According to the present invention, there is provided an optical device comprising, a plurality of light sources each operable to provide a light beam; at least one beam combiner which is operable to combine the light beams from the plurality of light sources, to provide a combined light beam; a beam splitter, which is arranged to receive the combined light beam and to split the combined light beam into a primary light beam and a secondary light beam, wherein one or more characteristics of the secondary light beam are indicative of one or more characteristics of the primary light beam, wherein the beam splitter comprises a first surface through which the primary light beam is emitted from the beam splitter and a second surface through which the secondary light beam is emitted from the beam splitter; a mirror component which comprises a mirror, wherein the mirror component is arranged such that the mirror can reflect the primary light beam which is emitted through the first surface of the beam splitter and wherein the mirror can oscillate about at least one oscillation axis to scan the primary light beam; wherein the optical device further comprises a photodiode which is configured to receive the secondary light beam and to detect one or more characteristics of the secondary light beam, wherein the photodiode is configured to be offset from being parallel to at least one of the first surface or second surface of the a beam splitter, to reduce the amount of parasitic light which is directed to the mirror. There is further provided a corresponding method of projecting an image.