JPH08304702A - Zoom lens - Google Patents

Abstract

PURPOSE: To provide an inexpensive and compact zoom lens having high performance. CONSTITUTION: This zoom lens is provided with a 1st lens group G1 having positive refractive power, a 2nd lens group G2 having negative refractive power, and a diaphragm S arranged between the 1st and the 2nd lens groups in order from an object side. The 1st lens group G1 is constituted of a negative plastic lens L1 which has gentle power and whose surface on the object side is aspherical, a negative lens L2 and a positive lens L3 from the object side. Then, the 2nd lens group G2 is constituted of a positive plastic lens L4 which has the gentle power and whose surface on the object side is aspherical and the positive lens L5 from the object side. Thus, the inexpensive zoom lens having the excellent performance is realized with five-lens constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens, and more particularly to a compact zoom lens having a short back focus suitable for a lens shutter camera, a video camera and the like.

[0002]

2. Description of the Related Art Compact and inexpensive ones have been developed for zoom lenses used in lens shutter cameras and the like. Among them, a first lens group having a positive refractive power and a second lens group having a negative refractive power are developed. A two-group zoom lens using lens groups is known as the simplest type zoom lens. For example, in Japanese Unexamined Patent Publication No. 4-161914, a first lens group is composed of four lenses, and
A zoom lens in which a second lens group is composed of a single lens is described. In a two-group zoom lens, it is desirable to use an aspherical surface in order to obtain good performance by correcting aberrations. In this conventional lens system, a lens having almost no power is first used.
To the second lens group and
The lens surfaces are aspherical. Therefore, the number of lenses forming each lens group increases, and it is difficult to reduce the cost and the size.

On the other hand, in the zoom lens disclosed in Japanese Patent Laid-Open No. 4-42114, the first lens group is composed of the minimum number of two lenses, and the second lens group is also composed of two lenses. Since it is configured, the entire system is a zoom lens including a minimum number of four lenses. However, for example, at least one lens of the first lens group has aspherical surfaces on both sides, and these aspherical lenses also require a certain amount of power for achromatization. Therefore, it takes a lot of time and money to process a lens having these aspherical surfaces, and it is difficult to reduce the cost of the entire zoom lens. Furthermore, these lenses can be manufactured using plastic lenses, but it is difficult to reduce the cost, and since it will be a plastic lens with a certain amount of power,
It is easily affected by temperature and humidity.

[0004]

In order to realize a compact zoom lens that can be supplied at low cost, it is of course necessary to reduce the number of lenses constituting the zoom lens. However, if the manufacturing cost of each lens increases due to the reduction in the number of lenses, the cost of the entire zoom lens cannot be reduced. Also, unless the refractive powers of the first and second lens groups are properly distributed, the amount of movement will be large and the zoom lens cannot be made compact, and the performance and compactness will depend on the ratio of the focal length and the thickness of each lens group. It will also affect the conversion.

Therefore, an object of the present invention is to provide a compact zoom lens which can be manufactured at low cost by balancing the refractive powers of the first and second lens groups. Further, it is an object of the present invention to find a configuration of each lens group that is in tune with performance, cost, miniaturization, and requirements, and to provide a zoom lens that can sufficiently meet each requirement.

[0006]

The zoom lens according to the present invention has a positive refracting power first from the object side toward the image side.
Lens group, a second lens group having a negative refractive power, and an aperture stop arranged between the first and second lens groups, and changing the air gap between the first and second lens groups. In the zoom lens that performs zooming by performing the above, the first lens group includes, in order from the object side, a first lens and a second lens having a negative refractive power, and a third lens having a positive refractive power. The second lens group includes, in order from the object side, a fourth lens having a positive refractive power and a fifth lens having a negative refractive power. Then, the lenses forming the first and second lens groups are selected within a range satisfying the following conditions.

0.05 <f _F / | f ₁ | <0.15 (1) 0.35 <| f _R | / f ₄ <0.65 (2) 0.9 <| f _R | / f _F <1.3 (3) 0.4 <D _F / f _F <0.5 (4) 0.25 <D _R / | f _R | <0.35 (5) where f ₁ is the focal length of the first lens, f ₄ is the focal length of the fourth lens, f _F is the combined focal length of the first lens group,
f _R is the combined focal length of the second lens group.

D _F is the thickness from the most object side lens surface to the most image side lens surface of the first lens group,
It corresponds to the distance from the object-side lens surface of the first lens to the image-side lens surface of the third lens. D _R is the thickness from the most object side lens surface of the second lens group to the most image side lens surface, and from the object side lens surface of the fourth lens to the image side lens surface of the fifth lens. Equivalent to distance.

[0009]

In the zoom lens of the present invention, as described above, the first lens group is composed of three lenses, and the second lens group is composed of two lenses. Therefore, the whole system is 5
It is a zoom lens with a simple structure that can be composed of one lens. The lenses forming the first and second lens groups are selected so as to satisfy the conditions of the expressions (1) to (5).

First, the expressions (1) and (2) relate to the focal lengths of the first lens and the fourth lens.
This is a condition in which the powers of the first lens and the fourth lens with respect to the respective powers of the lens group and the second lens group can be appropriately adjusted. By setting the values to be equal to or lower than the upper limits of the expressions (1) and (2), the ratio of the power of the first and fourth lenses to the power of each lens group becomes small, and plastic lenses are used for the first and fourth lenses. However, high performance can be maintained. That is, since the plastic lens has a large temperature dependency of the refractive index, the fluctuations of the focal position and the field curvature become large when the temperature changes. However, by setting it to the upper limit value or less of the equations (1) and (2), Since the power ratio of the fourth lens is reduced, deterioration of performance due to temperature fluctuation can be prevented even if a plastic lens is used. Further, since the first lens has a negative refracting power and the fourth lens has a positive refracting power, changes in the focal position and the like due to temperature fluctuations are canceled to some extent. On the other hand, when the values are equal to or lower than the lower limits of the expressions (1) and (2), the powers of the first and fourth lenses become too small, and in order to make the principal point positions of the first and second lens groups the same, It is necessary to increase the distance between the lenses, which is against the miniaturization. Therefore, it is desirable to set it within the range of the expressions (1) and (2).

By complying with the conditions of the expressions (1) and (2), it becomes possible to use plastic lenses for the first and fourth lenses. Therefore, the cost of the zoom lens can be reduced. It is also easy to introduce aspherical surfaces into the first and fourth lenses. Since the powers of the first and fourth lenses are small, they can be manufactured at low cost even if an aspherical surface is adopted, and aberrations can be improved by using these lenses, and a high-performance zoom lens can be provided. It is desirable to make the object side lens surface of the first lens and the object side lens surface of the fourth lens aspherical, and further improve the performance by making the image side lens surface of the first lens also aspherical. it can.

Expression (3) relates to the ratio of the focal lengths of the first and second lens groups, and defines the movement amount Δx of the second lens group. The movement amount Δx is represented by the following formula.

[0013] _{Δx = (| f R | /} f F) × (f T -f W) ··· (6) where, f _T is the focal length of the entire system at the telephoto end,
f _W is the focal length of the entire system at the wide-angle end.

As can be seen from the equation (6), the moving amount Δx of the second lens group is the amount defined by the equation (3) | f _R | / f
Subordinate to _F. Therefore, when the value exceeds the upper limit of the expression (3), the movement amount Δx of the second lens unit becomes large, which is against the size reduction. Also, the back focus becomes long. On the other hand, when the value goes below the lower limit of the expression (3), the size becomes compact, but the aberration generated in the second lens group, particularly the distortion aberration, becomes large and the performance deteriorates. Further, since the back focus becomes short, the diameter of the second lens group, especially the fifth lens becomes large, which is not preferable.

The expression (4) defines the thickness of the first lens unit within an appropriate range. When the value exceeds the upper limit of the expression (4), the lens thickness becomes large and the zoom lens becomes large.
It is also not preferable in that the light amount around the lens is reduced. On the other hand, if the value goes below the lower limit, the size will be reduced,
The coma aberration cannot be corrected well, and the performance of the zoom lens deteriorates. Further, the expression (5) defines the thickness of the second lens group to an appropriate value, and if it exceeds the upper limit value, it is against the miniaturization. If the lower limit is exceeded,
It is not preferable because the refracting power of each lens becomes large and it becomes difficult to correct coma.

[0016]

EXAMPLES Examples 1 to 3 of the zoom lens of the present invention will be described below.
Will be described. The lens data of each example is as described below. Further, the basic configuration is the same as in Examples 1 to 3, and the wide-angle end (f = 30.7) of Example 1 is shown in FIG.
5) and a lens cross section at the telephoto end (f = 58.5). As can be seen from the figure, the zoom lenses in Examples 1 to 3 are two-group zooms composed of a first lens group G1 and a second lens group G2 arranged in order from the object side to the image side. A first lens group G1
A diaphragm S is provided between the first lens group G2 and the second lens group G2. First
The second lens group G2 has a positive refractive power, and the second lens group G2 has a negative refractive power. Therefore, the first lens group G1 and the second lens group G2 from the wide-angle state to the telephoto state.
Move toward the object side while reducing the distance d ₇ from each other.

The first lens group G1 includes, in order from the object side, a negative plastic lens L1 and a negative lens L having a loose power.
2 and the positive lens L3. In Example 1, the object-side surface of the plastic lens L1 is made an aspherical surface to ensure sufficient performance, and at the same time, the lens is easily manufactured and managed. Examples 2 and 3
In the above, in addition to the object-side surface of the plastic lens L1, the image-side surface is an aspherical surface to realize a zoom lens with higher performance.

The second lens group G2 includes, in order from the object side, a positive plastic lens L4 and a negative lens L4 whose powers are gentle.
5, the surface of the plastic lens L4 on the object side is an aspherical surface to improve the performance.

In the lens data of Examples 1 to 3 shown below, f is the focal length (mm) of the entire system, F _NO is the F number, 2ω is the angle of view, and r _{1 to} r ₁₁ are arranged in order from the object side. The radius of curvature of each lens surface, d _{1 to} d ₁₀ are the distances between the lens surfaces arranged in order from the object side (d ₆ is the distance from the diaphragm, and d ₇ is the variable length), n _{1 to} n ₅ are the refractive indexes (d lines) of the lenses arranged in order from the object side, ν _{1 to} ν
₅ is the Abbe number (d
Line). Further, the aspherical shape is expressed by the following equation (7), where x is the optical axis direction and y is the direction orthogonal to the optical axis.

X = (y ² / r) / [1+ {1- (1 + K) (y ² / r ² )} ^1/2 ] + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ (7) Here, r Is a paraxial radius of curvature, K is a quadric surface parameter,
Furthermore, A to D represent aspherical surface coefficients.

[Example 1] f = 30.75 to 58.5 F _NO = 4.0 to 7.5 2ω = 57.6 ° to 33.0 ° r ₁ = 14.435 d ₁ = 1.80 n ₁ = 1.58400 ν ₁ = 31.0 r ₂ = 12.257 d ₂ = 0.70 r ₃ = 42.279 d ₃ = 1.53 n ₂ = 1.68893 ν ₂ = 31.1 r ₄ = 16.760 d ₄ = 2.76 r ₅ = 23.134 d ₅ = 2.80 n ₃ = 1.48749 ν ₃ = 70.2 r ₆ =-9.250 d ₆ = 1.2 r ₇ = 0.0 d ₇ = 9.075 to 2.152 r ₈ = -38.692 d ₈ = 3.21 n ₄ = 1.58400 ν ₄ = 31.0 r ₉ = -14.039 d ₉ = 2.08 r ₁₀ = _{- 7.930 d 10 = 1.10 n 5} = 1.74400 ν 5 = 44.8 r 11 = - 44.112 aspherical coefficients first surface K = -8.05277 A = 0.95317 × 10 -4 B = -0.78895 × 10 -5 C = 0.99106 × 10 - ⁸ D = -0.65403 × 10 ^-9 8th surface K = -183.83311 A = -0.22337 × 10 ^-3 B = -0.14449 × 10 ^-4 C = -0.30581 × 10 ^-6 D = 0.33294 × 10 ^-8 Zoom distance Focus Distance 30.75 to 45 to 58.5 Variable interval d ₇ 9.075 ~ graphs showing various aberrations at the wide angle end of the present embodiment of the zoom lens in the 4.453 to 2.152 2, shows various aberrations at the telephoto end in FIG. The astigmatism diagram shows the meridional image (M) and the sagittal image (S), and the spherical aberration diagram shows the d line (587.6 nm), g line (435.8 nm) and C line.
The line (656.3 nm) is shown.

Note that f _F / | f ₁ of the zoom lens of this example
| Is 0.104, | f _R | / f ₄ is 0.599, | f _R
| / F _F is 1.035, D _F / f _F is 0.460, and further, D _R / | f _R | is 0.297. Therefore, the lens forming the zoom lens of this example satisfies the conditions of the above-described formulas (1) to (5).

[Example 2] f = 30.75 to 58.5 F _NO = 4.0 to 7.5 2ω = 57.6 ° to 32.9 ° r ₁ = 17.561 d ₁ = 2.80 n ₁ = 1.58400 ν ₁ = 31.0 r ₂ = 14.368 d ₂ = 0.56 r ₃ = 51.691 d ₃ = 1.60 n ₂ = 1.80518 ν ₂ = 25.4 r ₄ = 20.241 d ₄ = 1.95 r ₅ = 28.846 d ₅ = 4.50 n ₃ = 1.57250 ν _{3 = 57.8 r 6 = -11.809 d 6} = 1.20 r 7 = 0.0 d 7 = 11.790 ~2.000 r 8 = -36.206 d 8 = 2.75 n 4 = 1.58400 ν 4 = 31.0 r 9 = -19.738 d 9 = 3.90 r 10 = -10.704 d ₁₀ = 1.20 n ₅ = 1.72000 ν ₅ = 46.0 r ₁₁ = -56.548 Aspheric coefficient 1st surface K = -7.38355 A = -0.67382 × 10 ^-4 B = -0.41906 × 10 ^-5 C = -0.40813 × 10 ^-8 D = 0.22817 × 10 ^-9 2nd surface K = -1.71995 A = -0.72127 × 10 ^-4 B = -0.24166 × 10 ^-5 C = -0.37175 × 10 ^-8 D = 0.61309 × 10 ^-9 8th Surface K = -62.85683 A = -0.10578 × 10 ^-3 B = 0.28994 × 10 ^-5 C = -0 .30920 × 10 ^-8 D = 0.17930 × 10 ^-9 Zoom distance Focal length 30.75 to 45 to 58.5 Variable distance d ₇ 11.790 to 5.254 to 2.000 FIG. 4 shows the zoom lens of this example. FIG. 5 shows various aberration diagrams at the wide-angle end, and FIG. 5 shows various aberration diagrams at the telephoto end.

Note that f _F / | f ₁ of the zoom lens of this example
| Is 0.121, | f _R | / f ₄ is 0.495, | f _R
| / F _F is 1.075, D _F / f _F is 0.470, and D _R / | f _R | is 0.300. Therefore, the lens forming the zoom lens of this example satisfies the conditions of the above-described formulas (1) to (5).

[Example 3] f = 30.75 to 58.5 F _NO = 3.5 to 6.5 2ω = 57.6 ° to 32.9 ° r ₁ = 16.476 d ₁ = 2.55 n ₁ = 1.58400 v ₁ = 31.0 r ₂ = 13.615 d ₂ = 0.76 r ₃ = 67.356 d ₃ = 1.60 n ₂ = 1.80518 v ₂ = 25.4 r ₄ = 23.484 d ₄ = 1.63 r ₅ = 30.954 d ₅ = 4.50 n ₃ = 1.57250 v _{3 = 57.8 r 6 = -11.956 d 6} = 1.20 r 7 = 0.0 d 7 = 12.386 ~2.000 r 8 = -37.862 d 8 = 2.80 n 4 = 1.58400 ν 4 = 31.0 r 9 = -20.192 d 9 = 3.77 r 10 = _{-11.152 d 10 = 1.20 n 5 =} 1.71700 ν 5 = 47.9 r 11 = -62.661 first surface K = -5.94315 aspherical coefficients ^{A = -0.89972 × 10 -4 B =} -0.50417 × 10 -5 C = 0.35834 × 10 ^-9 D = 0.23027 × 10 ^-9 2nd surface K = -1.83978 A = -0.84108 × 10 ^-4 B = -0.41596 × 10 ^-5 C = 0.25466 × 10 ^-7 D = 0.43876 × 10 ^-9 8th surface K = -76.17929 A = -0.11868 × 10 ^-3 B = 0.30710 × 10 ^-5 C = -0 .32244 × 10 ⁻⁷ D = 0.17067 × 10 ⁻⁹ Zoom interval Focal length 30.75 to 45 to 58.5 Variable interval d ₇ 12.386 to 5.453 to 2.000 FIG. 6 shows the zoom lens of this example. FIG. 7 shows various aberration diagrams at the wide-angle end, and FIG. 7 shows various aberration diagrams at the telephoto end.

Note that f _F / | f ₁ of the zoom lens of this example
| Is 0.124, | f _R | / f ₄ is 0.389, | f _R
| / F _F is 1.098, D _F / f _F is 0.446, and further, D _R / | f _R | is 0.286. Therefore, the lens forming the zoom lens of this example satisfies the conditions of the above-described formulas (1) to (5).

[0027]

As described above, according to the present invention, a compact zoom lens having a two-group structure is realized by using five lenses, and by setting the conditions of these lenses within the above-mentioned appropriate range. It is possible to provide a cheap and high-performance zoom lens. In particular, a plastic lens can be used for the first lens and the fourth lens, and cost reduction can be achieved, and at the same time, various performances of the zoom lens can be improved by using an aspherical surface. Further, by appropriately distributing the refractive power of each group, it is possible to keep the amount of movement of the lens group and the back focus within an appropriate range, and it is possible to provide a more compact and high-performance zoom lens.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a lens of Example 1 of the present invention.

FIG. 2 is a diagram of various types of aberration at the wide-angle end of Example 1.

FIG. 3 is a diagram of various types of aberration at the telephoto end of the first example.

FIG. 4 is a diagram of various types of aberration at the wide angle end of Example 2;

FIG. 5 is a diagram of various types of aberration at the telephoto end of Example 2;

FIG. 6 is a diagram of various types of aberration at the wide-angle end of Example 3;

FIG. 7 is a diagram of various types of aberration at the telephoto end of the third example.

[Explanation of symbols]

 G1 ... First lens group G2 ... Second lens group S ... Aperture L1-L5 ... Lens

Claims (3)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a portion between the first and second lens groups in order from the object side to the image side. And a diaphragm disposed in the zoom lens for zooming by varying the air space between the first and second lens groups, wherein the first lens group is a negative lens in order from the object side. The first and second lenses of positive power and the third lens of positive power
The second lens group includes, in order from the object side, a fourth lens having a positive refracting power and a fifth lens having a negative refracting power. These lenses are as follows. A zoom lens that meets the requirements. (1) 0.05 <f _F / | f ₁ | <0.15 (2) 0.35 <| f _R | / f ₄ <0.65 (3) 0.9 <| f _R | / f _F <1.3 (4) 0.4 <D F / f F <0.5 (5) 0.25 <D R / | f R | <0.35 However, f ₁ is the focal length of the first lens , F ₄ is the focal length of the fourth lens, f _F is the composite focal length of the first lens group, f _R is the composite focal length of the second lens group, D _F is the object of the first lens Side lens surface to the image side lens surface of the third lens, D _R
Is the fifth lens from the object side lens surface of the fourth lens.
The distances to the image-side lens surface of the lens are shown respectively. 2. The zoom lens according to claim 1, wherein the first lens and the fourth lens are plastic lenses. 3. The zoom lens according to claim 1, wherein the object-side lens surface of the first lens and the object-side lens surface of the fourth lens are aspherical surfaces.