Projection lens system - has lens dispersing indices determined by formula taking indices of refraction into account

摘要

The projection-lens system comprises front and rear lens groups. In succession from the objective end, the front group comprises positive first and second lenses and a negative third one. The rear group comprises a negative fourth lens, and positive fifth and sixth ones. The lens dispersion indices are determined by the following formulae taking account of their indices chromatic aberrations. -0.0015 <= ( eta 2- eta 3)/( nu 2- nu 3) <= 0 -0.0015 <= ( eta 5- eta 4)/( nu 5- nu 4) <= 0 where the eta an nu are the dispersion indices of the corresponding lens elements given by eta = (ng-nF)/(nF-nC) nu = (nd-1)/(nF nC) where ng, nF, nC and nd are the sum indices of the lens elements along the lines g, F, C and d.