US Patent 8248699 Reflection reducing film, optical member and optical system

A reflection reducing film is provided on a surface of an optical substrate, and is sequentially provided with a buffer layer and a reflection reducing layer. The reflection reducing layer includes first to eighth layers sequentially laminated from the side of the buffer layer. The first and sixth layers are made of a low-refractive index material having a refractive index in the range of 1.35 to 1.50 at the d-line, the third, fifth and seventh layers are made of an intermediate-refractive index material having a refractive index in the range of 1.55 to 1.85 at the d-line, and the second, fourth and eighth layers are made of a high-refractive index material having a refractive index in the range of 1.70 to 2.50 at the d-line.