摘要 |
An optical element of which diffraction efficiency hardly varies with wavelength is provided by using an optical material satisfying the conditions that n<SUB>d</SUB>>-6.667x10<SUP>-3</SUP>v<SUP>d</SUP>+1.70 and theta<SUB>g,F</SUB><=-2x10<SUP>-3</SUP>nu<SUB>d</SUB>+0.59 where n<SUB>d </SUB>is a refractive index at d-line, nu<SUB>d </SUB>is an Abbe number at the d-line, and theta<SUB>g,F </SUB>is a second order dispersion at d-line, whereby diffraction efficiency is improved in any working visible wavelength region and more precise chromatic aberration correction is obtained.
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