1. A depth camera system comprising: a plurality of cameras with at least partially overlapping field of views; a plurality of sources, each arranged to project a structured light pattern; a controller arranged to control a plurality of source-camera pairs to reduce the interference between projected structured light patterns and to receive signals from each of the cameras for use in depth determination, controlling a plurality of source-camera pairs comprising controlling a plurality of sources and a plurality of cameras, the controller being further arranged to control the movement of a source-camera pair relative to other source-camera pairs such that the structured light pattern projected by the source is fixed relative to the camera; and a depth calculation module configured to calculate a depth value from data received from one or more of the plurality of cameras; wherein a plurality of the plurality of cameras and a plurality of the plurality of sources are each part of a plurality of a depth camera units, each depth camera unit comprising at least one source and at least one camera, and wherein the controller is arranged to set an operating wavelength of each depth camera unit, such that at least some overlapping structured light patterns are at different operating wavelengths.