Compounds having an effect as i. An interpolated shape measurement data at intersecting points of a radial line passing through a center of the lens shape and the spiral measurement path is acquired by interpolating the shape measurement data, and a compensated machining amount for removing a machining error at each of the intersecting points is calculated from the interpolated shape measurement data by interpolation. The scaling may involve linear or non-linear scaling factors. The loop filter utilizes the compensating unit to compensate the offset between the two input terminals of the amplifier. An arm extends from the clamp to an auxiliary cradle that supports the auxiliary lens assembly.