Cokin Square Holder Filter P-Series BPW-400A
The Cokin BPW-400A is Cokin’s wide angle P-Type Holder, and attaches to your P-Type adapter ring in the same way as a standard P-Type filter holder. The Cokin BPW-400A is an extra slim holder that helps to eliminate vignetting down to 20mm focal length.
Whereas a standard filter holder can carry three filters at a time, the Cokin BPW400A can only hold one filter (can be a polarizer) and allows the use of filters with super wide lenses (focal lengths under 20mm) 35mm format. Cokin part number: BPW400A.