The effect of nontelecentricity and spherical aberration on GCA DSW imaging.

The effects of a condenser lens defocus and incorrect operating conjugate ratio on the performance of the reduction lens in GCA DSWs have been examined. When the condenser lens is not focused at the entrance pupil of the reduction lens, the reduction lens will not be telecentric on the image side, resulting in radial image placement errors of = +- 0.50micron depending on the water focus position. In addition, the condenser lens focus will result in a reduction of the partial coherence for the DSW of = 50%, decreasing the resolution and depth of focus capabilities. The result of using the condenser lens at an incorrect conjugate ratio is an increase in condenser lens sperical aberration affecting the apparent reduction lens distortion. Data will be presented for improperly and properly tuned DSWs to indicate the potential effect on the capability to mix DSWs. A set-up procedure, requiring ~15 minutes per DSW, will be presented which assures that the optical system has minimal spheric aberration, the reduction lens is telecentric on the image side, and the DSW is being used with the correct partial coherence factor allowing maximum performance of the imaging system.