Optical imaging system including seven lenses of +−++−+−, +−+−++− or +−+−+−− refractive powers
An optical imaging system including, sequentially from an object side to an image side along an optical axis, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens. The first lens and the third lens each has a positive refractive power. The second lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens each has a positive or a negative refractive power. An object-side surface of the first lens is convex, and an image-side surface thereof is concave. An image-side surface of the second lens is concave. An object-side surface of the third lens is convex. An object-side surface of the seventh lens is convex, and an image-side surface thereof is concave. A total effective focal length f of the system and an entrance pupil diameter EPD of the system satisfy: f/EPD≤1.5.
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 from an object side to an image side along an optical axis,
wherein,
the first lens and the third lens each has a positive refractive power;
the second lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens each has a positive refractive power or a negative refractive power;
an object-side surface of the first lens is a convex surface and an image-side surface of the first lens is a concave surface;
an image-side surface of the second lens is a concave surface;
an object-side surface of the third lens is a convex surface;
an object-side surface of the seventh lens is a convex surface and an image-side surface of the seventh lens is a concave surface;
the optical imaging system satisfies:
f /EPD≤1.5;
−1.5<( f 2− f 4)/( f 2+ f 4)<−0.5; and
1<CT7/CT5×TAN(HFOV)<2,
where f is a total effective focal length of the optical imaging system, EPD is an entrance pupil diameter of the optical imaging system, f 2 is an effective focal length of the second lens, and f 4 is an effective focal length of the fourth lens, CT 7 is a center thickness of the seventh lens on the optical axis, CT 5 is a center thickness of the fifth lens on the optical axis, and HFOV is half of a maximal field-of-view of the optical imaging system.
2. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: −3<(R 1 +R 2 )/(R 1 −R 2 )<−2,
where R 1 is a radius of curvature of the object-side surface of the first lens, and R 2 is a radius of curvature of the image-side surface of the first lens.
3. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: −0.5<f/R 3 −f/R 5 <0.3,
where f is the total effective focal length of the optical imaging system, R 3 is a radius of curvature of an object-side surface of the second lens, and R 5 is a radius of curvature of the object-side surface of the third lens.
4. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: 1.5<DT 71 /DT 31 <2.5,
where DT 71 is a maximum effective radius of the object-side surface of the seventh lens, and DT 31 is a maximum effective radius of the object-side surface of the third lens.
5. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: 0.5<|SAG 62 /CT 6 |<2,
where SAG 62 is an axial distance from an intersection of an image-side surface of the sixth lens and the optical axis to an apex of a maximum effective radius of the image-side surface of the sixth lens, and CT 6 is a center thickness of the sixth lens on the optical axis.
6. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: 0<(1/f 5 +1/f 6 )/(1/f 1 +1/f 3 )<0.5,
where f 1 is an effective focal length of the first lens, f 3 is an effective focal length of the third lens, f 5 is an effective focal length of the fifth lens, and f 6 is an effective focal length of the sixth lens.
7. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: 1.0≤CT 3 /T 34 <1.5,
where CT 3 is a center thickness of the third lens on the optical axis, and T 34 is a spaced distance of the third lens and the fourth lens on the optical axis.
8. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: TTL/ImgH<1.5,
where TTL is a distance on the optical axis from the object-side surface of the first lens to an imaging plane of the optical imaging system, and ImgH is half of a diagonal length of an effective pixel area on the imaging plane of the optical imaging system.
9. The optical imaging system according to claim 1 , wherein the optical imaging system satisfies: 4.5<ΣAT/(T 56 +T 12 )<6,
where ΣAT is a sum of spaced distances on the optical axis between adjacent lenses of the first lens to the seventh lens, T 56 is a spaced distance of the fifth lens and the sixth lens on the optical axis, and T 12 is a spaced distance of the first lens and the second lens on the optical axis.