The Formatt 4 x 4" Combination Light Balancing 81EF/Neutral Density (ND) 0.9 Schott-Desag B270 Crown Optical Glass Filter combines the effects of an 81EF Light Balancing filter with a Neutral Density filter.
An 81EF filter (the strongest in the 81 series) will more than replace the yellow missing from the image and place all skin tones on a distinctly "warmish" level.
Neutral Density (ND)
ND filters appear grey and reduce the amount of light reaching the film. They have no effect on color balance. They are very useful when you want to shoot high-speed film outdoors on a very bright day.
Often it is necessary or desirable to balance the light intensity in one part of a scene with another. This is especially true in situations where you don't have total light control, as in bright contrasty landscapes. Exposing for the foreground will produce a washed-out, over-exposed sky while exposing for the sky will leave the foreground dark and under-exposed. This filter enables cloud detail to be kept correctly exposed in the picture.
Determining which graduated neutral density filter yields ideal results for any given lighting situation takes knowledge, experience and a collection of such filters. Choose the filter strength which adjusts the lighting to stay within the exposure latitude (greatest difference between bright/dark values) which still shows details in both of the digital or film medium in use.
Speaking generally, the 2-stop value (ND 0.6 - the filter's clear portion allows 4x more light to pass vs. darkest portion) effectively compensates average bright sky-to-foreground situations, and the soft transition is applicable more often to a scene than the hard transition
Formatt, a company with three generations of professional filter-making experience, produces every filter to the highest technical standards. The finest materials, together with state of-the-art production technology, have resulted in a standard of optical excellence unmatched anywhere else.