Patent ID: 7413689

Claim:
A method for fabrication of a lens element comprising: a) shaping a lens blank from a polyetherimide or polyethersulfone thermoplastic resin; b) conditioning a surface of the lens blank by an extended annealing process comprising: i) increasing the temperature of the lens blank to a soak temperature greater than 165 degrees C. over a ramp-up period of more than 2.5 hours, increasing the temperature during the ramp-up period by no more than 2 degrees C. per minute, on average; ii) maintaining the lens blank at the soak temperature for a soak period of at least 3 hours; iii) lowering the temperature of the lens blank back to room temperature during a ramp-down period at a rate no faster than 1.5 degrees C. per minute, on average, forming a conditioned lens blank thereby; and, c) diamond-turning the conditioned lens blank to obtain an optical quality surface with an RMS peak-to-valley surface roughness of less than 100 Angstroms RMS.