Abstract: A CCD camera is used to measure the diameter of a growing crystal through optical recognition of the luminous ring at a crystal-melt interface. The result is an optical diameter control method and apparatus that eliminates the negative effects of orbit, melt-level and incorrect camera angle. The CCD camera is positioned such that it focuses on a full half of the circumference of the crystal as it is being grown. An automatic control system uses two points diametrically opposed on the crystal to measure the diameter, and a third point on the crystal closest to the camera to compute the melt level error. The automatic control system controls a crucible height and a crystal pull rate to optimize crystal diameter.