A low cost IR filter can be made from an exposed piece of color negative film. Using a piece of Kodak's Kodacolor negative film, ASA100 speed, exposed to ordinary flourescent light for 5 seconds at normal office or room ambient levels, and developed normally in C41 chemicals (The standard everyday Minilab process method) the developed film becomes the filter material. Data on optical transmission follows: Wavelength Approx. Transmission % ------------------------- --------------------------- Visible light <700 nanometers below 3 percent 700 nm 3 750 nm 10 800 nm 70 850 nm 90 900 nm 88 950 nm 87 1000 nm 83 1050 nm 80 1100 nm 75 The transmission characteristics are good for IR leds, laser diodes, CCD cameras, IR tubes and such operating in the 800-1100 nm near IR range. The film is cheap and readily available and you might try the blackened ends often found on a roll of the film after processing. The film however is delicate, scratches easily and is not moisture resistant, but it might be sandwiched between glass or plastic for protection. It might be useful as a first try before purchase of a more expensive material.January 15, 2004
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