JP3380009B2 - Zoom lens system - 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 system suitable for a compact camera having a small back focus restriction, and in particular, it is compact as a whole and can achieve a high zoom ratio of about 3 times. Regarding the zoom lens system.

[0002]

2. Description of the Related Art A zoom lens system for a compact camera, which has a zoom ratio of about 3 times, has conventionally been positive, positive, negative, or negative.
A positive and negative three-group configuration is known.

However, in these zoom lens systems, the total lens length on the long focus side (distance from the first surface to the image plane)
However, if the total length is large or the total length is small, the back focus is small and the lens diameter of the third lens group is large, so that it is not possible to sufficiently meet the demand for compactness.

Further, there is a problem that if the conventional zoom lens system is used to reduce the total lens length, the positive distortion tends to increase.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to reduce the overall lens length and diameter of the lens to make the entire lens compact and to favorably correct aberrations. The purpose is to provide the system.

[0006]

In order to achieve the above object, a zoom lens system according to the present invention comprises, in order from the object side, a positive first lens group, a positive second lens group, and a negative lens group. A second lens group, which is configured by arranging a third lens group
Is a negative 2a lens group and a positive 2b lens group in order from the object side.
A second lens group and a second lens group
Each group includes at least negative and positive cemented lenses.
Rarely and satisfying the following conditions, the third lens group includes a positive lens having a double-sided aspherical surface with a convex surface facing the image side, which is provided closest to the object side, and at least 1 having a concave surface facing the object side.
A negative lens, and when moving from the short focal length side to the long focal length side, all of the first, second, and third lens groups are moved to the object side, and the following conditions are satisfied: Is characterized by.

(A) 0 <ΔX3G1 / fs (b) −0.75 <ΔX3G2 / ΔX3G1 <0 (c) −1.5 <r3G2 / fs <−0.5 (g) 0.9 < fs / f2G <1.4 (h) 40 <ν2GaN (i) ν2GbN <40 , where ΔX3G1: the object side of the third lens group, the aspheric amount of the object side surface of the positive lens, ΔX3G2: the object of the third lens group Aspherical amount on the image side of the positive side lens, r3G2: paraxial radius of curvature of the image side aspherical surface of the object side positive lens of the third lens group, fs: focal length of the entire system on the short focus side , f2G: second lens Focal length of group, ν2GaN: Negative of cemented lens in negative 2a lens group
Abbe number of lens, ν2GbN: negative of cemented lens in positive 2b lens group
The Abbe number of the lens.

[0008]

Embodiments of the present invention will be described below. For example, as shown in FIG. 1, the zoom lens system according to the example is a positive first lens group composed of two lenses represented by surfaces r1 to r4 in order from the object side on the left side of the drawing. And a positive second lens group composed of two cemented lenses represented by the r5 surface to the r12 surface and one positive lens, and a double-sided aspherical positive lens represented by the r13 surface to the r16 surface. And a negative third lens group including a negative lens.

By adopting a positive, positive, and negative three-group structure which is advantageous for compactness, the total lens length on the long focus side and the third
It is possible to obtain a zoom ratio of about 3 times while keeping the lens system of the lens group small. Further, by making the object-side positive lens of the third lens group aspheric on both sides, it is possible to correct distortion.

The above conditions (a) and (b) define the aspherical shape of the object-side positive lens of the third lens group. By setting the amount of aspherical surface on the object side surface to be positive and the amount of aspherical surface on the image side surface to be negative, the power is set to gradually increase toward the lens periphery on both surfaces, and the distortion correction effect is shared by both surfaces. . This makes it easy to correct other aberrations in a well-balanced manner, which is more advantageous in making the entire system compact. When the value goes below the lower limit of the condition (b), the aspherical amount of the image side surface having a small radius of curvature becomes excessively large, and aberration fluctuations due to manufacturing errors or the like increase.

The condition (c) defines the paraxial radius of curvature of the image-side aspherical surface of the object-side positive lens of the third lens group. If the upper limit of this condition is exceeded, the radius of curvature of the image-side convex surface will be too small, and higher-order aberrations will occur, and aberration fluctuations due to errors in the aspherical shape will increase. When the value is below the lower limit, the positive power in the negative third lens group becomes small, it becomes difficult to correct the aberration in the third lens group, and the fluctuation of the aberration due to zooming increases.

The zoom lens system of the embodiment further satisfies the following conditions.

(D) 0.1 <ΔV3G1 <0.5 (e) 0.0 <ΔV3G2 <0.3 where ΔV3G1 and ΔV3G are the focal lengths of the entire system on the short focal side, respectively. 3 by the object-side aspherical surface of the object-side positive lens and the image-side aspherical surface of the third lens group when converted to 0.0
It is the amount of change in the distortion aberration coefficient of the secondary aberration coefficient.

The conditions (d) and (e) more specifically define the aspherical shape of the object-side positive lens of the third lens group. If the lower limit of each condition is not satisfied, the distortion is insufficiently corrected, and if the upper limit is exceeded, it is advantageous to correct the distortion, but it is difficult to correct other aberrations such as spherical aberration.
Since the image-side aspherical surface has a smaller radius of curvature and has a larger effect on aberrations, it is easier to manufacture if the aspherical surface amount is smaller than the object-side aspherical surface, and aberration fluctuations due to manufacturing errors can be suppressed. .

Now, the relationship between the aspherical shape and the aberration coefficient will be described. The aspherical surface has a distance x from the tangent plane of the aspherical vertex of the coordinate point on the aspherical surface whose height from the optical axis is y, a curvature (1 / r) of the aspherical vertex c, and a conic coefficient K. Four
Next, sixth and eighth aspherical coefficients are represented by the following formula (1), where A4, A6 and A8 are used.

X = (cy ² / (1 + √ (1- (1 + K) c ² y ² ))) + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ (1)

The relationship between the aspherical surface coefficient and the aberration coefficient represented by each conditional expression will be described below. In order to convert the conical coefficient K of the expression (1) representing the aspherical surface into 0, the aspherical surface coefficient B is expressed by the following expressions (2) to (5).
Replace with 4, B6, B8, B10. When Expression (1) is expressed using these coefficients, Expression (6) is obtained.

B4 = A4 + (1/8) Kc ³ (2) B6 = A6 + (1/16) (K ² + 2K) C ⁵ (3) B8 = A8 + (5/128) (K ³ + 3K ^{2 + 3K) c 7 ... (4} ) B10 = A10 + (7/256) (K 4 + 4K 3 + 6K 2 + 4K) c 9 ... (5) x = (cy 2 / (1 + √ (1-c 2 y 2)) ) + B4y ⁴ + B6y ⁶ + B8y ⁸ + B10y ¹⁰ (6)

Further, in order to normalize the focal length to 1.0, x, y, and c are respectively expressed by the following equation (7) by X,
In Y and C, B4, B6, B8 and B10 are expressed by α4,
Substituting α6, α8, and α10, the above equation (6) becomes equation (9).

X = x / f, Y = y / f, C = fc (7) α4 = f ³ B4, α6 = f ⁵ B6, α8 = f ⁷ B8, α10 = f ⁹ B10 (8) X ^{= (CY 2 / (1 +} √ (1-C 2 Y 2))) + α4Y 4 + α6Y 6 + α8Y 8 + α10Y 10 ... (9)

In the equation (9), the second and subsequent terms on the right side define the aspherical amount of the aspherical surface. The relationship between the coefficient α4 and the third-order aberration coefficient Φ of the aspherical surface is described by the following equation (10), where N is the refractive index of the medium before the aspherical surface and N ′ is the refractive index of the medium after the aspherical surface.

Φ = 8 (N'-N) α4 (10)

The third-order aspherical surface coefficient Φ takes a value as shown in the following equations (11) to (15) according to the type of third-order aberration.

ΔI = h ⁴ Φ (11) ΔII = h ³ h′Φ (12) ΔIII = h ² h ′ ² Φ (13) ΔIV = h ² h ′ ² Φ (14) ΔV = hh ′ ³ Φ… (15)

Where I is the spherical aberration coefficient, II is the coma aberration coefficient, III is the astigmatism coefficient, IV is the field curvature coefficient in the sagittal plane, V is the distortion aberration coefficient, and h is the axial paraxial axis. The height at which a light ray passes through each lens surface, and h'denotes the height at which an off-axis paraxial ray passing through the pupil center passes through each lens surface.

Further, in the embodiment, the object side positive lens of the third lens group is a plastic lens, which satisfies the following conditions.

(F) 0.3 <fs / f3GP <0.8 where f3GP is the focal length of the plastic lens.

The condition (f) defines the power of the object-side positive lens of the third lens group. Since this lens has aspherical surfaces on both sides, it is possible to correct aberration fluctuations in the third lens group without increasing the power, and suppress changes in power due to changes in temperature, humidity, etc. even if a plastic lens is used. be able to. When the value exceeds the upper limit, the power of the plastic lens becomes excessively large, the power changes largely due to changes in temperature, humidity and the like, and the aberration fluctuates, which is not preferable. Below the lower limit, the positive power becomes too small,
Aberrations in the third lens group having negative power as a whole cannot be corrected.

In order to increase the power while suppressing the thickness of the second lens group, the second lens group is formed by arranging a negative second a lens group and a positive second b lens group in order from the object side. However, it is desirable that each of the second-a lens group and the second-b lens group includes at least a negative and a positive cemented lens, and that the following conditions are satisfied.

(G) 0.9 <fs / f2G <1.4 (h) 40 <ν2GaN (i) ν2GbN <40 where f2G is the focal length of the second lens group, and ν2GaN is the negative second a lens group. Abbe number of the negative lens of the cemented lens of ν2GbN: Abbe number of the negative lens of the cemented lens in the positive 2b-th lens group.

The condition (g) defines the power of the second lens group. When the value exceeds the upper limit, the aberration variation due to zooming increases, and when it falls below the lower limit, the entire lens system becomes large.

The conditions (h) and (i) define the dispersion of the negative lens of the cemented lens in the second lens group. By satisfying these conditions, it is possible to increase the power while suppressing the thickness of the second lens group.

Further, the lens of the example has the following conditions.
The aspherical surface that satisfies the condition (k) and satisfies the condition (k) is the second b.
At least one surface is provided in the lens group.

(J) 0.2 <Σd2G / fs <0.4 (k) −35 <ΔI2Gb <−5 where Σd2G is the sum of the surface distances of the second lens group, and ΔI2Gb is the inside of the 2bth lens group. Is the amount of change in the spherical aberration coefficient of the third-order aberration coefficient due to the aspherical surface.

The condition (j) directly defines the sum of the surface distances of the second lens group. When the upper limit is exceeded, the size becomes large, and when the lower limit is exceeded, it is difficult to secure the edge thickness.

The condition (k) defines the aspherical shape of the 2b-th lens group. By providing a divergent aspherical surface satisfying this condition in the second b lens group close to the diaphragm, it is possible to correct spherical aberration generated by increasing the power while reducing the thickness of the second lens group. . If the upper limit is exceeded, the effect of aberration correction by the aspherical surface will be small, and if the lower limit is exceeded, overcorrection will occur.

If the first lens group and the third lens group are moved integrally as in the second, third and fourth embodiments,
This is advantageous because the mechanism is simplified.

[0038]

Example 1 FIG. 1 shows a lens configuration of a zoom lens system according to Example 1. Specific numerical configurations are shown in Tables 1 and 2. In the table, f is the focal length, f
B is back focus, FNO. Is F number, ω is half angle of view,
r is the radius of curvature, d is the lens thickness or air space, and n is d-
Refractive index at line (588 nm), ν is Abbe number. In addition,
The 12th, 13th and 14th surfaces in the lens are aspherical surfaces, and their aspherical coefficients are shown in Table 3.

2, 3, and 4 show spherical aberration SA at wide-angle end, intermediate focal length, and telephoto end, sine condition SC, and
The chromatic aberration, the chromatic aberration of magnification, the astigmatism (S: sagittal, M: meridional), and the distortion aberration indicated by the spherical aberration at d line, g line, and C line are shown.

[0040]

[Table 1] Aperture position 0.90 mm from the 12th surface to the image side

[0041]

[Table 2] f 39.30 60.00 111.00 fB 11.17 25.07 57.52 FNo. 1: 4 1: 6 1: 9 ω 28.3 ° 19.2 ° 10.8 ° d4 3.14 8.60 14.88 d12 13.84 8.36 2.58

[0042]

[Table 3] 12th surface 13th surface 14th surface K = 0.000000 K = -0.100000 × 10 K = 0.000000 A4 = 0.630085 × 10 ^-4 A4 = 0.539342 × 10 ^-4 A4 = -0.151596 × 10 ^-4 A6 =- 0.516754 × 10 ^-7 A6 = 0.991590 × 10 ^-7 A6 = -0.138459 × 10 ^-6 A8 = 0.105593 × 10 ^-8 A8 = -0.142415 × 10 ^-8 A8 = 0.000000 A10 = 0.000000 A10 = 0.346817 × 10 ^-10 A10 = 0.000000

[0043]

Second Embodiment FIG. 5 shows a second embodiment of the present invention. Specific numerical configurations are shown in Tables 4 and 5. FIGS. 6, 7, and 8 show various aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively, according to this configuration.

In this example, the 12th, 13th and 14th surfaces are aspherical surfaces, and the aspherical surface coefficients thereof are shown in Table 6.

[0045]

[Table 4] Aperture position 0.90 mm from the 12th surface to the image side

[0046]

[Table 5] f 39.30 60.00 111.00 fB 11.00 24.86 57.03 FNo. 1: 4 1: 6 1: 9 ω 28.2 ° 19.2 ° 10.8 ° d4 3.19 9.18 16.15 d12 13.84 8.36 2.58

[0047]

[Table 6] 12th surface 13th surface 14th surface K = 0.000000 K = -0.100000 × 10 K = 0.000000 A4 = 0.630085 × 10 ^-4 A4 = 0.599608 × 10 ^-4 A4 = -0.150353 × 10 ^-4 A6 =- 0.516754 × 10 ^-7 A6 = -0.1515 41 × 10 ^-6 A6 = -0.353870 × 10 ^-6 A8 = 0.105593 × 10 ^-8 A8 = 0.434336 × 10 ^-8 A8 = 0.253505 × 10 ^-8 A10 = 0.000000 A10 = 0.151904 × 10 ^-10 A10 = 0.000000

[0048]

Third Embodiment FIG. 9 shows a third embodiment of the present invention. Specific numerical configurations are shown in Tables 7 and 8. 10, 11, and 12 show various aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively, according to this configuration.

In this example, the 12th, 13th and 14th surfaces are aspherical surfaces, and the aspherical surface coefficients thereof are shown in Table 9.

[0050]

[Table 7] Aperture position 0.90 mm from the 12th surface to the image side

[0051]

[Table 8] f 39.30 65.00 111.00 fB 10.91 28.15 58.15 FNo. 1: 4 1: 6 1: 9 ω 28.2 ° 17.9 ° 10.9 ° d4 3.19 9.67 14.51 d12 13.91 7.44 2.59

[0052]

[Table 9] 12th surface 13th surface 14th surface K = 0.000000 K = -0.100000 × 10 K = 0.000000 A4 = 0.630085 × 10 ^-4 A4 = 0.476345 × 10 ^-4 A4 = -0.239783 × 10 ^-4 A6 =- 0.516754 × 10 ^-7 A6 = 0.365195 × 10 ^-6 A6 = 0.129833 × 10 ^-6 A8 = 0.105593 × 10 ^-8 A8 = -0.453219 × 10 ^-8 A8 = -0.265741 × 10 ^-8 A10 = 0.000000 A10 = 0.432496 × 10 ^-10 A10 = 0.000000

[0053]

[Fourth Embodiment] FIG. 13 shows a fourth embodiment of the present invention. Specific numerical configurations are shown in Tables 10 and 11. Figure 1
4, FIG. 15, and FIG. 16 show various aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively, according to this configuration.

In this example, the 12th, 13th and 14th surfaces are aspherical surfaces, and their aspherical surface coefficients are shown in Table 12.

[0055]

[Table 10] Aperture position 0.90 mm from the 12th surface to the image side

[0056]

[Table 11] f 39.30 65.00 111.00 fB 10.61 27.97 58.17 FNo. 1: 4 1: 6 1: 9 ω 28.3 ° 17.9 ° 10.9 ° d4 3.08 9.70 14.66 d12 14.31 7.69 2.74

[0057]

[Table 12] 12th surface 13th surface 14th surface K = 0.000000 K = -0.100000 × 10 K = 0.000000 A4 = 0.630085 × 10 ^-4 A4 = 0.560058 × 10 ^-4 A4 = -0.212586 × 10 ^-4 A6 =- 0.516754 x 10 ^-7 A6 = 0.159977 x 10 ^-6 A6 = 0.963554 x 10 ^-7 A8 = 0.105593 x 10 ^-8 A8 = -0.350420 x 10 ^-8 A8 = -0.824290 x 10 ^-8 A10 = 0.000000 A10 = 0.830418 x 10 ^-10 A10 = 0.754321 × 10 ^-10

Table 13 below shows the correspondence between the above-mentioned conditional expressions and the embodiments.

[0059]                         Example 1 Example 2 Example 3 Example 4 (a) △ X3G1 / fs 0.0075 0.0078 0.0067 0.0075 (b) △ X3G2 / ∆X3G1 -0.41 -0.43 -0.50 -0.46 (c) r3G2 / fs -0.82 -0.66 -0.61 -0.72 (d) △ V3G1 0.27 0.31 0.25 0.32 (e) △ V3G2 0.10 0.10 0.17 0.16 (f) fs / f3GP 0.62 0.67 0.65 0.68 (g) fs / f2G 1.13 1.14 1.11 1.09 (h) ν2GaN 44.2 47.9 47.9 43.7 (i) ν2GbN 36.3 30.1 31.1 30.1 (j) Σd2G / fs 0.30 0.29 0.29 0.29 (k) △ I2Gb -22.1 -20.3 -20.5 -19.9

[0060]

As described above, according to the present invention, the total lens length can be suppressed to about 0.9 times the focal length, and the back focus on the short focus side is 10 mm.
By ensuring the above, the lens diameter of the third lens group can be suppressed to be small, the overall size of the lens can be reduced, and a zoom lens system in which aberrations are well corrected can be provided.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a zoom lens system according to a first example.

FIG. 2 is a diagram of various types of aberration at the short focal length extremity of the lens of Example 1;

FIG. 3 is a diagram of various types of aberration at the intermediate focal length of the lens of Example 1.

FIG. 4 is a diagram of various types of aberration at the long focal length extremity of the lens of Example 1;

FIG. 5 is a lens configuration diagram of a zoom lens system according to a second example.

FIG. 6 is a diagram of various types of aberration at the short focal length extremity of the lens of Example 2;

FIG. 7 is a diagram of various types of aberration at the intermediate focal length of the lens of Example 2;

FIG. 8 is a diagram of various types of aberration at the long focal length extremity of the lens of Example 2;

FIG. 9 is a lens configuration diagram of a zoom lens system according to a third example.

FIG. 10 is a diagram of various types of aberration at the short focal length extremity of the lens of Example 3;

FIG. 11 is a diagram of various types of aberration at the intermediate focal length of the lens of Example 3;

FIG. 12 is a diagram of various types of aberration at the long focal length extremity of the lens of Example 3;

FIG. 13 is a lens configuration diagram of a zoom lens system according to a fourth example.

FIG. 14 is a diagram of various types of aberration at the short focal length extremity of the lens of Example 4;

FIG. 15 is a diagram of various types of aberration at the intermediate focal length of the lens of Example 4;

FIG. 16 is a diagram of various types of aberration at the long focal length extremity of the lens of Example 4;

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-113539 (JP, A) JP-A-5-88085 (JP, A) JP-A-5-72476 (JP, A) JP-A-4- 78814 (JP, A) JP-A 2-103014 (JP, A) JP-A 2-10307 (JP, A) JP-A 6-67093 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (2)

(57) [Claims] 1. A positive first lens group, a positive second lens group, and a negative third lens group are arranged in order from the object side, and the second lens group is arranged from the object side. Negative second a in order
It consists of a lens group and a positive 2b lens group.
Lens group and the 2b-th lens group, at least negative and positive, respectively.
Includes a cemented lens and meets the following conditions
And, the third lens group has a two-sided aspheric positive lens having a convex surface directed toward the image side that is provided closest to the object side, and at least one negative lens with its concave surface facing the object side, a short At the time of zooming from the focal length side to the long focal length side, the first, second,
A zoom lens system characterized in that all of the third lens group is moved to the object side and the following conditions are satisfied. (a) 0 <ΔX3G1 / fs (b) −0.75 <ΔX3G2 / ΔX3G1 <0 (c) −1.5 <r3G2 / fs <−0.5 (g) 0.9 <fs / f2G <1.4 (h) 40 <ν2GaN (i) ν2GbN <40 However, ΔX3G1: the aspherical amount of the object side surface of the object side positive lens of the third lens group, ΔX3G2: the object side positive lens of the third lens group Amount of aspherical surface on the image side, r3G2: paraxial radius of curvature of the image side aspherical surface of the object side positive lens of the third lens group, fs: focal length of the entire system on the short focal side , f2G: focus of the second lens group Distance, ν2GaN: Negative of cemented lens in negative 2a lens group
Abbe number of lens, ν2GbN: negative of cemented lens in positive 2b lens group
The Abbe number of the lens. 2. The zoom lens system according to claim 1, wherein the object-side positive lens of the third lens group is a plastic lens and satisfies the following condition. (f) 0.3 <fs / f3GP <0.8 where f3GP is the focal length of the plastic lens.