This is a simple mask the goes over the sensor on the� Hamamatsu UVTron Flame Detector Kit.� The piece is made from wood with a hole machined into it and slot milled through to the hole. The slot yields about a 20 degree field of view.� The slots do not significantly reduce the ability to detect a flame, it only reduces the field of view.� Check out the video we have with a Trekker using the sensor to find the location of a flame.�