Lens system with frontal aperture stop

Claim 2

A frontal aperture lens system consisting, consecutively from the object to the image side, of: an aperture stop, a first positive lens component having a front surface convex to the object side, a second biconcave lens component, a third positive meniscus lens component convex to the image side, and a fourth positive lens component having a front surface convex to the object side, characterized in that the third positive meniscus lens component is a doublet consisting of a negative lens and a positive lens which is cemented to the negative lens at the image side thereof.

Claim 3

The invention of claim 1, wherein each of the first, second and fourth lens components consists of a single lens.

Claim 4

The invention of claim 2, wherein the positive lens of the third lens component is made of a glass of greater refractive index and greater Abbe Number than those of the negative lens of the third lens component.

Claim 5

The invention of claim 3, wherein the third lens component fulfills the following conditions: 0.25 > |N.sub.3 - N.sub.4 | 0.03 (1) 25 > |V.sub.3 - V.sub.4 | >5 (2) 0.013 φ <N.sub.4 -N.sub.3 /R.sub.6 < 0.09 φ (3) 1.0 < R.sub.5 /R.sub.7 < 3.0 (4) wherein N 3 and N 4 represent the refractive index for the negative and positive lenses of the third lens component, respectively; V 3 and V 4 represent the Abbe Number for the negative and positive lenses of the third lens component, respectively; φ represents the refractive power of the lens system and R 5 , R 6 , and R 7 represent the radius of curvature for the front, intermediate and rear surfaces of the third lens component, respectively.

Claim 6

The invention of claim 4, wherein the lens system further fulfills the following conditions: 1.84 > N.sub.1 > 1.6 (5) 65 > V.sub.1 > 44 (6) 0.7 > D.sub.1 + D.sub.2 /ΣD > 0.3 (7) 1.5 > |R.sub.3 |R.sub.4 > 0.5 ( 8) wherein N 1 and V 1 represent the refractive index and the Abbe Number for the first lens component, respectively; D 1 represents the thickness of the first lens component on the optical axis; D 2 represents the distance between the rear surface of the first lens component and the front surface of the second lens component on the optical axis; ΣD represents the sum of the axial distances from the front surface of the first lens component to the rear surface of the fourth lens component; and R 3 and R 4 represent the radius of curvature for the front and rear surfaces of the second lens component.

Claim 7

The invention of claim 1, wherein the F-number of the lens system is less than 2.

Claim 8

The invention of claim 1, wherein the third lens component fulfills the following conditions: 0.25 > |N.sub.3 -N.sub.4 | >0.03 25 > |V.sub.3 -V.sub.4 | > 5 wherein N 3 and N 4 represent the refractive index for the negative and positive lenses of the third lens component, respectively; and V 3 and V 4 represent the Abbe Number for the negative and positive lenses of the third lens component, respectively.

Claim 9

The invention of claim 1, wherein the third lens component further fulfills the following conditions: 0.013φ < N.sub.4 -N.sub.3 /R.sub.6 < 0.09φ 1.0 < r.sub.5 /r.sub.7 < 3.0 wherein φrepresents the refractive power of the lens system; and R 5 , and R 6 and R 7 represent the radius of curvature for the front, intermediate and rear surfaces of the third lens component, respectively.

Claim 10

The invention of claim 7, wherein the lens system further fulfills the following conditions: 1.84 > N.sub.1 > 1.6 65 > V.sub.1 > 44 0.7 > D.sub.1 +D.sub.2 /ΣD > 0.3 1.5 > |R.sub.3 |/R.sub.4 > 0.5

Claim 11

The invention of claim 1, wherein the lens system comprises a design parameter of approximate values within the following specifications; ______________________________________ Radius of Axial Refractive Abbe Curvature Distance Index Number ______________________________________ R.sub.1 = 14.900 R.sub.2 = 174.773 D.sub.1 = 4.3 N.sub.1 = 1.69100 V.sub.1 = 54.75 R.sub.3 = -17.325 D.sub.2 = 3.7 R.sub.4 = 18.827 D.sub.3 = 0.9 N.sub.2 = 1.68300 V.sub.2 = 31.52 R.sub.5 = -24.507 D.sub.4 = 1.5 R.sub.6 = 156.406 D.sub.5 = 1.0 N.sub.3 = 1.64769 V.sub.3 = 33.88 R.sub.7 = -12.985 D.sub.6 = 2.9 N.sub.4 = 1.77250 V.sub.4 = 49.63 R.sub.8 = 21.466 D.sub.7 = 0.15 R.sub.9 = 71.587 D.sub.8 = 3.4 N.sub.5 = 1.77250 V.sub.5 = 49.63 ______________________________________

Claim 12

The invention of claim 1, wherein the lens system comprises a design parameter of approximate values within the following specifications; ______________________________________ Radius of Axial Refractive Abbe Curvature Distance Index Number ______________________________________ R.sub.1 = 17.990 R.sub.2 = 243.494 D.sub.1 = 4.569 N.sub.1 = 1.7725 V.sub.1 = 49.60 R.sub.3 = -17.104 D.sub.2 = 4.686 R.sub.4 = D.sub.3 = 0.850 N.sub.2 = 1.73300 V.sub.2 = 28.24 R.sub.5 = -21.047 D.sub.4 = 1.550 R.sub.6 = 71.412 D.sub.5 = 0.850 N.sub.3 = 1.63980 V.sub.3 = 34.66 R.sub.7 = -13.146 D.sub.6 = 3.450 N.sub.4 = 1.75700 V.sub.4 = 47.73 R.sub.8 = D.sub.7 = 0.150 R.sub.9 =-411.188 D.sub.8 = 4.123 N.sub.5 = 1.78831 V.sub.5 = 47.32 ______________________________________

Claim 13

In a multi-lens system for use with a camera having a front aperture stop capable of providing a normal photographic field angle, and having means for the refractive transmittance of a real image including at least four lens elements, the improvement comprising: a positive doublet formed from a negative and positive lens positioned as a third lens element from an object side having a design parameter within the following ranges; 0.25 > |N.sub.3 - N.sub.4 | > 0.03 (1) 25 > |V.sub.3 - V.sub.4 | > 5 (2) 0.013 φ< N.sub.4 -N.sub.3 /R.sub.6 < 0.09 φ (3) 1.0 < R.sub.5 /R.sub.7 < 3.0 (4) wherein N 3 and N 4 represent the refractive index for the negative and positive lenses of the doublet respectively; V 3 and V 4 represent the Abbe number for the negative and positive lenses of the doublet, respectively; φrepresents the refractive power of the lens system and R 5 , R 6 , and R 7 represent the radium of curvature for the front, intermediate and rear surfaces of the doublet, respectively, whereby the correction of spherical aberration, astigmatism, coma and chromatic aberration is improved.

Claim 14

In a multi-lens system for use with a camera having a front aperture stop capable of providing a normal photographic field angle, and having means for the refractive transmittance of a real image including at least four lens elements, the improvement comprising: a positive doublet formed from a negative and positive lens positioned as a third lens element from an object side having a design parameter within the following ranges; 0.25 > |N.sub.3 - N.sub.4 | > 0.03 (1) 25 > |V.sub.3 - V.sub.4 | > 5 (2) 0.013 φ< N.sub.4 -N.sub.3 /R.sub.6 < 0.09 φ (3) 1.0 < R.sub.5 /R.sub.7 < 3.0 (4) wherein N 3 and N 4 represent the refractive index for the negative and positive lenses of the doublet respectively; V 3 and V 4 represent the Abbe number for the negative and positive lenses of the doublet, respectively; φrepresents the refractive power of the lens system and R 5 , R 6 , and R 7 represent the radium of curvature for the front, intermediate and rear surfaces of the doublet, respectively, whereby the correction of spherical aberration, astigmatism, coma and chromatic aberration is improved.

Claim 15

The invention of claim 12 wherein the means for the refractive transmittance of a real image further includes a first, second and fourth lens component and satisfies the following conditions; 1.84 > N.sub.1 > 1.6 (5) 65 > V.sub.1 > 44 (6) 0.7 > D.sub.1 + D.sub.2 /ΣD > 0.3 (7) 1.5 > |R.sub.3 |/R.sub.4 > 0.5 (8) wherein N 1 and V 1 represent the refractive index and the Abbe Number for the first lens component, respectively; D 1 represents the thickness of the first lens component on the optical axis; D 2 represents the distance between the rear surface of the first lens component and the front surface of the second lens component on the optical axis; ΣD represents the sum of the axial distances from the front surfaces of the first lens component to the rear surface of the fourth lens component; and R 3 and R 4 represent the radius of curvature for the front and rear surfaces of the second lens component.