Optical imaging system including five lenses of −+−+−, −+−++, −+−−+ or −+−−− refractive powers

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

• a first lens having a negative refractive power with a concave object-side surface and a concave image-side surface;
• a second lens having a refractive power;
• a third lens having a negative refractive power;
• a fourth lens having a refractive power, a concave object-side surface and a convex image-side surface;
• and
• a fifth lens having a refractive power;
• wherein −2.3≤f1/f2<−1.5, where f1 is an effective focal length of the first lens and f2 is an effective focal length of the second lens;
• wherein 2.5<ΣAT/CT2<3.5,
• wherein ΣAT is a sum of spaced intervals along the optical axis between each two adjacent lenses of the first lens to the fifth lens and CT2 is a center thickness of the second lens along the optical axis.