Because the imaging device is designed to be sensitive in low light conditions it is easily over exposed in bright situations. The Neutral Density filter is used to help control this situation as well as to gain more control over depth of field. Up to now ND filters made with dyes did this job, but passed small amounts of red and near infra-red light to create their transitional slope between attenuating visual and passing infra-red.
Putting Them to the Test
“This filter works perfectly.” “The Tiffen IR ND filters are the only filters that effectively cut far red contamination on those cameras [Panavision Genesis/Sony F35/F23].” “I have to state how impressed I am that they [Tiffen] came up with this dye formula to cut far red….” “That makes the Tiffen IRND filters the best choice …., and the fact that there’s no dichroic Hot Mirror coating reduces the cost ….”