JPH1114903A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide good aberration correction with high zoom ratio including a wide-angle region, comprising two groups. SOLUTION: (a) is a wide-angle state, (b) is an intermediate state, (c)
Indicates a telephoto state, and has, in order from the object side, a positive first lens group 1, a diaphragm S, and a negative second lens group 2, and the first lens group 1 is divided with the largest air interval among them. Front lens group 1a having low refractive power and rear lens 1b having positive refractive power
Consists of The image side or the adjacent lens surface of the second lens L2, which is the negative lens disposed closest to the object side in the negative lens of the front lens group 1a, is made to be aspheric, and N1an, Assuming that ν1an is the refractive index and Abbe number of the second lens L2 which is a negative lens, the following conditional expression is satisfied. 1.7 <N1an <1.935 <ν1an <45

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens comprising two lens groups suitable for a lens shutter camera, a video camera and the like.

[0002]

2. Description of the Related Art Recently, with the downsizing of a lens shutter camera, a video camera, and the like, a small zoom lens having a short total lens length has been demanded. In particular, it is desired to mount a zoom lens even in the field of a small camera such as a lens shutter camera which does not perform lens replacement, and a small zoom lens having a length approximately the same as a conventionally used single focus lens is demanded.

[0003] The present applicant has previously disclosed Japanese Patent Application Laid-Open No. 57-201213.
JP-A-60-170816, JP-A-60-170816
In JP-A-191216 and JP-A-62-56917, two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, are sequentially arranged from the object side. Small so-called 2 that changes magnification by changing the distance between groups
A group zoom lens was proposed.

In these publications, a two-unit zoom lens having high optical performance is adopted in which positive and negative refractive power arrangements are employed in order from the object side, the back focus is relatively short, and the overall length of the lens is shortened. Have achieved.

In addition, Japanese Patent Application Laid-Open Nos. Sho 62-284319, 62-256915, and 64-5
Japanese Patent Application Laid-Open No. 2111 and Japanese Patent Application Laid-Open No. 1-193807 and the like include a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. A two-unit zoom lens that performs zooming by moving the zoom lens forward is disclosed.

[0006] In addition, JP-A-2-50118, JP-A-2-71220, and JP-A-2-1908.
No. 2, Japanese Patent Application Laid-Open No. 4-145408 and the like include a first lens group having a positive refractive power and a second lens group having a negative refractive power, and perform zooming by changing the distance between both lens groups. A two-unit zoom lens having a relatively high zoom ratio is disclosed.

[0007]

However, in the above-described conventional example, the above-described two lens groups, the first lens group having a positive refractive power and the second lens group having a negative refractive power, are used.
In the group zoom lens, the wide-angle lens has a good correction of distortion on the wide-angle side and a small overall lens system while securing a predetermined amount of light around the screen. It is necessary to appropriately set the lens configuration of each lens group in order to obtain a good optical performance over the entire zooming range with a zoom ratio of about 3 times at an angle.

In general, in a two-unit zoom lens, if the refractive power of both the first lens unit and the second lens unit is increased, it is easy to increase the zoom ratio, and the amount of movement of each lens unit during zooming is reduced. Thus, the overall length of the lens can be reduced. However, if the refractive power of each lens group is simply increased, aberration fluctuation accompanying zooming becomes large, and it becomes difficult to satisfactorily correct the aberration.

An object of the present invention is to provide a wide-angle zoom lens by appropriately setting the lens configuration of a first lens unit having a positive refractive power and / or a second lens group having a negative refractive power in a so-called two-unit zoom lens. Smoothly corrects distortion on the camera side, satisfactorily corrects aberration fluctuations due to zooming while securing a predetermined amount of light at the periphery of the screen, and provides a zoom ratio of about 3 and a shooting angle of view at the wide-angle end of about 72 degrees. Another object of the present invention is to provide a zoom lens having a wide angle of view and high optical performance over the entire zoom range where the lens length is short.

[0010]

A zoom lens according to the present invention for achieving the above object has, in order from the object side, a first positive lens unit and a second negative lens unit. In a zoom lens that changes magnification by changing an air interval, the first lens unit includes a front lens unit having a low refractive power and a rear lens having a positive refractive power and divided by sandwiching a maximum air interval. A zoom lens, wherein the image side or the adjacent lens surface of the negative lens disposed closest to the object in the negative lens of the front lens group is aspheric, and the following conditional expression is satisfied with respect to the negative lens: . 1.7 <N1an <1.935 <ν1an <45 where N1an and ν1an are the refractive index and Abbe number of the negative lens, respectively.

A zoom lens according to the present invention has a first positive lens unit and a second negative lens unit in order from the object side, and performs zooming by changing the air gap between both lens units. In the zoom lens, the second lens group includes two lenses, a positive lens and a negative lens, wherein the positive lens has at least one aspheric surface and satisfies the following conditional expression. 35 <ν2p <50 2.5 <β2t / β2w <3.8

Where ν2p is the Abbe number of the positive lens,
β2w and β2t are magnifications of the second lens group at the wide-angle end and the telephoto end, respectively.

Further, the zoom lens according to the present invention has a positive first lens unit and a negative second lens unit in order from the object side, and performs zooming by changing the air gap between both lens units. Wherein the first lens group includes a front lens group having a low refractive power and a rear lens having a positive refractive power, and is located on the image side or adjacent to the negative lens disposed closest to the object side in the negative lens of the front lens group. Lens surface to be aspherical,
A zoom lens characterized by satisfying the following conditional expression. 0.5 <(R1p + R2p) / (R1p−R2p) <1.5

Here, Rip and R2p are the radius of curvature of the object side and the image side of the positive lens adjacent to the image side of the negative lens, respectively.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 is a configuration diagram of the first embodiment, in which (a)
Indicates a wide-angle state, (b) indicates an intermediate state, and (c) indicates a telephoto state. A zoom lens having a positive first lens unit 1, a stop S, and a negative second lens unit 2 in order from the object side, and performs zooming by changing the air gap between the two lenses I and 2; The lens unit 1 includes a front lens unit 1 a having a low refractive power and a rear lens 1 having a positive refractive power, which are divided with a maximum air interval therebetween.
b. The second lens group includes a positive meniscus lens 2a having a convex surface on the image side and a negative meniscus lens 2a having a convex surface on the image side.

The front lens unit 1a includes a first lens L1 of a positive meniscus lens having a concave surface on the object side, a second lens L2 of a biconcave lens having a strong curvature on the object side, and a thick positive lens having a thick curvature on the image side. The third lens L3 includes a fourth lens L4 of a negative meniscus lens having a convex surface on the image side. The rear lens 1b is a positive meniscus lens having a convex surface on the image side.
Have a five-piece configuration.

The first lens L1 and the second lens L2, and the third lens L3 and the fourth lens L4 are cemented lenses. The image side or the adjacent lens surface of the second lens L2, which is the negative lens disposed closest to the object side in the negative lens of the front lens group 1a, is made aspheric, and the second lens which is this negative lens
L2 satisfies the following conditional expression. 1.7 <N1an <1.9 (1) 35 <ν1an <45 (2)

Here, N1an and v1an are the refractive index and Abbe number of the second lens L2, which is a negative lens, respectively.

Conditional expression (1) is for the second lens L2 which is a negative lens.
When the refractive index is lower than the lower limit, the Petzval sum increases in the negative direction, and the image surface characteristic deteriorates. On the other hand, if the refractive index exceeds the upper limit and the refractive index becomes too high, the cost of the glass material and the manufacturing cost increase, which is not good.

Conditional expression (2) indicates that the second lens L2 is a negative lens.
The chromatic aberration of magnification in a wide-angle castle increases as the dispersion increases beyond the lower limit. When the variance becomes smaller than the upper limit, the spherical aberration of the color in the telephoto range becomes larger.

The second lens group 2 comprises a positive lens 2a and a negative lens 2b. The positive lens 2a has at least one aspheric surface and satisfies the following conditions. 35 <ν2p <50 (3) 2.5 <β2t / β2w <3.8 (4)

Where ν2p is the Abbe number of the positive lens 2a,
β2w and β2t are magnifications of the second lens unit 2 at the wide-angle end and the telephoto end, respectively.

Conditional expression (3) relates to the Abbe number of the positive lens 2a. If the dispersion exceeds the lower limit, the chromatic aberration of magnification in a wide-angle castle becomes difficult to correct. If the variance becomes smaller than the upper limit, it becomes difficult to correct axial chromatic aberration due to zooming.

Conditional expression (4) relates to the ratio between the magnification at the wide-angle end and the magnification at the telephoto end of the second lens unit 2. When the magnification at the telephoto end becomes lower than the lower limit, a predetermined zoom ratio is obtained. Can not be secured. If the magnification at the telephoto end becomes too high beyond the upper limit, it becomes difficult to correct various aberrations accompanying zooming.

Further, it is preferable to satisfy the conditional expressions (3) and (4) and also satisfy the following conditional expression. 1.7 <N2p (5) where N2p is the refractive index of the positive lens 2a in the second lens group 2.

Condition (5) relates to the refractive index of the positive lens 2a in the second lens group 2. If the lower limit value is exceeded, it becomes difficult to satisfactorily correct coma in the wide-angle range.

Further, the image side or the adjacent lens surface of the second lens L2, which is the negative lens disposed closest to the object side in the negative lens of the front lens group 1a, is made aspherical, and the following condition is satisfied. ing. 0.5 <(R1p + R2p) / (R1p−R2p) <1.5 (6)

Here, Rip and R2p are the object side of the positive lens adjacent to the image side of the second lens L2, which is a negative lens, respectively.
The radius of curvature on the image side.

Conditional expression (6) is for the second lens L2 which is a negative lens.
The first lens L1 or the third lens L1, which is a positive lens adjacent to the image side of
This relates to the shape factor of the lens L3. If the value exceeds the lower limit, it is difficult to correct distortion in a wide-angle range. If the value exceeds the upper limit, it becomes difficult to correct coma aberration in a wide angle range.

In Embodiment 2 shown in FIG. 2, the third lens L3 and the fourth lens L4 are cemented lenses.

In Embodiment 3 shown in FIG. 3, the first lens unit 1 has a configuration in which the first lens L1 in FIGS. 1 and 2 is omitted, and the second lens L2 is a biconcave lens having a sharp object-side curvature. The third lens L2 is a thick positive lens having a large curvature on the image side, the fourth lens L4 is a negative meniscus lens having a convex surface on the image side, and the rear lens 1b is a positive meniscus lens having a convex surface on the image side. I have. The third lens L3 and the fourth lens L4 are cemented lenses.

In the first to third embodiments, the image side of the second lens L2, which is the negative lens closest to the object side among the negative lenses of the first lens group 1, is made aspheric.

In the embodiment 4 shown in FIG. 4, the structure of the number of lenses is almost the same as that of FIG. 3, but the second lens, which is the negative lens disposed closest to the object side in the negative lens of the first lens group 1, is used. Third lens which is a positive lens adjacent to the image side of lens L2
The object side of L3 is aspheric.

In the first to fourth embodiments, the image side of the positive lens 2a disposed on the object side of the second lens unit 2 is aspheric.

The numerical ranges of the conditional expressions (1) to (6) are as follows.
More preferably, the following conditions are satisfied. 1.72 <N1an <1.89 (1) '37 <νi an <43 (2)' 37 <ν2p <43 (3) '2.7 <β2t / β2w <3 .2 (4) '1.71 <N2p (5)' 0.75 <(R1p + R2p) / (R1p-R2p) <1.2 (6) '

Next, numerical examples of the first to fourth embodiments will be described. Note that Ri, Di, Ni, and νi are i-th from the object side, respectively.
Radius of curvature of the lens surface, on-axis thickness or spacing between lenses,
The refractive index and Abbe number, the radius of curvature Ri, the axial thickness, and the distance between lenses Di are shown in the sectional views of FIGS. 5 and 6 in Examples 1 and 2, respectively, and in Examples 3 and 4. According to the cross-sectional view shown in FIG.

Numerical Example 1 f = 29.72 to 84.39 Fno = 4.6 to 10.15 2ω = 72.1 to 28.8 R1 = -30.381 D1 = 2.06 N1 = 1.672700 ν1 = 32.1 R2 = -14.749 D2 = 1.25 N1 = 1.727820 ν2 = 40.6 * R3 = 1049.438 D3 = 0.39 R4 = 1279.888 D4 = 4.32 N1 = 1.487490 ν3 = 70.2 R5 = -8.932 D5 = 1.25 N1 = 1.806098 ν4 = 41.0 R6 = -13.666 D6 = 1.11 R7 = -58.998 D7 = 3.09 N1 = 1.487490 ν5 = 70.2 R8 = -10.931 D8 = 0.75 R9 = Aperture D9 = Variable R10 = -47.405 D10 = 2.58 N1 = 1.727820 ν6 = 40.6 * R11 = -23.594 D11 = 4.25 R12 = -10.438 D12 = 2.26 N1 = 1.772499 ν7 = 49.6 R13 =- 91.614 ＼Focal length 29.72 59.89 84.39 Variable spacing＼ D9 12.43 4.42 2.13 Aspherical surface coefficient Three planes R3: k = 0 A = 0 B = 1.81991 / ^10-4 C = 1.9565 / ^10-6 D = -1.21309 / ^10-8 E = 8.98239 ・ 10 ^-10 Surface R11: k = 4.65658 ・ 10 ⁰ A = 0 B = -1.00680 ・ 10 ^-5 C = 1.63963 ・ 10 ^-7 D = -6.39846 ・ 10 ^-9 E = 6.61504 ・ 10 ^-11

Numerical Example 2 f = 29.72 to 84.39 Fno = 4.6 to 10.14 2ω = 72.1 to 28.8 R1 = -39.720 D1 = 1.74 N1 = 1.620041 ν1 = 36.3 R2 = -19.387 D2 = 0.13 R3 = -17.750 D3 = 1.25 N2 = 1.727820 ν2 = 40.6 * R4 = 587.339 D4 = 0.45 R5 = -334.722 D5 = 4.51 N3 = 1.487490 ν3 = 70.2 R6 = -10.527 D6 = 1.25 N4 = 1.785896 ν4 = 44.2 R7 = -15.087 D7 = 1.16 R8 = -72.901 D8 = 2.96 N5 = 1.487490 ν5 = 70.2 R9 = -11.161 D9 = 0.75 R10 = Aperture D10 = Variable R11 = -57.783 D11 = 3.08 N6 = 1.727820 ν6 = 40.6 * R12 = -24.019 D12 = 4.05 R13 = -10.743 D13 = 2.13 N7 = 1.804000 ν7 = 46.6 R14 = -100.693 ＼ Focal length 29.72 60.04 84.39 Variable spacing ＼ D10 12.68 4.23 1.84 Aspherical surface coefficient Four sides R4: k = -3.97102 ・ 10 ¹ A = 0 B = 1.83193 ・ 10 ^-4 C = 1.77523 ・10 ^-6 D = -7.15102 ・ 10 ^-9 E = 7.62065 ・ 10 ^-10 12 faces R12: k = 4.32094 ・ 10 ⁰ A = 0 B = -1.39729 ・ 10 ^-5 C = 4.95615 ・ 10 ^-8 D = -3.51679・ 10 ^-9 E = 3.00982 ・ 10 ^-11

Numerical Example 3 f = 29.72 to 84.40 Fno = 4.6 to 10.14 2ω = 72.1 to 28.8 R1 = -36.644 D1 = 1.88 N1 = 1.727820 ν1 = 40.6 * R2 = 626.012 D2 = 0.54 R3 = -168.909 D3 = 4.81 N2 = 1.487490 ν2 = 70.2 R4 = -12.198 D4 = 1.50 N3 = 1.882997 ν3 = 40.8 R5 = -16.591 D5 = 0.95 R6 = -80.783 D6 = 3.09 N4 = 1.487490 ν4 = 70.2 R7 = -11.280 D7 = 0.75 R8 = Aperture D8 = Variable R9 = -53.451 D9 = 2.99 N5 = 1.727820 ν5 = 40.6 * R10 = -22.639 D10 = 3.74 R11 = -10.531 D11 = 2.13 N6 = 1.804000 ν6 = 46.6 R12 = -90.846 ＼ Focal length 29.72 60.05 84.40 Variable interval＼ D8 12.98 4.49 2.09 Aspheric coefficient 2 plane R2: k = 0 A = 0 B = 1.81840 / 10 ^-4 C = 1.86655 / 10 ^-6 D = -1.22958 / 10 ^-8 E = 1.03601 / 10 ^-9 10 plane R10: k = 4.39926 ・ 10 ⁰ A = 0 B = -8.67175 ・ 10 ^-6 C = 4.07873 ・ 10 ^-7 D = -1.23457 ・ 10 ^-8 E = 1.19790 ・ 10 ^-10

Numerical Example 4 f = 29.72 to 84.39 Fno = 4.6 to 0.13 2ω = 72.1 to 28.8 R1 = -31.131 D1 = 1.88 N1 = 1.882997 ν1 = 40.8 R2 = 169.917 D2 = 0.38 * R3 = 68.562 D3 = 6.30 N2 = 1.583126 ν2 = 59.4 R4 = -8.581 D4 = 1.50 N3 = 1.834807 ν3 = 42.7 R5 = -13.086 D5 = 0.82 R6 = -26.188 D6 = 3.09 N4 = 1.487490 ν4 = 70.2 R7 = -11.653 D7 = 0.75 R8 = Aperture D8 = Variable R9 = -64.313 D9 = 3.00 N5 = 1.727820 ν5 = 40.6 * R10 = -25.223 D10 = 3.97 R11 = -10.932 D11 = 2.13 N6 = 1.804000 ν6 = 46.6 R12 = -119.722 ＼focal length 29.72 60.05 84.39 variable interval＼D8 12.94 4.53 2.15 Aspherical surface coefficient R3 on three surfaces: k = 0 A = 0 B = -2.27917 · 10 ^-4 C = −1.23887 · 10 ^-6 D = −3.52373 · 10 ^-8 E = 2.39110 · 10 ^-10 10 surface R10: k = 5.36300 ・ 10 ⁰ A = 0 B = -1.40034 ・ 10 ^-5 C = 2.64322 ・ 10 ^-7 D = -7.84775 ・ 10 ^-9 E = 7.53613 ・ 10 ^-11

Numerical values of conditional expressions (1) to (6) in each embodiment. Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 (1) N1an 1.73 1.73 1.73 1.88 (2) νian 40.6 40.6 40.6 40.8 (3) ν2p 40.6 40.6 40.6 40.6 (4) β2t / β2v 2.84 2.84 2.84 2.84 (5) N2p 1.73 1.73 1.73 1.73 (6) (R1p + R2p) / (R1p−R2p) 0.99 1.06 1.16 0.78 Note that FIGS. 4 shows various aberration diagrams.

[0042]

As described above, the zoom lens according to the present invention has a positive and negative first lens unit and a second lens unit, includes a wide-angle region, and has a high zoom ratio of about three times, and is excellent. Enables aberration correction.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a first embodiment in a wide-angle, intermediate, and telephoto state.

FIG. 2 is a lens configuration diagram of a wide-angle, intermediate, and telephoto state according to a second embodiment.

FIG. 3 is a diagram illustrating a lens configuration of a wide-angle, middle, and telephoto state according to a third embodiment.

FIG. 4 is a lens configuration diagram of a wide-angle, intermediate, and telephoto state according to a fourth embodiment.

FIG. 5 is a lens cross-sectional view of Example 1.

FIG. 6 is a sectional view of a lens according to a second embodiment.

FIG. 7 is a lens cross-sectional view of Examples 3 and 4.

FIG. 8 is a diagram illustrating various aberrations of the first embodiment in a wide-angle state.

FIG. 9 is a diagram illustrating various aberrations of the intermediate state of the first embodiment.

FIG. 10 is a diagram illustrating various aberrations of the first embodiment in a telephoto state.

FIG. 11 is a diagram illustrating various aberrations of the second embodiment in a wide-angle state.

FIG. 12 is a diagram illustrating various aberrations of the intermediate state of the second embodiment.

FIG. 13 is a diagram illustrating various aberrations of the second embodiment in a telephoto state.

FIG. 14 is a diagram illustrating various aberrations of the third embodiment in a wide-angle state.

FIG. 15 is a diagram illustrating various aberrations of the third embodiment in an intermediate state.

FIG. 16 is a diagram illustrating various aberrations of the third embodiment in a telephoto state.

FIG. 17 is a diagram illustrating various aberrations of the fourth embodiment in a wide-angle state.

FIG. 18 is a diagram showing various aberrations of the fourth embodiment in the intermediate state.

FIG. 19 is a diagram illustrating various aberrations of the fourth embodiment in a telephoto state.

[Explanation of symbols]

 Reference Signs List 1 first lens group 2 second lens group 1a front lens group 1b rear lens 2a positive lens 2b negative lens S sagittal curve M meridional curve d d line g g line

Claims (11)

[Claims] 1. A zoom lens having a positive first lens group and a negative second lens group in order from the object side and performing zooming by changing an air gap between the two lens groups, wherein the first lens group is A negative lens, which is composed of a front lens unit having a low refractive power and a rear lens having a positive refractive power and divided with a maximum air interval therebetween, and which is disposed closest to the object side in the negative lens of the front lens unit. Wherein the image side or the adjacent lens surface is aspherical, and the following conditional expression is satisfied with respect to the negative lens. 1.7 <N1an <1.935 <ν1an <45 where N1an and ν1an are the refractive index and Abbe number of the negative lens, respectively. 2. The zoom lens according to claim 1, wherein all the lenses except the negative lens have the strongest convex surface on the image plane side. 3. The zoom lens according to claim 1, wherein an image-side lens following the negative lens includes a positive lens having a strong convex surface on the image side and a negative meniscus lens having a convex image side subsequent to the negative lens. 4. The zoom lens according to claim 3, wherein the two lenses following the negative lens are cemented lenses. 5. A zoom lens having a positive first lens group and a negative second lens group in order from the object side and performing zooming by changing an air gap between the two lens groups, wherein the second lens group is A zoom lens comprising a positive lens and a negative lens, wherein the positive lens has at least one aspheric surface and satisfies the following conditional expression. 35 <ν2p <50 2.5 <β2t / β2w <3.8 where ν2p is the Abbe number of the positive lens, and β2w and β2t are magnifications of the second lens unit at the wide-angle end and the telephoto end, respectively. 6. The zoom lens according to claim 5, wherein the following conditional expression is satisfied. 1.7 <N2p where N2p is the refractive index of the positive lens. 7. A zoom lens having a positive first lens group and a negative second lens group in order from the object side and performing zooming by changing an air gap between the two lens groups, wherein the first lens group is The image side or the adjacent lens surface of the negative lens disposed closest to the object side in the negative lens of the front lens group is composed of a front lens unit having a low refractive power and a rear lens having a positive refractive power. And a zoom lens satisfying the following conditional expression. 0.5 <(R1p + R2p) / (R1p−R2p) <1.5 where Rip and R2p are the radius of curvature of the object side and the image side of the positive lens adjacent to the image side of the negative lens, respectively. 8. The zoom lens according to claim 7, wherein a stop is provided on the image side of said front lens group. 9. The zoom lens according to claim 7, wherein all the lenses except the negative lens have the strongest convex surface on the image surface side. 10. The image-side lens following the negative lens,
8. The zoom lens according to claim 7, comprising a positive lens having a strong convex surface on the image side and a negative meniscus lens having a convex image side subsequent thereto. 11. The zoom lens according to claim 10, wherein the two lenses following the negative lens are cemented lenses.