In the past recent years, shape recovery using image focus has been investigated a lot. Traditionally, generalized Gaussian models are used to approximate the focus curves obtained after applying the focus measure. In this paper, we have proposed a new approximation model for the focus curve, using Lorentzian-Cauchy function. The focusing of light rays, by the imaging device, are approximated by using a Gaussian beam, which has the intensity profile along the propagation axis defined by Lorentzian-Cauchy function. Experiments performed on the simulated and real objects have shown the effectiveness of the proposed scheme.