has function filter function material separation device optical filter 720 LP filter, 580/30 BP filter An optical filter is an optical subsystem that selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light), while blocking the remainder. They are commonly used in photography, in many optical instruments, and to colour stage lighting Optical filters can be arranged to segregate and collect light by wave length. John Quinn http://en.wikipedia.org/wiki/Optical_filter optical filter metadata incomplete