| 摘要 |
PROBLEM TO BE SOLVED: To minimize reflection on the entire lens element by forming a multi- layered reflection preventive film of two-layered constitution which has a specific reflection factor. SOLUTION: The lens has the two-layered reflection preventive film, which has a reflection factor of <=1.0% to a light beam of specific wavelength made incident at a specific angle. The two-layered constitution has two kinds of different refractive index by, for example, SiO as the 1st layer and MgF2, etc., as the 2nd layer and the film thickness 28 and 29 are made optimum not to a light beam 26 which is made incident vertically on a lens element 9, but to a light beam 27 which is made incident at an angle θ approximately a quarter as large as the maximum incidence angle. This constitution minimize the incidence angle dependency and minimizes the reflection over the entire lens element surface. Because of the two-layered constitution, the base material and film are nearly equal in expansion and contraction difference due to a temperature difference and the stress applied to the film is reduced to suppress peeling and obtain high reliability. |
