JP3134611B2 - 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 zoom lens suitable for a photographic camera for 35 mm film, a video camera of an electronic recording system, an SV camera, and the like. The entire lens group has two lens groups, and by appropriately setting the lens configuration of these two lens groups, the overall lens system is reduced in size. The zoom ratio is 2.3 to 2.9, and the wide-angle end. F number 2.9-3.
6. It relates to a negative lead type zoom lens having a shooting angle of view of about 73 ° at the wide-angle end.

[0002]

2. Description of the Related Art Conventionally, a so-called negative lead type zoom lens in which a lens unit having a negative refractive power precedes has a relatively wide angle of view. Is widely used.

For example, Japanese Patent Publication No. 49-29146 and Japanese Patent Laid-Open Publication No. 52-20018 have two lens groups, a first group having a negative refractive power and a second group having a positive refractive power, in order from the object side. A so-called two-unit zoom lens in which zooming is performed by changing the distance between both lens units has been proposed.

In the above two-unit zoom lens, the second lens unit having a positive refractive power is divided into three lens units having positive, negative, and positive refractive powers. A four-group zoom lens is disclosed in, for example, JP-A-53-34.
No. 539, JP-A-60-68311, JP-A-63-241511, JP-A-1-193709 and the like.

Japanese Patent Laid-Open Publication No. Sho 60-68311 discloses a lens arrangement of the second group in this four-group zoom lens, which comprises a negative lens, a cemented lens of a positive lens, a positive lens, and a cemented lens of a negative lens. Kaisho 63-24151
In Japanese Patent Application Laid-Open Publication No. HEI 1 (1993) -1995, the system is composed of three cemented lenses, a negative lens, a positive lens, and a negative lens, and two positive lenses.
In JP-A-193709, a negative lens, a positive lens, and a negative lens are composed of three cemented lenses and a positive lens.

In addition, Japanese Patent Publication No. 49-23912 and Japanese Patent Application Laid-Open No. 57-163213 disclose a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a negative refractive power in order from the object side. The third lens unit has a fourth lens unit having a positive refractive power, and the fourth lens unit has a positive refractive power. The first lens unit is moved to the image plane side during zooming from the wide-angle end to the telephoto end. Move the group to the object side,
A zoom lens in which the third group is fixed or moved has been proposed.

[0007]

In recent years, as a standard zoom lens used for a single-lens reflex camera, a video camera, or the like, a zoom lens having a wide angle of view and a high zoom ratio has been demanded. For example, in a single-lens reflex camera for 35 mm film, a wide-angle zoom lens having a focal length of about 28 mm to 70 mm has already been used as a standard zoom lens.

In general, in a negative-lead type zoom lens, while ensuring a predetermined back focus, a shooting angle of view of about 75 ° at the wide-angle end, a zoom ratio of about 3, and an F-number of about 3 at the wide-angle end are all maintained. In order to obtain good optical performance over the zoom range, it is necessary to appropriately set the refractive power arrangement of each lens group. If the refractive power arrangement or the lens configuration of each lens group is inappropriate, even if the number of lenses is increased, the aberration variation accompanying zooming becomes large, and it becomes difficult to obtain high optical performance over the entire zoom range.

According to the present invention, in a zoom lens composed of two negative-lead type lens groups which are preceded by a lens group having a negative refractive power, by appropriately setting the refractive power and the lens configuration of each lens group, a predetermined back light is obtained. While minimizing the size of the entire lens system that has high optical performance over the entire zoom range of about 75 ° at the wide-angle end, a zoom ratio of 2.8, and an F-number of 2.8 at the wide-angle end while having focus. The objective is to provide the intended zoom lens.

[0010]

A zoom lens according to the present invention comprises, in order from the object side, a front group having a negative refractive power and a positive lens LP.
1, the 21st lens group having a positive refractive power, the 22nd lens group having a negative refractive power, and the 2nd lens having a positive refractive power, including a cemented lens in which three lenses of a negative lens LN2 and a positive lens LP3 are cemented.
As a whole, the zoom lens has a rear group having a positive refractive power including three groups, and when zooming from the wide-angle end to the telephoto end, the distance between the front group and the twenty-first group is reduced. A zoom lens in which the distance between the 22nd lens unit increases and the distance between the 22nd lens unit and the 23rd lens unit decreases, wherein the first lens surface on the object side of the cemented lens has a convex surface facing the object side, The radius of curvature of the first, second, third, and fourth lens surfaces of the cemented lens is Ra in order from the object side.
1, Ra2, Ra3, and Ra4, where the refractive power of the second lens surface is positive, the refractive power of the third lens surface is negative, and the refractive power of the fourth lens surface is positive, -0.5 < Ra1 / Ra2 <0.8 (1) 0.07 <Ra3 / Ra1 <0.8 (2) −0.3 <Ra3 / Ra4 <0.3 (3) It is characterized by:

[0011]

1 to 3 are sectional views of a lens at a wide-angle end according to Numerical Embodiments 1 to 3 of the present invention. In the drawing, LF denotes a front group having a negative refractive power, LR denotes a rear group having a positive refractive power, SP denotes an aperture stop, and FP denotes a flare stop. Arrows indicate the movement trajectories of the respective lens units when zooming from the wide-angle end to the telephoto end.

In the numerical embodiment 1 shown in FIG. 1, the front unit LF is composed of an eleventh unit L11 having a negative refractive power and a twelfth unit L12 having a negative refractive power.
The rear unit LR is composed of three lens units, a 21st unit L21 having a positive refractive power, a 22nd unit L22 having a negative refractive power, and a 23rd unit L23 having a positive refractive power. ing. The zooming from the wide-angle end to the telephoto end decreases after the interval between the eleventh lens unit L11 and the twelfth lens unit L12 increases, and decreases in the twelfth lens unit L1.
The distance between the second lens unit and the twenty-first lens unit L21 decreases, and the twenty-first lens unit L21
Each lens unit is moved on the optical axis so that the distance between the lens unit L22 and the lens unit L22 increases and the distance between the lens unit L22 and the lens unit L23 decreases.

In the numerical examples 2 and 3 shown in FIGS.
F is composed of an eleventh lens unit L11 having a negative refractive power, and a rear lens unit LR.
Is composed of three lens units, a 21st lens unit L21 having a positive refractive power, a 22nd lens unit L22 having a negative refractive power, and a 23rd lens unit L23 having a positive refractive power. Zooming from the wide-angle end to the telephoto end is the first
The distance between the first lens unit L11 and the twenty-first lens unit L21 is reduced,
Each lens group is moved on the optical axis so that the distance between the group L21 and the 22nd lens group L22 increases and the distance between the 22nd lens group L22 and the 23rd lens group L23 decreases.

In this embodiment, the rear unit LR is composed of three lens units, and each lens unit is moved on the optical axis during zooming as described above, so that the principal point of the rear unit LR is shifted from the wide-angle end to the telephoto end. When changing the magnification to, the lens is moved from the image plane side to the object side. Thereby, the zooming effect by the front group LF and the rear group LR is increased, and a predetermined zooming ratio is effectively obtained.

The 21st lens group in the rear lens group LR is sequentially arranged from the object side with a positive lens LP1, a negative lens LN2 and a positive lens L
It is configured to have a cemented lens in which three lenses of P3 are cemented and two positive lenses, and effectively corrects various aberrations associated with zooming, particularly spherical aberration and chromatic aberration.

In particular, by disposing the cemented lens in the twenty-first unit on the object side, the chromatic aberration of magnification is effectively corrected by utilizing the fact that the off-axis light beam passes most outside the optical axis. Further, by forming the cemented lens by joining positive, negative and positive lenses, the thickness of the lens and the outer diameter of the lens are reduced.

In this embodiment, as described above, the lens condition is appropriately set by appropriately setting the refractive power of each lens unit, the moving condition of each lens unit during zooming, and the lens configuration of the 21st unit in the rear unit. A zoom lens that has a wide angle of view and high optical performance over the entire zoom range while shortening the overall length has been obtained.

The zoom lens of the present invention further satisfies the following conditions (1) to (3) in order to secure high optical performance over the entire zoom range and over the entire screen.

The first lens surface on the object side of the cemented lens has a convex surface facing the object side, and the curvature radii of the first, second, third and fourth lens surfaces of the cemented lens are set in order from the object side. Ra1, Ra2, Ra3, Ra4, when the refractive power of the second lens surface is positive, the refractive power of the third lens surface is negative, and the refractive power of the fourth lens surface is positive, -0.5 <Ra1 /Ra2<0.8 (1) 0.07 <Ra3 / Ra1 <0.8 (2) -0.3 <Ra3 / Ra4 <0.3 (3) The following condition must be satisfied.

Conditional expression (1) relates to the ratio of the radii of curvature of the first lens surface and the second lens surface of the cemented lens in the 21st lens unit of the rear unit LR, and is mainly for favorably correcting chromatic aberration. is there. Exceeding the upper limit of conditional expression (1), the lens surface Ra2
When the positive refractive power of becomes strong, the axial and lateral chromatic aberrations in the 21st lens group become insufficiently corrected, and when the lower limit is exceeded, the axial and lateral chromatic aberrations become overcorrected. Becomes difficult to correct with another lens group.

Conditional expression (2) relates to the ratio of the radii of curvature of the first lens surface and the third lens surface of the cemented lens, and is mainly for favorably correcting spherical aberration. If the negative refractive power of the third lens surface is weakened beyond the upper limit of conditional expression (2), spherical aberration will be insufficiently corrected, and if the negative refractive power of the third lens surface is exceeded beyond the lower limit, Many high-order aberrations are generated, and it becomes difficult to correct these aberrations with another lens surface in a well-balanced manner.

Conditional expression (3) relates to the ratio of the radius of curvature of the third lens surface to the fourth lens surface of the cemented lens, and is mainly for correcting various aberrations in a well-balanced manner. When the positive refractive power of the fourth lens surface is increased beyond the upper limit value of conditional expression (3), various aberrations generated from the fourth lens surface are increased, and the positive lens surface of the fourth lens surface is exceeded beyond the lower limit value. When the refractive power of is weakened, the weakened positive refractive power of the twenty-first unit must be borne by the other lens surfaces, and as a result, it becomes difficult to correct various aberrations in a well-balanced manner.

In the present invention, it is more preferable to satisfy the following conditions. (1-1) The Abbe number of the material of the positive lens LP1 is νP
1. When the refractive index and Abbe number of the material of the negative lens LN2 are NN2 and νN2, respectively, and the refractive index of the material of the positive lens LP3 is NP3, 0.1 <NN2-NP3... (4) 1 / νP1-1 / νN2 <−0.012 (5) The following condition must be satisfied.

Conditional expression (4) is for defining the refractive index N _P3 of the material of the positive lens LP3 with respect to the refractive index N _N2 of the material of the negative lens LN2, and is mainly for favorably correcting spherical aberration. Things. When the difference between the refractive indices is smaller than the lower limit value of conditional expression (4), the absolute value of the negative spherical aberration coefficient generated on the cemented lens surface of these lenses is reduced, and as a result, the absolute value of the negative spherical aberration coefficient is generated in this lens group. The positive spherical aberration coefficient becomes large, and it becomes difficult to correct this with another lens group in a well-balanced manner.

Condition (5) relates to the difference between the reciprocal of the Abbe number of the material of the positive lens LP1 and the negative lens LN2, and is mainly for correcting chromatic aberration in a well-balanced manner. When the value exceeds the upper limit of conditional expression (5), correction of chromatic aberration on the cemented lens surface of these lenses becomes insufficient.

[0026]

[0027]

(1-2) The focal length of the second i-th lens unit is f2
i, when the F number and the focal length of the entire system at the telephoto end are FNOT and fT, respectively, 1.1 <f21 · FNOT / fT <2.3 (6) 0.3 <| f22 | / fT <0.8 (7) 0.4 <f23 / fT <1.1 ... (8) The following condition must be satisfied.

Conditional expression (6) defines the focal length f21 of the twenty-first lens group with respect to the F-number FNO of the telephoto end of the entire system and the focal length fT12 of the telephoto end. If the refractive power is weak, it is preferable in terms of aberration correction, but the overall optical length becomes long. If the refractive power of the 21st lens group is increased beyond the lower limit value, it is advantageous for reducing the overall length of the lens. However, various aberrations generated in the 21st lens group become large, and this must be corrected by other lens groups. Becomes difficult.

Condition (7) is the focal length f of the telephoto end of the entire system.
T defines the refractive power of the 22nd lens group. If the negative refractive power of the 22nd lens group is weakened beyond the upper limit, the zooming effect of the rear lens group is weakened, and as a result, the overall length of the lens is increased. Leads to. If the negative refractive power of the 22nd lens unit is increased beyond the lower limit, it is advantageous for compactness, but it is difficult to achieve high optical performance.

Conditional expression (8) represents the focal length f at the tele end of the entire system.
This stipulates the focal length f23 of the 23rd lens group with respect to T. If the positive refractive power of the 23rd lens group is weakened beyond the upper limit, aberration correction, particularly correction of lateral chromatic aberration, is preferable. Is becoming more difficult. If the positive refractive power of the 23rd lens unit becomes stronger beyond the lower limit, it becomes necessary to increase the refractive power of the 23rd lens unit, which is not preferable for aberration correction.

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

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 spacing 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.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

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 B, C, D, and E are aspheric coefficients, respectively,

[0041]

(Equation 1) It is represented by the following equation. (Numerical Example 1) F = 29 to 68 FNO = 1: 2.9 2ω = 73.2 ° to 35.2 ° R 1 = 110.38 (aspherical surface) D 1 = 3.00 N 1 = 1.71300 ν 1 = 53.8 R 2 = 34.13 D 2 = Variable R 3 = -530.03 D 3 = 2.35 N 2 = 1.80400 ν 2 = 46.6 R 4 = 46.11 D 4 = 0.45 R 5 = 45.17 D 5 = 4.70 N 3 = 1.84666 ν 3 = 23.9 R 6 = 129.34 D 6 = Variable R 7 = 65.99 D 7 = 2.80 N 4 = 1.77250 ν 4 = 49.6 R 8 = 288.80 D 8 = 1.80 N 5 = 1.84666 ν 5 = 23.9 R 9 = 31.29 D 9 = 7.10 N 6 = 1.64850 ν 6 = 53.0 R10 = -479.47 D10 = 0.15 R11 = 101.44 D11 = 3.70 N 7 = 1.65160 ν 7 = 58.5 R12 = -495.97 D12 = 0.15 R13 = 43.36 D13 = 4.70 N 8 = 1.80610 ν 8 = 41.0 R14 = 190.09 D14 = Variable R15 = (Aperture Aperture) D15 = 1.50 R16 = -359.19 D16 = 3.55 N 9 = 1.75550 ν 9 = 25.1 R17 = -33.45 D17 = 1.40 N10 = 1.80400 ν10 = 46.6 R18 = 48.33 D18 = 2.50 R19 = -64.10 D19 = 2.00 N11 = 1.80518 ν11 = 25.4 R20 = -37.80 D20 = 1.40 N12 = 1.48749 ν12 = 70.2 R21 = -3631.59 D21 = Variable R22 = -671.83 D22 = 5.00 N13 = 1.51633 ν13 = 64.2 R23 = -23.26 D23 = 1.40 N14 = 1.66446 ν14 = 35.8 R24 = -33.08 D24 = 0.15 R25 = 58.57 D25 = 5.00 N15 = 1.65160 ν15 = 58.5 R26 = -50 .02 D26 = 2.81 R27 = -36.55 D27 = 1.40 N16 = 1.84666 ν16 = 23.9 R28 = -459.50 D28 = Variable R29 = Flare aperture Aspherical coefficient B = 1.046 × 10 ^-6 C = 3.940 ×
10 ^-10 D = -4.980 × 10 ^-13 E = 2.584 × 10 ^-16

[0042]

[Table 1] (Numerical Example 2) F = 29 to 68 FNO = 1: 2.92ω = 73.3 ° to 35.3 ° R 1 = 65.01 (aspherical surface) D 1 = 3.00 N 1 = 1.71300 ν 1 = 53.8 R 2 = 28.93 D 2 = 14.54 R 3 = -135.00 D 3 = 2.35 N 2 = 1.80400 ν 2 = 46.6 R 4 = 53.36 D 4 = 0.52 R 5 = 49.19 D 5 = 5.30 N 3 = 1.84666 ν 3 = 23.9 R 6 = 234.40 D 6 = Variable R 7 = 75.87 D 7 = 2.90 N 4 = 1.77250 ν 4 = 49.6 R 8 = 208.67 D 8 = 1.80 N 5 = 1.84666 ν 5 = 23.9 R 9 = 30.75 D 9 = 7.00 N 6 = 1.65160 ν 6 = 58.5 R10 = -372.36 D10 = 0.20 R11 = 93.56 D11 = 3.10 N 7 = 1.65160 ν 7 = 58.5 R12 = -780.75 D12 = 0.15 R13 = 45.47 D13 = 4.00 N 8 = 1.80610 ν 8 = 41.0 R14 = 356.57 D14 = Variable R15 = Aperture) D15 = 1.50 R16 = -243.62 D16 = 3.65 N 9 = 1.75550 ν 9 = 25.1 R17 = -35.66 D17 = 1.35 N10 = 1.80400 ν10 = 46.6 R18 = 56.88 D18 = 2.78 R19 = -68.24 D19 = 1.65 N11 = 1.80518 ν11 = 25.4 R20 = -37.22 D20 = 1.30 N12 = 1.48749 ν12 = 70.2 R21 =-208.46 D21 = Variable R22 = -1013.89 D22 = 5.80 N13 = 1.51633 ν13 = 64.2 R23 = -22.91 D23 = 1.40 N14 = 1.64769 ν14 = 33.8 R24 = -31.58 D24 = 0.15 R25 = 60.63 D25 = 5.40 N15 = 1.65160 ν15 = 58.5 R26 = -56.33 D 26 = 2.66 R27 = -37.45 D27 = 1.40 N16 = 1.84666 ν16 = 23.9 R28 = -325.82 D28 = Variable R29 = Flare stop Aspherical coefficient B = 1.156 × 10 ^-6 C = 6.235 ×
10 ^-10 D = -4.682 × 10 ^-13 E = 3.672 × 10 ^-16

[0043]

[Table 2] (Numerical Example 3) F = 29 to 83 FNO = 1: 3.6 to 4.6 2ω = 73.5 ° to 29.3 ° R 1 = 332.15 D 1 = 2.00 N 1 = 1.77250 ν 1 = 49.6 R 2 = 39.29 D 2 = 6.00 R 3 = 436.47 D 3 = 5.00 N 2 = 1.80100 ν 2 = 35.0 R 4 = -73.82 D 4 = 0.15 R 5 = -200.05 D 5 = 1.80 N 3 = 1.77250 ν 3 = 49.6 R 6 = 33.83 D 6 = 1.70 R 7 = 30.70 D 7 = 2.65 N 4 = 1.84666 ν 4 = 23.9 R 8 = 42.82 D 8 = Variable R 9 = 41.29 D 9 = 2.40 N 5 = 1.78650 ν 5 = 50.0 R10 = 150.04 D10 = 1.18 N 6 = 1.84666 ν 6 = 23.9 R11 = 19.85 D11 = 5.80 N 7 = 1.62588 ν 7 = 35.7 R12 = -190.05 D12 = 0.20 R13 = 30.98 D13 = 3.50 N 8 = 1.65160 ν 8 = 58.5 R14 = -604.98 D14 = Variable R15 = (Aperture) D15 = 1.00 R16 = -82.43 D16 = 2.25 N 9 = 1.80518 ν 9 = 25.4 R17 = -24.25 D17 = 1.00 N10 = 1.72600 ν10 = 53.6 R18 = 39.62 D18 = Variable R19 = 157.03 D19 = 4.80 N11 = 1.65160 ν11 = 58.5 R20 = -32.57 D20 = 0.20 R21 =-158.85 D21 = 3.10 N12 = 1.65160 ν12 = 58.5 R22 = -50.51 D22 = 2.20 R23 = -26.56 D23 = 1.25 N13 = 1.72825 ν13 = 28.5 R24 = -2257.22

[0044]

[Table 3]

[0045]

As described above, according to the present invention, in a zoom lens composed of two negative-lead type lens groups which are preceded by a lens group having a negative refractive power, the refractive power and the lens configuration of each lens group are appropriately adjusted. , The shooting angle of view 75 at the wide-angle end while having a predetermined back focus.
It is possible to achieve a zoom lens that has high optical performance over the entire zoom range of about 2.8, a zoom ratio of 2.8, and an F-number of about 2.9 at the wide-angle end, and has a reduced size as a whole lens system.

[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 an aberration diagram at a wide angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention;

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

[Explanation of symbols]

 LF front group LR rear group L11 11th group L12 12th group L21 21st group L22 22nd group L23 23rd group SP Aperture stop FP Flare stop d d line gg line S. C Sine condition ΔS Sagittal image plane ΔM Meridional image plane

Claims (3)

(57) [Claims] 1. a front group having a negative refractive power, in order from the object side;
Positive lens LP1, negative lens LN2 and positive lens LP3
Including a cemented lens in which the three lenses are cemented, a 21st lens group having a positive refractive power, a 22nd lens group having a negative refractive power, and a 23rd lens group having a positive refractive power. A rear group, and at the time of zooming from the wide-angle end to the telephoto end, the distance between the front group and the 21st group decreases, the distance between the 21st group and the 22nd group increases, and the 22nd group. And the distance between the 23rd group and the zoom lens is reduced, wherein the first lens surface on the object side of the cemented lens has a convex surface facing the object side, and the first and the first lenses of the cemented lens are arranged in order from the object side. The radii of curvature of the second, third, and fourth lens surfaces are Ra1, Ra2, Ra3, and Ra4, respectively.
The refractive power of the lens surface is positive, the refractive power of the third lens surface is negative,
Assuming that the refractive power of the fourth lens surface is positive, -0.5 <Ra1 / Ra2 <0.8 0.07 <Ra3 / Ra1 <0.8 -0.3 <Ra3 / Ra4 <0.3 A zoom lens that satisfies the conditions. 2. The Abbe number of the material of the positive lens LP1 is ν _P1 , the refractive index and Abbe number of the material of the negative lens LN2 are N _N2 and ν _N2 , respectively, and the refractive index of the material of the positive lens LP3 is N _P3. when _{a, 0.1 <N N2 -N P3 1} / ν P1 -1 / ν N2 < zoom lens according to claim 1, characterized by satisfying the -0.012 following condition. 3. The focal length of the second lens unit is f2i, and the F number and focal length of the entire system at the telephoto end are FNO.
Assuming that T and fT, 1.1 <f21 · FNOT / fT <2.3 0.3 <| f22 | / fT <0.8 0.4 <f23 / fT <1.1 The zoom lens according to claim 1, wherein: