Imaging lens system

摘要

An imaging lens system includes, from the object side, an aperture stop, a positive first lens convex to the object side, a negative second lens, a positive third lens convex to the object side, a positive meniscus fourth lens convex to the image side, and a negative biconcave fifth lens, and fulfills the conditional formulae 0.8

主权项

1. An imaging lens system for imaging a subject image on an image sensing surface of an image sensing device, the imaging lens system comprising, from an object side:
an aperture stop; a first lens element having a positive optical power and convex to the object side; a second lens element having a negative optical power; a third lens element having a positive optical power and convex to the object side; a fourth lens element having a positive optical power and having a meniscus shape convex to the image side; and a fifth lens element having a negative optical power and having a biconcave shape, wherein an image-side surface of the fifth lens element has, on a sectional plane including an optical axis, a point, other than an intersection with the optical axis, at which a tangent line is perpendicular to the optical axis, conditional formulae (1) to (4) below are fulfilled:
0.8 f represents a focal length of the entire imaging lens system; f1 represents a focal length of the first lens element; f4 represents a focal length of the fourth lens element; d3 represents an axial thickness of the second lens element; d4 represents an axial aerial distance between the second and third lens elements; and R3—1 represents a radius of curvature of the object-side surface of the third lens element on the optical axis; and wherein an image-side surface of the third lens element has a negative optical power in a peripheral part.