Variable magnification optical system and imaging apparatus

Patent metadata

Field	Value
Publication number	US-9726867-B2
Application number	US-201514708749-A
Country	US
Kind code	B2
Filing date	May 11, 2015
Priority date	May 27, 2014
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

A variable magnification optical system consists of a first lens-group having negative refractive-power, a stop and a second lens-group having positive refractive-power in this order from an object-side. The first lens-group includes an L 11 negative meniscus lens, an L 12 negative lens and a C 11 cemented lens, in which a biconcave lens and a positive lens are cemented together in this order from the object-side, in this order from the object-side. The second lens-group includes an L 21 positive lens that is arranged closest to the object-side and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image-side of the L 21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object-side. The following conditional expressions (1) and (2) are satisfied:

−1.0< Rf 11/ Rf 12<0.7  (1); and

55.0<ν d ave1  (2).

First claim

What is claimed is:

1. A variable magnification optical system consisting of:
a first lens group having negative refractive power:
a stop; and
a second lens group having positive refractive power in this order from an object side, and
the variable magnification optical system being configured to change magnification by changing a distance between the first lens group and the second lens group in an optical axis direction and to perform correction of the position of an image plane necessitated by the change in magnification by moving the first lens group in the optical axis direction,
wherein the first lens group comprises, in this order from the object side, an L 11 negative meniscus lens, an L 12 negative lens and a C 11 cemented lens, the C 11 cemented lens comprising, in this order from the object side, a biconcave lens and a positive lens cemented together, and
wherein the second lens group comprises an L 21 positive lens that is arranged closest to the object side of all lenses in the second lens group and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image side of the L 21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object side, and one of the cemented lenses closer to the object side being a C 21 cemented lens and the other one of the cemented lenses closer to the image side being a C 22 cemented lens,
wherein the C 21 cemented lens and the C 22 cemented lens each have a positive refractive power, and
wherein the following conditional expressions (1) and (2) are satisfied:
−1.0< Rf 11/ Rf 12<0.7  (1); and

55.0 <νd ave1  (2), where

Rf11: a curvature radius of an object-side surface of the L 11 negative meniscus lens,
Rf12: a curvature radius of an object-side surface of the L 12 negative lens, and
νdave1: an average of Abbe numbers for d-line of all negative lenses arranged toward the object side of the positive lens constituting the C 11 cemented lens.

2. The variable magnification optical system, as defined in claim 1 , wherein the second lens group moves to vary magnification and wherein the following conditional expression (3) is satisfied:
2.00< T 2/ STR 2<3.20  (3), where

T2: a distance from a vertex of a surface closest to the object side in the second lens group to a vertex of a surface closest to the image side in the second lens group, and
STR2: a movement amount of the second lens group from a wide-angle end to a telephoto end.

3. The variable magnification optical system, as defined in claim 1 , wherein the following conditional expressions (4) and (5) are satisfied:
1.47< ndC 21 n< 1.60  (4); and

1.70< ndC 22 n< 2.00  (5), where

ndC21n: a refractive index for d-line of the negative lens constituting the C 21 cemented lens, and
ndC22n: a refractive index for d-line of the negative lens constituting the C 22 cemented lens.

4. The variable magnification optical system, as defined in claim 1 , wherein the following conditional expression (6) is satisfied:
70.0<ν dC 21ave  (6), where

νdC21ave: an average of Abbe numbers for d-line of the two lenses constituting the C 21 cemented lens.

5. The variable magnification optical system, as defined in claim 1 , further comprising:
a negative meniscus lens toward the image side of the C 11 cemented lens, and an object-side surface of which is concave.

6. The variable magnification optical system, as defined in claim 1 , wherein the second lens group consists of five lenses of a positive lens including at least one aspheric surface, a cemented lens consisting of a negative meniscus lens having a concave image-side surface and a biconvex lens, and a cemented lens consisting of a negative meniscus lens having a concave image-side surface and a biconvex lens in this order from the object side.

7. The variable magnification optical system, as defined in claim 1 , wherein the following conditional expression (4-1) is satisfied:
1.47< ndC 21 n< 1.50  (4-1), where

ndC21n: a refractive index for d-line of the negative lens constituting the C 21 cemented lens.

8. An imaging apparatus comprising:
the variable magnification optical system, as defined in claim 1 , wherein the variable magnification optical system provides an image on an object and further comprising an imaging device that images an image of the object formed by the variable magnification optical system.

9. A variable magnification optical system consisting of:
a first lens group having negative refractive power:
a stop; and
a second lens group having positive refractive power in this order from an object side, and
the variable magnification optical system being configured to change magnification by changing a distance between the first lens group and the second lens group in an optical axis direction and to perform correction of the position of an image plane necessitated by the change in magnification by moving the first lens group in the optical axis direction,
wherein the first lens group comprises, in this order from the object side, an L 11 negative meniscus lens, an L 12 negative lens and a C 11 cemented lens, the C 11 cemented lens comprising, in this order from the object side, a biconcave lens and a positive lens cemented together, and
wherein the second lens group comprises an L 21 positive lens that is arranged closest to the object side of all lenses in the second lens group and includes at least one aspheric surface, and an object-side surface of which is convex, and only two cemented lenses toward an image side of the L 21 positive lens, and each of which consists of a negative lens and a positive lens cemented together in this order from the object side, and one of the cemented lenses closer to the object side being a C 21 cemented lens and the other one of the cemented lenses closer to the image side being a C 22 cemented lens, and
wherein the following conditional expressions (1) and (2) are satisfied:
−1.0< Rf 11/ Rf 12<0.7  (1); and

55.0 <νd ave1  (2), where

Rf11: a curvature radius of an object-side surface of the L 11 negative meniscus lens,
Rf12: a curvature radius of an object-side surface of the L 12 negative lens, and
νdave1: an average of Abbe numbers for d-line of all negative lenses arranged toward the object side of the positive lens constituting the C 11 cemented lens, and
wherein the following conditional expression (7) is satisfied:
|θ CA′C 21 n−θCA′C 21 p|< 0.02  (7), where

θCA′C21n: a partial dispersion ratio of C-line and A′-line of the negative lens constituting the C 21 cemented lens, and
θCA′C21p: a partial dispersion ratio of C-line and A′-line of the positive lens constituting the C 21 cemented lens.

10. The variable magnification optical system, as defined in claim 9 , wherein the second lens group moves to vary magnification and wherein the following conditional expression (3) is satisfied:
2.00< T 2/ STR 2<3.20  (3), where

T2: a distance from a vertex of a surface closest to the object side in the second lens group to a vertex of a surface closest to the image side in the second lens group, and
STR2: a movement amount of the second lens group from a wide-angle end to a telephoto end.

11. The variable magnification optical system, as defined in claim 9 , wherein the following conditional expressions (4) and (5) are satisfied:
1.47< ndC 21 n< 1.60  (4); and

1.70< ndC 22 n< 2.00  (5), where

ndC21n: a refractive index for d-line of the negative lens constituting the C 21 cemented lens, and
ndC22n: a refractive index for d-line of the negative lens con

Assignees

• Fujifilm Corp

Inventors

• Tomioka Ukyo

Classifications

• G02B13/0045

  having five or more lenses · CPC title

• G02B15/161 Primary

  Physics · mapped topic

• G02B15/177

  having a negative front lens or group of lenses · CPC title

• G02B13/04

  Reversed telephoto objectives · CPC title

• G02B13/008

  designed for infrared light · CPC title