JP3520495B2 - Zoom lens for digital camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a zoom ratio of 2.5
About zoom lens for digital camera of about double, especially,
The present invention relates to a zoom lens which is compact as a two-group lens configuration and has an increased light amount and resolution of the entire screen in the entire zoom region.

[0002]

2. Description of the Related Art A first lens group having a negative refractive power and a second lens group having a positive refractive power are sequentially arranged from the object side.
There has been proposed a zoom lens for a camera having a two-group lens configuration in which the first and second lens groups are moved along the optical axis to change the magnification.

This zoom lens is a zoom lens having a compact structure in which the first lens group and the second lens group are moved relative to each other to change the magnification, and are mainly used for film cameras (for example, Leica cameras). To be equipped.

[0004]

The above-mentioned conventional zoom lens has the lens performance of reducing the amount of light around the screen and lowering the resolution around the screen.

Therefore, a film camera has no problem in lens performance and can be evaluated as a zoom lens having a compact structure. However, when this zoom lens is used for a digital camera, it is excellent in that the structure can be made compact, but there is a problem in mounting the zoom lens because the lens performance cannot be sufficiently supported.

In a light receiving element (for example, a CCD element) provided in a recent digital camera, the density of pixels has been increased with the improvement of ultra-fine processing technology. Therefore, in the above-described zoom lens having a small amount of light and a low resolution around the screen, all the pixels of the light receiving element cannot be fully utilized, and the function of the light receiving element is reduced by half.

In view of the above circumstances, the present invention is suitable for compactness as a two-group lens structure, and has a zoom ratio of about 2.5 times that can increase the light quantity and resolution of the entire screen in the entire zoom area. It is an object of the present invention to propose a zoom lens for a digital camera.

[0008]

In order to achieve the above object , the present invention provides a first lens which is a convex lens from the object side.
Lenses, second and third lenses that are concave lenses, and convex lenses
A first lens having a negative refractive power and a fourth lens
Lens group and a fifth lens which is a convex lens from the subject side,
Sixth lens which is a concave lens, seventh lens which is a concave lens
And the eighth lens which is a convex lens, the object side
A second lens group having a positive refractive power sequentially arranged a convex meniscus lens having a convex surface directed toward provided, these first, by moving the second lens unit each other on the optical axis zooming The present invention relates to a zoom lens for a digital camera having a configuration.

[0009] Then, a diagram of the present invention - zoom lens is provided with a lens having an aspherical at least one side in the second lens group and the focal length f of the focal length f ₁ and the second lens group of the first lens group ₂ satisfies the following condition: 12 ≦ | f ₁ | ≦ 13 11.5 ≦ f ₂ ≦ 12.5 1.0 ≦ | f ₁ | / f ₂ ≦ 1.1

[0010]

The zoom lens according to the present invention has a two-group lens configuration in which an aspheric lens is provided in the second lens group, and the first lens group and the second lens group are moved relative to each other for zooming. Thus, a zoom lens that is advantageous for shortening the overall length of the lens and for making it compact is obtained.

In addition, in this zoom lens, in addition to providing an aspherical lens in the second lens group, the focal lengths f ₁ and f ₂ of the first and second lens groups are set according to the above equation. The lens performance is high in light amount and resolution in all screens in the entire zoom region.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an optical system diagram showing the arrangement of a zoom lens. Reference numeral 10 denotes a first lens group, 20 denotes a second lens group, 30 denotes a stop, and 40 denotes an image forming plane. FIG.
Indicates a state in which the first lens group 10 and the second lens group 20 are at WIDE (wide-angle shooting) movement positions. WIDE
Zooming from the side to the TELE (telephoto shooting) side is shown in FIG.
As shown in FIG. 3, the first lens group 10 is moved to the image plane side, and the second lens group 20 is moved to the subject side. 2 shows a standard zooming state, and FIG. 3 shows a telephoto zooming state.

The first lens group 10 includes a convex lens from the object side.
Lens 11 as a lens, and second lens 1 as a concave lens
2. The third lens 13 which is a concave lens and the third lens which is a convex lens
4 lens 14 sequentially front lens disposed the four lenses and has the first lens group 10 a negative refractive power, also, the focal length has a f _1. Second lens group 20, subject side
The fifth lens 21 which is a convex lens and the fifth lens which is a biconcave lens
Sixth lens 22, seventh lens 23 which is a concave lens and convex lens
Lens cemented with the eighth lens 24, which is convex on the subject side
In five-lens configuration of a rear lens are sequentially disposed a convex meniscus lens 25 with its surface, the second lens group 20 has a positive refractive power, also, it has a focal length f _2.

[0014] On the other hand, the focal length f ₂ of the focal length f ₁ and the second lens group 20 of the first lens group 10 are constructed the following conditional expression Mitsurusu so. 12 ≦ | f ₁ | ≦ 13 (1) 11.5 ≦ f ₂ ≦ 12.5 (2) 1.0 ≦ | f ₁ | / f ₂ ≦ 1.1 (3) Further, the image formation side of the second lens group 20 closest to the image (right end side in the figure)
The convex meniscus lens 25 has an aspherical front surface.

In the zoom lens constructed as described above, the refracting power of the first lens group 10 and the second lens group 20 is restricted by the above-mentioned conditional expressions (1), (2) and (3). If the focal length f ₁ of the first lens group 10 is set to 12 ≦ | f ₁ | ≦ 13 and 1.0> | f ₁ | / f ₂ , the first lens group 10
Becomes large, the distortion becomes under, and the meridional image plane of astigmatism becomes over on the TELE side. However, the back focus extends.

Similarly, the focal length f ₁ of the first lens group 10
Is set to 12 ≦ | f ₁ | ≦ 13, and | f ₁ | / f ₂ > 1.1
If so, the refractive power of the first lens group 10 becomes small, so that the astigmatism meridional image surface becomes under on the WIDE side. However, distortion is improved.

Further, the second condition is satisfied by the conditional expression (2).
The refractive power of the lens group 20 is limited. When the focal length f ₂ of the second lens group 20 is other than the condition of 11.5 ≦ f ₂ ,
The spherical aberration, astigmatism, and chromatic aberration of magnification are under, and f
When the condition is not ₂ ≦ 12.5, the above is reversed, and the spherical aberration, astigmatism, and chromatic aberration of magnification are over.

The convex meniscus lens 2 of the second lens group 20
By using the aspherical lens 5, the light amount and resolution of the entire screen can be increased in the entire zoom region, and the lens performance can be improved.

As described above, since the aspherical lens is provided in the second lens group 20, even if the total length of the lens is shortened, the spherical aberration, astigmatism and the like do not become under.

The fifth lens 21 of the second lens group 20
Is a cemented achromatic lens, or the seventh lens 23
Chromatic aberration can be improved by achromatizing.

As described above, when the refractive power of the first lens unit 10 is increased, the distortion becomes under, the meridional image plane of astigmatism becomes more over on the TELE side, and the zooming is performed. The balance of aberration at each position is significantly deteriorated. When the refractive power of the first lens group 10 is reduced, a phenomenon opposite to the above appears. This embodiment solves this problem with a configuration that satisfies the conditional expressions (1), (2), and (3) described above.

Further, in the present embodiment, by providing an aspheric lens in the second lens group 20, a compact structure of the zoom lens and a reduction in the overall length of the lens are achieved, and the lens performance is improved.

Next, the radius of curvature of each lens, the thickness (interval) of each lens, the spatial interval, the refractive index, the dispersion, the first lens group 1
The focal length f ₁ of _0, for example was carried defines the focal length f ₂ of the second lens group 20 <br/> specifically described. Note that ri is the radius of curvature of the i-th lens surface in order from the subject side, and di is the i-th lens thickness and
N represents a spatial interval, n represents a refractive index, and ν represents dispersion.

The symbol * indicates an aspherical surface, which is obtained by the following equation.

(Equation 1) In this equation, Z is a coordinate in the optical axis direction with the intersection of the aspherical surface and the optical axis as the origin, and h is a coordinate in a direction passing through the origin and orthogonal to the optical axis.

C is c = 1 / ri (i = 1.2.3.
...), And the aspherical surface has a radius of curvature ri near the optical axis, a conical constant K, a higher order aspherical coefficient A,
B, C, and D.

[0026]

[Example] Surface curvature radius (mm) Interval (mm) Refractive index n dispersion ν r ₁ 65.71225 d ₁ 1.500936 1.48749 70.4 r ₂ -54.91553 d ₂ 0.2010252 r ₃ 67.50795 d ₃ 0.9138250 1.88300 40.8 r ₄ 6.705763 d ₄ 1.622002 _{r 5 79.01024 d 5 0.8965933 1.80420 46.5} f 6 13.38520 d 6 0.7298600 r 7 10.35136 d 7 1.495272 1.84666 23.8 r 8 46.35503 d 8 15.41002 r 9 down Ri _{d 9 1.800000 r 10 8.805314 d 10} 2.006398 1.69680 55.5 r 11 -26.00814 d 11 1.546117 _{r 12 -6.812535 d 12 0.7000000 1.64769 33.8} r 13 34.09029 d 13 0.2000000 r 14 -262.9159 d 14 0.7000000 1.84666 23.8 r 15 26.76179 d 15 1.631428 1.69680 55.5 r 16 -6.782819 d 16 0.2087221 r 17 * 88.46669 d 17 2.003471 1.69350 53.3 r 18 60.88319 d ₁₈ 12.67636

[0027]

(Equation 2)

Paraxial data WIDE NORMAL TELE Focal length 6.2046 10.5461 14.7090 FNo. 2.8 3.4 4.1 Back focus 12.6764 16.6598 20.4795 Variable interval d ₈ 15.14 5.15 1.0

In the case of this embodiment, f ₁ = −12.982
2, f ₂ = 11.9117, and it is clear that f ₁ and f ₂ satisfy the above conditional expressions (1) and (2).
₁ | / f ₂ = 1.09, the above conditional expression (3)
Meets. FIG. 4 shows spherical aberration, field curvature, distortion, and chromatic aberration obtained by zooming to the WIDE side. FIG. 5 shows spherical aberration, field curvature, distortion, and distortion obtained by standard zooming. FIG. 6 shows chromatic aberration.
This figure shows spherical aberration, field curvature, distortion, and chromatic aberration obtained by zooming to the E side. In these drawings, d is 587.600 nm and g is 435.800 n.
m and c indicate respective wavelengths of 656.300 nm, M indicates a meridional image plane, S indicates a sagittal image plane, and ω / 2 indicates a half angle of view.

When the present invention is carried out as described above, the focal length fw on the WIDE side and the focal length ft on the TELE side are as follows: 6.2 ≦ fw ≦ 6.3 14.6 ≦ ft ≦ 14.8 Is preferred. Specifically, in this embodiment, fw
= 6.2, ft = 14.7.

Further, the total track Tw on the WIDE side is used.
And the total track Tt on the TELE side preferably satisfies 46 ≦ Tw ≦ 47 39 ≦ Tt ≦ 40. Specifically, in the present embodiment, Tw
= 46.1 mm and Tt = 39.7 mm. That is, in zooming of WIDE, the total lens length is 33.
5 mm and the back focus is 12.6 mm. In telephoto zooming, the total lens length is 19.2 mm.
mm and the back focus is 20.5 mm.

In this embodiment, ft = 14.7,
If Tt = 41, spherical aberration is under, and astigmatism is over. If ft = 14.7, Tt = 38, spherical aberration is over, and astigmatism is under.
If fw = 6.2 and Tw = 45, the spherical aberration is under, the astigmatism is under, and fw = 6.2,
When Tw = 48, it was confirmed that the spherical aberration was over and the astigmatism was over.

[0033]

As described above, the zoom lens according to the present invention has a compact structure in which the entire length of the lens is shortened, and can increase the light quantity and resolution around the screen in the entire zoom area. Therefore, a compact zoom lens having a high lens performance can be obtained, so that the zoom lens can be sufficiently used as a photographing lens of a digital camera.
Mulens.

[Brief description of the drawings]

FIG. 1 shows the arrangement of zoom lenses, where each lens is a W lens.
FIG. 2 is an optical system diagram showing a state where an IDE is at a movement position.

FIG. 2 is an optical system diagram similar to FIG. 1, showing a state where each lens is moved to a reference position.

FIG. 3 is an optical system diagram similar to FIG. 1, showing a state where each lens is moved to the TELE side.

FIG. 4 shows spherical aberration, field curvature, distortion, and chromatic aberration in WIDE of a zoom lens embodying the present invention.

FIG. 5 shows a spherical aberration, a field curvature, a distortion, and a chromatic aberration in a standard zoom lens embodying the present invention.

FIG. 6 shows spherical aberration, field curvature, distortion, and chromatic aberration in TELE of the zoom lens embodying the present invention.

[Explanation of symbols]

Reference Signs List 10 First lens group 20 Second lens group 21 Fifth lens 22 Sixth lens 23 Seventh lens 24 Eighth lens 25 Convex meniscus lens 30 Aperture 40 Image plane

Claims (1)

(57) [Claims] 1. A first lens which is a convex lens from a subject side.
Lenses, second and third lenses that are concave lenses, and convex lenses
A first lens having a negative refractive power, in which a fourth lens is sequentially disposed.
Lens group, a fifth lens that is a convex lens from the object side, a biconcave
A sixth lens which is a lens, a seventh lens which is a concave lens,
A cemented lens with the eighth lens which is a convex lens, on the subject side
A second lens group having a positive refractive power sequentially arranged a convex meniscus lens having a convex surface directed toward providing, these first, second
In a camera zoom lens having a configuration in which the lens groups are moved on the optical axis to change the magnification, a second lens group is provided with a lens having at least one aspherical surface, and a focal length of the first lens group. f ₁ and the focal length _{f 2} of the second lens _{group, 12 ≦ | f 1 | ≦} 13 11.5 ≦ f 2 ≦ 12.5 1.0 ≦ | f 1 | / condition _{f 2} ≦ 1.1 A zoom lens for a digital camera, characterized in that the zoom lens is configured to satisfy the following.