We have made an interference optical microscope (IOM) capable of improved resolutions, both vertically and laterally. Atomic steps of graphite have been imaged in phase shift mode (PSM) at large field of view through a proper averaging time during acquisition. We discuss the influence of the illumination and the CCD resolution on the ultimate achievable vertical resolution. To improve the lateral resolution, we report on the integration of the IOM to an atomic force microscope (AFM) in order to take advantage of the 2 nm resolution provided by AFM.