From the ManufacturerThe images on the left was taken without any filter.The image on the right was taken using aB+W Graduated ND filter.Click for larger view. B+W Graduated ND (501) Filter - Darken Half Your Image up to 1 F-StopThis filter has a graduated density from clear to gray. The neutral gray half of this filter transmits 50% of the incoming light. You will use it to darken part of the scene by one f-stop (50%) without altering its colors. For example, when the sky is too bright in relation to the landscape, this filter can give you good detail rendition in the clouds. This keeps the sky from being “washed out” by over-exposure.B+W graduated ND filters are preferably used for darkening mostly of the sky or sometimes of the foreground. They come in a rotatable mount that permits the exact upward or downward alignment of the neutral gray half when the filter is screwed tight. UncoatedThis filter, made of CR-39 optical acrylic, is uncoated. This is common with special effects filters, where coating is either an impossibility or would work against the effect the filter is trying to attain. Side view of F-Pro RotatingMount. Click for larger view. F-Pro Brass Filter MountThis filter uses a rotating B+W F-Pro filter mount for added creative options. The mount has a front accessory thread and is made of brass. Compared to the earlier standard mount, the F-Pro mount, introduced in 2001, has become thinner. Now it can be used with wide angle lenses, including most 24mm focal lengths on a full frame body, without vignetting. Another advantage of the F-Pro mount is its modified retaining ring, which is no longer threaded in from the front, but holds the filter glass in place from the back. When removing a filter or lens hood that has been screwed on too tight to the filter, the retaining ring is not at risk of loosening.Product DescriptionThe neutral gray half of this filter transmits 50% of the incoming light, so that it darkens the respective portion of the subject by one f-stop without altering its colors. For example, when the sky is too bright in relation to the landscape, this is an ideal amount for good detail rendition in the clouds and for preventing the sky from being "washed out" by over-exposure.