Optical system, lens module, and electronic device

An optical system comprising, in order from an object side to an image side along an optical axis:

• a first lens with a positive refractive power, wherein the first lens has an object-side surface which is convex and an image-side surface which is concave at the optical axis;
• a second lens with a negative refractive power, wherein the second lens has an object-side surface which is convex and an image-side surface which is concave;
• a third lens with a refractive power, wherein the third lens has an object-side surface which is convex at the optical axis and an image-side surface which is concave at the optical axis;
• a fourth lens with a refractive power;
• a fifth lens with a refractive power, wherein the fifth lens has an object-side surface which is convex at the optical axis and an image-side surface which is concave at the optical axis;
• a sixth lens with a refractive power;
• and
• a seventh lens with a negative refractive power, wherein the seventh lens has an image-side surface which is concave at the optical axis, wherein the optical system further comprises a stop, and the optical system satisfies the following expression:
• 1.5<TTL/D<2.5;
• wherein TTL represents a distance on the optical axis from the object-side surface of the first lens to an imaging plane of the optical system, and D represents an aperture of the stop;
• wherein the optical system further satisfies the following expression:
• 2.52<(R1+R2)/f1<4.5;
• wherein R1 represents a radius of curvature of the object-side surface of the first lens, R2 represents a radius of curvature of the image-side surface of the first lens, and f1 represents an effective focal length of the first lens;
• and
• wherein the optical system satisfies the following expression:
• 1<f14/f<1.5;
• wherein f14 represents a combined focal length of the first lens, the second lens, the third lens, and the fourth lens, and f represents an effective focal length of the optical system.

A lens module, comprising:

• a lens barrel;
• and
• an optical system comprising, in order from an object side to an image side along an optical axis:
• a first lens with a positive refractive power, wherein the first lens has an object-side surface which is convex and an image-side surface which is concave at the optical axis;
• a second lens with a negative refractive power, wherein the second lens has an object-side surface which is convex and an image-side surface which is concave;
• a third lens with a refractive power, wherein the third lens has an object-side surface which is convex at the optical axis and an image-side surface which is concave at the optical axis;
• a fourth lens with a refractive power;
• a fifth lens with a refractive power, wherein the fifth lens has an object-side surface which is convex at the optical axis and an image-side surface which is concave at the optical axis;
• a sixth lens with a refractive power;
• and
• a seventh lens with a negative refractive power, wherein the seventh lens has an image-side surface which is concave at the optical axis, wherein the optical system further comprises a stop, and the optical system satisfies the following expression:
• 1.5<TTL/D<2.5;
• wherein TTL represents a distance on the optical axis from the object-side surface of the first lens to an imaging plane of the optical system, and D represents an aperture of the stop;
• wherein the first to seventh lenses of the optical system are received in the lens barrel;
• wherein the optical system further satisfies the following expression:
• 2.52<(R1+R2)/f1<4.5;
• wherein R1 represents a radius of curvature of the object-side surface of the first lens, R2 represents a radius of curvature of the image-side surface of the first lens, and f1 represents an effective focal length of the first lens;
• and wherein the optical system satisfies the following expression:
• 0.6<L/Imgh<0.8;
• wherein L represents a clear aperture diameter of the first lens, and Imgh represents half of a diagonal length of an effective pixel area of the imaging plane of the optical system.