JPH07181390A - Compact macro-lens - Google Patents

Abstract

PURPOSE:To provide a compact macro-lens having a relatively small delivering quantity in focusing, and capable of performing a high power photographing having a photographing distance to some degree. CONSTITUTION:This lens is formed of, in order from object side, a first group Gr1 having negative refracting power, a second group Gr2 having positive refracting power, and a third group Gr3 having positive refracting power. An affocal system is substantially formed by the Gr1 and Gr2, and at the focusing from infinite object side to near object side, all the Gr1-Gr3 are moved on the object side and focused so that the air space between the Gr1 and Gr2 is slightly reduced, and the air space between the Gr2 and Gr3 is slightly increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a macro lens, and more particularly to a macro lens for a compact camera incorporating a macro lens.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for shortening the close-up shooting distance in compact cameras.

[0003]

However, the conventional compact camera cannot obtain sufficient close-up shooting performance because the image plane falls when focusing on a close-up object. Further, in a general photographing lens, if the extension amount in focusing is reduced, the photographing distance becomes short even at the same photographing magnification, which is disadvantageous in actual photographing.

The present invention has been made in view of such a situation, and provides a compact macro lens which has a relatively small amount of extension in focusing and is capable of high magnification photographing with a certain photographing distance. With the goal.

[0005]

In order to achieve the above object, a macro lens according to the present invention comprises, in order from the object side, a first group having a negative refractive power and a second group having a positive refractive power. , In a photographing optical system including a third group having a positive refractive power, the first group and the second group form an afocal system, and at the time of focusing from the infinite object side to the near object side, From the first group to the third group, the air gap between the first group and the second group is slightly reduced, and the air gap between the second group and the third group is slightly increased. Both are characterized by moving to the object side to perform focusing.

In the present invention, as described above, the negative, positive, and positive 3
In the group structure, by adopting floating for focusing, macro photography is possible while maintaining good performance. That is, since the axial rays passing through the second lens group become close to parallel due to the afocal system, the air gap between the first lens group and the second lens group and the second lens group and the third lens group during focusing on a near object. The field curvature can be corrected without changing the spherical aberration and the like even if the air space between and is slightly changed. Therefore, the aberration variation can be reduced from infinity shooting to close-up shooting. You can do it.

Further, since the focusing method described above is almost the same as the entire extension, the fluctuation of the focal length of the entire system can be reduced. Therefore, the photographing distance at the time of high-magnification photographing can be lengthened to a certain extent, and the above configuration is advantageous in actual use.

In the configuration of the present invention, the following conditional expression (1)
It is desirable to satisfy (4). _{0.2 <f / f 2 <1.0} ... (1) 1.0 <D 2 / D 1 <1.2 ... (2) D 1 = D 3 ... (3) -0.1 <f / f 1,2 <0.3 ... (4) where , F: focal length of the entire system f ₂ : focal length of the second group D _i : amount of movement of the i-th group (where i = 1,2,3) f _1,2 : first and second groups And is the combined focal length.

Conditional expression (1) gives the ratio between the focal length of the second lens unit and the focal length of the entire system. If the lower limit of conditional expression (1) is exceeded, it will be difficult to suppress the negative field curvature that occurs during proximity. If the upper limit of conditional expression (1) is exceeded, the curvature of field will be excessively large when approaching.

If the upper limit of conditional expression (1) is exceeded, the amount of movement of each group during high-magnification photography becomes large. In particular, when the amount of movement of the second lens group becomes large, the first lens group and the second lens group will move during infinity shooting.
It is necessary to increase the axial distance from the group, which impairs compactness. If the lower limit of conditional expression (1) is exceeded, it will be difficult to maintain a long shooting distance during high-magnification shooting.

Conditional expression (2) gives the ratio of the amount of movement of the first and second groups. When the value goes below the lower limit of the conditional expression (2), it becomes difficult to suppress the negative curvature of field that occurs when approaching.
If the upper limit of conditional expression (2) is exceeded, the curvature of field will be excessively large when approaching.

Conditional expression (3) indicates that the first group and the third group move integrally. By moving as a unit, the configuration of the lens barrel becomes simple. On the contrary, if the conditional expression (3) is not satisfied, the lens barrel structure becomes very complicated, which leads to an increase in cost.

Conditional expression (4) gives the ratio of the combined focal length of the first and second lens units to the focal length of the entire system. Conditional expression (4)
When the value exceeds the upper limit of, spherical aberration is excessively negatively generated when close to each other. If the lower limit of conditional expression (4) is exceeded, it will be difficult to suppress positive spherical aberration that occurs at the time of proximity.

The present invention comprises, in order from the object side, a first group consisting of a negative meniscus lens convex to the image side, and a second group consisting of a positive meniscus lens convex to the object side and a negative meniscus lens convex to the object side. If the third lens unit is composed of a biconvex positive lens and a biconcave negative lens, the entire system is composed of five lenses, so that the total lens thickness is small, so that a compact structure can be obtained. Here, if aspherical surfaces are provided in the second group and the third group, it is possible to further improve the performance.

With the above-mentioned structure, it is possible to obtain a photographic optical system having a good imaging performance from an infinitely distant object to a near object.

[0016]

EXAMPLES Examples of macro lenses according to the present invention will be shown below. However, in each embodiment, f is the focal length of the entire system, FNO is the F number, ri (i = 1,2,3, ...) is the radius of curvature of the i-th surface counted from the object side, di (i = 1,2,3, ...) is the i-th axial upper surface distance counted from the object side, and Ni (i = 1,2,3, ...), νi
(i = 1,2,3, ...) Indicates the refractive index and Abbe number of the i-th lens for the d-line counting from the object side.

It should be noted that in each of the embodiments, the surface with a radius of curvature marked with * indicates that it is a surface composed of an aspherical surface, and is defined by the following formula 1 representing the surface shape of the aspherical surface. And

[0018]

[Equation 1]

However, in the equation (1), x: amount of displacement from the aspherical vertex in the optical axis direction at a distance y: distance in the direction perpendicular to the optical axis C ₀ : curvature at the aspherical vertex ε: quadratic Surface parameter Ai: i-th order aspherical coefficient.

<Example 1> f = 51.00 FNO = 4.08 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 -34.601 d1 1.945 N1 1.67339 ν1 29.25 r2 -81.583 d2 2.122 r3 13.124 d3 2.000 N2 1.80420 ν2 46.50 r4 21.023 d4 1.591 r5 * 25.462 d5 1.500 N3 1.80 358 ν3 25.38 r6 * 16.110 d6 5.478 r7 25.823 d7 3.000 N4 1.76780 ν4 49.47 r8 * -34.553 d8 3.000 r9 -45.470 d9 1.500 N5 1.58144 ν5.

[Aspherical coefficient] r5: ε = 0.3785 A4 = 0.12165952 × 10 ^-3 A6 = -0.22882786 × 10 ^-5 A8 = 0.50122213 × 10 ^-7 A10 = -0.60770994 × 10 ^-9 A12 = 0.25968980 × 10 ^-11 r6: ε = 0.3158 A4 = 0.20507513 × 10 ^-3 A6 = -0.18850322 × 10 ^-5 A8 = 0.20794483 × 10 ^-7 A10 = 0.75567714 × 10 ^-9 A12 = -0.14674397 × 10 ^-10 r8: ε = 0.5646 A4 = 0.13666592 × 10 ^-4 A6 = -0.57265074 × 10 ^-7 A8 = 0.27496503 × 10 ^-9 A10 = 0.16291024 × 10 ^-10 A12 = -0.18871881 × 10 ^-12

<Example 2> f = 51.00 FNO = 4.08 [Radius of curvature] [Axis upper surface spacing] [Refractive index] [Abbe number] r1 -43.970 d1 1.945 N1 1.67339 ν1 29.25 r2 -296.109 d2 2.122 r3 11.976 d3 2.000 N2 1.80420 ν2 46.50 r4 16.878 d4 1.591 r5 * 21.414 d5 1.500 N3 1.80358 ν3 25.38 r6 * 15.074 d6 5.478 r7 23.543 d7 3.000 N4 1.76780 ν4 49.47 r8 * -40.121 d8 3.000 r9 -77.333 d9 1.500 N5 1.58144 105.

[Aspherical coefficient] r5: ε = -0.6485 A4 = 0.86197339 × 10 ^-4 A6 = -0.11068942 × 10 ^-6 A8 = -0.17597132 × 10 ^-7 A10 = 0.44803792 × 10 ^-9 A12 = -0.30106206 × 10 ^-11 r6: ε = 0.3005 A4 = 0.16172453 × 10 ^-3 A6 = 0.26757421 × 10 ^-6 A8 = -0.22170621 × 10 ^-7 A10 = 0.79812461 × 10 ^-9 A12 = -0.60754747 × 10 ^-11 r8: ε = 0.8191 A4 = 0.17523841 × 10 ^-4 A6 = -0.23081150 × 10 ^-7 A8 = 0.11590827 × 10 ^-8 A10 = -0.28136889 × 10 ^-10 A12 = 0.22741227 × 10 ^-12

<Embodiment 3> f = 51.00 FNO = 4.08 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 -37.530 d1 1.945 N1 1.75000 ν1 25.14 r2 -59.687 d2 2.122 r3 11.114 d3 2.000 N2 1.80420 ν2 46.50 r4 15.182 d4 1.591 r5 * 22.727 d5 1.500 N3 1.80358 ν3 25.38 r6 * 14.355 d6 5.478 r7 25.808 d7 3.000 N4 1.76780 ν4 49.47 r8 * -40.986 d8 3.000 r9 -55.888 d9 1.500 N5 1.5653 r5 43.956710

[0025] [aspherical coefficients] r5: ε = -1.0344 A4 = 0.71835431 × 10 -4 A6 = 0.90529916 × 10 -6 A8 = -0.56481224 × 10 -7 A10 = 0.14527613 × 10 -8 A12 = -0.12363902 × 10 - ¹⁰ r6: ε = 0.3219 A4 = 0.15343583 × 10 ^-3 A6 = 0.12038775 × 10 ^-5 A8 = -0.34916121 × 10 ^-7 A10 = 0.11699775 × 10 ^-8 A12 = -0.77506914 × 10 ^-11 r8: ε = -0.4054 A4 = 0.11945229 × 10 ^-4 A6 = -0.10320729 × 10 ^-6 A8 = 0.25816250 × 10 ^-8 A10 = -0.38679635 × 10 ^-10 A12 = 0.21046511 × 10 ^-12

<Example 4> f = 51.00 FNO = 4.08 [Radius of curvature] [Space between upper surfaces of axes] [Refractive index] [Abbe number] r1 -34.488 d1 1.945 N1 1.83350 ν1 21.00 r2 -42.128 d2 2.000 r3 11.280 d3 2.000 N2 1.80420 ν2 46.50 r4 15.690 d4 1.591 r5 * 24.967 d5 1.500 N3 1.80358 ν3 25.38 r6 * 14.499 d6 4.978 r7 31.555 d7 3.000 N4 1.76780 ν4 49.47 r8 * -34.654 d8 3.000 r9 -44.539 d9 1.500 N5 1.54072 ν5 47.50

[0027] [aspherical coefficients] r5: ε = -1.3859 A4 = 0.71976031 × 10 -4 A6 = 0.73802308 × 10 -6 A8 = -0.47127891 × 10 -7 A10 = 0.10520051 × 10 -8 A12 = -0.69934596 × 10 - ¹¹ r6: ε = 0.4787 A4 = 0.14333159 × 10 ^-3 A6 = 0.18975852 × 10 ^-5 A8 = -0.70323124 × 10 ^-7 A10 = 0.14914081 × 10 ^-8 A12 = -0.39514393 × 10 ^-11 r8: ε = -0.3371 A4 = 0.42492408 × 10 ^-5 A6 = -0.21842196 × 10 ^-6 A8 = 0.68685337 × 10 ^-8 A10 = -0.10775119 × 10 ^-9 A12 = 0.59876438 × 10 ^-12

<Example 5> f = 51.00 FNO = 4.08 [radius of curvature] [axis upper surface spacing] [refractive index] [Abbe number] r1 -40.213 d1 1.945 N1 1.73300 ν1 28.24 r2 -101.460 d2 2.122 r3 10.716 d3 2.000 N2 1.80420 ν2 46.50 r4 16.132 d4 1.591 r5 * 20.773 d5 1.500 N3 1.80358 ν3 25.38 r6 * 13.834 d6 5.478 r7 26.746 d7 3.000 N4 1.76780 ν4 49.47 r8 * -49.843 d8 3.000 r9 -37.619 d9 1.500 N5 1.5656710 ν43.

[0029] [aspherical coefficients] r5: ε = -0.9455 A4 = 0.11760101 × 10 -3 A6 = 0.12629534 × 10 -5 A8 = -0.56919076 × 10 -7 A10 = 0.13759374 × 10 -8 A12 = -0.11675943 × 10 - ¹⁰ r6: ε = 0.2869 A4 = 0.22673611 × 10 ^-3 A6 = 0.20790283 × 10 ^-5 A8 = -0.26038619 × 10 ^-7 A10 = 0.10491854 × 10 ^-8 A12 = -0.37925711 × 10 ^-11 r8: ε = 0.5878 A4 = 0.146 14978 × 10 ^-4 A6 = -0.11575168 × 10 ^-6 A8 = 0.18047347 × 10 ^-8 A10 = -0.24025808 × 10 ^-10 A12 = 0.32402464 × 10 ^-13

1, FIG. 3, FIG. 5, FIG. 7 and FIG. 9 are lens configuration diagrams in the photographing state of the object distance at infinity corresponding to Embodiments 1 to 5, respectively. The first group Gr1, the second group Gr2, and the third group Gr3 upon focusing from the state to the closest object photographing state
Each movement is indicated by an arrow.

By focusing from the object photographing state at infinity to the closest object photographing state, the axial upper surface distance d2 between the first group Gr1 and the second group Gr2 and between the second group Gr2 and the third group Gr3 are set. The axial upper surface distance d6 changes as follows from the value of the construction data (object distance at infinity).

In the first embodiment, d2 = 2.122 to d2 = 0.056, d6
= 5.478 to d6 = 7.543, and in Example 2, d2 = 2.122 to d2 = 0.021, d6 = 5.478 to d6 = 7.578, and in Example 3, d2 = 2.122 to d2 = 0.682, d6 = 5.478 to d6 = 6.918. In Example 4, d2 = 2.000 to d2 = 0.620, d6 = 4.978 to d6 = 6.358, and in Example 5, d2 = 2.122 to d2 = 0.0.
53, d6 = 5.478 to d6 = 7.547.

In each of Examples 1 to 5, the first group Gr1 is composed of a negative meniscus lens concave to the object side (convex toward the image side) and a positive meniscus lens convex to the object side in order from the object side. And a negative meniscus lens concave on the image side (convex on the object side)
A second group Gr2 composed of (aspherical surfaces on both sides), a third lens composed of a biconvex positive lens (aspherical surface on the image side) and a biconcave negative lens.
From the group Gr3, it is composed of 5 sheets in total.

2, FIG. 4, FIG. 6, FIG. 8 and FIG. 10 are aberration charts corresponding to the first to fifth embodiments. In each drawing, [A] shows the aberration in the shooting state at the infinite object distance, and [B] shows the aberration in the closest object shooting state. The aberrations in each figure [B] are obtained when focusing was performed at a conjugate length of 0.221 m with D ₁ : D ₂ : D ₃ = 1: 1.05: 1 in Examples 1 and 2. Then conjugate length 0.220
m when D ₁ : D ₂ : D ₃ = 1: 1.04: 1 was used for focusing, and in Example 5, the conjugate length was 0.223 m and D ₁ : D ₂ : D ₃
= 1: 1.05: 1, when focusing.

The solid line (d) represents the spherical aberration for the d line, and the broken line (SC) represents the sine condition. Furthermore, the dashed line
(DM) and solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

Table 1 shows the values of f / f ₂ and f / f _1,2 corresponding to the conditional expressions (1) and (4) in each example.
Table 2 shows the value of D ₂ / D _{1 in} the conditional expression (2) and the value of D ₁ (= D ₃ ) in the conditional expression (3) in each example.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

As described above, according to the present invention, the first group having negative refracting power, the second group having positive refracting power, and the first group having positive refracting power are arranged in this order from the object side. In a photographing optical system including three groups, the first group and the second group substantially form an afocal system, so that the axial rays passing through the second group are nearly parallel. Here, when focusing from the infinity object side to the near object side, the first group and the second group
All of the first to third groups are moved toward the object side so that the air distance to the group is slightly decreased and the air distance between the second group and the third group is slightly increased. With this configuration, the amount of extension in focusing is relatively small, and high-magnification shooting with a certain shooting distance is possible. Further, since the change in the air gap is slight, it is possible to correct the field curvature without changing the spherical aberration and the like. Therefore, focusing can be performed with a small aberration variation from infinity photography to close-up photography. It is possible to realize a compact macro lens capable of Further, since this focusing method is almost the same as the whole feeding, it is possible to reduce the fluctuation of the focal length of the entire system. For this reason,
The shooting distance during high-magnification shooting can be lengthened to some extent.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

FIG. 2 is an aberration diagram of Example 1 of the present invention.

FIG. 3 is a lens configuration diagram of a second embodiment of the present invention.

FIG. 4 is an aberration diagram of Example 2 of the present invention.

FIG. 5 is a lens configuration diagram of a third embodiment of the present invention.

FIG. 6 is an aberration diagram for Example 3 of the present invention.

FIG. 7 is a lens configuration diagram of Example 4 of the present invention.

FIG. 8 is an aberration diagram for Example 4 of the present invention.

FIG. 9 is a lens configuration diagram of a fifth embodiment of the present invention.

FIG. 10 is an aberration diagram of Example 5 of the present invention.

[Explanation of symbols]

 Gr1 ... 1st group Gr2 ... 2nd group Gr3 ... 3rd group

Claims (1)

[Claims] 1. A first lens element having a negative refractive power in order from the object side.
In a photographing optical system composed of a group, a second group having a positive refractive power, and a third group having a positive refractive power, the first group and the second group form an afocal system, During focusing from the object side at infinity to the near object side, the air space between the first group and the second group slightly decreases, and the air space between the second group and the third group slightly increases. As described above, the macro lens, wherein all the first to third groups are moved to the object side for focusing.