Plane Perspective

The surface on which the picture is thrown, or the transparent surface or plane through which the object represented may be supposed to be viewed.

Persulphate of Ammonia

(See Ammonium Persulphate.)

Petzval Lens

(See Lens, Petzval.)

Phosphoric Acid

(See Acid Phosphoric.)

Photo-Engraving

A process in which the photographic image is transferred to, and then etched on, metal. Zinc and copper are most usually employed.

Photogram

A synonymous term with photograph.

Photogrammetry

Surveying by means of photography. Photograph.

(a) A picture produced by any process of photography.

(b) To produce a likeness by means of photography.

Composite Photograph

A single photographic portrait produced from more than one subject. The negatives from the individuals that are to enter into the composite photograph are so made as to show the faces as nearly as possible of the same size and lighting, and in the same position. These negatives are then printed so as to register together upon the same piece of paper, each being exposed to the light for the same fraction of the full time required for printing. Another method of making a composite photograph is to reproduce a number of different subjects on the same negative, carefully registering the eyes of all so that they will appear in identically the same spot on the negative. The exposure given each subject is the fractional part of the full time required for a properly exposed negative. It is believed that by study and comparison of such photographs made from a large series of subjects, types of countenance, local, general, etc., can be obtained.

Photographer

One who makes pictures by means of photography.

Amateur Photographer

One who has a special love for photography and does not pursue it professionally or with a view to gain.

Professional Photographer

One who makes photography a business or a means of livelihood.

Photographic

Pertaining to or produced by photography

Photography

The art of producing images of objects by an application of the chemical changes produced in certain substances, as silver chloride, bromide, or iodide, by the action of light, or more generally by radiant energy. The rays which are in general most active in this way are those of the upper part of the spectrum, as the blue-violet and Ultra-violet rays. The red and yellow rays produce a much less marked effect on an ordinary sensitive plate; but it has been found possible to prepare a special gelatino-bromide plate, which is highly sensitive even to the less refrangible rays, as those in the infra-red region of the spectrum. Photography rests on the fact that silver nitrate and various other chemicals are decomposed by certain solar rays and reduced, becoming dark or black, or in other ways affected according to the intensity and amount of actinic rays received on them. The process consists (a) in properly exposing a surface made sensitive to actinic rays to a projected image of the object to be reproduced; (b) in rendering visible if merely latent, or in coloring or toning, the reproduction of this image; (c) in removing the sensibility of those parts of the surface which have not been acted on, and in fixing permanently the image produced; and (d) if the image obtained is a negative, as in the majority of processes, in the mechanical production of positive copies from it. - (Century Dictionary.)