A rotary position encoder for determining a rotary position of a shaft includes a rigid substrate having a planar surface and mounted on the shaft to rotate with the shaft; an optical disk having at least a transparent polycarbonate layer and a reflective layer on the transparent polycarbonate layer, affixed to the planar surface of the substrate, the optical disk having a first circumferential track encoded therein having binary data; an optics assembly for interrogating the optical disk and providing an output signal indicative of data received from the interrogation of the optical disk; and a tracking motor for driving the optics assembly radially with respect to the optical disk.