This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
(See Magnesium Sulphate.)
III. (See Focus, Equivalent.)
(a) The process of reducing the density of the photographic film, usually the high-lights on hard negatives; also outlining figures, altering draperies, placing hand work on landscape and architectural negatives, etc. (6) A photo-mechanical process. Eating away certain portions of zinc or copper plates with a dilute solution of nitric, or other, acid.
Ethyl Oxide, or Sulphuric Ether. Light, transparent, colorless, inflammable liquid; sweet taste. Keep cool in well stoppered bottle away from the fire. Used with alcohol and gun cotton in making collodion; also as a solvent for pyroxyline (gun cotton), oils, most resins, gums, balsams and India rubber.
See Lens, Euryscope.)
To change into vapor. Liquids evaporated at temperatures below their boiling point.
(b) the aperture of the lens; (c) the nature and distance of the object; (d) the sensitiveness of the plate. In PRINTING the length of exposure is influenced by: (a) sensitiveness of the paper; (b) opacity of the negative; (c) quality of the light; (d) distance from the light; (e) and, in enlarging, the degree of the enlargement as well as the aperture of the lens. The strength of the developer also influences the required amount of exposure.
The various systems of stops or diaphragms are usually marked with their fractional value, which is found by dividing the focal length of the lens by the diameter of their openings. Under precisely the same conditions the required exposures are proportionately the squares of the denominators of these fractions.
Making two exposures on one plate or sheet of paper. Exposure for At-home Portraiture - VI. Exposure for Copies - V. Exposure for Exterior Work - III. Exposure for Lantern-Slides - V. Exposure for Papers - IV. Exposure for Portraits (Studio) - VII.
Exposure, Latitude of.
A term applied to the extent to which it is possible to deviate either way from the exact exposure required for plates or papers without harmfully affecting the character of the resulting image.
The result of allowing the light to act for too long a period of time upon the sensitive photographic materials, such as plates and papers. Slight over-exposure can be corrected in development by proper manipulation. Ex. If pyro is the developing agent, the slight addition of a 10% solution of potassium bromide together with rapidly rocking the tray which contains only enough developer to barely cover the plate, will cause rapid oxidization, therefore, rapid reduction of the salts which have been affected to the greatest degree by the light. The bromide of potassium retards the action of the developer on the parts least affected by the light. This manipulation tends to produce contrast. As a general rule, over-exposed plates should be over-developed and then reduced with potassium ferricyanide. (See Reducer, Farmer's.)