Horseman Center Filter for the 90mm f/5.6 Lens for the SW-617 Camera - When working with ultra-wide-angle lenses, the fall off of illumination towards the corners is sometimes disturbing. For this reason, concentrically graduated Center Filters are available to compensate for this.

For maximum results and definition when using the a center filter, it is recommended to increase the exposure approximately 1.5 stops. It is also recommended that the lens be stopped down approximately two full stops below maximum aperture, since only then can the maximum compensating effect of the center filter be achieved.