LOW COST IR FILTER

      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.