Optical imaging system

An optical imaging system, along an optical axis from an object side to an image side sequentially comprising:

• a first lens having negative refractive power;
• a second lens having positive refractive power, and an object-side surface of the second lens being a convex surface;
• a third lens having refractive power, an object-side surface of the third lens at a paraxial area being a convex surface, and an image-side surface of the third lens at the paraxial area being a convex surface;
• and
• a fourth lens having refractive power, and an object-side surface of the fourth lens at the paraxial area being a concave surface,
• wherein a number of lenses having refractive powers in the optical imaging system is four,
• a total effective focal length f of the optical imaging system and half of a maximum field-of-view Semi-FOV of the optical imaging system satisfy:
• f×tan(Semi-FOV)≥4.0 mm;
• and
• the total effective focal length f of the optical imaging system and an entrance pupil diameter EPD of the optical imaging system satisfy:
• f/EPD<2.35.