We discuss the ring focus measurements for the Advanced X-ray Astrophysics Facility (AXAF) x-ray optics -- the high resolution mirror assembly (HRMA). The HRMA is an assembly of four pairs of nested Wolter Type-I grazing incidence mirrors coated with iridium (Ir). The ring focus measurements are an essential part of the AXAF ground calibration carried out at the X-Ray Calibration Facility (XRCF) at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The ring focus measurements reveal aspects of the test system distortions and the mirror surface figures which are difficult or impossible to detect in the focal plane. The measurement results show periodic modulations of the ring width which was caused by gravity and strain in the epoxy bonds that are part of the mechanical support system. The strongest component of the modulation has 12-fold symmetry due to the 12 flexures that support each mirror shell. We discuss the ring focus model and compare it with the test results to understand the test system distortions an the mirror glass imperfection, and to predict the impact for the AXAF mirror on-orbit performance.