Optical imaging system

1. An optical imaging system, comprising:

a first lens comprising a positive refractive power;

a second lens comprising a negative refractive power and a concave image-side surface;

a third lens comprising a negative refractive power, and a concave image-side surface;

a fourth lens comprising a convex image-side surface;

a fifth lens comprising a negative refractive power and a concave image-side surface; and

a sixth lens comprising a positive refractive power and further comprising a convex object-side shape along an optical axis of the optical imaging system,

wherein the optical imaging system satisfies the following conditional expression,

0.1< D 45/ TL< 0.7

where TL represents a distance from an object-side surface of the first lens to an imaging plane, and D45 represents a distance from an image-side surface of the fourth lens to an object-side surface of the fifth lens.

2. The optical imaging system of claim 1 , wherein the fourth lens comprises a convex object-side surface along the optical axis.

3. The optical imaging system of claim 1 , wherein the first to sixth lenses are disposed comprising an interval between each respective lens.

4. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

0.7< TL/f< 1.0

where TL represents a distance from an object-side surface of the first lens to an imaging plane, and f represents a total focal length of the optical imaging system.

5. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

0.15< R 1/ f< 0.32

where R1 represents a radius of curvature of an object-side surface of the first lens, and f represents a total focal length of the optical imaging system.

6. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

−3.5< f/f 2<−0.5

where f represents a total focal length of the optical imaging system, and f2 represents a focal length of the second lens.

7. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

1.60< Nd 6<1.75

where Nd6 represents a refractive index of the sixth lens.

8. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

0.3<tan θ<0.5

where θ represents a half angle of view of the optical imaging system.

9. The optical imaging system of claim 1 , wherein the optical imaging system satisfies the following conditional expression,

2.0< f/EPD< 2.7

where f represents a total focal length of the optical imaging system, and EPD represents a diameter of an entrance aperture.

10. An optical imaging system, comprising:

a first lens, a second lens, a third lens comprising a negative refractive power, a fourth lens, a fifth lens, and a sixth lens comprising a convex object-side surface in a paraxial portion sequentially arranged from an object side to an image side,

wherein the optical imaging system satisfies the following conditional expressions,

0.7< TL/f< 1.0

0.1< D 45/ TL< 0.7

where TL represents a distance from an object-side surface of the first lens to an imaging plane, f represents a total focal length of the optical imaging system, and D45 represents a distance from an image-side surface of the fourth lens to an object-side surface of the fifth lens.

11. The optical imaging system of claim 10 , wherein the sixth lens comprises a shape in which an image-side surface is convex along an optical axis of the optical imaging system and an inflection point is formed on the image-side surface.