Focus monitoring for a photolithographic applications is provided by illuminating a photoresist layer with a light beam transmitted through a first binary mask to define a circuit pattern on an underlying substrate and then illuminating the photoresist layer with an unbalanced off-axis light beam transmitted through a second binary mask. The second mask contains a shifting feature configuration in one portion, while another portion blocks light transmission to the chip design area of the photoresist. After development of the photoresist layer, the pattern formed by illumination of the second mask can be compared with a predefined reference feature on the photoresist layer to determine whether a shift, if any, is within acceptable focus limits.