Tiffen 138mm Letterbox Diopter (+3, 15mm)

The 138mm Letterbox Diopter from Tiffen, in +3 strength and 15mm format, is considered the reverse of the Strip Diopters. With an open slot in the center, similar to a slot in a mail box, it is flanked by diopter glass on either side. This motion picture and television filter allows users to create interesting effects while experimenting and achieve varied focus, diffusion, and double imaging effects.