avoid damage to the film. The Kodak HIE film was sensitive to 900 nm. As of November 2, 2007, "KODAK is preannouncing the discontinuance" of HIE Infrared 35 mm film stating the reasons that, "Demand for these products has been declining significantly in recent years, and it is no longer practical to continue to manufacture given the low volume, the age of the product formulations and the complexity of the processes involved." At the time of this notice, HIE Infrared 135-36 was available at a street price of around $12.00 a roll at US mail order outlets. Arguably the greatest obstacle to infrared film photography has been the increasing difficulty of obtaining infrared-sensitive film. As of 2020-10-20, the discontinuance of Kodak HIE and Efke's IR820 has now narrowed the selection for black and white infrared film to the Rollei Infrared 400 film, which has become the only IR film on the market with good sensitivity beyond 750 nm; the Rollei film does extend beyond 750 nm but IR sensitivity falls off very rapidly. Color infrared film Color infrared transparency films have three sensitized layers that, because of the way the dyes are coupled to these layers, reproduce infrared as red, red as green, and green as blue. All three layers are sensitive to blue so the film must be used with a yellow filter, since this will block blue light but allow the remaining colors to reach the film. The health of foliage can be determined from the relative strengths of green and infrared light reflected; this shows in color infrared as a shift from red (healthy) towards magenta (unhealthy). Early color infrared films were developed in the older E-4 process, but Kodak later manufactured a color transparency film that could be developed in standard E-6 chemistry, although more accurate results were obtained by developing using the AR-5 process. In general, color infrared does not need to be refocused to the infrared index mark on the lens. In 2007 Kodak announced that production of the 35 mm version of their color infrared film (Ektachrome Professional Infrared/EIR) would cease as there was insufficient demand. Since 2011, all formats of color infrared film have been discontinued. Specifically, Aerochrome 1443 and SO-734. There is no currently available digital camera that will directly produce the same results as Kodak color infrared film although the equivalent images can be produced by taking two exposures, one