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From: firstname.lastname@example.org Subject: RE: REPLY: Photographic cameras employed during the Great War Date: March 9, 2010 8:33:24 PM EST To: H-NET Military History Discussion List <H-WAR@H-NET.MSU.EDU> Reply-To: email@example.com An interesting website can be found at www.worldwaronecolorphotos.com, showing, as the URL suggests, a collection of color photographs taken by French photographers during WWI. Since an early form of color photography had been marketed by the Lumiere Brothers in France as early as 1903, it's not surprising that a French photographic product would be used to document the Great War. To my knowledge, however, Autochromes were only made in the form of glass plates, so the cameras used would have to have been larger than pocket-sized. Autochrome plates were never, as far as I know, made in roll film formats. The method of recording a color image, which involved spreading a thin layer of transparent red, green, and blue-dyed potato starch granules on the surface of the glass plate, then coating it with a standard black-and-white sensitive emulsion, required that the image be of sufficient size to hide the pattern of red-green-blue dots which, when the emulsion was processed as a positive rather than the usual negative image, would replicate the original colors of the scene. National Geographic used Autochromes early on, and I have had the opportunity to look at an original 5X7 inch Autochrome plate dating from 1912. Even at limited magnification, the pointillist dot pattern of an Autochrome photograph becomes visible. The color plates reproduced on the URL mentioned above show the same pattern, resembling a grainy B/W image, but what you are actually seeing is the dot pattern from the starch granules. The principle of the Autochrome system is simple: The transparent starch granules act as filters in front of the panchromatic emulsion. If a particular part of the image coming through the lens and striking the plate is red, red rays of light pass through the red dye granules but are blocked by the blue and green granules. The B/W emulsion directly below the starch layer is thus exposed primarily to red light. When a B/W film is exposed to light and processed in the usual way, the image shows as black, but when the film is reverse-processed, black areas of the negative become clear in proportion to how much exposure the film received. Thus, if light that was disproportionately red passed through to expose the plate, when the positive image is developed, those areas of the plate are clear, and when light is passed through the plate and hence through the layer of starch grains, the viewer sees red. Forget what you remember from mixing paints in kindergarten---when you are using light, rather than dye, the primary colors are red, green and blue. These three primary colors can make any color you want if you vary the ratio of red to green to blue light. Your color TV works this way, and so do the new digital billboards. You can demonstrate this principle if you can find three old slide projectors and primary color filters in red, green and blue. Put one filter in each project and aim all three at the same part of a white wall. Red+Green=Yellow. Red+Blue=Magenta Green+Blue=Cyan. Overlap all three primary color images and you have white light. Computer users who are familiar with basic inkjet or laser color printers will note that the three basic dyes used to print full color images are cyan, magenta and yellow, the complementary colors of red, green and blue.. Polaroid briefly experimented with their own low-resolution variant of Autochromes in 35mm format, but the product didn't stay on the market very long. Properly processed, Autochrome images have greater image stability than many later methods of recording color, and many photographers regard Autochromes as the most faithful way to record subtle gradations of color (even though the world of color photography has been dominated from 1938 to this year by the punch colors of the just-discontinued Kodachrome film.) Brian Gordon firstname.lastname@example.org ----- For subscription help, go to: http://www.h-net.org/lists/help/ To change your subscription settings, go to http://h-net.msu.edu/cgi-bin/wa?SUBED1=h-war -----