An optical photographing system comprising eight lens elements (E1, E2, E3, E4, E5, E6, E7, E8), the eight lens elements (E1, E2, E3, E4, E5, E6, E7, E8) being, in order from an object side to an image side along an optical path, a first lens element (E1), a second lens element (E2), a third lens element (E3), a fourth lens element (E4), a fifth lens element (E5), a sixth lens element (E6), a seventh lens element (E7) and an eighth lens element (E8), and each of the eight lens elements (E1, E2, E3, E4, E5, E6, E7, E8) having an object-side surface facing toward the object side and an image-side surface facing toward the image side; wherein a total number of lens elements (E1-E8) of the optical photographing system is eight, the first lens element (E1) has negative refractive power, the object-side surface of the first lens element (E1) is convex in a paraxial region thereof, the image-side surface of the first lens element (E1) is concave in a paraxial region thereof, the third lens element (E3) has negative refractive power, the object-side surface of the third lens element (E3) is concave in a paraxial region thereof, the fourth lens element (E4) has positive refractive power, the fifth lens element (E5) has positive refractive power, the image-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, the sixth lens element (E6) has positive refractive power, the seventh lens element (E7) has negative refractive power, the object-side surface of the seventh lens element (E7) is concave in a paraxial region thereof, and the image-side surface of the seventh lens element (E7) is concave in a paraxial region thereof; and wherein the sixth lens element (E6) and the seventh lens element (E7) are cemented to each other; characterized in that the optical photographing system further comprises an aperture stop (ST) located between the second lens element (E2) and the third lens element (E3), and in that a sum of central thicknesses of all lens elements (E1, E2, E3, E4, E5, E6, E7, E8) of the optical photographing system is ΣCT, a sum of axial distances between each of all adjacent lens elements (E1, E2, E3, E4, E5, E6, E7, E8) of the optical photographing system is ΣAT, and the following condition is satisfied: 3.0 < ∑ CT / ∑ AT . wherein a total number of lens elements (E1-E8) of the optical photographing system is eight, the first lens element (E1) has negative refractive power, the object-side surface of the first lens element (E1) is convex in a paraxial region thereof, the image-side surface of the first lens element (E1) is concave in a paraxial region thereof, the third lens element (E3) has negative refractive power, the object-side surface of the third lens element (E3) is concave in a paraxial region thereof, the fourth lens element (E4) has positive refractive power, the fifth lens element (E5) has positive refractive power, the image-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, the sixth lens element (E6) has positive refractive power, the seventh lens element (E7) has negative refractive power, the object-side surface of the seventh lens element (E7) is concave in a paraxial region thereof, and the image-side surface of the seventh lens element (E7) is concave in a paraxial region thereof; and wherein the sixth lens element (E6) and the seventh lens element (E7) are cemented to each other; characterized in that the optical photographing system further comprises an aperture stop (ST) located between the second lens element (E2) and the third lens element (E3), and in that a sum of central thicknesses of all lens elements (E1, E2, E3, E4, E5, E6, E7, E8) of the optical photographing system is ΣCT, a sum of axial distances between each of all adjacent lens elements (E1, E2, E3, E4, E5, E6, E7, E8) of the optical photographing system is ΣAT, and the following condition is satisfied: 3.0 < ∑ CT / ∑ AT . <EOS>