Short overall length imaging lens system with four lenses

A short overall length imaging lens system with four lenses along an optical axis from an object side to an image side comprising:

• a first lens with positive power that is a meniscus lens with a convex surface on the object side,
• an aperture stop,
• a second lens with negative power that is a meniscus lens with a convex surface facing the object side and at least one aspherical optical surface,
• a third lens with positive power that is a meniscus lens with a concave surface on the object side and at least one aspherical optical surface, and
• a fourth lens with negative power that is a biconcave lens with an aspherical surface on the image side and at least one inflection point in effective diameter range ranging from a lens center to lens edge on the image side;
• wherein the imaging lens system satisfied the equations:
• 0.25
• ≤
• d
• ⁢
• ⁢
• 2
• +
• d
• ⁢
• ⁢
• 4
• +
• d
• ⁢
• ⁢
• 6
• f
• s
• ≤
• 0.40
• 0.8
• ≤
• Y
• ·
• tan
• ⁡
• (
• ω
• )
• Bf
• ≤
• 2.7
• wherein d2 is distance from the image side of the first lens to the object side of the second lens on the optical axis, d4 is distance from the image side of the second lens to the object side of the third lens on the optical axis, d6 is distance from the image side of the third lens to the object side of the fourth lens on the optical axis, Bf is back focal length of the imaging lens system, fs is effective focal length of the imaging lens system, TL is distance from the object side of the first lens to an image plane on the optical axis, ω is half of maximum field angle (degree), and Y is half of maximum diagonal of imaging height.