Patent ID: 7710670

Claim:
An ND filter, comprising: a transparent substrate; and a lamination consisting of the following layers: (a) Al 2 O 3 of 63.06 nm in thickness, (b) TiO of 6.00 nm in thickness, (c) Al 2 O 3 of 41.35 nm in thickness, (d) TiO of a value in the range of 6.00 nm to 8.00 nm in thickness, (e) Al 2 O 3 of 43.06 nm in thickness, (f) TiO of a value in the range of 15.99 nm to 26.48 nm in thickness, (g) Al 2 O 3 of 42.59 nm in thickness, (h) TiO of a value in the range of 6.00 nm to 8.00 nm in thickness, (i) Al 2 O 3 of 36.65 nm in thickness, (j) TiO of 6.00 nm in thickness, and (k) MgF 2 of 79.15 nm in thickness, which layers are formed on the transparent substrate in the stated order from a side of the transparent substrate, wherein the ND filter has a transmittance of 4% or more and 11% or less, in an entire visible region of 400 nm or more to 700 nm or less.