A system and method is provided for adjusting a depth of focus in a refractive material without introducing spherical aberration as a result of the focal adjustment. The system and method provide a novel optical path in which a ramped prism is situated between an objective lens and a refractive material. The bottom surface of the prism is positioned parallel to and in close proximity with the top surface of the recording medium. The objective lens and, as appropriate, one or more associated mirrors are positioned so that light exiting the lens is directed along an optic axis that is oriented substantially perpendicular with respect to the ramped top surface of the prism. In operation, light passes through the objective lens and is focused at a fixed optical depth in the refractive block consisting of the prism and recording medium. The objective lens and other optics in the optical path may be moved up or down the prism ramp to adjust the physical depth of focus in the recording medium. Since the optical depth of focus in the refractive block remains constant, additional spherical aberration is not introduced as a result of changing the physical focal depth in the recording medium.