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 a paraxial region thereof;

a second lens having a negative refractive power;

a third lens having a negative refractive power;

a fourth lens having a positive refractive power, a convex object-side surface in a paraxial region thereof, and a convex image-side surface in a paraxial region thereof;

a fifth lens having a refractive power;

a sixth lens having a refractive power; and

a seventh lens having a negative refractive power,

wherein the first to seventh lenses are sequentially disposed 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 surface of an image sensor,

the optical imaging system has a total of seven lenses,

a conditional expression n2+n3+n4>4.85 is satisfied, where n2 is a refractive index of the second lens, n3 is a refractive index of the third lens, and n4 is a refractive index of the fourth lens, and

a conditional expression 1.4<|f23|/f1<2.8 is satisfied, where f23 is a composite focal length of the second lens and the third lens, and f1 is a focal length of the first lens.