Invention

Part 12 - Colour

In 1855, James Clerk Maxwell, a Scottish physicist, suggested a method of making durable colour photographs and, 6 years later, Thomas Sutton used three projectors having red, green, and blue colour filters to combined images of three black-and-white photographs each taken through similar filters.

In the 1870's, Richard Maddox invented the dry plate where a gelatine coating provided a similar speed and quality to wet plates.   

In 1873, Hermann Wilhelm Vogel found that adding small amounts of different aniline dyes to fresh photographic emulsion added sensitivity to parts of the spectrum corresponding to wavelengths of light absorbed by the dyes, including red as well as orange, green and yellow. In the early 1890s, Vogel's son Ernst and William Kurtz used dye sensitization and three-colour photography to mass-produce full-colour prints with a printing press.

On early cameras, exposure times were controlled by removed the lens cap for the minutes needed for exposure but more sensitive photographic emulsions required cameras with mechanically timed, shutter mechanisms for the seconds of exposure required.

In 1884 George Eastman of Rochester, New York, devised a dry gel on a paper roll, eliminating the need for boxes of plates and toxic chemicals. He sold his first camera, the "Kodak," in 1888 and quickly switched to celluloid film rolls. In 1901, he introduced a simple box camera, with a non focussing lens, that held 100 film exposures, the Brownie. The camera, with the fully exposed roll of film, was returned to Eastman for processing and reloading. 

The photographer could frame the subject through a small telescope (the view finder) that introduced a parallax error because it was mounted above and to one side of the camera lens. The error was small for distant scenes but large for close-ups. 

Developed around 1870, the twin-lens reflex (TLR) camera reduced the parallax error with a viewfinder lens, that was the same size and focal length as the camera lens, mounted above the camera lens. A large mirror mounted at 45° reflected the image onto a ground glass screen on top of the camera. The camera was then held at waist level. Both lenses were focussed at the same time so a sharp image on the screen indicated that both lenses were correctly focussed.

Single-lens reflex (SLR) cameras have a mirror between the lens and the film so the image is viewed directly through the lens. The mirror is quickly removed before the shutter opens to expose the film which has the advantage that lenses can be interchanged while the viewfinder always shows exactly the image exposed to the film.

The view finder in a SLR typically has an optical glass pentaprism (or pentamirror) that turns the image right side up and left to right so that the photographer sees the image just as it appears.

(The retina in the human eye records an upside down image that is flipped by the brain).

Auguste and Louis Lumière introduced a practical method of colour photography in 1907. The Autochrome plate had a filter layer with about five million dyed potato grains per square inch on a plate surface. A five ton press was used to flatten these grains and this was finally coated with silver bromide.

This produce a coloured image but a reversal processing was used to make the plate into a transparent positive that could be viewed directly or with a projector. Unfortunately, it was expensive and required an exposure time of at least a second in bright daylight. An indoor portrait required a filter, to prevent the photograph from being excessively blue, and an exposure time of several minutes. 

The era of popular colour photography began with the invention of Kodachrome film that was available for 16 mm home movies and 35 mm slides in 1935 and 1936.  Three layers of emulsion captured the red, green, and blue colour components of light and a complex processing operation produced complementary cyan, magenta, and yellow dye images in those layers, resulting in a subtractive colour image (a colour negative).