| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical element, an optical system and an optical instrument having an antireflection film excellent in antireflection characteristics.SOLUTION: The optical element includes a substrate 110 that is transparent to light in a wavelength region for use, and an antireflection film 120 formed on the substrate. A refractive index Nk of the substrate, a refractive index Nm of first, third, fifth and seventh layers, a refractive index Nh of second, fourth, sixth and eighth layers, and a refractive index Ns of a tenth layer for light at a wavelength of 550 nm, and a sum Da of optical film thicknesses from the first to fifth layers, an optical film thickness D6 of the sixth layer, a sum Db of optical film thicknesses from the seventh to ninth layers, and an optical film thickness D10 of the tenth layer satisfy the following conditional expressions:1.40≤Nk≤2.10, 0.40≤|Nm-Nh|≤0.59, 1.15≤Ns≤1.30, 200 nm≤D6≤350 nm, 180 nm≤Da≤310 nm, 100 nm≤Db≤220 nm, and 100 nm≤D10≤150 nm. |
