An improved optimization method for designing a doublet lens

We presented an efficient method to achieve the optimized design of a doublet lens. Using the third-order aberrations to obtain directly a minimal area from the ray-fan diagram was suggested. We took the specification of F/#=3.333 and a half field of view 1° as the design example. The optimization technique was utilized to control the third order aberrations such as spherical aberration and coma, and used the third-order spherical and coma aberrations to correct directly the on-axis aberrations. In order to minimize increasing the tendency of the off-axis aberration at the 1.0 field angle, during the correction of the on-axis aberration a small value, then had a tendency to increase. Our solution is taking the RMS value of spot diagram less than the diffraction limited value of point spread function (PSF) as an evaluated criterion for the on-axis aberrations. Finally, the optimized value of the system design is obtained by adjusting lens thickness and lens spacing. Two design examples of the doublet, one glass lens and one plastic lens, are well presented in this article.