| 摘要 |
PURPOSE:To obtain an antireflection film having low residual reflectance in the whole visible wavelength region by specifying the refractive index of a substance forming each of the 1st - the 5th layers and by regulating the optical thickness of the 4th layer in accordance with the refractive index of a glass substrate. CONSTITUTION:An antireflection film is composed of five layers, the 1st - the 5th layers from the air side. When the refractive indexes of the 1st - the 5th layers are represented by n1-n5, the optical thicknesses are represented by n1d1-n5d5, and a set wavelength is represented by lambda, conditions shown by the formula 1 are satisfied. The 1st, the 3rd and the 5th layers are made of MgF2 having 1.38 refractive index, stable optical characteristics and superior wear and moisture resistances. The 2nd and the 4th layers are made of a ZrO2-Ta2O5 mixture having 2.00 refractive index and stable optical characteristics. The optical thickness of only the 4th layer is varied. The set wavelength is 500nm. |
