From Manufacturer
This 2 to 5-stop, 77mm Freewell Standard Day Variable ND Filter is designed to mount onto lenses with 77mm front filter threads and provides an exposure reduction of 2 to 5-stops. Its 0.6 to 1.5 density creates a darkening of the entire image, allowing you to photograph with a wider aperture or slower shutter speed than normally possible. 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 or add motion blur. For easier, repeatable control over density settings, the front ring is visually demarcated with numbers representing the different stop values and features side knurlings to further enable fast and precise positioning.
This filter is constructed from Schott B270 glass for enhanced clarity and color fidelity. Each glass surface is multi-coated to help eliminate internal ghosting and reflections. The Freewell 77mm Standard Day Variable Neutral Density 0.6 to 1.5 Filter is also coated for resistance to oil, dust, and scratches, offering greater protection to the filter and helping it to stay clean for longer than with uncoated filters. The coatings are hydrophobic as well, resulting in an improved beading effect when in contact with water for greater cleaning efficiency.