Abstract: A zoom lens assembly for projecting images from an object plane to the image plane at magnifications from approximately 17 times to approximately 29 times and operating in the wavelength range from 0.38 to 0.54 microns. The zoom lens assembly comprises four members, including a front fixed member, two cam controlled moving members, and a rear fixed member. A diaphragm is mounted within the rear moving member and is controlled by a third cam to maintain a constant f/number aperture at the long conjugate. In a preferred embodiment, the cams which control the movable members are designed so that equal angular rotations of the cam sleeve into which the cam slots are cut changes the magnification by equal amounts.