Orthochromatic
Encyclopedia

Orthochromatic photography

Orthochromatic photography refers to a photographic emulsion
Photographic emulsion
Photographic emulsion is a light-sensitive colloid, such as gelatin, coated onto a substrate. In silver-gelatin photography, the emulsion consists of silver halide crystals suspended in gelatin, and the substrate may be glass, plastic film, paper or fabric....

 that is sensitive to only blue and green light, and thus can be processed with a red safelight
Safelight
A safelight is a light source suitable for use in a photographic darkroom. It provides illumination only from parts of the visible spectrum to which the photographic material in use is nearly or completely insensitive.- Design :...

. The increased blue sensitivity causes blue objects to appear lighter and red ones darker. A cyan
Cyan
Cyan from , transliterated: kýanos, meaning "dark blue substance") may be used as the name of any of a number of colors in the blue/green range of the spectrum. In reference to the visible spectrum cyan is used to refer to the color obtained by mixing equal amounts of green and blue light or the...

 lens filter—which removes red light—can be used with standard panchromatic film to produce a similar effect.

Orthochromatic films were first produced by Hermann Wilhelm Vogel in 1873 by adding small amounts of certain aniline-based dyes to photographic emulsions which had hitherto been sensitive to blue light only. This work was extended by others including Josef Maria Eder
Josef Maria Eder
Josef Maria Eder 16 March 1855 – 18 October 1944) was an Austrian chemist who specialized in the chemistry of photography.-Life and work:Eder was born in Krems an der Donau in 1855. He studied chemistry, physics and mathematics at the Vienna University of Technology and at the University of Vienna...

, who introduced the use of the red dye erythrosine
Erythrosine
Erythrosine, also known as Red No. 3, is an organoiodine compound, specifically a derivative of fluorone. It is cherry-pink synthetic, primarily used for food coloring. It is the disodium salt of 2,4,5,7-tetraiodofluorescein...

in 1884.
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