Abstract: A slit device for use in optical systems, and in particular for use in spectrophotometers. The device comprises an integral plate structure having two jaw assemblies, each of which includes two jaws arranged to define a slit between them, and flexible hinge means interconnecting the two jaws to permit relative movement such that the slit width can be varied. Each hinge means includes a part of the plate structure which has been turned on edge relative to the plate structure parts forming the associated jaws so as to have maximum flexibility in the general direction of relative movement of the jaws. Two bridging portions are also formed as integral parts of the plate structure, and each bridging portion connects one of the jaws of one jaw assembly with a jaw of the other assembly. Thus, movement of one jaw in one assembly is transmitted to a jaw of the other assembly through one of the bridging portions.