A optical device comprises a colour wheel, the colour wheel having a hub portion configured to act as a rotor for coupling to a motor and having a disk-shaped surface; an optically active radial portion, attached to or integrated with the hub portion and configured to optically process incident light; and a balancing adaptation to the disk-shaped surface of the hub portion, comprising one or more of: (a) a recess in the disk-shaped surface extending to an edge of the disk-shaped surface; (b) an annular groove in the disk-shaped surface having a non-uniform width and/or being non-concentric with the disk-shaped surface; (c) an annular groove in the disk-shaped surface, at least a portion of which is filled by a balancing mass part; and (d) a groove and/or a matrix of recesses in the disk-shaped surface arranged to define a portion of an annulus in shape.