Abstract: An optical slip ring comprises a rotatable output member and a second rotatable member located intermediate the output member and a stationary input member, the input member having a plurality of equispaced light inputs and the output member having a corresponding number of light outputs and the second rotatable member having a coherent strip formed of a plurality of bundles of optical fibres for transmitting light from the light inputs on the input member to the light outputs, on the output member, the arrangement being such that a continuous light output is produced from the light outputs on the output member only when the intermediate rotatable member is rotated at half the speed of the output member.