JPH06230281A - Zoom lens - Google Patents

Abstract

(57) [Summary] [Purpose] A compact, wide-angle lens system that has three lens groups as a whole and is designed to have a compact lens system by appropriately setting the refractive power and lens configuration of each lens group. Getting a zoom lens. [Structure] Three lens groups, a first group having a negative refracting power, a second group having a negative refracting power, and a third group having a positive refracting power, are arranged in this order from the object side. When performing zooming by moving the group on the optical axis, the first group includes a positive meniscus eleventh lens having a convex surface facing the object side and a negative meniscus twelfth lens having a convex surface facing the object side. And the second group includes at least one negative lens and a meniscus positive lens having a convex surface directed toward the object side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and in particular, it is preceded by a lens unit having a negative refractive power and has three lens units as a whole, and two of these lens units are moved to change the magnification. The present invention relates to a zoom lens suitable for a small still camera having a wide angle of view, a video camera and the like.

[0002]

2. Description of the Related Art Conventionally, a zoom lens designed to shorten the total lens length and the outer shape of the lens has been disclosed in, for example, Japanese Patent Laid-Open No.
9-142515, JP-A-59-64811, and the like.

In these publications, there is a so-called short zoom lens which has two lens groups, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and performs zooming by changing the distance between the two lens groups. is suggesting.

The short zoom lens is often used in a single-lens reflex camera because it can relatively easily ensure a predetermined back focus even if the focal length is set shorter than the screen size.

A so-called three-group zoom lens in which a third lens group having a positive or negative refractive power is newly arranged on the image side in the short zoom lens to secure a predetermined zoom ratio and to shorten the total lens length is provided. For example, it is proposed in JP-A-58-9016 and JP-A-58-111013.

Further, in the three-group zoom lens, by appropriately setting the refracting power and lens configuration of each lens group, high zooming and high optical performance over the entire zooming range can be achieved, for example, Japanese Patent Laid-Open No. 61-183613,
JP-A-61-240217, JP-A-62-879
25, JP-A-62-112115, JP-A-1-189622, and the like.

In addition to this, a wide-angle zoom lens having an angle of view at the wide-angle end of 90 degrees or more is proposed in Japanese Patent Laid-Open No. 58-5707.

Further, a short zoom lens and negative, positive,
Japanese Unexamined Patent Publication (Kokai) No. 2-201310 proposes a four-group zoom lens including four lens groups having negative and positive refracting powers.

[0009]

Generally, in a zoom type in which a lens unit having a negative refractive power precedes, a predetermined back focus is ensured, and in addition, in order to shorten the total lens length while keeping the lens diameter small, each lens unit needs to be shortened. It must give strong refracting power.

However, when the refracting power of each lens unit is strengthened, deterioration of the peripheral portion of the screen on the wide-angle side, that is, aberration, in other words, image field curvature, astigmatism, and distortion are significantly increased. Further, a lot of high-order spherical aberration and astigmatism occur on the telephoto side, and it becomes difficult to satisfactorily correct these. In particular, astigmatism on the telephoto side tends to be over at a low angle of view and under at a high angle of view.

In JP-A-58-5707 and JP-A-2-201310, aberration correction is performed by using an aspherical surface in the front group having a negative refractive power. When correcting aberrations using an aspherical surface, it is important to properly set the lens surface on which the aspherical surface is applied in order to sufficiently obtain the effect of the aspherical surface.

Further, in the three-group zoom lens, the negative refracting power of the front group cannot be increased beyond the limit in terms of aberration correction. As a result, there is a problem that the peripheral light amount cannot be sufficiently secured unless the front lens diameter is increased because the distance to the diaphragm is increased. For this reason, when an attempt is made to widen the angle of view with the three-group zoom lens, the size of the entire lens system tends to increase.

Generally, when the size of the entire lens system is increased, a lens group having a large lens diameter and a large weight must be driven during autofocusing, which is very disadvantageous in terms of driving force and driving speed.

According to the present invention, in a zoom lens composed of three lens groups as a whole having a predetermined refracting power, by appropriately specifying the refracting power and the lens configuration of each lens group, there is little aberration variation due to zooming, and total variation. An object of the present invention is to provide a zoom lens having a high optical performance over a double range and having a wide angle of view and a short overall lens length, which is suitable for a photographic camera or a video camera.

[0015]

The zoom lens of the present invention comprises (1-1) a first group having a negative refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. When the second lens unit and the third lens unit are moved on the optical axis to perform zooming, the first lens unit has a meniscus-shaped positive first lens unit with a convex surface facing the object side. A lens and a negative meniscus twelfth lens having a convex surface directed toward the object side, wherein the second group has at least one negative lens and a meniscus positive lens having a convex surface directed toward the object side. Is characterized by.

[0016]

1 to 3 are sectional views of a zoom lens according to the present invention at the wide-angle end in Numerical Examples 1 to 3 which will be described later.

FIGS. 4 to 6 are aberration diagrams of the wide-angle end, middle, and telephoto ends of the numerical embodiment 1 of the present invention at a magnification of −0.02 times, and FIGS. 7 to 9 are diagrams of the numerical embodiment 2 of the present invention. Aberrations at wide-angle end, middle, and telephoto ends of -0.02 times, FIGS. 10 to 12 are aberrations at wide-angle end, middle, and telephoto ends of -0.02 times in Numerical Example 5 of the present invention. It is a figure.

In the figure, L1 is a first group having a negative refractive power, L2 is a second group having a positive refractive power, L3 is a third group having a negative refractive power, SP is an aperture stop, and FP is an image plane.

Next, numerical examples 1 of FIGS. 1, 2 and 3 will be described.
A few zoom lenses will be described.

The zoom lenses of Numerical Embodiments 1, 2 and 3 are arranged in order from the object side.
It is composed of three lens units, that is, a lens unit and a third lens unit having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the third lens unit is moved to the object side as shown by the arrow to perform zooming, and the image plane variation associated with zooming is reciprocally moved in correspondence with the second lens unit. I am correcting it. Focusing is performed by moving the second group.

As described above, in Numerical Embodiments 1, 2, and 3, the second group and the third group are moved as described above during zooming, and the first group is a meniscus-shaped positive first lens whose convex surface faces the object side.
It comprises one lens and a negative meniscus twelfth lens having a convex surface facing the object side, and the second lens group comprises at least one negative lens and a meniscus positive lens having a convex surface facing the object side.

Specifically, the second group is composed of two meniscus negative lenses having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side. By constructing the first lens unit having a negative refracting power so as to include the above-mentioned two lenses having the lens shape, distortion and astigmatism, which remarkably occur mainly on the wide angle side, are well corrected.

Further, the compensator for correcting the image plane variation due to the magnification change in the second lens unit having a negative refracting power makes the function allotment independent, and each lens has an optimum lens shape and the refraction power allotment is compared. I am able to choose freely. As a result, the overall lens length and lens diameter can be reduced, and the overall lens system can be made compact and aberrations can be corrected well.

Focusing may be performed by moving the first lens group, or by moving the first lens group and the second lens group integrally or simultaneously at a predetermined ratio. In the present embodiment, the small and lightweight second lens group is used to facilitate autofocus.

The second lens unit has a lens structure including a negative lens and a positive meniscus lens, and satisfactorily corrects spherical aberration that tends to occur mainly on the telephoto side and corrects spherical aberration and coma aberration that fluctuate during focusing. There is.

It is preferable to use two negative lenses in the second lens group because the image plane curvature and astigmatism can be corrected well.

In Numerical Embodiments 1 and 2, the third lens group is a positive 31st lens whose both lens surfaces are convex surfaces, a diaphragm, a positive 32nd lens whose both lens surfaces are convex surfaces, a negative 33rd lens and a positive 34th lens. It is composed of a first cemented lens cemented with a lens, a negative meniscus 35th lens having a convex surface facing the object side, a positive 36th lens, and a positive 37th lens.

In Numerical Embodiment 3, the positive thirty-first lens whose both lens surfaces are convex, the diaphragm, and the third positive lens whose both lens surfaces are convex.
It is composed of two lenses, a negative thirty-third lens, a positive thirty-fourth lens, a negative meniscus thirty-fifth lens having a convex surface facing the object side, a positive thirty-sixth lens, and a positive thirty-seventh lens.

In Numerical Embodiment 3, as compared with Numerical Embodiments 1 and 2, the 33rd lens and the 34th lens are separated and an air lens is provided, whereby spherical aberration and sagittal halo in the peripheral portion of the screen are improved. Correcting.

In Numerical Embodiments 1, 2, and 3, by setting each element as described above, it is possible to shorten the overall lens length and to cover the entire zoom range from the wide angle of view to the standard zoom ratio of about 2. We have obtained a zoom lens with good optical performance.

In Numerical Embodiments 1, 2, and 3, the photographing field angle is about 93 ° to 65 ° and the F number is 3.5 to 4.5.

In Numerical Embodiments 1, 2, and 3, (2-1) When the focal length of the i-th group is fi, f3 <| f2 | <| f1 | ... (1) There is.

Conditional expression (1) is for appropriately setting the refracting power of each lens unit to reduce the overall lens length and the lens outer diameter.

In particular, the negative refractive power is divided more by the second lens group than the first lens group, and the absolute value of the positive refractive power of the third lens group is made stronger than that of the first and second lens groups. A predetermined amount of movement is effectively performed with a relatively small amount of movement.

(2-2) When the refractive indices of the materials of the eleventh lens and the twelfth lens are N11 and N12, respectively, N11 <N12 (2) ).

Conditional expression (2) is a condition for favorably correcting distortion and astigmatism mainly generated on the wide angle side. The distortion and the relative point aberration are satisfactorily corrected by increasing the curvature difference of the positive lens surface without increasing the refractive power of each lens surface of the negative lens of the first group. (2-3) When the refractive index or the average refractive index of the material of the negative lens in the second group is N2 _N 1.6 <N2 _N・ (3).

Conditional expression (3) is for correcting the astigmatism that tends to occur on the wide angle side by using a negative lens having a high refractive index in the second lens group, and also for correcting the distortion favorably.

Next, numerical examples of the present invention will be shown. 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 gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Numerical Example 1 f = 20.60 to 34.09 fno = 1: 3.5 to 4.5 2 ω = 92.8 °
~ 64.8 ° R 1 = 80.59 D 1 = 4.10 N 1 = 1.62299 ν 1 = 58.2 R 2 = 202.04 D 2 = 0.10 R 3 = 48.14 D 3 = 1.70 N 2 = 1.78590 ν 2 = 44.2 R 4 = 21.61 D 4 = Variable R 5 = 39.85 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.65 D 6 = 4.65 R 7 = 141.29 D 7 = 1.30 N 4 = 1.77250 ν 4 = 49.6 R 8 = 32.48 D 8 = 2.80 R 9 = 25.81 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 70.11 D 10 = Variable R11 = 77.91 D 11 = 2.20 N 6 = 1.58313 ν 6 = 59.4 R12 = -77.90 D 12 = 1.78 R13 = (Aperture) D 13 = 0.92 R14 = 34.17 D 14 = 6.90 N 7 = 1.62606 ν 7 = 39.2 R15 = -39.89 D 15 = 3.50 R16 = -15.90 D 16 = 2.50 N 8 = 1.84666 ν 8 = 23.8 R17 = -417.04 D 17 = 3.80 N 9 = 1.78590 ν 9 = 44.2 R18 = -20.50 D 18 = 0.20 R19 = 82.47 D 19 = 1.20 N10 = 1.83400 ν10 = 37.2 R20 = 25.23 D 20 = 1.65 R21 = -111.96 D 21 = 2.50 N11 = 1.51633 ν11 = 64.2 R22 = -25.61 D 22 = 0.20 R23 = -343.40 D 23 = 2.15 N12 = 1.51633 ν12 = 64.2 R24 = -47.31

[0040]

[Table 1] Numerical Example 2 f = 20.55 to 34.14 fno = 1: 3.5 to 4.5 2 ω = 92.9
° ~ 64.7 ° R 1 = 83.36 D 1 = 4.07 N 1 = 1.60311 ν 1 = 60.7 R 2 = 216.05 D 2 = 0.10 R 3 = 47.63 D 3 = 1.70 N 2 = 1.80610 ν 2 = 41.0 R 4 = 21.58 D 4 = Variable R 5 = 40.41 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.50 D 6 = 4.72 R 7 = 157.04 D 7 = 1.30 N 4 = 1.80400 ν 4 = 46.6 R 8 = 31.97 D 8 = 2.28 R 9 = 25.65 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 89.80 D 10 = Variable R11 = 73.03 D 11 = 3.36 N 6 = 1.60311 ν 6 = 60.7 R12 = -78.75 D 12 = 1.78 R13 = (Aperture ) D 13 = 0.92 R14 = 33.46 D 14 = 7.12 N 7 = 1.58921 ν 7 = 40.9 R15 = -39.53 D 15 = 3.68 R16 = -15.90 D 16 = 2.54 N 8 = 1.84666 ν 8 = 23.8 R17 = -388.18 D 17 = 3.42 N 9 = 1.78590 ν 9 = 44.2 R18 = -20.52 D 18 = 0.20 R19 = 82.76 D 19 = 1.20 N10 = 1.83400 ν10 = 37.2 R20 = 25.65 D 20 = 1.65 R21 = -115.32 D 21 = 2.50 N11 = 1.60311 ν11 = 60.7 R22 = -25.76 D 22 = 0.20 R23 = -335.66 D 23 = 2.15 N12 = 1.60311 ν12 = 60.7 R24 = -69.47

[0041]

[Table 2] Numerical Example 3 f = 20.60 to 34.25 fno = 1: 3.5 to 4.5 2 ω = 92.8 °
~ 64.6 ° R 1 = 81.48 D 1 = 4.14 N 1 = 1.60311 ν 1 = 60.7 R 2 = 213.04 D 2 = 0.10 R 3 = 48.41 D 3 = 1.70 N 2 = 1.80610 ν 2 = 41.0 R 4 = 21.57 D 4 = Variable R 5 = 39.84 D 5 = 1.40 N 3 = 1.80610 ν 3 = 41.0 R 6 = 16.43 D 6 = 4.79 R 7 = 170.12 D 7 = 1.30 N 4 = 1.80400 ν 4 = 46.6 R 8 = 32.61 D 8 = 2.07 R 9 = 25.25 D 9 = 3.00 N 5 = 1.84666 ν 5 = 23.8 R10 = 87.42 D 10 = Variable R11 = 72.78 D 11 = 3.56 N 6 = 1.60311 ν 6 = 60.7 R12 = -92.69 D 12 = 1.50 R13 = (Aperture) D 13 = 0.50 R14 = 34.93 D 14 = 7.16 N 7 = 1.58921 ν 7 = 40.9 R15 = -42.15 D 15 = 4.17 R16 = -14.67 D 16 = 1.94 N 8 = 1.80518 ν 8 = 25.4 R17 = 735.27 D 17 = 0.22 R18 = 368.24 D 18 = 2.59 N 9 = 1.78590 ν 9 = 44.2 R19 = -18.91 D 19 = 0.20 R20 = 90.59 D 20 = 1.40 N10 = 1.83400 ν10 = 37.2 R21 = 25.84 D 21 = 1.80 R22 = -115.83 D 22 = 2.60 N11 = 1.60311 ν11 = 60.7 R23 = -25.72 D 23 = 0.20 R24 = -228.15 D 24 = 2.00 N12 = 1.51633 ν12 = 64.2 R25 = -51.29

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

According to the present invention, by specifying the refracting powers and lens configurations of the three lens groups as described above, it is possible to achieve a wide angle of view and downsizing of the entire lens system. It is possible to achieve a compact zoom lens having good optical performance over the variable power range.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide-angle end according to Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 4 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 5 is an intermediate aberration diagram of Numerical example 1 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 7 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 8 is an intermediate aberration diagram of Numerical example 2 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 11 is an intermediate aberration diagram of Numerical Example 3 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

[Explanation of symbols]

L ₁ First group L ₂ Second group L ₃ Third group SP Aperture stop P Flare stop FP Image plane

Claims (4)

[Claims] 1. A three-lens group including a first group having a negative refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. When performing zooming by moving the third lens unit on the optical axis, the first lens unit includes a positive meniscus eleventh lens element having a convex surface facing the object side and a negative meniscus lens element having a convex surface facing the object side. A zoom lens having twelve lenses, wherein the second group has at least one negative lens and a meniscus-shaped positive lens having a convex surface facing the object side. 2. The zoom lens according to claim 1, wherein f3 <| f2 | <| f1 | when the focal length of the i-th group is fi. 3. The zoom lens according to claim 1, wherein N11 <N12 when the refractive indices of the materials of the eleventh lens and the twelfth lens are N11 and N12, respectively. 4. The zoom lens according to claim 1, wherein when the refractive index or average refractive index of the material of the negative lens in the second group is N2 _N , 1.6 <N2 _N.