The filter have a clear spot in the center and allow for the portrayal of an object in diffused surroundings. It is intended to be used with wide angle lenses. The filter effect is directly influenced by the f-stop and the focal length. It consists of a gray outer area. The portion outside of the image center will be reproduced less sharp than the center.
The transformation is softer with wider apertures. The size of the clear circular area increases relatively with the selection of longer focal lengths.