The Tiffen 4 x 4" Graduated Neutral Density (ND) ND 1.2 Glass Filter enables the shooter to adjust exposure without affecting color balance. Neutral density filters are available in 1, 2, 3, or 4 stops to suit individual situations. 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. The Soft or Hard label indicates the degree of color graduation. Horizontal/Vertical indicates the direction of the graduation.
