Features smaller than the coherent point spread function of an optical microscope can be detected by looking at the phase of an image rather than simply looking at the reflected intensity. To get an accurate determination of feature size, object reconstruction techniques need to be applied to remove the effects of the optical system. This paper discusses the use of simulated annealing to determine the width and average height of an object feature as well as the defocus and spherical aberration present in the imaging system. Results show that errors of less than 5% are obtained for features as small as 1/6th of the optical resolution of the system and less than 2% for features as small as 1/2 of the resolution. When noise is included in the modeling, errors of 5% are obtained for S/N of 10 and less than 2% for S/N of 100.