Optical imaging system

1. An optical imaging system comprising:

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 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,

wherein an image-side surface of the seventh lens is concave in a paraxial region thereof, and

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.

2. The optical imaging system of claim 1 , wherein an object-side surface of the first lens is convex.

3. The optical imaging system of claim 1 , wherein at least one inflection point is formed on either one or both of an object-side surface and an image-side surface of the sixth lens.

4. The optical imaging system of claim 1 , wherein at least one inflection point is formed on either one or both of an object-side surface and an image-side surface of the seventh lens.

5. The optical imaging system of claim 1 , wherein a distance along the optical axis from an object-side surface of the first lens to the imaging plane is 6.0 mm or less.

6. The optical imaging system of claim 1 , wherein an object-side surface of the second lens is convex.

7. The optical imaging system of claim 1 , wherein an object-side surface of the third lens is convex.

8. The optical imaging system of claim 1 , wherein an object-side surface of the fourth lens is convex.

9. The optical imaging system of claim 1 , wherein an object-side surface or an image-side surface of the fifth lens is convex.

10. The optical imaging system of claim 1 , wherein the sixth lens has a positive refractive power.

11. The optical imaging system of claim 1 , wherein the seventh lens has a negative refractive power.

12. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies 0.1<L1w/L7w<0.3, where L1w is a weight of the first lens, L7w is a weight of the seventh lens, and L1w and L7w are expressed in a same unit of measurement.

13. The optical imaging system of claim 1 , further comprising a spacer disposed between the sixth and seventh lenses,

wherein the optical imaging system further satisfies 0.5<S6d/f<1.2, where S6d is an inner diameter of the spacer, f is the overall focal length of the optical imaging system, and S6d and f are expressed in a same unit of measurement.

14. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies 0.4<L1TR/L7TR<0.7, where L1TR is an overall outer diameter of the first lens, L7TR is an overall outer diameter of the seventh lens, and L1TR and L7TR are expressed in a same unit of measurement.

15. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies 0.5<L1234TRavg/L7TR<0.75, where L1234TRavg is an average value of overall outer diameters of the first to fourth lenses, L7TR is an overall outer diameter of the seventh lens, and L1234TRavg and L7TR are expressed in a same unit of measurement.

16. The optical imaging system of claim 1 , wherein the optical imaging system further satisfies 0.5<L12345TRavg/L7TR<0.76, where L12345TRavg is an average value of overall outer diameters of the first to fifth lenses, L7TR is an overall outer diameter of the seventh lens, and L12345TRavg and L7TR are expressed in a same unit of measurement.

17. The optical imaging system of claim 1 , wherein the second lens has a positive refractive power.

18. The optical imaging system of claim 1 , wherein the third lens has a positive refractive power.

19. The optical imaging system of claim 1 , wherein a paraxial region of an object-side surface of the seventh lens is concave.