Apochromat optical system

Claim 1

An apochromat optical system comprising: a stop provided along the optical axis of the system; a first lens group including: a first lens having a positive power, said first lens having a convex surface which is directed to an object; a second lens made of Kultz Flint glass having an Abbe's number within the range from 45.0 through 34.0, said second lens having a negative power and having a concave surface which is directed to an image; and a third lens in the form of meniscus having a positive power, said third lens having a convex surface which is directed to the object, said first through third lenses being successively disposed in order from the object side of the system, and a second lens group including the substantially same configurations of lenses as those in the first lens group, lenses of said first and second lens groups being approximately symmetrical with respect to said stop; the lenses of said first lens group satisfying the following: n₃ > n₂ 1.08 > {(n₁ + n₃)/2}/n₂ > 1.01 ν₁ > ν₂ ν₃ > ν₂ 1.3 > {(ν₁ + ν₃)/2}/ν₂ > 1.0 and where n₁, n₂ and n₃ are a refractive index of the first, second and third lenses, respectively; and ν₁, ν₂ and ν₃ are an Abbe's number of the first, second and third lenses, respectively.

Claim 4

An apparatus for color reproduction comprising: a light source for illuminating an original to be reproduced; an original holder for holding a color original thereon; photosensitive means for reproducing an image of the original upon receiving light from the original to be reproduced; an optical system of apochromat disposed optically between said original holder and said photosensitive means, said optical system comprising: a stop provided along the optical axis of the apparatus; a first lens group including: a first lens having a positive power, said first lens having a convex surface which is directed to the original; a second lens made of Kultz Flint glass having an Abbe's number within the range from 45.0 through 34.0, said second lens having a negative power and having a concave surface which is directed to the photosensitive means; and a third lens in the form of meniscus having a positive power, said third lens having a convex surface which is directed to the original, said first through third lenses being successively disposed in order from the original side of the optical system; and a second lens group including the substantially same configurations of lenses as those in the first lens group, lenses of said first and second lens groups being approximately symmetrical with respect to said stop; and lenses of the first lens group satisfying the following: n₃ > n₂ 1.08 > {(n₁ + n₃)/2}/n₂ > 1.01 ν₁ > ν₂ ν₃ > ν₂ 1.3 > {(ν₁ + ν₃)/2}/ ν₂ > 1.0 and where n₁, n₂ and n₃ are a refractive index of the first, second and third lenses, respectively; and ν₁, ν₂ and ν₃ are an Abbe's number of the first, second and third lenses, respectively.

Claim 5

An apparatus for color reproduction comprising: a light source for illuminating an original to be reproduced; an original holder for holding a color original thereon; photosensitive means for reproducing an image of the original upon receiving light from the original to be reproduced; an optical system of apochromat disposed optically between said original holder and said photosensitive means, said optical system comprising: a stop provided along the optical axis of the apparatus; a first lens group including: a first lens having a positive power, said first lens having a convex surface which is directed to the original; a second lens made of Kultz Flint glass having an Abbe's number within the range from 45.0 through 34.0, said second lens having a negative power and having a concave surface which is directed to the photosensitive means; and a third lens in the form of meniscus having a positive power, said third lens having a convex surface which is directed to the original, said first through third lenses being successively disposed in order from the original side of the optical system; and a second lens group including the substantially same configurations of lenses as those in the first lens group, lenses of said first and second lens groups being approximately symmetrical with respect to said stop; and lenses of the first lens group satisfying the following: n₃ > n₂ 1.08 > {(n₁ + n₃)/2}/n₂ > 1.01 ν₁ > ν₂ ν₃ > ν₂ 1.3 > {(ν₁ + ν₃)/2}/ ν₂ > 1.0 and where n₁, n₂ and n₃ are a refractive index of the first, second and third lenses, respectively; and ν₁, ν₂ and ν₃ are an Abbe's number of the first, second and third lenses, respectively.