The Diopter Frame 138mm from ARRI allows for select 138mm diopters of up to +2 to be used in a lightweight matte box such as the ARRI LMB 4x5 or LMB-25. The frame features two 4 x 5.65" filter frames and fits into a 2- or 3-filter stage. A safety mechanism prevents the diopter from falling out of the frame, and two 1/4"-20 threads allow the frame to be attached to an articulating arm.