Zoom lens system and electronic imaging apparatus using the same

Patent metadata

Field	Value
Publication number	US-9690083-B2
Application number	US-201313777110-A
Country	US
Kind code	B2
Filing date	Feb 26, 2013
Priority date	Mar 2, 2012
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

A zoom lens system includes first through fourth lens groups. Upon zooming from the short to long focal length extremities, the second and third lens groups move while the distance between the first and second lens groups increases, and the distance between the second and third lens groups decreases. The fourth lens group includes a positive lens element having a convex surface on the object side; a cemented lens having a positive lens element and a negative lens element; a biconvex positive lens element, and a negative meniscus lens element having a convex surface on the image side. The following condition (1) is satisfied:

1.6< f 1/ f 4<3.0. . .   (1),

wherein f1 and f4 designate the focal lengths of the first and fourth lens groups, respectively.

First claim

What is claimed is:

1. A zoom lens system comprising:
a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, in that order from an object side, the positive first lens group comprising first and second sub lens groups, the second sub lens group being movable for focusing, the positive fourth lens group including both cemented and non-cemented lenses,
wherein upon zooming from a short focal length extremity to a long focal length extremity, at least said second lens group and said third lens group move along an optical axis direction so that a distance between said first lens group and said second lens group increases, and a distance between said second lens group and said third lens group decreases, and
wherein upon zooming from the short focal length extremity to the long focal length extremity, said first lens group and said fourth lens group do not move relative to an imaging plane, and
wherein the following conditions are satisfied:
1.6 <f 1 /f 4<3.0
1.4 <f 3 /f 4<5.0;

and
−8.0 <f 3 /f 2<−3.0

wherein
f1 designates a focal length of said first lens group,
f2 designates a focal length of said second lens group,
f3 designates a focal length of said third lens group, and
f4 designates a focal length of said fourth lens group.

2. The zoom lens system according to claim 1 , wherein the following condition is satisfied:
−0.7 <f 2 /f 4<−0.35.

3. The zoom lens system according to claim 1 , wherein the following condition is satisfied:
80<vd4p<94.96

wherein
vd4p designates an Abbe number, with respect to the d-line, of at least one positive lens element in said fourth lens group.

4. The zoom lens system according to claim 1 , wherein the following condition is satisfied:
1.56<Nd4p<1.64

wherein
Nd4p designates a refractive index at the d-line of a positive lens element, which is provided closest to the object side within said fourth lens group.

5. The zoom lens system according to claim 1 , wherein the following condition is satisfied:
1.70<Nd4n<1.80518

wherein
Nd4n designates a refractive index at the d-line of a negative meniscus lens element, which is provided closest to the image side within said fourth lens group.

6. The zoom lens system according to claim 1 , wherein said first lens group comprises at least one negative lens element, and
wherein the following condition is satisfied:
vd1n<22.85

wherein
vd1n designates an Abbe number, with respect to the d-line, of said negative lens element, which is provided closest to the object side within said first lens group.

Assignees

• Pentax Ricoh Imaging Co Ltd
• Ricoh Imaging Co Ltd

Inventors

• Saori Masakazu

Classifications

• H04N23/69

  Control of means for changing angle of the field of view, e.g. optical zoom objectives or electronic zooming · CPC title

• G02B15/173

  arranged +-+ · CPC title

• G02B15/24

  having a front fixed lens or lens group and two movable lenses or lens groups in front of a fixed lens or lens group · CPC title

• G02B15/22

  with movable lens means specially adapted for focusing at close distances · CPC title

• G02B15/14 Primary

  by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective · CPC title