ZOOM LENS AND IMAGE PICKUP APPARATUS INCLUDING THE SAME

• US 20120134031A1
• Filed: 11/17/2011
• Published: 05/31/2012
• Est. Priority Date: 11/25/2010
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Eguchi, Kaoru, Hiasa, Norihito
• Granted Patent: US 8,570,662 B2
• Time in Patent Office: Days
• US Class Current: 359/686
• CPC Class Codes: G02B 15/144109 arranged +--+
• CPC Class Codes: G02B 15/144113 arranged +-++
• CPC Class Codes: G02B 15/145129 arranged +-+++
• CPC Class Codes: G02B 15/1461 the first group being positive
• CPC Class Codes: G02B 15/17 arranged +--

Abstract

A zoom lens includes, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive or negative refractive power, and a rear lens group including one or more lens units, an aperture stop is provided on the image side of the second lens unit. A sum of relative anomalous partial dispersion ΔθgF of materials of negative lenses included in the second lens unit, a sum of power of a negative lens formed of a material having relative anomalous partial dispersion that is equal to or more than an average value of relative anomalous partial dispersion of the materials of the negative lenses included in the second lens unit, and a refractive power of the second lens unit are appropriately set.

Claims

1. A zoom lens comprising:

a first lens unit having positive refractive power;

a second lens unit having negative refractive power;

a third lens unit having positive or negative refractive power; and

a rear lens group including one or more lens units,

wherein the first lens unit, the second lens unit, the third lens unit and the rear lens group are arranged in order from an object side to an image side along an optical axis of the zoom lens,

wherein, during zooming from a wide-angle end to a telephoto end, the second lens unit moves along the optical axis so that a distance between the first lens unit and the second lens unit increases,

wherein an aperture stop is provided on the image side of the second lens unit, and

wherein, when a sum of relative anomalous partial dispersion Δ

θ

gF of materials of negative lenses included in the second lens unit is indicated by SUM(Δ

θ

gF_2N), a sum of optical power of negative lenses formed of a material having relative anomalous partial dispersion Δ

θ

gF that is equal to or more than an average value of relative anomalous partial dispersion Δ

θ

gF of the materials of the negative lenses included in the second lens unit is indicated by φ

_2SUM, and an optical power of the second lens unit is indicated by φ

₂, the following conditions are satisfied;

0.065<

SUM(Δ

θ

gF_2N)<

0.200

0.4<

φ

_2SUM/φ

₂<

2.0.

2. The zoom lens according to claim 1, wherein the second lens unit includes a negative lens formed of a material satisfying a condition of 70<

υ

_2N<

100 when an Abbe number of the material of the negative lens is indicated by υ

_2N.

3. The zoom lens according to claim 1, wherein, when a sum of relative anomalous partial dispersion Δ

θ

gF of materials of positive lenses included in the first lens unit is indicated by SUM(Δ

θ

gF_1P), the following condition is satisfied;

0.030<

SUM(Δ

θ

gF_1P)<

0.300.

4. The zoom lens according to claim 1, wherein, when a focal length of the first lens unit is indicated by f₁, a focal length of the second lens unit is indicated by f₂, a focal length of the third lens unit is indicated by f₃, a focal length of the entire zoom lens at the wide-angle end is indicated by f_w, and a focal length of the entire zoom lens at the telephoto end is indicated by f_t, the following conditions are satisfied:

2.0<

f₁/√

(f_w×

f_t)<

10.0

−

1.5<

f₂/√

(f_w×

f_t)<

−

0.5

−

10.0<

f₁/f₂<

−

1.0

0.05<

|f₂/f₃|<

0.60.

5. The zoom lens according to claim 1, wherein the rear lens group includes a fourth lens unit having positive refractive power at the most object side, and

wherein during zooming from the wide-angle end to the telephoto end, the second lens unit monotonously moves towards the image side, the third lens unit moves along a locus that is of convex shape towards the object side so that a distance between the third lens unit and the second lens unit changes, and the fourth lens unit moves so that a distance between the fourth lens unit and the third lens unit changes.

6. The zoom lens according to claim 1, wherein the second lens unit includes, in order from the object side to the image side, a negative lens having a concave surface facing the image side, a negative lens having a concave surface facing the image side, and, on the image side thereof, two or more negative lenses and one or more positive lenses disposed in no particular order.

7. The zoom lens according to claim 1, wherein, when a relative anomalous partial dispersion of a material of at least one positive lens of positive lenses included in the second lens unit is indicated by Δ

θ

gF_2P and a refractive index of the material of at least one positive lens of the positive lenses included in the second lens unit is indicated by N_2P, the following conditions are satisfied;

−

0.050<

Δ

θ

gF_2P<

0.017

1.40<

N_2P<

1.70.

8. The zoom lens according to claim 1, wherein the second lens unit includes, in order from the object side to the image side, a negative lens having a concave surface facing the image side, a negative lens having a concave surface facing the image side, a cemented lens obtained by cementing a positive lens and a negative lens, and a cemented lens obtained by cementing a positive lens and a negative lens.

9. The zoom lens according to claim 1, wherein the second lens unit includes, in order from the object side to the image side, a negative lens having a concave surface facing the image side, a negative lens having a concave surface facing the image side, a negative lens, a negative lens, and a positive lens.

10. An image pickup apparatus comprising:

a zoom lens; and

a solid-state image sensor configured to receive an image formed by the zoom lens,

wherein the zoom lens includes, in order from an object side to an image side;

a first lens unit having positive refractive power;

a second lens unit having negative refractive power;

a third lens unit having positive or negative refractive power; and

a rear lens group including one or more lens units,

wherein during zooming from a wide-angle end to a telephoto end, the second lens unit moves along an optical axis so that a distance between the first lens unit and the second lens unit increases,

wherein an aperture stop is provided on the image side of the second lens unit, and

wherein, when a sum of relative anomalous partial dispersion Δ

θ

gF of materials of negative lenses included in the second lens unit is indicated by SUM(Δ

θ

gF_2N), a sum of power of negative lenses formed of a material having relative anomalous partial dispersion Δ

θ

gF that is equal to or more than an average value of relative anomalous partial dispersion Δ

θ

gF of the materials of the negative lenses included in the second lens unit is indicated by φ

_2SUM, and an optical power of the second lens unit is indicated by φ

₂, the following conditions are satisfied;

0.065<

SUM(Δ

θ

gF_2N)<

0.200

0.4<

φ

_2SUM/φ

₂<

2.0.