Patent ID: 7508600

Claim:
An optical system, comprising: at least one of a movable lens unit movable in an optical axis direction and a fixed lens unit that is not movable in the optical axis direction, wherein the at least one lens unit includes a plurality of refractive optical elements, the refractive optical elements being made of resin and having focal lengths of the same sign, wherein, when N gi , N Fi , N di , and N Ci indicate refractive indices, with respect to g-line, F-line, d-line, and C-line, respectively, of a material of the i th refractive optical element from an object side, an Abbe number νi, and a partial dispersion ratio θi of the material of the i th refractive optical element are determined as follows: ν i= ( N di −1)/( N Fi −N Ci ) θ i= ( N gi −N Fi )/( N Fi −N Ci), and wherein the lens unit including the refractive optical elements has one or more negative lenses, and when φi is a refractive power, with respect to d-line, of the i th refractive optical element, φG is a refractive power of one of the negative lenses that is made of a material having the highest dispersion, and φa is an average refractive power for d-line of the refractive optical elements, the following conditions are satisfied: - 2.100 × 10 - 3 · ν ⁢ ⁢ i + 6.93 × 10 - 1 < θ ⁢ ⁢ i < 0.9 ν ⁢ ⁢ i < 30 ⁢ - 0.9 < ∑ i = 1 n ⁢ ϕ ⁢ ⁢ i / ϕ ⁢ ⁢ G ⁢ < - 0.1 ⁢ ⁢ 0.3 < ϕ ⁢ ⁢ i / ϕ ⁢ ⁢ a < 3.0 wherein i=1, 2, . . . , n, and n ≧ 2.