Abstract: A lens mounting arrangement (10) for, for example, an optical telescope, permits movement of the lens from an initial position to an accurately defined first position. The arrangement comprises a track (16) including a first stop (18) at a first end of the track, a lens carriage (12) moveable along the track, and a rotating drive (20) coupled to the lens carriage for moving the lens along the track and into contact with the stop, the stop defining the first position. A coupling (22, 26) is provided between the drive and the lens carriage and includes a resilient link (26) such that the lens carriage may be brought into positive contact with the stop, deformation of the resilient link accommodating excess movement of the drive.