there is disclosed apparatus for moving an optical element in an opto - mechanical system , comprising at least one circularly symmetric flexure surrounding said optical element , and means for moving said optical element along an axis perpendicular to and extending through the centre of said at least one flexure . a number of flexures may be provided in a stack with spacers therebetween , and the optical element may be mounted in a tubular member support by two paced apart stacks . means are also provided for damping end of movement vibrations .