color of the support.
If a dry plate be exposed for some length of time more than required to produce a negative, a reversal of the image takes place and a positive is the result, usually very defective, however.
Colonel Waterhouse has recently discovered a most important method of obtaining direct positives upon ordinary silver bromide dry plates. By the addition of minute quantities of certain derivatives of carbamide (urea) to the developer a reversed action is obtained, and a positive produced instead of a negative. The process has not as yet been per fected, although, from the results of experiments, there is no doubt that it is only a matter of time and careful study.