Optical imaging system

An optical imaging system, comprising:

• a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens, which have refractive power and are sequentially arranged from an object side of the optical imaging system to an image side of the optical imaging system along an optical axis of the optical imaging system,
• wherein,
• an object-side surface of the second lens is convex in a paraxial region thereof, and an image-side surface of the second lens is concave in a paraxial region thereof;
• an object-side surface of the fourth lens is convex in a paraxial region thereof, and an image-side surface of the fourth lens is concave in a paraxial region thereof;
• an object-side surface of the fifth lens is concave in a paraxial region thereof, and an image-side surface of the fifth lens is convex in a paraxial region thereof;
• each of the third lens and the sixth lens has positive refractive power;
• wherein 1.0<TTL/ImgH<1.5, where TTL is a distance along the optical axis from an 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;
• and
• 0.5<f4/f8<2.0,
• where f4 is an effecthe focal length of the fourth lens, and f8 is an effective focal length of the eighth lens.