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 convex image-side surface in a 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 a paraxial region thereof;
• a third lens having a negative refractive power;
• and
• a fourth lens having a positive refractive power,
• wherein the first to fourth 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 plane of the optical imaging system,
• the optical imaging system has a total of four lenses,
• the first lens is made of a first plastic material, and the second lens and the third lens are made of plastic materials having optical characteristics different from optical characteristics of the first plastic material, and
• 0.8<TTL/f<1.5 is satisfied, where TTL is a distance along the optical axis from the object-side surface of the first lens to the imaging plane, and f is an overall focal length of the optical imaging system.