Two components objective lens with aspheric end surface which has 10 cm focal length with F number 2 is designed. It is designed at the wave length λ=1.06410㎛ ($Nd^{+3}$: YAG laser line), and for the condition that the field angle is less than 2 degrees using BK-7. The front lens is a negative meniscus and has the function of the dome bearing the high aerodynamic pressure. The rear lens is equiconvex with aspherized last surface.
In the present design work, firstly, wave front aberration is corrected by Seidel 1st order aberration calculation. Then, the finite ray aberration is worked out for longitudinal spherical ray aberration. Finally aspherization is performed on the 4th surface by two methods. First method is to set up the linear equations for nullifying the finite ray aberration and solve simultaneously. The surface is then corrected according to the solutions. Second method is to correct the aberration using the deformation of the surface sequently from the low incident height to the high incident height point.
Both methods gave the design for all rays passing through the Gaussian image plane within an Airy disk and found to be efficient for aspherization of lens system. However, the second method is superior in economizing the computing time and programming.
