In the disclosed device, light radiated from an object image formed on the focal plane by an objective lens is directed to a photo-cell using a condenser lens. The condenser lens has reflection areas formed in portions of the surfaces thereof. According to an embodiment, the surface closer to the oncoming light is mirrored at the central portion and the more remote surface is mirrored marginally. In another embodiment, the more remote area is recessed to receive the photo-cell.