This Genustech 77mm Variable Neutral Density and Circular Polarizer Filter is a filter that combines a solid variable neutral density element with a circular polarizer element. The variable neutral density element provides an exposure reduction of 2 to 8 stops. Its 0.6 to 2.4 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than would normally be required. The degree of density is easily controlled by rotating the front filter ring, helping you to predetermine the additional exposure length required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily.
Behind this filter's variable neutral density element is an independently-rotating circular polarizer element that can be applied to reduce reflections and glare by filtering out light that has become polarized due to reflection from a non-metallic surface. The light from the sun naturally becomes partially polarized due to reflecting off electrons in air molecules, causing the light to scatter into what appears as haze. A polarizing filter element arranges, and filters, this directionally polarized light perpendicularly to the reflected light, allowing for the absorption of much of this light. This results in a noticeable reduction of glare and reflections from non-metallic surfaces and an increase in the saturation of skies and foliage.
A circular polarizer only differs from a linear polarizer in that it contains a quarter wave plane in addition to the linear polarizing filter. The addition of this quarter wave plane is to circularly polarize the linearly polarized light for the use of auto focus and exposure functions. Due to how the light is broken down and filtered with a linear polarizer, auto focus and exposure accuracy become skewed during use. When the light becomes circularly polarized, it permits the use of these functions.
The Genustech 77mm Variable Neutral Density and Circular Polarizer Filter is constructed from Water White glass for increased clarity as well as color fidelity. Each side of this filter includes a layer of anti-reflection coating to prevent internal ghosting and reflections. It also features an oversized front mount which helps to reduce the likelihood to vignetting when used with wide-angle lenses. The filter rings are made from aluminum alloy for durability while remaining lightweight, and for easier, repeatable control over density settings, the front ring for the variable neutral density element is visually demarcated with index markers that indicate different density values.