Wide angle lens

Claim 2

A wide angle photographic lens consisting of a front lens unit which comprises, from an object side, a positive first lens, a negative second lens and a positive third lens, and a rear lens unit comprising a negative meniscus lens greatly curved toward an image side, wherein at least one surface of said positive lenses is a first aspheric surface and at least one surface of said rear lens unit is a second aspheric surface, and wherein the following conditions are satisfied: 0.45<f/|f.sub.4 |<2.5, f.sub.4 <0 1.7<N.sub.2 where f: combined focal length of the entire lens system f 4 : focal length of the rear lens unit N 2 : refractive index of a second lens (a negative lens in the front lens unit).

Claim 3

The wide angle lens of claim 1 wherein where said first aspheric surface is provided on the object side of said first positive lens, an amount of displacement ΔX(φ) due to formation of the aspheric surface satisfies the relationship -0.5×10.sup.-2 <ΔX(0.13f)/f<-0.1×10.sup.-4 where ΔX(φ) is represented by the following formula: ##EQU5## C*=C+2A 2 φ: height from an optical axis.

Claim 4

The wide angle lens of claim 1 wherein where said first aspheric surface is provided on the image side of said first positive lens, an amount of displacement ΔX(φ) satisfies the relationship: 0.1×10.sup.-4 <ΔX(0.13f)/f<0.1×10.sup.-1.

Claim 5

The wide angle lens of claim 1 wherein where said first aspheric surface is provided on the object side of the third positive lens, an amount of displacement ΔX(φ) is: -0.5×10.sup.-2 <ΔX(0.1f)/f<-0.1×10.sup.-4.

Claim 6

The wide angle lens of claim 1 wherein where said first aspheric surface is provided on the image side of the third positive lens, an amount of displacement ΔX(φ) is: 0.1×10.sup.-4 <ΔX(0.1f)/f<0.5×10.sup.-2.

Claim 7

The wide angle lens of claim 1 wherein where said second aspheric surface is provided in a concave surface on the object side, an amount of displacement ΔX(φ) is: 0.5×10.sup.-3 <ΔX(0.13f)/f<0.3.

Claim 8

The wide angle lens of claim 1 wherein said second aspheric surface is provided in a convex surface on the image side of the fourth negative lens, an amount of displacement ΔX(φ) is: 0.5×10.sup.-1 <ΔX(0.14f)/f<-0.1×10.sup.-4.

Claim 9

The wide angle lens of claim 1 wherein the following relationship is established: 1.15<f/f.sub.123 <2.0 where f 123 is the combined focal length of said front lens unit.

Claim 10

The wide angle lens of claim 1 wherein the positive third lens consists of a single lens.

Claim 11

The wide angle lens of claim 1 wherein the positive third lens consists of a positive- and negative cemented lens.

Claim 12

The wide angle lens of claim 1 wherein an additional aspheric surface is formed in addition to said first and second aspheric surfaces, and amounts of displacement ΔX(φ) of the front unit and rear unit, respectively, due to formation of aspheric surface are: for the front unit: 0.5×10.sup.-2 f<ΔX.sub.1 (0.18f)+ΔX.sub.3 (0.1f)+ΔX.sub.5 (0.1f)-ΔX.sub.2 (0.13f)-ΔX.sub.4 (0.1f)-ΔX.sub.6 (0.1f)<-0.1×10.sup.-4 f and for the rear unit: 0.1×10.sup.-3 f<ΔX.sub.7 (0.13f)-ΔX.sub.8 (0.14f)<0.3f ΔX 1 (φ): amount of displacement on the object side of the first positive lens ΔX 2 (φ): amount of displacement on the image side of the first positive lens ΔX 3 (φ): amount of displacement on the object side of the second negative lens ΔX 4 (φ): amount of displacement on the image side of the second negative lens ΔX 5 (φ): amount of displacement on the object side of the third positive lens ΔX 6 (φ): amount of displacement on the image side of the third positive lens ΔX 7 (φ): amount of displacement on the object side of the rear unit ΔX 8 (φ): amount of displacement on the image side of the rear unit.

Claim 13

The wide angle lens of claim 11 wherein where the additional aspheric surface is formed on the object side of the second negative lens, an amount of displacement ΔX(φ) is: -0.5×10.sup.-2 <ΔX(0.1f)/f<-0.1×10.sup.-4.

Claim 14

The wide angle lens of claim 11 wherein where the additional aspheric surface is formed on the image side of the second negative lens, an amount of displacement ΔX(φ) is: 0.1×10.sup.-4 <ΔX(0.1f)/f<0.5×10.sup.-2.

Claim 15

The wide angle lens of claim 1 wherein the positive third lens consists of two positive lenses.

Claim 16

The wide angle lens of claim 14 wherein an additional aspheric surface is formed in addition to said first and second aspheric surfaces, and amounts of displacement ΔX(φ) of the front unit and rear unit, respectively, due to formation of an aspheric surface are: for the front unit: -1.0×10.sup.-2 f<ΔX.sub.5 (0.1f)×ΔX.sub.7 (0.1f)-ΔX.sub.6 (0.1f)-ΔX.sub.8 (0.1f)<-0.5×10.sup.-4 f for the rear unit: 0.2×10.sup.-3 f<ΔX.sub.9 (0.13f)-ΔX.sub.10 (0.14f)<0.3f where ΔX 5 (φ): amount of displacement of the object surface of a lens on the object side of the third positive lens ΔX 6 (φ): amount of displacement of the image surface of a lens on the object side of the third positive lens ΔX 7 (φ): amount of displacement of the object surface of a lens on the image side of the third positive lens ΔX 8 (φ): amount of displacement of the image surface of a lens on the image side of the third positive lens ΔX 9 (φ): amount of displacement of the object surface of the rear unit ΔX 10 (φ): amount of displacement of the imge surface of the rear unit.

Claim 17

A wide angle lens consisting of a front unit which comprises, from an object side, a positive first lens, a negative second lens and a positive third lens, and a rear lens unit comprises a negative meniscus lens greatly curved toward an image side, wherein at least one positive lens in the front lens unit and the rear lens unit consists of plastic lenses to prevent variation in focal position due to a variation in temperature.

Claim 18

A wide angle lens consisting of a front unit which comprises, from an object side, a positive first lens, a negative second lens and a positive third lens, and a rear lens unit comprises a negative meniscus lens greatly curved toward an image side, wherein at least one positive lens in the front lens unit and the rear lens unit consists of plastic lenses to prevent variation in focal position due to a variation in temperature.

Claim 19

The wide angle lens of claim 16 wherein either at least one of said positive lenses or said rear lens unit includes at least one aspheric surface, and the lens formed with said aspheric surface consists of a plastic lens.

Claim 20

The wide angle lens of claim 16 wherein the following relation is established: 0.5<f.sub.LP /|f.sub.4 |<5.0 wherein f LP is a focal length of the plastic lens in the third positive lens.