Patent ID: 11971609
Assignee: LARGAN PRECISION CO., LTD.
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 7:
8. A photographing optical system comprising eight lens elements, the eight lens elements being, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, a seventh lens element and an eighth lens element, and each of the eight lens elements having an object-side surface facing toward the object side and an image-side surface facing toward the image side;
wherein the first lens element has positive refractive power, the object-side surface of the second lens element is convex in a paraxial region thereof, the fifth lens element has positive refractive power, the image-side surface of the seventh lens element is concave in a paraxial region thereof, the eighth lens element has negative refractive power, the image-side surface of the eighth lens element is concave in a paraxial region thereof, at least one lens surface of at least one lens element of the photographing optical system has at least one critical point in an off-axis region thereof, and an axial distance between the seventh lens element and the eighth lens element is a maximum value among axial distances between each of all adjacent lens elements of the photographing optical system;
wherein a focal length of the photographing optical system is f, a focal length of the first lens element is f1, a focal length of the fifth lens element is f5, a focal length of the seventh lens element is f7, a focal length of the eighth lens element is f8, a composite focal length of the first lens element and the second lens element is f12, a curvature radius of the object-side surface of the second lens element is R3, and the following conditions are satisfied:

0<f5/f1<9.5;

−7.5<f′8/f7<−0.55;

0.35<f/f12<0.75; and

0<R3/f<2.0;

wherein a vertical distance between a non-axial critical point on the object-side surface of the seventh lens element and an optical axis is Yc71, a vertical distance between a non-axial critical point on the image-side surface of the seventh lens element and the optical axis is Yc72, and the object-side surface and the image-side surface of the seventh lens element each have at least one critical point in an off-axis region thereof satisfying the following condition:

0.80<Yc72/Yc71<1.5.