Using a Gaussian standing wave at lambda=589 nm as an atom optical lens, we have focused a thermal atomic sodium beam. We have examined the limits of the resolution of this focusing technique, and have made structures with linewidths of 13 nm and contrast of 6:1 with a short focal length atom optical lens. While numerical simulations predict that smaller structures should be attainable with shorter focal lengths, we find that the resolution deteriorates for focal length shorter than f approximate to 16 mu m.