This Hybrid Pro Neutral Density/Polarizer Kit from Sandmarc contains three filters that are compatible with lenses that feature 67mm front filter threads. Each filter combines a solid neutral density effect with a circular polarizer effect. The filters provide a 4-, 5-, and 6-stop exposure reduction, respectively. Their densities create a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally required. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily.
Each filter can simultaneously help 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 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.
These filters are constructed from optical glass for clarity as well as color fidelity and feature aluminum alloy filter rings that can be rotated in order to adjust the intensity of the polarization effect.