The Tokina 6.6 x 6.6" PRO IRND 1.8 Filter is compatible with filter holders that can accommodate filters that are 6.6" wide and 4mm thick. It is an ND filter with a 64x filter factor that provides a 6-stop exposure reduction. This filter's 1.8 density creates 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. Neutral density filters are intended to not affect the coloration of the image and are ideal for pairing with other filters.