Methods to determine best fit sphere for large off-axis aspheric lenses

The key factor for fast manufacturing of large off-axis aspheric lenses is the selection of the best-fit sphere. A method is presented to determine the best-fit sphere for an aspheric lens with a circular cross section by calculating the transformation matrix between the off-axis aspheric workpiece's coordinate system and the manufacturing coordinate system. The material removal from the sphere to the aspheric shape is analyzed in terms of the residual errors. The method is then used to select a best-fit sphere for a 770 mm × 200 mm aspheric lens, the efficiency of the final design shows that this method can quickly select a best-fit sphere that minimizes the material removal.