The diopter frame allows 138 mm diopters of up to +2 to be used in a lightweight matte box such as the ARRI LMB 4x5 or LMB-25. The frame has the width of two 4x 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 during exchange, while two 1/4 threads permit the frame to be attached to an articulating arm. Note: Limited clearance with some +2 Diopters.