Heliopan 77mm Graduated Neutral Density (ND) 0.3 (2x) Glass Filter - 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. Grad ND filters are part clear, part neutral density (available in grades of 0.3 (1 stop), 0.6 (2 stops), 0.9 (3 stops)). They allow the transition to be blended into the scene, often imperceptibly. A GND 0.6-to-clear, with a two stop differential, will generally compensate the average bright sky-to-foreground situation and is also the most popular density of the series.
Graduated Neutral Density Factors
- GND.3 (exposure factor = 2x; exposure adjustment = 1 stop; reduces ISO 1/2)
- GND.6 (exposure factor = 4x; exposure adjustment = 2 stops; reduces ISO 1/4)
- GND.9 (exposure factor = 8x; exposure adjustment = 3 stops; reduces ISO 1/8)
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