Abstract: A device for positioning an object in an opening of a frame in a predetermined position with respect to a plane extending in the direction of the plane of the frame (plane X-Y), wherein the object includes a first spherical segment at a first side and a second spherical segment at a second side situated opposite the first side, wherein at least one positioning means which, after placing the object, exerts a force with a component in the radial and tangential direction on the object at the first spherical segment, the tangential component reaching a minimum in the situation in which the object is situated in the predetermined position, and a recess in which the second spherical segment can be pressed by the positioning means.