An atom lens generated by a near-resonant light standing wave can be used to produce nanometer-scale structures. Our calculations are based on a Monte Carlo scheme and the trajectory tracing method. The influences of optical potential and source imperfection such as velocity spread and beam spread on the shape of chromium feature are analyzed using this approach. Results have shown that the focus depth for real source is longer than that for perfect source. Feature separation can be reduced by changing the detuning of the standing wave laser field from blue to red halfway through the deposition time.