JPH1039212A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small zoom lens composed of two lens groups, having high optical performance over all variable power ranges and variable power ratio of about 2.7, and having a short total length of the lens and a wide viewing angle. SOLUTION: In the zoom lens comprising, in order from the object side, two lens groups of a first group L1 having positive refractive power and a second group L2 having negative refractive power and performing power variation by changing the interval between both lens groups, the second group L2 has a 21st positive lens and a 22nd negative lens, the lens surface of the 21st lens on the object side is composed of an aspherical surface and the refractive index Pn and the Abbe number Pν of the material of the 21st lens are set as 1.65<Pn, 38<Pν.

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, and more particularly, to properly correcting aberrations by appropriately setting the lens configuration of each lens group. The present invention relates to a zoom lens having a wide angle of view of about 74 degrees at a wide angle end and a zoom ratio of about 2.7, in which the overall length of the lens (the distance from the first lens surface to the image plane) is shortened. is there.

[0002]

2. Description of the Related Art Recently, with the downsizing of lens shutter cameras, video cameras, and the like, a small zoom lens having a short overall 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 similar to that of 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 group having a positive refractive power and a second group having a negative refractive power, are sequentially arranged from the object side. A small so-called two-unit zoom lens that changes magnification by changing the interval has been proposed.

In this publication, a two-unit zoom lens having high optical performance which employs positive and negative refractive power arrangements in order from the object side to make the back focus relatively short and to shorten the overall length of the lens. Have achieved.

In addition, Japanese Patent Application Laid-Open Nos. Sho 62-284319, 62-256915, and 64-5
In Japanese Patent Application Laid-Open No. 2111 and Japanese Patent Application Laid-Open No. 1-193807, the first lens unit has a positive refractive power and the second lens unit has a negative refractive power. A two-unit zoom lens that is moved and zoomed is disclosed.

In addition, JP-A-2-50118, JP-A-2-71220, JP-A-2-19082, JP-A-4-145408 and the like disclose a first group having a positive refractive power and a negative group having a negative refractive power. A two-unit zoom lens having a relatively high zoom ratio, which includes a second lens unit having a refractive power and changes the magnification by changing the distance between both lens units, is disclosed.

[0007]

In the above-described two-unit zoom lens system including the first lens unit having the positive refractive power and the second lens unit having the negative refractive power, the distortion on the wide-angle side is favorably corrected. The overall size of the lens system is reduced while securing a predetermined amount of light around the screen. The wide-angle shooting angle of view at the wide-angle end is about 74 degrees, and the zoom ratio is about 2.7 times. However, in order to obtain good optical performance over the entire zoom range, it is necessary to appropriately set the lens configuration of each lens group.

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

The present invention provides a so-called two-unit zoom lens, in which the first lens unit having a positive refracting power and / or the second lens unit having a negative refracting power is appropriately set, so that distortion on the wide-angle side is achieved. Satisfactorily corrected, and the amount of light at the periphery of the screen was secured in a predetermined amount while aberration fluctuations caused by zooming were corrected satisfactorily. At a zoom ratio of about 2.7, the shooting angle of view at the wide-angle end was about 74 degrees. It is an object of the present invention to provide a zoom lens having a wide angle of view and high optical performance over the entire zoom range where the entire length of the lens is short.

[0010]

The present invention is roughly divided into two inventions, a first invention and a second invention (hereinafter referred to as a first invention).
The invention and the second invention are referred to as "the present invention". ).

The zoom lens according to the first aspect of the present invention includes (1-
1) A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between both lens groups. The second group includes a positive twenty-first lens and a negative twenty-second lens, and the object-side lens surface of the twenty-first lens is formed of an aspheric surface. The refractive index and Abbe number of the material of the twenty-first lens are Pn, When Pν is satisfied, the following condition is satisfied: 1.65 <Pn (1) 38 <Pν (2)

The zoom lens according to the second aspect of the present invention includes (1-
2) A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between both lens groups. In the first group, the eleventh group and the twelfth lens having a positive refractive power are separated by the widest air gap.
The second lens unit includes two negative lens units. The eleventh lens unit includes a negative 111th lens having an aspheric surface on the image side, a positive 112th lens having a convex surface on the image side, and a concave surface on the object side. A negative 113th lens in a meniscus shape, and the twelfth group has a positive first lens.
R4, the radius of curvature of the lens surface on the image side of the 112th lens is R4, the radius of curvature of the lens surface on the object side of the 113th lens is R5, and the connection between the wide-angle end and the telephoto end of the second lens unit. When the image magnifications are β2w and β2T, respectively, 1 ≦ R4 / R5 <1.5 (3) 2.2 <β2T / β2w <3.5 (3) (4) It is characterized by satisfying the following conditions.

[0013]

1 to 3 are lens sectional views of Numerical Examples 1 to 3 of the present invention. In the lens sectional views, (A) shows the zoom position at the wide angle end, (B) shows the middle position, and (C) shows the zoom position at the telephoto end.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, and both lens groups are moved toward the object side as indicated by arrows while decreasing the distance between the two lens groups. Moving the zoom from the wide-angle end to the telephoto end. SP denotes an aperture, which is moved integrally with the first lens unit in the present invention.

The first lens unit includes two lens units, an eleventh lens unit L11 having a positive or negative refractive power and a twelfth lens unit having a positive refractive power, with the widest air gap as a boundary. The first invention and the second invention are based on the above configuration.

First, the features of the first invention will be described.
The first invention is based on the above basic constitution, wherein the second group is a positive second
It has one lens and a negative twenty-second lens, and the object-side lens surface of the twenty-first lens is made of an aspheric surface. When the refractive index and Abbe number of the material of the twenty-first lens are Pn and Pν, respectively,
Conditional expressions (1) and (2) are satisfied.

In the first invention, in order to favorably correct aberration fluctuations such as coma and distortion upon zooming, the first lens unit is positively connected to the eleventh lens unit over the widest air gap. Refractive power first
The second lens unit includes two lens units, a negative eleventh lens unit having an aspheric surface on the image surface side, a positive lens unit 112 having a convex surface facing the image surface side, and a concave lens unit on the object side. The lens unit has a negative 113th lens in a meniscus shape, the twelfth lens unit includes a positive 121th lens, a radius of curvature of a lens surface on an image plane side of the 112th lens is R4, and an object of the 113th lens is When the radius of curvature of the lens surface on the side is R5, and the imaging magnifications of the second group at the wide-angle end and the telephoto end are β2w and β2T, respectively, conditional expressions (3) and (4) are satisfied.

In the first invention, the focal length of the second lens unit is set to f2, and the wide-angle end of the entire system and the telephoto lens are set in order to satisfactorily correct aberration fluctuations during zooming while shortening the overall length of the lens. The focal lengths at the ends are respectively fw and fT, and the diagonal length of the effective angle of view is Y
0.23 <f2 / fT <0.3 (5) 0.55 <fw / Y <0.75 (6) I have to.

On the other hand, the second invention is based on the basic constitution,
The group has two lens groups, an eleventh lens group and a twelfth lens group having a positive refractive power, at the boundary of the widest air gap. The eleventh lens group is a negative 111th lens having an aspheric surface on the image surface side. A positive 112th lens with a convex surface facing the image surface side, a meniscus negative 113th lens with a concave surface facing the object side, and the twelfth group is composed of a positive 121st lens. The radius of curvature of the lens surface on the image plane side of the lens is R4, the radius of curvature of the lens surface on the object side of the 113th lens is R5, and the imaging magnifications of the second group at the wide-angle end and the telephoto end are β2w and β2T, respectively. In this case, conditional expressions (3) and (4) are satisfied.

In the second invention, the focal length of the second lens unit is set to f2, the wide-angle end of the entire system and the telephoto end, in order to satisfactorily correct aberration fluctuations during zooming while reducing the overall length of the lens. The focal lengths at the ends are respectively fw and fT, and the diagonal length of the effective angle of view is Y
0.23 <f2 / fT <0.3 (5) 0.55 <fw / Y <0.75 (6) I have to.

Since the technical meanings of the conditional expressions (1) to (6) for the first invention and the second invention are the same, the technical meanings will be described collectively.

Conditional expressions (1) and (2) satisfy the positive second
This is for appropriately setting the refractive index and Abbe number of the material of one lens to favorably correct mainly the chromatic aberration of magnification on the wide-angle side and the coma around the screen. If conditional expression (1) is not satisfied, it becomes difficult to satisfactorily correct the coma around the screen on the wide-angle side. If the material of the 21st lens becomes highly dispersed out of the conditional expression (2), it becomes difficult to correct lateral chromatic aberration on the wide-angle side.

Conditional expression (3) mainly sets an appropriate ratio between the radii of curvature R4 and R5 of the lens surface on the image side of the 112th lens and the lens surface on the object side of the 113th lens in the first lens unit. This is for favorably correcting coma and distortion on the wide-angle side. Exceeding the upper limit of conditional expression (3), the radius of curvature R5
Is too strong compared to the radius of curvature R4, it becomes difficult to correct coma on the wide-angle side. The radius of curvature R exceeds the lower limit.
If 5 is too weak compared to the radius of curvature R4, it will be difficult to secure a predetermined amount of light at the periphery of the screen, because the lens will have a distortion on the wide-angle side.

Conditional expression (4) sets the ratio of the imaging magnification of the second lens unit at the wide-angle end and the telephoto end appropriately, and satisfactorily corrects various aberrations while mainly maintaining a predetermined zoom ratio. It is for doing.
If the imaging magnification at the telephoto end becomes larger than the imaging magnification at the wide-angle end beyond the upper limit value of the conditional expression (4), fluctuations of various aberrations accompanying zooming become large, and this can be corrected well. Becomes more difficult. If the imaging magnification at the telephoto end is smaller than the imaging magnification at the wide-angle end beyond the lower limit, it becomes difficult to secure a predetermined zoom ratio.

Condition (5) relates to the ratio between the focal length of the second lens unit and the focal length of the entire system at the telephoto end.
This is for obtaining a predetermined back focus while reducing the size of the camera. If the refractive power of the second lens unit becomes weaker beyond the upper limit of conditional expression (5), it becomes difficult to obtain a predetermined amount of back focus at the wide-angle end, and the rear lens diameter increases, which is not good. . If the refractive power of the second lens unit becomes too strong beyond the lower limit, the fluctuation of aberrations accompanying zooming becomes large, and it becomes difficult to satisfactorily correct this.

Conditional expression (6) is to appropriately set the ratio between the focal length at the wide-angle end and the diagonal length of the effective screen, and to facilitate aberration correction on the wide-angle side while mainly shortening the overall length of the lens. belongs to. If the diagonal length becomes shorter than the upper limit of conditional expression (6), the total lens length at the wide-angle end becomes longer. If the lower limit value is exceeded, it becomes difficult to satisfactorily correct various aberrations on the wide-angle side.

In the first and second aspects of the present invention, in order to further maintain good optical performance of the entire screen during zooming, the numerical limits of the conditional expressions (1) to (6) are preferably set as follows. .

1.66 <Pn... (1a) 40 <Pν... (2a) 1 ≦ R4 / R5 <1.3. (3a) 2.5 <β2T / β2w <3.0 (4a) 0.25 <f2 / fT <0.29 (5a) 0.6 <Fw / Y <0.7 (6a) In Numerical Example 1 of FIG. 1, the first lens unit includes a negative lens having both lens surfaces concave, a positive lens having both lens surfaces convex, It is composed of a meniscus negative lens with a concave surface facing the object side, and a positive lens in four groups.

In numerical embodiments 2 and 3 shown in FIGS. 2 and 3,
The first group comprises a negative lens having both concave lens surfaces, a cemented lens in which a positive lens having both convex lens surfaces and a meniscus-shaped negative lens having a concave surface facing the object side are joined, and a positive lens having four elements in three groups It consists of. In Numerical Examples 1 to 3 shown in FIGS. 1 to 3, the second lens unit includes a positive lens having an aspherical surface and a negative meniscus lens having a convex surface facing the image surface side.

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-described 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 A, B, C, D, and E are aspheric coefficients, respectively,

[0033]

(Equation 1) It is represented by the following equation. The display of "e-0X" means "10- ^X ". (Numerical Example 1) F = 28.95 to 78.00 FNO = 3.62 to 9.75 2ω = 73.5 ° to 31.0 ° R 1 = -23.54 D 1 = 1.50 N 1 = 1.72874 ν 1 = 49.2 R 2 = 145.49 D 2 = 0.28 R 3 = 65.99 D 3 = 5.48 N 2 = 1.51633 ν 2 = 64.2 R 4 = -13.37 D 4 = 0.24 R 5 = -11.02 D 5 = 1.00 N 3 = 1.84665 ν 3 = 23.8 R 6 = -13.51 D 6 = 0.54 R 7 = -109.76 D 7 = 2.80 N 4 = 1.48749 ν 4 = 70.2 R 8 = -11.25 D 8 = 0.50 R 9 = Aperture D 9 = Variable R10 = -75.20 D10 = 2.80 N 5 = 1.73077 ν 5 = 40.6 R11 = -41.06 D11 = 4.92 R12 = -10.17 D12 = 1.50 N 6 = 1.77249 ν 6 = 49.6 R13 = -41.89

[0034]

[Table 1] Aspheric coefficient 2 plane K = 3.940e-01 A = 0 B = 1.876e-04 C = 1.895e-06 D = -6.440e-09 E = 6.828e-10 10 plane K = 6.695e + 01 A = 0 B = 8.199e-05 C = 1.020e-06 D = -1.057e-08 E = 1.944e-10 11 side K = 0 A = 0 B = 6.831e-06 C = 6.229e-07 D = -1.408e -08 E = 1.871e-10 (Numerical Example 2) F = 28.95 to 78.00 FNO = 3.62 to 9.75 2ω = 73.5 ° to 31.0 ° R 1 = -26.00 D 1 = 1.50 N 1 = 1.72874 ν 1 = 49.2 R 2 = 251.52 D 2 = 0.37 R 3 = 173.85 D 3 = 4.80 N 2 = 1.57500 ν 2 = 41.5 R 4 = -8.80 D 4 = 1.84 N 3 = 1.84665 ν 3 = 23.8 R 5 = -14.27 D 5 = 1.62 R 6 = -71.33 D 6 = 2.78 N 4 = 1.48749 ν 4 = 70.2 R 7 = -12.13 D 7 = 0.50 R 8 = Aperture D 8 = Variable R 9 = -67.96 D 9 = 3.13 N 5 = 1.72874 ν 5 = 49.2 R10 = -32.96 D10 = 4.61 R11 = -10.41 D11 = 1.50 N 6 = 1.77249 ν 6 = 49.6 R12 = -55.09

[0035]

[Table 2] Aspherical surface 2nd surface K = -4.550e + 03 A = 0 B = 2.023e-04 C = 1.695e-07 D = 3.029e-08 E = -3.671e-11 9th surface K = 5.091e + 01 A = 0 B = 6.747e-05 C = 4.808e-07 D = -1.369e-09 E = 1.273e-10 10 K = 0 A = 0 B = -1.104e-05 C = 2.762e-07 D =- 1.019e-08 E = 1.538e-10 (Numerical Example 3) F = 28.95-78.00 FNO = 3.62-9.75 2ω = 73.5 ° -31.0 ° R 1 = -20.30 D 1 = 1.50 N 1 = 1.78600 ν 1 = 41.0 R 2 = -1084.93 D 2 = 0.31 R 3 = 164.15 D 3 = 4.60 N 2 = 1.57500 ν 2 = 41.5 R 4 = -10.18 D 4 = 0.87 N 3 = 1.84665 ν 3 = 23.8 R 5 = -14.58 D 5 = 1.82 R 6 = -145.17 D 6 = 2.78 N 4 = 1.48749 ν 4 = 70.2 R 7 = -11.66 D 7 = 0.70 R 8 = Aperture D 8 = Variable R 9 = -58.00 D 9 = 2.80 N 5 = 1.66532 ν 5 = 55.4 R10 = -35.88 D10 = 4.82 R11 = -10.01 D11 = 1.50 N 6 = 1.72915 ν 6 = 54.7 R12 = -44.34

[0036]

[Table 3] Aspherical surface 2nd surface K = -4.550e + 03 A = 0 B = 1.736e-04 C = 1.074e-06 D = 1.431e-08 E = 1.0321e-10 9th surface K = 3.947e + 01 A = 0 B = 9.469e-05 C = 9.227e-07 D = -1.975e-09 E = 1.524e-10 10 face K = 0 A = 0 B = 1.503e-06 C = 6.886e-07 D = -1.226e -08 E = 1.938e-10

[0037]

[Table 4]

[0038]

As described above, according to the present invention, in the so-called two-unit zoom lens, the lens units of the first unit having a positive refractive power and / or the second unit having a negative refractive power are appropriately set. As a result, the distortion on the wide-angle side is satisfactorily corrected, the light amount around the screen is secured in a predetermined amount, and the aberration fluctuation accompanying the zooming is corrected satisfactorily. It is possible to achieve a zoom lens having a wide angle of view of about 74 degrees and a high optical performance over the entire zoom range where the entire length of the lens is short.

[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 intermediate aberration diagram of the numerical example 1 of the present invention.

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

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

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

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

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

[Explanation of symbols]

 L1 1st lens group L11 11th lens group L12 12th lens group L2 2nd lens group SP Aperture IP image plane d d-line g g-line S Sagittal image plane M Meridional image plane

Claims (4)

[Claims] 1. A zoom lens having a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side, and performing zooming by changing the distance between both lens units. The second group has a positive twenty-first lens and a negative twenty-second lens, and the object-side lens surface of the twenty-first lens is made of an aspheric surface. The refractive index and Abbe number of the material of the twenty-first lens are Pn and P respectively
A zoom lens characterized by satisfying the following condition: 1.65 <Pn 38 <Pν. 2. The first lens unit includes two lens units, an eleventh lens unit and a twelfth lens unit having a positive refractive power, with the widest air gap as a boundary, and the eleventh lens unit has an aspheric surface on the image plane side. Negative 111th
A lens, a positive 112th lens having a convex surface facing the image surface side, and a meniscus-shaped negative 113th lens having a concave surface facing the object side; the twelfth group includes a positive 121st lens; The radius of curvature of the lens surface on the image plane side of the 112 lens is R4,
Let the radius of curvature of the object-side lens surface of the 113th lens be R
5. The imaging magnification of the second group at the wide-angle end and the telephoto end is β2
2. The zoom lens according to claim 1, wherein, when w and β2T, 1 ≦ R4 / R5 <1.5 2.2 <β2T / β2w <3.5. 3. A zoom lens which has two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performs zooming by changing the distance between both lens groups. The first group has two lens groups, an eleventh lens group and a twelfth lens group having a positive refractive power, with the widest air gap as a boundary, and the eleventh lens group has a negative surface having an aspheric surface on the image plane side. The twelfth group includes a positive 121st lens, a 111th lens, a positive 112th lens having a convex surface facing the image surface side, and a meniscus negative 113th lens having a concave surface facing the object side. The radius of curvature of the lens surface on the image plane side of the 112th lens is R4, the radius of curvature of the lens surface on the object side of the 113th lens is R5, and the imaging magnifications of the second group at the wide-angle end and the telephoto end are respectively When β2w and β2T are satisfied, the following condition is satisfied: 1 ≦ R4 / R5 <1.5 2.2 <β2T / β2w <3.5 Zoom lens characterized by. 4. When the focal length of the second group is f2, the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and fT, and the diagonal length of the effective angle of view is Y, 0.23 <f2 / 4. The zoom lens according to claim 1, wherein a condition of fT <0.3 0.55 <fw / Y <0.75 is satisfied.