Optical imaging system

Abstract

An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens sequentially disposed in numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging plane of the optical imaging system, wherein the optical imaging system satisfies 1<∥f123457-f∥/f, where f123457 is a composite focal length of the first to seventh lenses calculated with an index of refraction of the sixth lens set to 1.0, f is an overall focal length of the optical imaging system, and f123457 and f are expressed in a same unit of measurement.

What is claimed is: 
     
         1 . An optical imaging system comprising:
 a first lens having a positive refractive power;   a second lens having a negative refractive power;   a third lens having a positive refractive power;   a fourth lens having a concave image-side surface in a paraxial region thereof;   a fifth lens having a concave object-side surface in a paraxial region thereof;   a sixth lens having a positive refractive power; and   a seventh lens having a refractive power,   wherein the first to seventh lenses are sequentially disposed in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging plane of the optical imaging system,   a radius of curvature of an image-side surface of the third lens in a paraxial region thereof is greater than a radius of curvature of an object-side surface of the third lens in a paraxial region thereof, where the radius of curvature of the image-side surface of the third lens in the paraxial region thereof and the radius of curvature of the object-side surface of the third lens in the paraxial region thereof are expressed in a same unit of measurement,   a thickness of the sixth lens along the optical axis is greater than a thickness of the fourth lens along the optical axis, where the thickness of the sixth lens along the optical axis and the thickness of the fourth lens along the optical axis are expressed in a same unit of measurement, and   the optical imaging system satisfies 0.01<R1/R4<1.3, where R1 is a radius of curvature of an object-side surface of the first lens in a paraxial region thereof, R4 is a radius of curvature of an image-side surface of the second lens in a paraxial region thereof, and R1 and R4 are expressed in a same unit of measurement.   
     
     
         2 . The optical imaging system of  claim 1 , wherein the fourth lens has a negative refractive power. 
     
     
         3 . The optical imaging system of  claim 1 , wherein the fifth lens has a positive refractive power. 
     
     
         4 . The optical imaging system of  claim 1 , The optical imaging system of  claim 1 , wherein the seventh lens has a negative refractive power. 
     
     
         5 . The optical imaging system of  claim 1 , wherein the object-side surface of the third lens is concave in the paraxial region thereof. 
     
     
         6 . The optical imaging system of  claim 1 , wherein the image-side surface of the third lens is convex in the paraxial region thereof. 
     
     
         7 . The optical imaging system of  claim 1 , wherein the fourth lens has a convex object-side surface in a paraxial region thereof. 
     
     
         8 . The optical imaging system of  claim 1 , wherein the fifth lens has a convex image-side surface in a paraxial region thereof. 
     
     
         9 . The optical imaging system of  claim 1 , wherein the sixth lens has a convex object-side surface in a paraxial region thereof. 
     
     
         10 . The optical imaging system of  claim 1 , wherein the sixth lens has a convex image-side surface in a paraxial region thereof. 
     
     
         11 . The optical imaging system of  claim 1 , wherein the seventh lens has a concave image-side surface in a paraxial region thereof. 
     
     
         12 . The optical imaging system of  claim 1 , wherein the optical imaging system satisfies 1<∥f123457-f∥/f, where f123457 is a composite focal length of the first to seventh lenses calculated with an index of refraction of the sixth lens set to 1.0, f is an overall focal length of the optical imaging system, and f123457 and f are expressed in a same unit of measurement. 
     
     
         13 . The optical imaging system of  claim 1 , wherein the optical imaging system satisfies 0.1<R1/R5<0.7, where R5 is the radius of curvature of the object-side surface of the third lens in the paraxial region thereof, and R1 and R5 are expressed in a same unit of measurement. 
     
     
         14 . The optical imaging system of  claim 1 , wherein the optical imaging system satisfies 0.6<(R11+R14)/(2*R1)<3.0, where R11 is a radius of curvature of an object-side surface of the sixth lens in a paraxial region thereof, R14 is a radius of curvature of an image-side surface of the seventh lens in a paraxial region thereof, and R1, R11, and R14 are expressed in a same unit of measurement. 
     
     
         15 . The optical imaging system of  claim 1 , wherein a radius of curvature of an image-side surface of the first lens in a paraxial region thereof is greater than a radius of curvature of an object-side surface of the second lens in a paraxial region thereof, where the radius of curvature of the image-side surface of the first lens in the paraxial region thereof and the radius of curvature of the object-side surface of the second lens in the paraxial region thereof are expressed in a same unit of measurement.