A free space optical communication system receiver (500) comprising: a central optical sensor (600); and a plurality of further optical sensors (601-604) disposed around a peripheral edge of the central optical sensor (600). The free space optical communication system receiver (500) may be coupled to means for moving the free space optical communication system receiver (500) relative to an incoming optical signal (510). A controller (508) may be configured to, using measurements of the incident optical signal (510) by the plurality of further optical sensors (601-604), control the means so as to move the free space optical communication system receiver (500) relative to the incident optical signal (510).