Compact photographic objective

Claim 2

A compact photographic objective comprising: from the front, a first positive meniscus lens convex toward the front and forming a surface toward the rear, a second negative lens forming a surface toward the front, a third positive lens, a fourth negative meniscus lens having a surface concave toward the front, the concave surface being aspheric, said first, second, third, and fourth lenses together forming a system having an axial direction and a focal length f, the opposing surfaces of the first and second lenses forming an air lens having a focal length fA, the values f and fA being related so that

Claim 3

-1. 5f<fA<-0.5f, taking the axial direction an an x-axis, a direction perpendicular to the optical axis as a y-axis, the forward direction of the light as positive, and the intersection of the vertex of one of the lenses and the x-axis as an origin, the aspheric surface being defined by the following formula for the x-axis directional difference Δx between the aspheric surface and an ideal spherical surface, the latter of which contributes to the determination of the focal length: ##EQU8## where r 7 is the radius of curvature of the paraxial region of the front surface of the 4th lens; r 7 * is the radius of curvature of the reference spherical surface of the lens defined by r 7 =1/(1/r 7 *+2a); ai are the even coefficients of the aspheric surface; and bi are the odd coefficients of the aspheric surface, whereby letting Δx (0.7r 7 ) denote the value of Δx at the height r 7 x0.7 in y coordinate, and Δx(0.5r 7 ) the value of Δx at the height of r 7 x0.5, and the condition ##EQU9## being satisfied.

Claim 4

-1. 5f<fA<-0.5f, taking the axial direction an an x-axis, a direction perpendicular to the optical axis as a y-axis, the forward direction of the light as positive, and the intersection of the vertex of one of the lenses and the x-axis as an origin, the aspheric surface being defined by the following formula for the x-axis directional difference Δx between the aspheric surface and an ideal spherical surface, the latter of which contributes to the determination of the focal length: ##EQU8## where r 7 is the radius of curvature of the paraxial region of the front surface of the 4th lens; r 7 * is the radius of curvature of the reference spherical surface of the lens defined by r 7 =1/(1/r 7 *+2a); ai are the even coefficients of the aspheric surface; and bi are the odd coefficients of the aspheric surface, whereby letting Δx (0.7r 7 ) denote the value of Δx at the height r 7 x0.7 in y coordinate, and Δx(0.5r 7 ) the value of Δx at the height of r 7 x0.5, and the condition ##EQU9## being satisfied.

Claim 5

A compact photographic objective according to claim 1, wherein said second lens is a negative lens in bi-concave form, and the said third lens is a positive lens in bi-convex form.

Claim 6

A compact photographic objective according to claim 1, wherein said fourth lens is made of a synthetic resin.

Claim 7

A compact photographic objective according to claim 1, further satisfying the following conditions: ##EQU10## where F 123 is the overall focal length of the 1st lens, said 2nd lens and said 3rd lens; F 4 is the focal length of said 4th lens; and D 6 is the axial air separation between said 3rd and said 4th lenses.

Claim 8

An objective as in claims 1, 2, 3, or 4, wherein the origin is the intersection of the vertex of the front surface of the fourth component and the x-axis.