A chromatic aberration-corrected optical system for broad-band through-the-lens (TTL) imaging and position detection of alignment marks deposed on a substrate located at the exposure plane of an exposure apparatus, for example, a stepper machine, uses a first projection lens capable of focusing a first broad-band alignment illumination and a second exposure illumination onto the substrate. A second achromat lens and a third refractive/diffractive hybrid lens are configured and designed to provide, in conjunction with the first projection lens, longitudinal and lateral chromatic aberration correction over a wavelength range from about 550-650 nm of the broad-band alignment illumination.