An assembly (100) and a method are provided for inputting a light beam into a light path extending from the confocal scanning head (102) to the microscope (104) of a scanning confocal microscope system to illuminate a selected region of a sample mounted in the microscope. The assembly comprises a light input for receiving a light beam from a light source; beam directing means (8, 12) for controlling the path of the light beam with reference to the shape of the selected region of the sample; and a beam coupler (16) for selective coupling the light beam into the light path from the confocal scanning head (102) to the microscope (104), with the beam direction being controlled by the beam directing means so as to illuminate the selected region. A scanning confocal microscope system including such an assembly is also described, together with a method of calibrating the system. In addition, an optical switch for selectively switching a light beam between two paths is disclosed.