JP2002365539A - Zoom lens and imaging device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high image quality in a zoom lens whose variable power ratio is about 5. SOLUTION: This zoom lens is constituted of a 1st positive lens group G1, a 2nd negative lens group G2, a 3rd positive lens group G3, a 4th positive lens group G4 and a 5th lens group G5 having weak refractive power, in this order from object side, and performs zooming by moving the 2nd and the 4th lens groups G2 and G4. The 5th lens group G5 is constituted of at least two groups of lenses, including a positive lens group including at least one positive lens and a negative lens group including at least one negative lens, where the zoom lens satisfies (1) 0.8<β5<1.05, and (2) 0.8<|fG2/fw|<1.3. And β5 is the image forming magnification of the 5th lens group, where the subject distance is infinity, fG2 is the focal distance of the 2nd lens group, and (fw) is the focal distance of a lens entire system at a short focal distance end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a zoom lens having a zoom ratio of about 5 and used in a video camera, a digital still camera or the like, and an image pickup apparatus using the same.

[0002]

2. Description of the Related Art In recent years, higher image quality has been demanded for video cameras, digital still cameras, and the like. Particularly, in digital still cameras and the like having a large number of pixels, image formation corresponding to a solid-state imaging device having a large number of pixels is required. There is a demand for a shooting lens having excellent performance, particularly a zoom lens.

A conventional zoom lens having an imaging performance corresponding to a solid-state imaging device having a large number of pixels is disclosed in JP-A-2001-2001.
As disclosed in JP-A-51196, a four-unit zoom lens including a positive first lens unit, a negative second lens unit, a positive third lens unit, and a positive fourth lens unit is arranged in order from the object side. Are known.

[0004]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
In the four-unit zoom lens disclosed in Japanese Patent Application Laid-Open No. 001-51196, the change in image flatness due to zooming is large,
To obtain a sufficiently high image quality over the entire zoom range, the negative second
It is necessary to weaken the power (refractive power) of the lens group, and to secure a high zoom magnification, it is necessary to increase the movable range of the negative second lens group, which causes an increase in the overall length and the diameter of the front lens. There is a point.

[0005] As described in Japanese Patent No. 2832092, there is a zoom lens for adding a negative fifth lens group to reduce the size, but it is a bright lens having a small F-number.
It is difficult to obtain an imaging performance that can withstand a digital still camera having a large number of pixels.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the image quality of a zoom lens having a zoom ratio of about 5 used for a video camera, a digital still camera, or the like.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve such an object.
The first lens unit includes a first positive lens unit, a second negative lens unit, a third positive lens unit, a fourth positive lens unit, and a fifth lens unit having a weak refractive power. Wherein the fifth lens group includes a positive lens group including at least one positive lens and a negative lens group including at least one negative lens. It consists of a group of lenses,
(1) 0.8 <β5 <1.05 and (2) 0.8 <| fG2 / fw | <
It satisfies 1.3. Here, β5 is the imaging magnification of the fifth lens group when the object distance is infinity, fG2 is the focal length of the second lens group, and fw is the focal length at the short focal length end of the entire lens system.

In the present invention, the above conditional expression (1)
The imaging magnification of the fifth lens group is set by the above, mainly spherical aberration is suppressed, and the total length of the lens is suppressed by the above conditional expression (2), so that both miniaturization and high image quality can be achieved. ing.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. The zoom lens of this embodiment includes, in order from the object side, a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a fifth lens group having weak power. The zooming is performed by moving the second lens group and the fourth lens group. When zooming from the short focal length end to the long focal length end, the second lens group moves from the object side to the image side. The lens groups are moved so as to maintain the image position.

Moreover, in the zoom lens of the present embodiment,
It satisfies the following conditional expressions (1) and (2).

0.8 <β5 <1.05 (1) 0.8 <| fG2 / fw | <1.3 (2) where β5 is the imaging magnification of the fifth lens unit at an infinite object distance, and fG2 is The focal length of the second lens group, fw, is
This is the focal length at the short focal length extremity of the entire lens system.

The conditional expression (1) defines the imaging magnification of the fifth lens group when the object distance is infinity. If the lower limit of the range of the conditional expression (1) is exceeded, the total length will be longer. Getting worse.

The conditional expression (2) defines the ratio between the focal length of the negative second lens unit and the focal length at the short focal length end of the entire lens system. If the lower limit of conditional expression (2) is exceeded, the fluctuation of astigmatism during zooming will increase. If the upper limit of conditional expression (2) is exceeded, the overall length will be long.

In this embodiment, it is desirable to satisfy the following conditional expression (3).

1.5 <| fG5- / fw | <3 (3) where fG5- is the focal length of the negative lens group included in the fifth lens group.

The conditional expression (3) defines the ratio of the focal length of the negative lens unit included in the fifth lens unit to the focal length at the short focal length end of the entire lens system. If the lower limit of conditional expression (3) is exceeded, the exit pupil will be close to the image, making it unsuitable for use in a solid-state image sensor such as a CCD. In order to obtain sufficient optical performance, the overall length of the lens becomes long.

Further, when the second lens group includes at least three negative lenses and at least one positive lens, fluctuation of astigmatism due to zooming can be further suppressed.

Further, the third lens group has at least one positive lens on the object side with respect to the diaphragm and at least one positive lens on the image side.
With the configuration including the negative lenses, the influence of the eccentricity of each lens in the third lens group on the tilt of the image plane can be reduced without increasing the total length.

FIG. 1 is a diagram showing a configuration of a zoom lens according to a first embodiment of the present invention. That is, this zoom lens includes, in order from the object side, a positive first lens group G1, a negative second lens group G2, and a positive third lens group G including a stop S.
3, the fourth lens group G4 having a positive refractive power, and the fifth lens group G5 having a weak refractive power.

FL denotes a filter including a low-pass filter, an infrared cut filter, and a cover glass of a CCD;
G represents an image plane. This zoom lens has a second lens group G
The zooming is performed by moving the second and fourth lens groups G4. When zooming from the short focal length end to the long focal length end, the second lens group G2 moves from the object side to the image side.
The lens group G4 is moved so as to maintain the image position (see the lower diagram in FIG. 1).

The first lens group G1 includes three negative lenses L
1, L2 and L3, and the second lens group G2 is
It is composed of three negative lenses L4, L5, L6 and one negative lens L7 from the object side. The third lens group G3 includes one positive lens L on the object side with respect to the stop S.
8. It is constituted by one negative lens L9 on the image side.
Also, by controlling the aperture diameter of the stop S, the open F-number near the end of the long focal length is limited.

Further, the fourth lens unit G4 has a first lens unit on the object side.
The fifth lens group G5 includes one positive lens L12 on the object side, one negative lens L13 on the image side, and a filter FL. Have been.

FIG. 2 is a diagram showing a configuration of a zoom lens according to a second embodiment of the present invention. As in the first embodiment, in order from the object side, a positive first lens group G1 and a negative second
The zoom lens includes a lens group G2, a third positive lens group G3 including a stop S, a fourth positive lens group G4, and a fifth lens group G5 having a low refractive power.

FL is a filter including a low-pass filter, an infrared cut filter, and a cover glass of a CCD;
G represents an image plane. This zoom lens has a second lens group G
The zooming is performed by moving the second and fourth lens groups G4. When zooming from the short focal length end to the long focal length end, the second lens group G2 moves from the object side to the image side.
The lens group G4 is moved so as to maintain the image position (see the lower diagram in FIG. 2).

The first lens group G1 includes three negative lenses L
1, L2 and L3, and the second lens group G2 is
It is composed of two negative lenses L4, L5, one positive lens L6, and one negative lens L7 from the object side. Further, the third lens group G3 includes one positive lens L8 on the object side and one negative lens L9 on the image side with the stop S interposed therebetween. Further, by controlling the aperture diameter of the stop, the open F-number at the vicinity of the intermediate focal length to the end of the long focal length is limited.

Further, the fourth lens unit G4 has a first lens unit on the object side.
The fifth lens group G5 includes one positive lens L12 on the object side, one negative lens L13 on the image side, and a filter FL. Have been.

Tables 1, 2 and 3 below show the specifications of the first and second embodiments, respectively.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

In each table, FNo. Is the F-number, f is the focal length, ω is the half angle of view, surface No. Is the number from the object side of the lens surface shown in FIGS. 1 and 2, R is the radius of curvature, d is the lens surface interval, nd is the refractive index for d-line, and νd is the Abbe number. The surface indicated by (ASP) is an aspheric surface, and the shape of the aspheric surface is a shape represented by the above equation (4).

X = (y ² / r) / {1+ (1-κ · y ² / r ² ) ^1/2 } + C4 · y ⁴ + C6 · y ⁶ + C8 · y ⁸ + C10 · y ¹⁰ (4) where x: distance in the optical axis direction from the vertex of the lens surface, r: radius of curvature at the vertex of the lens, κ: conical constant. Also, C4, C6, C8, and C10 are quaternary, 6
Next, the 8th and 10th order aspherical coefficients.

The focus of the zoom lens in the present embodiment can be achieved by moving the fourth lens group G4.

Table 3 shows each numerical value and each conditional expression for obtaining each condition of the conditional expressions (1) and (2) of the zoom lens shown in the first and second embodiments. The conditional expressions in the zoom lens according to the second embodiment are the same as those in the zoom lens according to the first embodiment.

FIGS. 3 to 5 and FIGS. 6 to 8 show various aberration diagrams of the first and second embodiments, respectively. In spherical aberration, the vertical axis focuses on the open F value, the horizontal axis focuses, and the solid line is the d-line (5
87.6 nm), the broken line indicates the g-line (435.8 nm), and the one-dot chain line indicates the spherical aberration at the C line (656.3 nm).
In the astigmatism, the vertical axis indicates the image height, the horizontal axis indicates the focus, the solid line indicates the sagittal, and the broken line indicates the meridional image plane. The vertical axis represents image height, and the horizontal axis represents distortion.

As is clear from Table 3 above, the zoom lenses according to the first embodiment and the second embodiment have the conditional expression (1).
As shown in the aberration diagrams, various anxiety is corrected in a well-balanced manner at the wide-angle end, at an intermediate focal length between the wide-angle end and the telephoto end, and at the telephoto end.

As described above, the zoom lenses according to the first embodiment and the second embodiment are preferably used for a digital still camera having a large number of pixels, because each aberration is well corrected. FIG. 9 is a schematic diagram of a main part of an imaging device including the zoom lens of the present embodiment, and FIG. 10 is a block diagram illustrating an internal configuration of the imaging device using the zoom lens of the present embodiment.

As shown in FIG. 9, the image pickup apparatus mainly comprises a digital still camera. An image pickup device 31 such as a CCD is attached to an optical system 30 using a zoom lens ZL of the present embodiment, and a housing 32 is provided. It has been incorporated into. In addition, an image or the like captured by the image sensor 31 is displayed on the liquid crystal panel 33, and can be viewed as a finder through the eyepiece 34.

As shown in FIG. 10, as an internal configuration of the image pickup apparatus, a CCD for converting light condensed through an optical system 30 using a zoom lens ZL of the present embodiment into an electric signal is used.
And the like, an image processing unit 41 that performs a correction process, a signal compression process, and the like on a captured image signal obtained by the image sensor 31, and an image storage unit 42 that stores an image signal compressed in a predetermined format. And an output I / F for outputting the image signal stored in the image storage unit 42 according to a predetermined protocol.
(Interface) 43, a user I / F 44 for performing various setting inputs and operations, a lens drive control unit 45 for driving a motor for performing zooming and focusing of the zoom lens ZL, and a CPU 46 for controlling each unit. ,
And a liquid crystal panel 33 for displaying a captured image and a stored image.

By applying the zoom lens ZL of this embodiment to such an image pickup apparatus, it is possible to reduce
In addition to zooming about twice, it is possible to obtain high-quality images with little aberration at various focal lengths.

It should be noted that the specific shapes and structures of the respective parts shown in the above-described embodiments are merely examples for embodying the present invention, and the technical scope of the present invention is not limited thereto. Is not limited.
In addition, an imaging device including a digital still camera has been described as an application example of the zoom lens according to the present embodiment. However, the imaging device may be applied to another device such as a video camera capable of acquiring a moving image.

[0042]

As described above, according to the zoom lens of the present invention, it is possible to reduce the size and improve the imaging performance by using the zoom lens in a digital still camera having a zoom ratio of about 5 times. Become.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment at a short focal length extremity.

FIG. 2 is a lens configuration diagram at a short focal length extremity of a second embodiment.

FIG. 3 is a diagram illustrating various aberrations at the short focal length extremity of the first example.

FIG. 4 is a diagram illustrating various aberrations of the first example at an intermediate focal length.

FIG. 5 is a diagram illustrating various aberrations at the long focal length extremity of the first example.

FIG. 6 is a diagram illustrating various aberrations at the short focal length extremity of the second example.

FIG. 7 is a diagram illustrating various aberrations of the second example at an intermediate focal length.

FIG. 8 is a diagram illustrating various aberrations at a long focal length extremity of a second example.

FIG. 9 is a schematic diagram of a main part showing an application example of the present embodiment.

FIG. 10 is a block diagram illustrating an internal configuration of an application example of the embodiment.

[Explanation of symbols]

Reference numeral 30: optical system, 31: imaging element, 33: liquid crystal panel, 4
DESCRIPTION OF SYMBOLS 1 ... Image processing part, 42 ... Image storage part, G1: 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, G4 ...
Fourth lens group, G5: fifth lens group, S: diaphragm

Continued on front page F-term (reference) 2H087 KA02 KA03 PA09 PA16 PA20 PB14 QA02 QA07 QA17 QA21 QA25 QA37 QA41 QA46 RA05 RA12 RA13 RA43 RA44 SA43 SA47 SA49 SA52 SA56 SA63 SA65 SA72 SA74 SA76 SB04 SB16 SB23 SB33 SB43

Claims (5)

[Claims] 1. A lens system comprising: a positive first lens group, a negative second lens group, a positive third lens group, a positive fourth lens group, and a fifth lens group having a weak refractive power, in order from the object side; In a zoom lens that performs zooming by moving the second lens group and the fourth lens group, the fifth lens group includes a positive lens group including at least one positive lens, and at least one negative lens. And at least two lenses including a negative lens group, and the following conditional expression (1):
A zoom lens characterized by satisfying (2). (1) 0.8 <β5 <1.05 (2) 0.8 <| fG2 / fw | <1.3, where β5 is the imaging magnification of the fifth lens group when the object distance is infinity, fG2 is the focal length of the second lens group, fw: focal length at the short focal length extremity of the entire lens system. 2. The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied. (3) 1.5 <| fG5- / fw | <3, where fG5-: the focal length of the negative lens group included in the fifth lens group,
And 3. The zoom lens according to claim 1, wherein the second lens group includes at least three negative lenses and at least one positive lens. 4. The third lens group includes at least one positive lens on the object side with respect to the stop, and at least one positive lens on the image side.
The zoom lens according to any one of claims 1 to 3, wherein the zoom lens is configured by a plurality of negative lenses. 5. An imaging apparatus using the zoom lens according to claim 1 in an optical system.