a first lens (10) with positive focal power;

a second lens (20) with negative focal power;

a third lens (30) with positive focal power; and

a fourth lens (40) with positive focal power;

wherein:

the first lens (10), the second lens (20), the third lens (30) and the fourth lens (40) are arranged sequentially along a light incident direction from an object side to an image side;

the first lens (10) includes a first surface (11) facing toward the object side and a second surface (12) facing toward the image side;

the second lens (20) includes a third surface (21) facing toward the object side and a fourth surface (22) facing toward the image side;

the third lens (30) includes a fifth surface (31) facing toward the object side and a sixth surface (32) facing toward the image side;

the fourth lens (40) includes a seventh surface (41) facing toward the object side and an eighth surface (42) facing toward the image side;

the first surface (11), the second surface (12), the third surface (21), the fourth surface (22), the fifth surface (31), the sixth surface (32), the seventh surface (41) and the eighth surface (42) are sequentially arranged along the light incident direction from the object side to the image side;

an image plane (50) is provided on the image side of the large-aperture four-piece optical lens to face the eighth surface (42);

an aperture diaphragm (60) is arranged on the object side of the large-aperture four-piece optical lens to face the first surface (11) or arranged between the second surface (12) and the third surface S3 (21);

a vignetting diaphragm (70) is arranged on the seventh surface (41);

the first surface (11), the second surface (12), the fifth surface (31), the sixth surface (32) and the seventh surface (41) are all convex surfaces, and the fourth surface (22) is a concave surface;

a distance between the aperture diaphragm (60) and a center of the large-aperture four-piece optical lens is ST, a distance between an object focal point of the large-aperture four-piece optical lens and the center of the large-aperture four-piece optical lens is F_obj, a distance between the aperture diaphragm (60) and the object focal point of the large-aperture four-piece optical lens is |ST-F_obj|, a focal length of the large-aperture four-piece optical lens is f₀, and |ST-F_obj|<0.7f₀;

an effective diameter of light passing through the first surface (11) is d₁, an effective diameter of light passing through the second surface (12) is d₂, an effective diameter of light passing through the third surface (21) is d₃, an effective diameter of light passing through the fourth surface (22) is d₄, an effective diameter of light passing through the fifth surface (31) is d₅, an effective diameter of light passing through the sixth surface (32) is d₆, an effective diameter of light passing through the seventh surface (41) is d₇, and an effective diameter of light passing through the eighth surface (42) is d₈;

the effective diameters d of the light passing through the first surface (11) to the eighth surface (42) satisfy the following relationship: d_i>0.9d_j, wherein i<j, i is an integer ranging from 1 to 7, and j is an integer ranging from 2 to 8;

a radius of curvature of the third surface (21) is r₃, a radius of curvature of the fourth surface (22) is r₄, |r₄|<|r₃|, a radius of curvature of the seventh surface (41) is r₇, a radius of curvature of the eighth surface (42) is r₈, |r₇|<|r₈|, an equivalent focal length of the fourth lens (40) is greater than that of the third lens (30), and the equivalent focal length of the fourth lens (40) is greater than that of the first lens (10); and

a distance between centers of the sixth surface (32) and the seventh surface (41) is G₆₇, a distance between centers of the S2 surface (12) and the third surface (21) is G₂₃, and G₆₇<G₂₃.