JP2988031B2 - Compact zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens, and more particularly to a lens group having a negative refractive power, which has three lens groups as a whole, of which two lens groups on the object side are moved. The present invention relates to a compact zoom lens suitable for use in a small and high-magnification still camera, video camera, or the like, which performs magnification.

[0002]

2. Description of the Related Art Conventionally, a zoom lens in which the total length of the lens is reduced and the outer diameter of the lens is reduced is disclosed in, for example, Japanese Patent Application Laid-Open No. 59-1984.
No. 16248 and Japanese Patent Laid-Open No. 62-87925.

In Japanese Patent Application Laid-Open No. 59-16248, there are provided two lens units, a first unit having a negative refractive power and a second unit having a positive refractive power, and the magnification is changed by changing the distance between the two lens units. A so-called short zoom lens has been proposed.

On the other hand, Japanese Patent Application Laid-Open No. 62-87925 is based on the earlier application of the present applicant, and in this publication, a first group of negative refractive power and a second group of positive refractive power are sequentially arranged from the object side. The zoom lens has three lens groups, a first lens group and a third lens group. The first lens group and the second lens group are moved to perform zooming, and the first lens group is provided with an aspherical surface. Has proposed a zoom lens that satisfactorily corrects aberration fluctuations.

[0005]

Generally, in a zoom lens having a standard angle of view, if the magnification ratio is increased, the range of the focal length (the range of the angle of view) is increased. As a result, photographing can be performed under various conditions without lens conversion, which is preferable.

However, if the magnification ratio is increased, the entire lens system becomes large, and the variation in aberrations accompanying the magnification increases, making it difficult to maintain good optical performance.

[0007] The present invention relates to Japanese Patent Application Laid-Open No. 62-87 of the present applicant.
Utilizing the refractive power arrangement of the zoom lens proposed in Japanese Patent Publication No. 925, the lens configuration of each lens group is further improved, and in particular, high magnification and shortening of the entire length of the lens are achieved, and high optical performance is provided over the entire zoom range. The objective is to provide a compact zoom lens.

[0008]

SUMMARY OF THE INVENTION A compact zoom lens according to the present invention comprises a first lens unit having a negative refractive power which moves on the optical axis in order from the object side to correct an image plane variation caused by zooming. A second lens unit having a positive refractive power that moves on the optical axis for zooming, and a third lens unit that is fixed during zooming, the first lens unit being arranged in order from the object side to the object side. A meniscus negative eleventh lens having a convex surface facing the lens surface, a twelfth lens having a concave refractive surface facing the image side compared with the object side, and a meniscus positive lens having a convex surface facing the object side. When the focal length of the i-th lens unit is fi and the focal length of the entire system at the telephoto end is fT, 0.4 <f2 / fT <0.5... ... (1) 0.5 <| f1 | / fT <0.6 (2) It is characterized in that.

[0009]

1 to 4 show a first embodiment of the present invention, which will be described later.
It is a lens cross-sectional view of No.-4.

FIGS. 5 to 7 are aberration diagrams at the wide-angle end, middle, and telephoto end of Numerical Embodiment 1 of the present invention, and FIGS. 8 to 10 are at the wide-angle end, middle, and telephoto end of Numerical Embodiment 2 of the present invention. Aberration diagrams, FIGS.
FIG. 13 is an aberration diagram at a wide angle end, a middle position, and a telephoto end in Numerical Example 3 of the present invention, and FIGS. 14 to 16 are aberration diagrams at a wide angle end, a middle position, and a telephoto end of Numerical Example 4 of the present invention. In the lens cross-sectional view, (A) shows the wide-angle end, and (B) shows the telephoto end.

In the figure, L1 is a first lens unit having a negative refractive power, L2 is a second lens unit having a positive refractive power, L3 is a third lens unit fixed during zooming, P is a flare stop having a constant aperture, and SP is an aperture. The diaphragm and FP are image planes.

In this embodiment, upon zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the object side as shown by the arrow to perform zooming, and the image plane fluctuation accompanying the zooming is reduced by the first lens unit. Corresponding to this, it is corrected by reciprocating movement.

Further, the flare stop P is disposed between the second and third units, and is moved toward the object side as indicated by an arrow together with the magnification, so that the image is mainly focused on the intermediate angle of view (magnification from the middle to the telephoto end). The flare component due to the meridional rays in the
Thereby, the refractive power of the second lens unit is increased.

As shown in FIGS. 1 to 4, the zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive or negative refractive power. The first lens unit and the second lens unit are moved as described above during zooming, and the refractive powers of the first lens unit and the second lens unit are set as in conditional expressions (1) and (2). doing. As a result, while shortening the overall length of the lens, the zoom lens is improved over the entire zoom range of a high zoom ratio of about 3 including the standard angle of view from a wide angle of view (74 °) to a telephoto angle (31 °). A compact zoom lens with optical performance has been obtained. A negative meniscus eleventh lens having the first lens unit having a convex surface facing the object side in order from the object side, and a twelfth lens having both concave lens surfaces having a stronger refracting surface facing the image surface side than the object side. And the three lenses of a positive meniscus thirteenth lens having a convex surface facing the object side to reduce the lens thickness of the entire first group, and to make the first group a negative lens, a negative lens, and a positive lens. The position of the principal point of the lens is appropriately set to facilitate shortening of the entire length of the lens. In addition, aberration fluctuation when focusing with the first lens unit is reduced.

Conditional expression (1) relates to the positive refracting power of the second lens unit, and provides a higher refracting power than the conventional zoom lens to secure a predetermined zoom ratio while mainly shortening the overall length of the lens. It is for.

If the positive refractive power of the second lens unit becomes too weak beyond the upper limit of conditional expression (1), the amount of movement of the second lens unit must be increased in order to secure a predetermined zoom ratio. The overall length of the lens increases. If the positive refractive power of the second lens unit becomes too strong beyond the lower limit, the overall length of the lens becomes short, but the aberration variation accompanying zooming increases, and it is necessary to maintain good optical performance over the entire zooming range. It becomes difficult.

Conditional expression (2) relates to the negative refracting power of the first lens unit and, in conjunction with conditional expression (1), favorably corrects the aberration fluctuation mainly due to zooming while shortening the total lens length. is there.

If the negative refractive power of the first lens unit becomes too weak beyond the upper limit of conditional expression (2), the amount of movement accompanying zooming increases, the overall length of the lens increases, and a predetermined amount of off-axis light flux is secured. In order to achieve this, the lens diameter must be increased and the entire lens system becomes larger. If the negative refractive power of the first lens unit becomes too strong beyond the lower limit, the amount of movement accompanying zooming is reduced, but it becomes difficult to satisfactorily correct aberration fluctuations caused by zooming.

The compact zoom lens of the present invention can be achieved by satisfying the above-mentioned conditions. However, in order to obtain good optical performance over the entire zoom range while further reducing the size of the entire lens system. It is good to constitute each element as follows.

[0020]

(A) The second unit is composed of at least two positive lenses in order from the object side, a negative lens having a refracting surface stronger on the image surface side than the object side, and a positive lens having both lens surfaces convex. thing. In this way, at least two positive lenses are arranged on the object side, the divergent light beams from the first group having a negative refractive power are sequentially converged, and the refractive power of the second group is increased as shown in conditional expression (1). In addition, the occurrence of spherical aberration when the total length of the lens is reduced is reduced.

(B) In the optical path between the second and third units, there is provided a flare stop having a constant diameter and moving on the optical axis smaller than the amount of movement of the second unit as the magnification changes. As a result, the refractive power of the second lens unit is increased as shown by the conditional expression (1), and the coma flare that occurs from the middle to the telephoto end when the total length of the lens is reduced is eliminated, thereby preventing a decrease in optical performance. doing.

(C) The object-side lens surface of the eleventh lens is formed of an aspheric surface having a shape in which negative refractive power becomes weaker as the distance from the optical axis increases, and / or the image surface of the twelfth lens on the image surface side. The lens surface should be composed of an aspheric surface whose negative refractive power becomes weaker as the distance from the optical axis increases. Thereby, coma as well as distortion occurring mainly on the wide-angle side is favorably corrected.

(D) Assuming that the radius of curvature of the object-side lens surface of the eleventh lens is R1, the following condition is satisfied: 0.4 <R1 / fT <0.7 (3) thing.

Conditional expression (3) is for performing close-up photography satisfactorily while reducing aberration fluctuation when focusing with the first lens unit.

If the refractive power of the lens surface becomes too weak beyond the upper limit of conditional expression (3), close-up photographing becomes difficult. On the other hand, if the refractive power exceeds the lower limit and the refractive power becomes too strong, the fluctuation of aberration during focusing increases, which is not good.

Next, numerical examples of the present invention will be described. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness and air space from the object side, and ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

The aspheric surface has an X-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When A, B, C, D, and E are aspherical coefficients, respectively It is represented by the following equation.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Numerical example 1 F = 28.9 to 77.4 FNO = 1: 3.5 to 5.6 2ω = 73.6 ° to 31.2 ° r 1 = 42.75 d 1 = 1.68 n 1 = 1.83400 ν 1 = 37.2 r 2 = 19.36 d 2 = 9.11 r 3 = -180.06 d 3 = 1.49 n 2 = 1.71300 ν 2 = 53.8 r 4 = 50.92 d 4 = 2.02 r 5 = 35.76 d 5 = 4.11 n 3 = 1.80518 ν 3 = 25.4 r 6 = 144.19 d 6 = Variable r 7 = 36.90 d 7 = 2.00 n 4 = 1.60311 ν 4 = 60.7 r 8 = -1565.08 d 8 = 1.88 d 8 = 0.69 r 9 = 26.76 d 9 = 3.94 n 5 = 1.56384 ν 5 = 60.7 r10 = 100.55 d10 = 0.15 r11 = 20.66 d11 = 2.84 n 6 = 1.56384 ν 6 = 60.7 r12 = 53.57 d12 = 0.56 r13 = 526.49 d13 = 5.65 n 7 = 1.76182 ν 7 = 26.5 r14 = 14.81 d14 = 1.67 r15 = 109.31 d15 = 2.05 n 8 = 1.63980 ν 8 = 34.5 r16 = -46.29 d16 = Variable moving aperture d17 = Variable r17 = -47.36 d18 = 1.29 n 9 = 1.80610 ν 9 = 41.0 r18 = 201.65 d19 = 3.80 n10 = 1.58144 ν 9 = 40.8 r19 = -35.01

[0030]

[Table 1] r4 surface is aspherical surface A = 0 B = −1.5014 × 10 ⁻⁶ C = −3.8535 × 10 ⁻⁹ D = −9.8386 × 10 ⁻¹³ E = −2.8625 × 10 ⁻¹⁴ Numerical implementation Example 2 F = 28.9 to 77.6 FNO = 1: 3.5 to 5.6 2ω = 73.6 ° to 31.2 ° r 1 = 46.22 d 1 = 1.68 n 1 = 1.83400 ν 1 = 37.2 r 2 = 19.62 d 2 = 9.78 r 3 = -161.45 d 3 = 1.49 n 2 = 1.71300 ν 2 = 53.8 r 4 = 56.82 d 4 = 1.65 r 5 = 37.45 d 5 = 4.11 n 3 = 1.80518 ν 3 = 25.4 r 6 = 174.76 d 6 = Variable r 7 = 38.39 d 7 = 2.80 n 4 = 1.60311 ν 4 = 60.7 r 8 = -12254.20 d 8 = 0.15 r 9 = 27.75 d 9 = 2.42 n 5 = 1.56384 ν 5 = 60.7 r10 = 91.96 d10 = 1.80 Aperture d11 = 0.80 r11 = 20.57 d12 = 3.43 n 6 = 1.56384 ν 6 = 60.7 r12 = 47.63 d13 = 0.66 r13 = 256.76 d14 = 5.63 n 7 = 1.80518 ν 7 = 25.4 r14 = 15.09 d15 = 1.41 r15 = 53.90 d16 = 1.86 n 8 = 1.63980 ν 8 = 34.5 r16 = -55.10 d17 = Variable moving aperture d18 = Variable r17 = -44.65 d19 = 1.29 n 9 = 1.80610 ν 9 = 41.0 r18 = 321.37 d20 = 3.69 n10 = 1.58144 ν10 = 40.8 r19 = -34.27

[0031]

[Table 2] r4 surface is aspherical surface A = 0 B = −1.5297 × 10 ⁻⁶ C = −4.6051 × 10 ⁻⁹ D = −9.8403 × 10 ⁻¹³ E = −2.862 × 10 ⁻¹⁴ Numerical implementation Example 3 F = 28.9 to 77.4 FNO = 1: 3.5 to 5.6 2ω = 73.6 ° to 31.2 ° r 1 = 37.84 d 1 = 1.80 n 1 = 1.83400 ν 1 = 37.2 r 2 = 19.21 d 2 = 9.22 r 3 = -253.03 d 3 = 1.50 n 2 = 1.69680 ν 2 = 55.5 r 4 = 46.00 d 4 = 0.03 n 3 = 1.56700 ν 3 = 42.8 r 5 = 44.68 d 5 = 2.85 r 6 = 34.52 d 6 = 4.00 n 4 = 1.80518 ν 4 = 25.4 r 7 = 97.19 d 7 = Variable r 8 = 38.05 d 8 = 2.50 n 5 = 1.60311 ν 5 = 60.7 r 9 = -220.56 d 9 = 1.80 Aperture r10 = 22.76 d10 = 2.81 n 6 = 1.58913 ν 6 = 61.2 r11 = 96.09 d11 = 0.15 r12 = 25.75 d12 = 3.55 n 7 = 1.54072 ν 7 = 47.2 r13 = 39.54 d13 = 1.00 r14 = -272.00 d14 = 5.34 n 8 = 1.80518 ν 8 = 25.4 r15 = 16.49 d15 = 1.39 r16 = 87.52 d16 = 2.16 n 9 = 1.63980 ν 9 = 34.5 r17 = -36.67 d17 = Variable moving aperture d18 = Variable r18 = -44.35 d19 = 1.20 n10 = 1.80610 ν 9 = 41.0 r19 = 807.44 d20 = 4.08 n11 = 1.58144 ν10 = 40.8 r20 = -34.32

[0032]

[Table 3] r5 surface is aspherical surface A = 0 B = −1.7071 × 10 ⁻⁶ C = −5.30119 × 10 ⁻⁹ D = −9.842 × 10 ⁻¹³ E = −2.8626 × 10 ⁻¹⁴ Numerical implementation Example 4 F = 28.9 to 77.4 FNO = 1: 3.5 to 5.6 2ω = 73.6 ° to 31.2 ° r 1 = 49.67 d 1 = 1.80 n 1 = 1.83400 ν 1 = 37.2 r 2 = 22.00 d 2 = 0.03 n 2 = 1.56700 ν 2 = 42.8 r 3 = 19.16 d 3 = 8.82 r 4 = -242.62 d 4 = 1.50 n 3 = 1.71300 ν 3 = 53.8 r 5 = 54.57 d 5 = 2.01 r 6 = 34.38 d 6 = 4.00 n 4 = 1.80518 ν 4 = 25.4 r 7 = 112.68 d 7 = Variable r 8 = 37.88 d 8 = 2.50 n 5 = 1.60311 ν 5 = 60.7 r 9 = -229.03 d 9 = 1.80 Aperture r10 = 23.78 d10 = 4.02 n 6 = 1.60311 ν 6 = 60.7 r11 = 88.96 d11 = 0.15 r12 = 22.41 d12 = 2.08 n 7 = 1.54072 ν 7 = 47.2 r13 = 40.59 d13 = 1.00 r14 = -1088.03 d14 = 5.67 n 8 = 1.80518 ν 8 = 25.4 r15 = 15.96 d15 = 1.56 r16 = 142.75 d16 = 1.88 n 9 = 1.63980 ν 9 = 34.5 r17 = -36.73 d17 = Variable moving aperture d18 = Variable r18 = -48.91 d19 = 1.20 n10 = 1.80610 ν10 = 41.0 r19 = 200.35 d20 = 4.00 n11 = 1.58144 ν11 = 40.8 r20 = -36.10

[0033]

[Table 4] r3 surface is aspherical surface A = 0 B = -1.1358 × 10 ⁻⁶ C = −1.6066 × 10 ⁻⁸ D = 7.9395 × 10 ⁻¹¹ E = −3.3834 × 10 ⁻¹³ (Table- 1)

[0034]

[Table 5]

[0035]

According to the present invention, the refractive power and the lens configuration of the three lens groups are specified as described above, so that the entire lens system can be miniaturized and the entire zoom range of about 3 can be achieved. A compact zoom lens having excellent optical performance can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 5 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 6 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 12 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 14 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 First lens group L2 Second lens group L3 Third lens group SP Aperture stop P Flare stop FP Image plane

Continuation of the front page (56) References JP-A-62-124516 (JP, A) JP-A-62-24211 (JP, A) JP-A-61-240217 (JP, A) JP-A-60-6914 (JP, A) JP-A-59-31923 (JP, A) JP-A-59-18917 (JP, A) JP-A-58-178316 (JP, A) JP-A-58-132207 (JP, A) 58-111013 (JP, A) JP-A-58-100115 (JP, A) JP-A-4-163512 (JP, A) JP-A-62-112115 (JP, A) JP-A-61-286812 (JP, A) A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (6)

(57) [Claims] 1. A first group of negative refractive power moving on the optical axis for correcting an image plane variation accompanying magnification in order from the object side, and a first group of positive refractive power moving on the optical axis for magnification. A zoom lens with three lens groups, two groups and a third group fixed during zooming
The first lens group has a convex surface facing the object side in order from the object side.
Negative meniscus eleventh lens, image plane compared to object side
12th lens with concave surfaces facing both lens surfaces
And a positive meniscus shape with the convex surface facing the object side.
When the focal length of the i-th lens unit is fi and the focal length of the entire system at the telephoto end is fT, 0.4 <f2 / fT <0.5 0.5 < | F1 | / fT <0.6 A compact zoom lens characterized by satisfying the following condition: 2. The second group includes at least two positive lenses in order from the object side, a negative lens having a refracting surface stronger on the image surface side than the object side, and a positive lens having both lens surfaces convex. 2. The compact zoom lens according to claim 1, wherein 3. A compact zoom according to claim 1, further comprising a flare stop having a constant aperture which moves on the optical axis with zooming in an optical path between said second group and said third group. lens. 4. The compact zoom lens according to claim 1, wherein the object-side lens surface of the eleventh lens is formed of an aspheric surface having a negative refractive power that decreases as the distance from the optical axis increases. 5. The compact zoom lens according to claim 1, wherein a lens surface on the image surface side of said twelfth lens is formed of an aspheric surface having a shape in which negative refractive power decreases as the distance from the optical axis increases. . 6. The compact lens according to claim 1, wherein the following condition is satisfied: 0.4 <R1 / fT <0.7, where R1 is the radius of curvature of the object-side lens surface of the eleventh lens. Zoom lens.