Design of a cooke triplet by optimization technique

A simple and direct method using these equations to correct real aberrations and to find the minimum aberration of the system has been suggested. The calculated third-order aberration can exactly meet the target values at each stage by means of the damped least-squares method. The spherical aberration is first targeted to get the minimal value of an on-axis aberration corresponding to the real aberration. Similarly, the coma and astigmatism target values are adjusted to force off-axis real aberrations at the 1.0 field angle down to the minimum. Finally, the minimum aberration at the field angle of 0.7 is fulfilled by the manual variation of the lens thickness and lens spacing. Two examples of triplet designs are presented.