The Schneider 5.65x5.65" Combo Graduated Neutral Density 1.2-1.8 Glass filter is an interesting variation on traditional graduated ND filters.
Half of this filter is a standard 1-stop Neutral Density (ND0.3) filter that transmits 50% of the incoming light while the remaining half of the filter is a graduated Neutral Density 1.2-1.8. In simpler terms, it is basically a solid ND filter combined with a graduated ND.
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 while "tweaking" the lower half of your image.
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.
The Soft or Hard label indicates the degree of color graduation. Horizontal/Vertical indicates the direction of the graduation.
The neutral gray half of this filter transmits 50% of the incoming light, so that it darkens the respective portion of the subject by one f-stop without altering its colors
Neutral Density filters have four main uses
To enable slow shutter speeds to be used, especially with high speed films, to record movement in subjects such as waterfalls, clouds, or cars
To decrease depth of field by allowing wider apertures to be used, which helps separate subjects from their background
To decrease the effective ISO of high speed film (above ISO 400) and allow it to be used outdoors in bright situations
To allow cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which could cause overexposure
Neutral Density factors
ND.3 (exposure adjustment = 1 stop, reduces ISO 1/2)
ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4)
ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8)
ND1.2 (exposure adjustment = 4 stops, reduces ISO 1/16)
ND1.5 (exposure adjustment = 5 stops, reduces ISO 1/32)
ND1.8 (exposure adjustment = 6 stops, reduces ISO 1/64)
Schneider Graduated Color filters feature crystal clear, water-white optical glass, protected against edge-chipping and delamination by Schneider's unique Edge Seal, which also significantly reduces edge reflections and flare
Schneider Quality Control
Schneider filters are ground and polished to a precise flatness and plane parallelism
Because all Schneider filters are designed and manufactured with the highest possible degree of consistency, you can swap like filters mid-shoot with no discernible variation in color or effect