Abstract: A variable magnification projection device includes a principal lens displaceable along its optical path and at least a supplementary lens movable into and out of the optical path at a fixed conjugate distance from the principal lens as the latter is displaced. The supplementary lens is linearly movable along a sliding rail extending perpendicular to the optical path and is so coupled to a fixed frame of the device that as the principal lens is displaced along the path, it is automatically moved from a first position remote from the path to a second position in which its optical axis and that of the principal lens coincide.