JP2005148435A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, high-performance two-group zoom lens which comprises a small number of lens elements. <P>SOLUTION: The zoom lens 10 comprises a 1st lens group G11 having negative refracting power and a 2nd lens group G12 having positive refracting power in order from an object side, and varies in power by varying the air gap between the 1st lens group G11 and 2nd lens group G12. The 1st lens group G11 comprises a 1st lens 11 having negative refracting power and a 2nd lens 12 having positive refracting power in order from the object side and the 2nd lens group G12 comprises a 3rd lens 13 having positive refracting power and a 4th lens 14 having negative refracting power in order from the object side. Then the lens satisfies (1) 1.55<f<SB>2</SB>/f<SB>w</SB><1.84 and (2) -0.100<1/R<SB>1</SB><0.015, where f<SB>2</SB>is the focal length of the 2nd lens group G12, f<SB>w</SB>is the composite focal length at the wide-angle end, and R<SB>1</SB>is the object-side radius of curvature of the 1st lens 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a two-group zoom lens that is suitable for a digital still camera, a video camera, and the like, and is intended to shorten the total lens length.

  The two groups of zoom lenses are roughly classified into a telephoto type having positive and negative refractive power and a retrofocus type having negative positive refractive power in order from the object side. In a digital camera, a telephoto type that is desirable in that the incident angle of light with respect to a solid-state imaging device such as a CCD is small and the utilization efficiency of subject light can be increased. In digital cameras, reduction in the number of lenses is important because downsizing and cost reduction are major issues. As a conventional zoom lens that satisfies these requirements, a two-group zoom lens composed of a total of four lenses including two front lens groups and two rear lens groups is known (see Patent Documents 1 and 2).

JP 9-33810 A JP 2002-365545 A

  The zoom lens described in Patent Document 1 is designed to be suitable for a 1 / 4-type CCD in order to reduce the size of the lens, and maintains good performance in an imaging region with an image height of 2.25 mm. However, as a high-pixel imaging device having 3 million pixels or more, the size of a 1 / 4-type CCD is small, and a size of about 1 / 2.7-type CCD (image height 3.33 mm) which is currently mainstream is required. A small-size CCD has a problem that the area of one pixel is reduced and the S / N ratio is deteriorated. For this reason, the zoom lens of Patent Document 1 cannot be used for a 1 / 2.7 type CCD, and cannot cope with an increase in the number of pixels. If the ratio of the lens dimensions is kept proportionally, the lens size increases. The zoom lens described in Patent Document 2 corresponds to a lens in which the power described in Patent Document 1 is proportionally enlarged although the power distribution is different, and the total length of the lens becomes longer as the number of pixels increases.

  Accordingly, an object of the present invention is to obtain a compact zoom lens that maintains good performance up to an image formation region having an image height of 3.33 mm so as to be compatible with a 1 / 2.7 type CCD.

In order to achieve the above object, the zoom lens of the present invention comprises, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the first lens group. In the zoom lens that performs zooming by changing the air space between the first lens group and the second lens group, the first lens group includes, in order from the object side, a first lens having a negative refractive power and a first lens having a positive refractive power. The second lens group includes, in order from the object side, a third lens having a positive refractive power and a fourth lens having a negative refractive power. The focal length f ₂ of the second lens group, the wide-angle end the combined focal length of the entire system f _w, the object-side radius of curvature of the first lens when the R ₁ in,
(1) 1.55 <f ₂ / f _w <1.84
(2) -0.100 <1 / R ₁ <0.015
It satisfies.

Further, when the Abbe number at the d-line of the second lens is ν ₂ , the Abbe number at the d-line of the third lens is ν ₃ , and the Abbe number at the d-line of the fourth lens is ν ₄ ,
(3) ν ₂ <25
(4) ν ₃ / ν ₄ > 2.7
Is preferably satisfied. Further, it is desirable that all four lenses constituting the first lens group and the second lens group are aspherical lenses.

(Function)
The present invention is a retrofocus type zoom lens in which zooming is performed from the wide end to the tele end by reducing the distance between the negative first lens group and the positive second lens group. Conditional expression (1) prescribes the power of the second lens group and can shorten the total length at the wide-angle end. If the upper limit of the expression (1) is exceeded, the power of the second lens group becomes weak, so that the total length becomes long. If the lower limit is not reached, the power of the second lens group becomes strong, making it difficult to correct spherical aberration and coma. A retrofocus type lens generally used in a digital camera or the like often has the longest overall length at the wide-angle end, and the collapsible thickness can be reduced if the overall length at the wide-angle end is shortened. When the camera is downsized, the flash light emitting unit and the lens barrel approach each other, and the lens barrel blocks part of the flash light, and the captured image is likely to be damaged, but by reducing the overall length at the wide-angle end, The problem is solved.

  Conditional expression (2) defines the object-side radius of curvature of the first lens. When the upper limit of expression (2) is exceeded, the positive curvature becomes stronger, and the lens diameter is secured to secure the peripheral light quantity at the wide-angle end. Will become bigger. On the other hand, when the value is below the lower limit, the negative curvature becomes strong and the negative distortion increases. The first lens uses an aspherical surface for correcting distortion, but requires high power. Therefore, an aspherical surface formed of plastic, which is a material having a low refractive index, has an excessively small radius of curvature, and aberrations are reduced. A glass with a high refractive index is selected because it causes an increase.

  Conditional expression (3) defines the Abbe number of the second lens. The present invention has a configuration in which a glass material having a high refractive index is used for the first lens in order to achieve shortening of the entire lens length and suppression of aberration, and dispersion of the first lens is increased. Therefore, it is desirable to cancel the chromatic aberration generated in the first lens by the second lens having the Abbe number satisfying the expression (3) in order to correct it.

  Conditional expression (4) defines the relationship between the Abbe numbers of the third lens and the fourth lens. In the present invention, since the second lens group includes only the third lens and the fourth lens, it is desirable that the two lenses are sufficiently achromatic, and the expression (4) is not satisfied. The difference in Abbe number between the two lenses becomes small, and chromatic aberration cannot be corrected.

  In the present invention, aspherical lenses are used for all four lenses constituting the first lens group and the second lens group. The first lens and the second lens correct the curvature of field that is tilted toward the image plane simultaneously with the correction of the distortion, and the third lens and the fourth lens correct the curvature of field that is tilted toward the object side simultaneously with the correction of the spherical aberration. To do. If any one of the lenses is changed to a spherical lens, the aberration correction becomes insufficient and the performance deteriorates. That is, in order to shorten the overall length of the wide-angle end and ensure performance, it is desirable that all lenses be aspheric lenses.

  According to the present invention, a compact zoom lens in which aberrations are favorably corrected can be obtained.

  Specific examples of the present invention will be described below.

  In FIG. 1, the zoom lens 10 includes, in order from the object side, a first lens group G11 having a negative refractive power and a second lens group G12 having a positive refractive power. The first group G11 includes a biconcave negative lens 11 having a concave surface with a small radius of curvature on the image plane side, and a biconvex positive lens 12 having a convex surface with a small radius of curvature on the object side. The second group G12 includes a biconvex positive lens 13 having a convex surface with a small radius of curvature on the object side, and a meniscus negative lens 14 having a concave surface on the object side. On the image plane side of the negative lens 14, an optical low-pass filter 15 and a cover glass 16 that covers the imaging element are provided as parallel plane plates.

  Table 1 shows the radius of curvature R (mm) of each lens surface of the zoom lens 10, the surface thickness D (mm) representing the center thickness of each lens and the air spacing of each lens, the refractive index N of each lens at the d-line, and the Abbe number. Indicates the value of ν. The numbers in the table represent surface numbers given to the refractive surfaces of the lenses from the object side. A surface marked with * in the left column of the surface number is an aspherical surface. FIG. 2 shows various aberrations at the short focal length end, the intermediate focal length, and the long focal length end, respectively.

  In Table 1, D4 and D9 mean values that change during zooming. In Table 2, assuming that the short focal length end (wide angle) is W, the intermediate focal length is M, and the long focal length end (telephoto end) is T, D4 and D9, the total focal length f (mm) of the entire system, F number F, The half angle of view ω is shown.

表１において、面番号の左欄に「＊」を付した非球面は、その面の頂点を原点、光軸方向にＸ軸をとった直交座標系において、Ｙを光軸からの高さ、Ｒを頂点の曲率半径、Ｋを円錐係数とし、Ａ，Ｂ，Ｃ，Ｄを非球面係数としたときに下記式で表される。

In Table 1, an aspherical surface with “*” in the left column of the surface number is the height from the optical axis in an orthogonal coordinate system in which the vertex of the surface is the origin and the X axis is in the optical axis direction, When R is the radius of curvature of the apex, K is the conical coefficient, and A, B, C, and D are aspherical coefficients, they are expressed by the following equations.

Table 3 shows the constants of the aspheric surface. “E-i” in the table represents “× 10 ⁻ⁱ ”.

The zoom lens 10 has characteristic values f ₂ / f _w = 1.81, respectively.
1 / R ₁ = −0.037
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And the conditional expression of the present invention (1) 1.55 <f ₂ / f _w <1.84
(2) -0.100 <1 / R ₁ <0.015
(3) ν ₂ <25
(4) ν ₃ / ν ₄ > 2.7
Satisfy all of the above.

  In FIG. 3, the zoom lens 20 includes a first group G21 having a negative refractive power and a second group G22 having a positive refractive power. The first group G21 includes a biconcave negative lens 21 having a concave surface with a small radius of curvature on the image surface side, and a meniscus positive lens 22 with the convex surface facing the object side. The second group G22 includes a biconvex positive lens 23 having a convex surface with a small curvature radius on the object side, and a meniscus negative lens 24 having a concave surface on the object side. Table 4 shows lens data of the zoom lens 20, Table 5 shows data at each zoom stage, and Table 6 shows aspheric coefficients. FIG. 4 shows various aberrations at each zoom stage.

The zoom lens 20 has characteristic values f ₂ / f _w = 1.79, respectively.
1 / R ₁ = −0.013
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 5, the zoom lens 30 includes a first group G31 having a negative refractive power and a second group G32 having a positive refractive power. The first group G31 includes a meniscus negative lens 31 having a concave surface directed toward the image surface side, and a meniscus positive lens 32 having a convex surface directed toward the object side. The second group G32 includes a biconvex positive lens 33 having a convex surface with a small curvature radius on the object side, and a meniscus negative lens 34 having a concave surface on the object side. Table 7 shows lens data of the zoom lens 30, Table 8 shows data at each zoom stage, and Table 9 shows aspheric coefficients. FIG. 6 shows various aberrations at each zoom stage.

The zoom lens 30 has characteristic values f ₂ / f _w = 1.83, respectively.
1 / R ₁ = 0.01
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 7, the zoom lens 40 includes a first group G41 having a negative refractive power and a second group G42 having a positive refractive power. The first group G41 includes a biconcave negative lens 41 having a concave surface with a small radius of curvature on the image surface side, and a biconvex positive lens 42 having a convex surface with a small radius of curvature on the object side. The second group G42 includes a biconvex positive lens 43 having a convex surface with a small curvature radius on the object side, and a meniscus negative lens 44 having a concave surface on the object side. Table 10 shows lens data of the zoom lens 40, Table 11 shows data at each zoom stage, and Table 12 shows aspheric coefficients. FIG. 8 shows various aberrations at each zoom stage.

The zoom lens 40 has characteristic values f ₂ / f _w = 1.82, respectively.
1 / R ₁ = −0.033
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 9, the zoom lens 50 includes a first group G51 having a negative refractive power and a second group G52 having a positive refractive power. The first group G51 includes a biconcave negative lens 51 having a concave surface with a small radius of curvature on the image surface side, and a meniscus positive lens 52 with the convex surface facing the object side. The second group G52 includes a biconvex positive lens 53 having a convex surface with a small radius of curvature on the object side, and a meniscus negative lens 54 having a concave surface on the object side. Table 13 shows lens data of the zoom lens 50, Table 14 shows data at each zoom stage, and Table 15 shows aspheric coefficients. FIG. 10 shows various aberrations at each zoom stage.

The zoom lens 50 has characteristic values f ₂ / f _w = 1.78, respectively.
1 / R ₁ = −0.004
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 11, the zoom lens 60 includes a first group G61 having a negative refractive power and a second group G62 having a positive refractive power. The first group G61 includes a biconcave negative lens 61 having a concave surface with a small radius of curvature on the image surface side, and a meniscus positive lens 62 with the convex surface facing the object side. The second group G62 includes a biconvex positive lens 63 having a convex surface with a small radius of curvature on the object side, and a meniscus negative lens 64 having a concave surface on the object side. Table 16 shows lens data of the zoom lens 60, Table 17 shows data at each zoom stage, and Table 18 shows aspheric coefficients. FIG. 12 shows various aberrations at each zoom stage.

The zoom lens 60 has characteristic values f ₂ / f _w = 1.70, respectively.
1 / R ₁ = −0.008
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.94
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 13, the zoom lens 70 includes a first group G71 having a negative refractive power and a second group G72 having a positive refractive power. The first group G71 includes a biconcave negative lens 71 having a concave surface with a small curvature radius on the image side, and a biconvex positive lens 72 having a convex surface with a small curvature radius on the object side. The second group G72 includes a biconvex positive lens 73 having a convex surface with a small curvature radius on the object side, and a meniscus negative lens 74 having a concave surface on the object side. Table 19 shows lens data of the zoom lens 70, Table 20 shows data at each zoom stage, and Table 21 shows aspheric coefficients. FIG. 14 shows various aberrations at each zoom stage.

The zoom lens 70 has characteristic values f ₂ / f _w = 1.80, respectively.
1 / R ₁ = −0.024
ν ₂ = 23.9
ν ₃ / ν ₄ = 2.95
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  In FIG. 15, the zoom lens 80 includes a first group G81 having a negative refractive power and a second group G82 having a positive refractive power. The first group G81 includes a biconcave negative lens 81 having a concave surface with a small radius of curvature on the image side, and a meniscus positive lens 82 with the convex surface facing the object side. The second group G82 includes a biconvex positive lens 83 having a convex surface with a small radius of curvature on the object side, and a meniscus negative lens 84 with a concave surface facing the object side. Table 22 shows lens data of the zoom lens 80, Table 23 shows data at each zoom stage, and Table 24 shows aspheric coefficients. FIG. 16 shows various aberrations at each zoom stage.

The zoom lens 80 has characteristic values f ₂ / f _w = 1.82, respectively.
1 / R ₁ = −0.049
ν ₂ = 23.9
ν ₃ / ν ₄ = 3.44
And all the conditional expressions (1) to (4) of the present invention are satisfied.

  The present invention is not limited to the above embodiment, and the shape, material, aspheric coefficient, etc. of each lens can be selected as appropriate.

FIG. 1 is a lens configuration diagram of the first embodiment of the present invention. Aberration diagram of the first embodiment The lens block diagram of 2nd Example of this invention Aberration diagram of the second embodiment Lens configuration diagram of the third embodiment of the present invention Aberration diagram of Example 3 Lens configuration diagram of the fourth embodiment of the present invention Aberration diagram of Example 4 Lens configuration diagram of the fifth embodiment of the present invention Aberration diagram of Example 5 Lens construction diagram of the sixth embodiment of the present invention Aberration diagram of Example 6 Lens configuration diagram of the seventh embodiment of the present invention Aberration diagram of Example 7 The lens block diagram of 8th Example of this invention Aberration diagram of Example 8

Explanation of symbols

10, 20, 30, 40, 50, 60, 70, 80 Zoom lenses G11, G21, G31, G41, G51, G61, G71, G81 First lens group G12, G22, G32, G42, G52, G62, G72, G82 2nd lens group

Claims (3)

In order from the object side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power are changed by changing the air gap between the first lens unit and the second lens unit. In a zoom lens that doubles
The first lens group includes, in order from the object side, a first lens having a negative refractive power and a second lens having a positive refractive power,
2. The zoom lens according to claim 1, wherein the second lens group includes, in order from the object side, a third lens having a positive refractive power and a fourth lens having a negative refractive power, and satisfies the following conditional expression.
(1) 1.55 <f ₂ / f _w <1.84
(2) -0.100 <1 / R ₁ <0.015
However,
f ₂ : Focal length of the second lens unit f _w : Total focal length of the entire system at the wide angle end R ₁ : Object side radius of curvature of the first lens The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
(3) ν ₂ <25
(4) ν ₃ / ν ₄ > 2.7
Where ν ₂ is the Abbe number of the second lens at the d-line ν ₃ is the Abbe number of the third lens at the d-line ν ₄ is the Abbe number of the fourth lens at the d-line   The zoom lens according to claim 2, wherein all four lenses constituting the first lens group and the second lens group have an aspherical shape.

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