Tuesday, August 24, 2010

Nice old optical technique

Traditional black and white photography uses chemicals that are sensitive to light, particularly silver halides. As they are sensitive to a broad range of wavelengths covering the visible, they will react under any light, and so cannot distinguish between them. Colour photos (not digital photos) work by having different layers that are sensitive to different wavelengths, red green and blue, and so each reacts to different parts of the spectrum and the image can be reconstructed. Early colour photography however had to use a different technique, as such sentitive dyes were not available until 1907 and did not become common until the 20s and 30s. There are famous examples of colour photos before this however, such as Sergei Mikhailovich Produkin-Gorskii's amazing photos of the Russian Empire taken between 1909 and 1912. His technique took three photos in relatively quick succession, passing each one through a red, green or blue filter, and the three pictures were later recombined to make these images. You can see the time lapse in a few of them, for example the rippling of the waves in picture 14, movement in the doorway, to the left of the door and (my favourite)  the man on the right scratching his nose in 19. These are great pictures which were quite technically difficult to achieve at the time