Graduated ND filter for matte box systems that darkens only one image area—typically sky against foreground in extreme contrast situations.
Technical Details
Standard sizes include 4x4 inches (100x100mm), 4x5.65 inches, and 6.6x6.6 inches for corresponding matte box systems. Density values range from 0.3 ND (1 stop reduction) to 1.8 ND (6 stops). Hard Half Grids have a defined separation line, while soft variants exhibit a gradient of 10-30mm width. The filter glass is made of optical glass with multi-layer coating to minimize reflections and color casts. Rotatable filter holders allow the separation line to be adjusted for different horizon or object positions.
History & Development
Half Grids evolved in the 1970s from landscape photography, where Singh-Ray and Cokin introduced the first commercial systems. Tiffen established professional variants for film production in 1982. With the introduction of digital cameras around 2000, discussions arose about the necessity of physical filters versus digital post-processing. However, modern ARRI and RED camera systems continue to use Half Grids for shooting, as preserving image information in highlights and shadows significantly improves post-production quality.
Practical Use in Film
Roger Deakins extensively used Half Grids in "Blade Runner 2049" (2017) for exterior shots with extreme contrast differences between the sky and landscape. When shooting with available light, they compensate for typical exposure differences of 3-6 stops between a bright sky and the foreground. In practice, the 1st AC positions the filter during the shot, with modern wireless follow focus systems also capable of remotely controlling filter rotation. The advantage lies in preserving image information without clipping; the disadvantage lies in potential artifacts with moving objects crossing the filter line.
Comparison & Alternatives
Unlike full-coverage ND filters, Half Grids have a partial effect. Center-spot NDs darken in a ring shape, while Half Grids operate linearly. Digital alternatives like HDR shooting or exposure bracketing require post-production and can lead to ghosting with movement. Graduated ND apps in camera software offer similar effects but do not achieve the quality of physical filters in extreme contrast ratios. Polarizing filters also reduce contrast but affect color saturation and reflections differently.