In this article we model and characterize the effects of the through-focus asymmetry induced by pixels with phases other than 0 and pi in micromirror arrays for maskless lithography. Analytic models for several mirror configurations are provided and shown to result in small deviations (+/- 1.5%) from simulation results. These models, together with full Simulations, are used to compare multiple-tilt and multiple-piston mirrors. ne results show that for comparable multiple-tilt and multiple-piston mirrors, the piston mirrors have better modulation characteristics. A test of off-grid printing is performed, suggesting that the four-piston mirror is the best configuration for maskless lithography. (c) 2005 American Vacuum Society.