A lens system including sequentially, from an object side to an image side, a first lens of a biconvex type having two aspherical surfaces, a second lens of a biconcave type having at least one aspherical surface, a third lens having two aspherical surfaces and having a positive refracting power, and a fourth lens having two aspherical surfaces and having a negative refracting power.
1. A lens system comprising:
a first lens of a biconvex type having two aspherical surfaces;
a second lens of a biconcave type having at least one aspherical surface;
a third lens having two aspherical surfaces and having a positive refracting power; and
a fourth lens having two aspherical surfaces and having a negative refracting power,
wherein the first lens, the second lens, the third lens, and the fourth lens are arranged sequentially from an object side of the lens system to an image side of the lens system;
wherein an aspherical surface of an image side of the fourth lens comprises an inflection point within an effective aperture range,
wherein |L1R1|>|L1R2|, where L1R1 is a radius of curvature of an object side of the first lens, and L1R2 is a radius of curvature of an image side of the first lens, and
wherein 0.8<|L1R2|/|L2R2|<1.1, where L2R2 is a radius of curvature of an image side of the second lens.
2. The lens system of claim 1 , wherein 1.0<f/|f2|<2.0, where f is an overall focal length of the lens system, and f2 is a focal length of the second lens.
3. The lens system of claim 2 , wherein 0.7<f1/|f2|<1.1, where f1 is a focal length of the first lens, and
wherein 0.7<f3/|f4|<1.2, where f3 is a focal length of the third lens, and f4 is a focal length of the fourth lens.
4. The lens system of claim 3 , wherein ν1−ν2>15, where ν1 is an Abbe's number of the first lens, and ν2 is an Abbe's number of the second lens, and
wherein 0.9<ν3/ν4<1.1, where ν3 is an Abbe's number of the third lens, and ν4 is an Abbe's number of the fourth lens.
5. The lens system of claim 1 , wherein ν1−ν2>15, where ν1 is an Abbe's number of the first lens and ν2 is an Abbe's number of the second lens, and
wherein 0.9<ν3/ν4<1.1, where ν3 is an Abbe's number of the third lens, and ν4 is an Abbe's number of the fourth lens.
6. The lens system of claim 1 , wherein a stop is disposed at the object side surface of the first lens.
7. The lens system of claim 1 , wherein 0.7<f1/|f2|<1.1, where f1 is a focal length of the first lens, and f2 is a focal length of the second lens, and
wherein 0.7<f3/|f4|<1.2, where f3 is a focal length of the third lens 3 , and f4 is a focal length of the fourth lens.
8. The lens system of claim 1 , wherein the lens system has a resolution corresponding to a pitch of a plurality of pixels that is less than approximately 1.75 μm.
9. The lens system of claim 1 , wherein the lens system is housed in a solid state imaging device, and
wherein a ratio T/D is less than 1, where D is a diagonal dimension of the solid state imaging device and T is an overall length of the lens system.
10. The lens system of claim 9 , wherein a stop is disposed at an object side surface of the first lens, and
wherein the overall length T of the lens system is a distance from a surface at a peak portion of at least one of the stop or the first lens, to a focal position of the lens system.
11. The lens system of claim 1 , wherein the lens system has a back focal length of 0.95 mm or more.
12. The lens system of claim 1 , wherein the lens system has a viewing angle of more than 70°.
13. An optical apparatus comprising:
a biconvex refracting element comprising two aspherical surfaces;
a biconcave refracting element comprising an aspherical surface;
a positive refracting element comprising two aspherical surfaces; and
a negative refracting element comprising two aspherical surfaces,
wherein the biconvex refracting element, the biconcave refracting element, the positive refracting element, and the negative refracting element are arranged sequentially along an optical axis, the biconvex refracting element being disposed on an object side of the optical apparatus and the negative refracting element being disposed on an image side of the optical apparatus;
wherein an aspherical surface of an image side of the fourth refracting element comprises an inflection point within an effective aperture range,
wherein |L1R1|>|L1R2|, where L1R1 is a radius of curvature of an object side of the biconvex refracting element, and L1R2 is a radius of curvature of an image side of the biconvex refracting element, and
wherein 0.8<|L1R2|/|L2R2|<1.1, where L2R2 is a radius of curvature of an image side of the biconcave refracting element.