Telephoto lens with two achromatic combination, the front lens being a positive lens with a focal length of 4 1/2 inches and a back negative lens with a focal length of 2 1/4 inch; mounted in a setting which permits a great variation in seperation. When used on the front of the lens, objects at different distances may readily be focused without altering the camera extension. When used alone, the ADON forms a complete telephoto lens, equal in magnification power to the ordinary combination of a rectilinear or anastigmat lens with a moderate power negative attachment. The equivalent focal length of the combination being twice the camera extension in use plus 4 1/2 inches, the ADON used with a 16 inch camera extension gives image the same size as that rendered by positive lens of 36 1/2 inches. Covers plate of any size up to 15 x 12 inches. J.H. Dallmeyer London, c.1905