The B+W 093 Infrared Filter blocks the entire visible spectrum and so to our eyes looks completely opaque. It makes pure infrared photography possible by eliminating the visible red component. Its transmission only begins to exceed 1% at 800 nm, rising to 88% at 900 nm, and remains that high far beyond the upper limit of sensitization covered by infrared films. This filter is used less frequently in pictorial photography because of the dramatic loss of effective ISO, but in the scientific field, materials research and forensics, the limitation to a strictly infrared range is often important. The filter factor is in the range of 20 to 40 but largely dependent on the illumination present and on the characteristics of IR film.
