The Formatt-Hitech 4 x 4" Firecrest Graduated ND 0.9 Filter helps to darken specific areas of an image, such as bright skies, while allowing for a normal, unaffected exposure in the other regions of the image. The filter is densest at the edge and tapers to clear by the middle, with a soft-edged line of transition between the density and clear areas. Neutral density filters do not affect the coloration of the image and the 0.9 density provides a 3 stop reduction in light from entering the lens.
The design of this filter has been optimized for use with digital sensors and promote nearly flat attenuation of visible, UV, and infrared light. Due to imaging sensors' greater susceptibility to infrared light, compared to traditional film, color casts can occur when photographing darker subjects that require increased exposure times. This filter provides a high level of neutrality across all three spectrums in order to eliminate color casts and ensure cleaner, truer blacks.
Sandwiched between layers of Schott Superwite glass is a 15-layer Firecrest multi-coating, which helps to minimize reflections and flare in order maintain truer colors and contrast. Since the coating is located within the middle of the filter, it is less prone to scratching or damage and results in a more durable and hydrophobic design. This filter measures 4 x 4" / 101.6 x 101.6mm and is 0.16" / 4mm-thick.