 |  |  |  |  |  |  |  |  |  |  |
To eliminate the disturbing illumination fall-off at the corners when working with ultra-wide angle lenses, concentrically graduated "Center Filters" have been designed to compensate for this vignetting. These filters have an absorption that diminishes gradually from the center to the edges where it reaches full transparency. This absorption is independent from the wave lengths of the visible spectrum. While the ND varies, you can expect approximatly a 1 1/2 stop exposure correction when using a center filter.
