An apparatus for providing temperature-dependent movement of an optical element, the apparatus comprising: a moveable mount for the optical element; a mount moving component attached to the moveable mount; and a guide attached to the mount moving component and configured to guide a movement of the moveable mount. The apparatus is configured such that a difference in thermal contraction or thermal expansion between the mount moving component and the guide in response to a change in temperature of the apparatus causes the mount moving component to move the moveable mount relative to the guide.