| 摘要 |
Provided is a retrofocus type optical system including a lens or a layer made of a material satisfying the following conditions of the Abbe constant nud and partial dispersion ratios thetagd and thetagF, <?in-line-formulae description="In-line Formulae" end="lead"?>nud<30,<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>thetagd<-3.333x10<SUP>-3</SUP>.nud+1.40,<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>thetagF<-2.615-10<SUP>-3</SUP>.nud+0.67.<?in-line-formulae description="In-line Formulae" end="tail"?> In the case that this layer is disposed on the front side of the aperture stop, the layer is designed to have a positive refractive power, and in the case that the layer is disposed on the rear side of the aperture stop, the layer is designed to have a negative refractive index.
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