JP2003029148A5

JP2003029148A5 -

Info

Publication number: JP2003029148A5
Application number: JP2002128696A
Authority: JP
Filing date: 2002-04-30
Publication date: 2004-11-18

Description

【０００６】
本発明によるズームレンズ系は、物体側から順に、正の屈折力を有する第１レンズ群と、負の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群と、負の屈折力を有する第４レンズ群、とから構成され、各群を光軸方向に移動させてズーミングを行い、次の条件式（１）ないし（３）を満足することを特徴としている。
（１）１．１＜ｆ_23T／ｆ_23W＜１．８
（２）０．２＜ＬＤ_23W／ｆ_W＜０．４５
（３）０．０１＜（Ｄ_23W−Ｄ_23T）／ｆ _T＜０．０５
但し、
ｆ_23W：短焦点距離端での第２レンズ群と第３レンズ群の合成焦点距離、
ｆ_23T：長焦点距離端での第２レンズ群と第３レンズ群の合成焦点距離、
ＬＤ_23W：短焦点距離端での第２レンズ群の最も物体側の面から第３レンズ群の最も像側の面までの距離、
ｆ_W：短焦点距離端での全系の焦点距離、
ｆ _T ：長焦点距離端での全系の焦点距離、
Ｄ_23W：短焦点距離端での第２レンズ群と第３レンズ群の軸上空気間隔、
Ｄ_23T：長焦点距離端での第２レンズ群と第３レンズ群の軸上空気間隔、
である。[0006]
The zoom lens system according to the present invention comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a negative lens. And a fourth lens group having a refractive power of, and moving each group in the optical axis direction for zooming to satisfy the following conditional expressions (1) to (3).
(1) 1.1 <f _23T / f _23W <1.8
(2) 0.2 <LD _{23 W} / f _W <0.45
(3) 0.01 <(D _23W −D _23T ) / f _T <0.05
However,
f _{23 W} : combined focal length of the second lens group and the third lens group at the short focal length extremity,
f _{23 T} : combined focal length of the second lens group and the third lens group at the long focal length extremity,
LD _{23 W} : The distance from the most object side surface of the second lens group to the most image side surface of the third lens group at the short focal length extremity
f _W : Focal length of the entire system at the short focal length extremity
f _T : focal length of the entire system at the long focal length extremity
D _{23 W} : axial air gap between the second lens group and the third lens group at the short focal length extremity,
D _{23 T} : On-axis air gap between the second lens group and the third lens group at the long focal length extremity
It is.

【００１６】
条件式（２）は、短焦点距離端での第２レンズ群の最も物体側の面から第３レンズ群の最も像側の面までの距離を規定するものである。
条件式（２）の下限を超えると、負の第２レンズ群と正の第３レンズ群の間隔が狭くなるため短焦点距離端においてバックフォーカスが極めて短くなり、第４レンズ群の径が大きくなってしまう。条件式（２）の上限を超えると、第２レンズ群と第３レンズ群の間隔が広くなりすぎるため、短焦点距離端において入射瞳位置が像面側に寄るので第１レンズ群の径が大きくなってしまい、径方向の小型化が困難となる。[0016]
Conditional expression (2) defines the distance from the most object side surface of the second lens unit to the most image side surface of the third lens unit at the short focal length extremity.
If the lower limit of conditional expression (2) is exceeded, the distance between the negative second lens group and the positive third lens group becomes narrow, so the back focus becomes extremely short at the short focal length extremity, and the diameter of the fourth lens group becomes large. turn into. If the upper limit of conditional expression (2) is exceeded, the distance between the second lens group and the third lens group becomes too large, and the entrance pupil position approaches the image plane side at the short focal length extremity. It becomes large, making it difficult to miniaturize in the radial direction.

Claims

From the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a negative refractive power What is claimed is: 1. A zoom lens system comprising a group of lenses, wherein each group is moved in the optical axis direction for zooming to satisfy the following conditional expressions (1) to (3).
(1) 1.1 <f _23T / f _23W <1.8
(2) 0.2 <LD _{23 W} / f _W <0.45
(3) 0.01 <(D _23W −D _23T ) / f _T <0.05
However,
f _{23 W} : combined focal length of the second lens group and the third lens group at the short focal length extremity,
f _{23 T} : combined focal length of the second lens group and the third lens group at the long focal length extremity,
LD _{23 W} : The distance from the most object side surface of the second lens group to the most image side surface of the third lens group at the short focal length extremity
f _W : Focal length of the entire system at the short focal length extremity
f _T : focal length of the entire system at the long focal length extremity
D _{23 W} : axial air gap between the second lens group and the third lens group at the short focal length extremity,
_D23T : On-axis air gap between the second lens unit and the third lens unit at the long focal length extremity.