Optical imaging system

An optical imaging system comprising:

• a first lens having a positive refractive power, a convex object-side surface in a paraxial region thereof, and a concave image-side surface in the paraxial region thereof;
• a second lens having a refractive power, a convex object-side surface in a paraxial region thereof, and a concave image-side surface in the paraxial region thereof;
• a third lens having a refractive power;
• a fourth lens having a refractive power, a convex object-side surface in a paraxial region thereof, and a concave image-side surface in the paraxial region thereof;
• a fifth lens having a refractive power;
• a sixth lens having a refractive power;
• a seventh lens having a positive refractive power;
• and
• an eighth lens having a negative refractive power,
• wherein the first to eighth lenses are sequentially arranged 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,
• the optical imaging system has a total of eight lenses,
• −0.5<(|Ri|−|Rj|)/(|Ri|+|Rj|)<0.5 is satisfied, where Ri is a radius of curvature of an object-side surface of the seventh lens at the optical axis, and Rj is a radius of curvature of an image-side surface of the seventh lens at the optical axis, and
• 64<Nmax≤1.75 is satisfied, where Nmax is a largest refractive index among a refractive index of the second lens, a refractive index of the third lens, and a refractive index of the fourth lens.