ZOOM LENS AND IMAGE PICKUP APPARATUS INCLUDING THE SAME

• US 20140320977A1
• Filed: 04/23/2014
• Published: 10/30/2014
• Est. Priority Date: 04/30/2013
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yakita, Shinichiro
• Granted Patent: US 9,104,017 B2
• Time in Patent Office: Days
• US Class Current: 359/686
• CPC Class Codes: G02B 15/144109 arranged +--+

Abstract

A zoom lens includes in order from an object side: a positive first lens unit; a negative second lens unit which moves during zooming; a third lens unit; a stop; and a positive fourth lens unit. The first lens unit includes, in order from the object side, a negative first lens subunit which does not move, a positive second lens subunit which moves during focusing, and a positive third lens subunit which does not move. The first lens subunit is composed of one or more negative lenses, and the second lens subunit includes a positive lens and a negative lens. An average value of Abbe constants of the first lens subunit, an average value of Abbe constants of the positive lenses of the second lens subunit, and an average value of Abbe constants of the negative lenses of the second lens subunit are appropriately set.

Claims

1. A zoom lens, comprising, in order from an object side to an image side:

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power which moves during zooming;

a third lens unit;

a stop; and

a fourth lens unit having a positive refractive power,

wherein the first lens unit includes, in order from the object side to the image side, a first lens subunit having a negative refractive power which does not move, a second lens subunit having a positive refractive power which moves during focusing, and a third lens subunit having a positive refractive power which does not move,

wherein the first lens subunit is composed of one or more negative lenses, and the second lens subunit includes at least one positive lens and at least one negative lens, and

wherein the following expression is satisfied;

9×

10⁶<

ν

11a³×

(ν

12ap−

ν

12an)<

45×

10⁶,

where ν

11a represents an average value of Abbe constants of the first lens subunit, ν

12ap represents an average value of Abbe constants of the at least one positive lens of the second lens subunit, ν

12an represents an average value of Abbe constants of the at least one negative lens of the second lens subunit, and Abbe constant ν

is defined as,

ν

=(Nd−

1)/(NF−

NC)

where NF represents a refractive index for F-line, Nd represents a refractive index for d-line, and NC represents a refractive index for C-line.

2. A zoom lens according to claim 1, wherein the following expressions are satisfied:

1.8<

|φ

11/φ

12|<

7.0, and

0.5<

|φ

11/φ

1|<

1.0,

where φ

11 represents a refractive power of the first lens subunit, φ

12 represents a refractive power of the second lens subunit, and φ

1 represents a refractive power of the first lens unit.

3. A zoom lens according to claim 1, wherein the following expression is satisfied:

0.020<

θ

11a×

(θ

12an−

θ

12ap)<

0.046,

where θ

11a represents an average value of partial dispersion ratios of the first lens subunit, θ

12ap represents an average value of partial dispersion ratios of the at least one positive lens of the second lens subunit, θ

12an represents an average value of partial dispersion ratios of the at least one negative lens of the second lens subunit, and partial dispersion ratio θ

is defined as,

θ

=(Ng−

NF)/(NF−

NC)

where NF represents a refractive index for F-line, Ng represents a refractive index for g-line, and NC represents a refractive index for C-line.

4. A zoom lens according to claim 1, wherein the following expressions are satisfied:

0.5<

ν

11a/(ν

13ap−

ν

13an)<

4.0, and

0.6<

φ

13/φ

1<

1.5,

where φ

13 represents a refractive power of the third lens subunit, and ν

13a represents an average value of Abbe constants of the third lens subunit.

5. A zoom lens according to claim 1, wherein the following expression is satisfied:

0.15<

|φ

1/φ

2|<

0.30,

where φ

2 represents a refractive power of the second lens unit.

6. An image pickup apparatus, comprising:

a zoom lens, comprising, in order from an object side to an image side;

a first lens unit having a positive refractive power;

a second lens unit having a negative refractive power which moves during zooming;

a third lens unit;

a stop; and

a fourth lens unit having a positive refractive power,

wherein the first lens unit includes, in order from the object side to the image side, a first lens subunit having a negative refractive power which does not move, a second lens subunit having a positive refractive power which moves during focusing, and a third lens subunit having a positive refractive power which does not move,

wherein the first lens subunit is composed of one or more negative lens, and the second lens subunit includes at least one positive lens and at least one negative lens, and

wherein the following expression is satisfied;

9×

10⁶<

ν

11a³×

(ν

12ap−

ν

12an)<

45×

10⁶,

where ν

11a represents an average value of Abbe constants of the first lens subunit, ν

12ap represents an average value of Abbe constants of the at least one positive lens of the second lens subunit, ν

12an represents an average value of Abbe constants of the at least one negative lens of the second lens subunit, and Abbe constant ν

is defined as,

ν

=(Nd−

1)/(NF−

NC)

where NF represents a refractive index for F-line, Nd represents a refractive index for d-line, and NC represents a refractive index for C-line; and

an image pickup element for receiving light from the zoom lens.