Patent ID: 6304395
Filing Date: 2001-10-16
Classification: G02B

Abstract:
A viewing optical instrument having a roof prism which is provided with a pair of reflection surfaces intersecting at a nominal face angle ofwherein a pupil is split by an edge line of said pair of reflection surfaces of the roof prism,wherein said reflection surfaces are provided with a multiple-layer coating having optical properties including that a change in the phase difference, before and after reflection, of light incident on each of said reflection surfaces is maintained within a predetermined value, andwherein said roof prism comprising a Pechan prism, whereby when the refractive index n of said Pechan prism is 1.46<n<1.60, said multiple-layer coating comprises first to ninth dielectric layers superimposed on the reflection surfaces of the Pechan prism in that order, said first to ninth layers having the following optical thicknesses d1 to d9 in nanometers and refractive indices M1, M2, M3, respectively, wherein 2.00<M1<2.10, 1.35<M2 1.40, 1.45<M3<1.50:1st layer: 34.0<d1<42.5 for index M1,2nd layer: 86.5<d2<102.0 for index M2,3rd layer: 58.0<d3<67.5 for index M1,4th layer: 152.0<d4<162.5 for index M3,5th layer: 64.0<d5<70.0 for index M1,6th layer: 100.0<d6<109.0 for index M3,7th layer: 130.9<d7<136.5 for index M1,8th layer: 223.0<d8<232.0 for index M2, and9th layer: 116.5<d9<121.5 for index M1.