Imaging lens system, imaging optical device, and digital appliance

摘要

A single-focal-length imaging lens system achieves focusing by, while keeping first and third lens groups stationary relative to the image plane, moving a second lens group along the optical axis. The second lens group includes a positive lens element. The third lens group includes an aspherically shaped lens element having an inflection point at a position other than the intersection with the optical axis. The first and second air lenses formed by the intervals between the first and second and between the second and third lens groups have negative and positive refractive powers respectively. The conditional formula 0≦|Fi1/Fi2|−|Fm1/Fm2|≦10 is fulfilled (Fi1 and Fi2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the infinite object distance; Fm1 and Fm2 representing the focal lengths of the first and second air lenses, respectively, when focusing on the closest object distance).

主权项

1. A single-focal-length imaging lens system comprising, in order from an object side:
a first lens group, the first lens group being composed of, in order from the object side, a first lens element having a positive refractive power and convex to the object side and a second lens element having a negative refractive power and concave to the image side; a second lens group which includes at least one positive lens element, the second lens group being composed of, in order from the object side, a third lens element convex to the object side and a fourth lens element having a positive refractive power and convex to the image side; and a third lens group which includes at least one aspherically shaped lens element having an inflection point at a position other than an intersection with an optical axis, the third lens group being composed of a fifth lens element having a negative refractive power and concave to the image side, wherein the imaging lens system performs focusing by, while keeping the first and third lens groups stationary relative to an image plane, moving the second lens group in an optical axis direction, an air lens formed by an interval between the first and second lens groups has a negative refractive power, an air lens formed by an interval between the second and third lens groups has a positive refractive power, and conditional formula (1) below is fulfilled;
0≦|Fi1/Fi2|−|Fm1/Fm2|≦10  (1) where, when the air lens formed by the interval between the first and second lens groups is referred to as a first air lens, and the air lens formed by the interval between the second and third lens groups is referred to as a second air lens, then
Fi1 represents a focal length of the first air lens when focusing on an infinite object distance;Fi2 represents a focal length of the second air lens when focusing on the infinite object distance;Fm1 represents the focal length of the first air lens when focusing on a closest object distance; andFm2 represents the focal length of the second air lens when focusing on the closest object distance.