JP3267435B2 - 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 small zoom lens having a high zoom ratio and a wide angle of view suitable for a lens shutter camera, a video camera, and the like. The present invention relates to a zoom lens which is excellent in portability and has a reduced length (distance from one lens surface to an image surface).

[0002]

2. Description of the Related Art Recently, in a lens shutter camera, a video camera, and the like, a small zoom lens having a short overall lens length has been demanded with the downsizing of the camera. In particular, lens shutter cameras are becoming smaller and smaller due to the development of peripheral technology such as electric circuits for driving the zoom, and the photographic lenses provided with them are also required to have high zoom ratios and compact zoom lenses. I have.

Conventionally, as a zoom lens for a lens shutter, a so-called two-group zoom lens comprising two lens groups having positive and negative refractive powers has been mainly used. Since the two-unit zoom lens has a simple lens configuration and a moving mechanism at the time of zooming, it has advantages such as downsizing of the camera and relatively low cost. However, since the zooming operation must be performed by only one lens group, the zooming ratio is about 1.6 to 2 times. Forcibly increasing the zooming ratio requires an increase in the size of the lens system. At the same time, it becomes difficult to maintain high optical characteristics.

On the basis of a two-unit zoom lens, the first unit is divided into two lens units having a positive refractive power.
A three-unit zoom lens which aims at high zoom ratio as a three-unit configuration having positive and negative refractive powers is disclosed in, for example, JP-A-3-282409, JP-A-4-37810, and JP-A-4-7651.
No. 1 publication and the like.

However, if an attempt is made to achieve a wide-angle zoom lens system having a half-angle of view of 35 ° or more with this lens group configuration, the change in the position of the entrance pupil during zooming becomes large. For this reason, it is very difficult to suppress aberration fluctuations due to zooming when achieving high zooming.

In addition, a zoom lens having a wide angle of view and a high zoom ratio by increasing the half angle of view at the wide angle end to about 38 ° and the zoom ratio by about 3.5 times by grouping a plurality of lenses is known, for example. Kaihei 2-
No. 72316 and Japanese Patent Application Laid-Open No. 3-249614. However, these zoom lens systems both have a large front lens diameter and a large overall lens length, and are not always sufficient as a photographing lens of a compact camera.

In particular, when applied to a camera using an external finder, there is a problem that the lens barrel covers the field of view of the finder at the wide angle end. As a result, there is a problem that the arrangement of the viewfinder and the form of the camera are restricted.

[0008]

Generally, in a zoom lens, if the refractive power of each lens unit is increased, the amount of movement of each lens unit for obtaining a predetermined zoom ratio is reduced, and the total length of the lens is reduced. High magnification can be achieved. However, if the refractive power of each lens group is simply increased, aberration fluctuations accompanying zooming increase, and it is necessary to obtain good optical characteristics over the entire zooming range especially when achieving high zooming and a wide angle of view. There is a problem that it becomes difficult.

The present invention comprises five lens groups as a whole, and appropriately sets the moving conditions, refractive power, and the like of each lens group during zooming, so that the photographic field angle at the wide-angle end is about 64 to 72 °,
It is an object of the present invention to provide a zoom lens having high optical characteristics over the entire zoom range with a zoom ratio of about 3.5.

[0010]

A zoom lens according to the present invention comprises , in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a positive lens unit. The fourth group of refractive power,
The fifth lens unit includes a fifth lens unit having a negative refractive power. At the telephoto end with respect to the wide-angle end, each lens unit is positioned on the object side.
The distance between the i-th lens unit and the (i + 1) -th lens unit at the wide-angle end is Diw, the distance between the i-th lens unit and the (i + 1) -th lens unit at the telephoto end is Dit, and the focal length of the entire system at the wide-angle end and the telephoto end is Fw. Assuming that Ft , the distance between the first and second groups at the zoom position where the focal length of the entire system is (Fw · Ft) ^1/2 is D1m , and the focal length of the fifth group.
Is f5 and the lateral magnification at the wide-angle end is β5w , D1w <D1m D1t <D1m D2w> D2t D3w <D3t D4w> D4t 0.45 <| f5 / fw | <1.5 1.2 <β5w <1. 7 are satisfied.

[0011]

FIG. 1 is an explanatory diagram of a paraxial refractive power arrangement of a zoom lens according to the present invention. In FIG. 1, (A) is the wide-angle end,
(B) shows the middle position, and (C) shows the telephoto end. FIGS. 2, 4, 6, and 8 are lens cross-sectional views at the wide-angle end of Numerical Examples 1 to 4, respectively, of the present invention. FIGS. 3, 5, 7, and 9 show various aberration diagrams of Numerical Examples 1 to 4 of the present invention.

In the drawing, LF denotes a front group having a positive refractive power, LR denotes a rear group, SP denotes an aperture, and IP denotes an image plane. Li (i = 1 to
5) is the i-th group. Arrows indicate the moving direction of each lens group when zooming from the wide-angle side to the telephoto side.

The front unit LF includes a first unit L1 having a positive refractive power, a second unit L2 having a negative refractive power, and a third unit L3 having a positive refractive power.
It consists of two lens groups, and the combined refractive power at the wide-angle end is a positive refractive power. The rear unit LR is a fourth unit L4 having a positive refractive power.
And a fifth lens unit L5 having a negative refractive power.

At the time of zooming from the wide-angle end to the telephoto end, the zoom lens is moved so as to satisfy the above equation. Each of the first, second, and third groups moves toward the object side, the second group moves while changing the relative positional relationship with the other lens groups, and the combined refractive power of the front group is at the telephoto end compared with the wide-angle end. Is moving to weaken. In addition, the fourth and fifth units are moved toward the object side so that the distance between them is reduced. At this time, each of the third and fourth units is moved toward the object side such that the distance between the third and fourth units is larger at the telephoto end than at the wide-angle end. Thus, the combined system of the third group and the fourth group viewed as an independent system is multiplied with magnification.

[0015] Then the focal length of the fifth group f5, when the Beta5w the lateral magnification at the wide-angle end, 0.45 <| f5 / fw | <1.5 (1) 1.2 <β5w <1.7 ( 2) The following condition is satisfied.

Thus, the focal length of the fifth lens unit and the lateral magnification at the wide-angle end are set as in conditional expressions (1) and (2), whereby a predetermined zoom ratio and a wide angle of view are effectively achieved. While reducing the size of the entire lens system.

Preferably, conditional expression (1) has the following range.

0.5 <| f5 / fw | <0.9 (1) 'By taking the above range, higher performance can be achieved.

In the present invention, at the wide-angle end, the combined refractive power of the first and second units is negative, and the third unit having a positive refractive power and the entire front unit are of a retrofocus type. As a result, the front principal point of the front group is located on the image plane side, and widening the angle of view is facilitated while preventing interference between the lens surfaces of the front group and the rear group. Also, the first lens unit has a positive refractive power,
The total length of the front group of the retrofocus type front group is shortened by moving the rear principal point position in the combined system of the first group and the second group at the wide-angle end toward the object side with the group having negative refractive power. Further, the first lens unit has a positive refractive power, and positive distortion at the wide-angle end is favorably corrected. Then, the fourth lens unit is moved toward the object side to focus from an object at infinity to an object at a short distance.

In the zoom lens of the present invention, the focal length f of the entire lens system is expressed by the following equation.

F = fA.beta.4.beta.5 (.beta.4> 0, .beta.5> 0) (a) where fA represents the combined focal length of the front group, and .beta.i represents the lateral magnification of the i-th group.

In the present invention, as can be understood from the equation (a), when changing the magnification from the wide-angle end to the telephoto end, the values of the lateral magnifications β4 and β5 are increased, and at the same time, the combined focal length fA of the front group is increased. By reducing the combined refracting power of the front group, a more efficient zooming effect is achieved. Also, the distance between the fourth lens unit having a positive refractive power and the fifth lens unit having a negative refractive power is made narrower (decreased) at the telephoto end than at the wide-angle end, thereby giving a zooming effect to the fifth lens unit. It facilitates high magnification. Also, the rear group has a more divergent (negative) refractive power at the telephoto end, and forms a telephoto type (telephoto type) together with the front group having a positive combined refractive power to reduce the size of the entire lens system. I have.

In the present invention, by adopting the paraxial refractive power arrangement as shown in FIG. 1, the widening view angle of the photographic field is achieved so that the focal length at the wide angle end is smaller than the screen diagonal length.

Specifically, the front group includes a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power.
During zooming from the wide-angle end to the middle, the distance between the first and second groups increases, and when zooming from the middle to the telephoto end, the distance between the first and second groups decreases. Each lens group moves toward the object side so that the distance between the third groups decreases. This enhances the zooming effect and the aberration correction effect of the front group.

In order to increase the angle of the lens system,
By arranging a lens group having a negative refractive power on the most object side of the lens system, it is possible to secure an appropriate back focus and to arrange the entrance pupil plane near the center of the lens system. This is advantageous. However, in order to obtain the effect while reducing the size of the lens system, it is necessary to make the negative lens group strong to some extent. As a result, a large negative distortion occurs.

For this reason, in the present embodiment, the first lens unit is a lens unit having a positive refractive power, and the second unit is a lens unit having a strong negative refractive power, thereby obtaining an effect of canceling distortion. Further, by bringing the first unit and the second unit close to each other at the wide-angle end, an increase in the lens diameter of the first unit for securing a constant peripheral light amount is prevented.

Also, in the variable magnification intermediate range, the spherical aberration generated in the first lens unit is favorably corrected in the second lens unit by increasing the distance between the first lens unit and the second lens unit. At the telephoto end, the first lens unit and the second lens unit are disposed so as to be close to each other, thereby reducing the overall length of the lens, which is advantageous for achieving a compact optical system.

Further, when D1w ≧ D1t, it is advantageous because the total length of the lens at the telephoto end is reduced.

In the present invention, in the above lens configuration, by satisfying conditional expressions (1) and (2), high optical performance is obtained over the entire zooming range while miniaturizing the entire lens system. .

Next, the technical meaning of each of the above conditional expressions will be described.

The conditional expression (1) is mainly for effectively changing the magnification with respect to the negative refractive power of the fifth lens unit. If the negative refractive power of the fifth lens unit becomes weaker beyond the upper limit of conditional expression (1), the zooming effect of the lens unit becomes weaker during zooming, so that a constant zoom ratio is obtained. For this purpose, the amount of movement of each lens group must be increased, and the overall length of the lens increases.

If the lower limit value of conditional expression (1) is exceeded, it means that at the wide-angle end, the combined refractive power of the first to fourth groups is positive and the refractive power of the fifth group is negative at the wide-angle end. The effect becomes too strong as a telephoto type.

As a result, the back focus of the lens system becomes too short, which leads to an increase in the outer diameter of the fifth lens group in order to secure a constant peripheral light amount, and at the same time, the refractive power of the lens group becomes strong. Too much distortion causes higher-order field curvature and astigmatism, which makes it difficult to correct them.

Conditional expression (2) relates to the lateral magnification at the wide-angle end of the fifth lens unit.

Now, assuming that the back focus of the lens system at the wide-angle end is BfW, BfW = f5 · (1−β5W).

Therefore, in the present invention, the total length of the lens system and various aberrations are corrected in a well- balanced manner by appropriately setting the value of the conditional expression (2) together with the conditional expression (1).

When the value exceeds the upper limit of conditional expression (2), the back focus becomes unnecessarily long, the total length of the lens increases, and it becomes difficult to make the lens compact. On the other hand, if the lower limit is exceeded, the back focus becomes too short and the outer diameter of the fifth lens unit increases, which is not good.

In the present invention, in order to widen the angle of view while reducing aberration fluctuations due to zooming and to ensure high optical performance over the entire screen, it is preferable to configure each lens unit as follows.

(1) _Assuming that the combined refractive power of the front unit at the wide-angle end is _φ123W , 0.3 <fw · _φ123W <1.2 (3) 0.6 <| f2 / fw | <3. 0 (4) It is preferable to satisfy the following condition.

Conditional expression (3) relates to the refractive power of the front lens group. When the value exceeds the upper limit of conditional expression (3), the refractive power of the front lens group becomes too strong at the wide-angle end, and the effect of the telephoto system becomes strong. It is difficult to obtain the back focus. or,
If the lower limit value is exceeded, the refractive power of the front group becomes too weak, and the overall length of the lens increases.At the same time, the refractive power of the rear group must be increased to maintain the focal length at the wide-angle end. It becomes difficult to balance.

Condition (4) relates to the negative refractive power of the second lens unit.
Since the refractive power of the group becomes too weak, the amount of movement of the lens group during zooming becomes large, which leads to an increase in the lens system. If the lower limit value is exceeded, the refracting power of the second lens unit becomes too strong, and high-order spherical aberration is generated strongly, so that it becomes difficult to correct this.

In the present invention, the upper limit and the lower limit of the above-mentioned conditional expressions (3) and (4) must be satisfied in order to satisfactorily correct the optical performance while reducing the overall length of the lens particularly at the wide-angle end. It is _{preferable to set} 0.35 <fw · φ _123W <0.9 (3a) and 0.75 <| f2 / fw | <2.0 (4a) as follows.

(2) When the combined refractive power of the front group at the telephoto end is φ _{123T and the} zoom ratio is Z, 0.6 <f3 / fW <2.0 (5) 0.2 <(φ _123W / φ _123T ) / Z <0.8 (6) 0.25 <β4W <0.7 (7) 0.1 <f5 · (1−β5W) / fW <0.6 (8) .

Condition (5) relates to the positive refractive power of the third lens unit.
Since the refracting power of the group is weak, the amount of movement of the lens group at the time of zooming is large, which leads to an increase in the lens system. If the lower limit is exceeded, the refractive power of the third lens unit becomes too strong, and accordingly, the negative refractive power of the second lens unit must be increased or the amount of movement of the second lens unit due to zooming must be increased. Come. Also, the magnification share for the rear group increases, which is not good.

Condition (6) relates to the zoom ratio of the front group. When the value exceeds the upper limit of conditional expression (6), the magnification change in the front unit becomes too large, the refractive power of the lens unit in the front unit becomes strong, and the movement amount of each lens unit at the time of zooming increases. Come. On the other hand, if the lower limit value is exceeded, the variable power allocation in the rear lens unit becomes too large, and the amount of movement of each lens unit in the rear lens unit to secure a predetermined zoom ratio is not good.

Conditional expression (7) relates to the lateral magnification of the fourth lens unit at the wide-angle end. When the value exceeds the upper limit of conditional expression (7), it becomes difficult to obtain a back focus at the wide-angle end, which results in an increase in the outer diameter of the fifth lens unit. If the lower limit value is exceeded, the refractive power of the other lens units will increase in order to obtain a constant focal length, making it difficult to correct aberration fluctuations during zooming. Further, the focal length of the front group must be made longer, which is not good because the overall length of the lens becomes longer.

Preferably, conditional expressions (5), (6),
(7) is preferably within the following range.

0.8 <f3 / fW <1.25 (5) '0.25 <( _φ123W / _φ123T ) / Z <0.5 (6)' 0.35 <β4W <0.6 (7 ) 'By doing so, the balance between miniaturization of the lens system and good optical performance can be further improved.

Conditional expression (8) is for appropriately setting the refractive power and the lateral magnification of the fifth lens unit, and mainly for obtaining a predetermined back focus. When the value exceeds the upper limit of conditional expression (8), the back focus becomes unnecessarily long at the wide-angle end, and the overall length of the lens increases. On the other hand, if the lower limit value is exceeded, it becomes difficult to obtain a predetermined back focus at the wide-angle end, and the outer diameter of the fifth lens unit increases, which is not good.

(3) The fourth group having a positive refractive power has at least 1
Each lens has a positive lens and a negative lens, of which the lens surface closest to the object side has a concave surface facing the object side, and the lens surface closest to the image surface has a convex surface facing the image surface side. Is good.

(4) When an aspherical surface is introduced into the zoom lens of the present invention, for example, if an aspherical surface is introduced into the fourth unit,
It is possible to easily correct field curvature at the telephoto end, face-to-face aberration, aberration variation due to zooming, and aberration correction of the entire screen. In the present invention, the last surface of the fourth lens unit is an aspheric surface. In addition, if it is introduced into the fifth lens group, mainly off-axis aberrations can be favorably corrected.

(5) The fifth group having a negative refractive power has at least 1
When there are a negative lens and a positive lens each having a concave surface facing the object side for each sheet, and the average values of Abbe numbers of the materials of the positive lens and the negative lens in the fifth group are ν5P and ν5N, respectively, 12 <ν5N −ν5P <35 It is preferable to satisfy the following condition. If the upper limit or the lower limit of conditional expression (9) is not met, chromatic aberration fluctuations during zooming will occur frequently, and it will be difficult to correct this with other lens groups.

(6) The stop should be placed in an air space between the lens surface closest to the image plane of the third lens unit and the lens surface closest to the image surface of the fourth lens unit, so that the entrance pupil is located at an appropriate position. Are preferable because aberration fluctuation due to zooming can be suppressed. The stop may be moved independently of the other lens groups when zooming, or may be moved integrally with the other lens groups. This makes it possible to arrange the stop position near the entrance pupil position that moves during zooming, which is advantageous for preventing a change in field curvature aberration at the time of a small stop.

When focusing is performed by the fourth lens unit, and when the fourth lens unit includes an aperture, moving the focus unit with the aperture fixed on the optical axis is a driving operation for moving the aperture mechanism during focusing. This is preferable because torque can be reduced.

(7) If the fourth unit is divided into two or more lens units, and the distance between the lens units is changed during zooming or during focusing, aberration variation during zooming and focusing is reduced. Is preferred.

(8) In the present invention, the focus is moved from the object at infinity to the object at a short distance by moving the fourth unit to the object side, but may be moved by moving another lens unit. . For example, a method of moving the front group to the object side may be used.

If the back focus is sufficient at the wide-angle end, the fifth unit may be moved to the image plane side, and this may be effective in reducing the outer diameter of the lens of the first unit. Becomes Alternatively, two or more lens groups in the first to fifth groups may be simultaneously moved.

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 aspherical shape 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, and R as a paraxial radius of curvature.
When A, B, C, D, and E are aspheric coefficients, respectively,

[0061]

[Outside 1]

[0062]

[Outside 2]

[0063]

[Outside 3]

[0064]

[Outside 4]

[0065]

[Outside 5]

[0066]

[Table 1]

[0067]

As described above, according to the present invention, it is possible to provide a zoom lens in which the photographing angle of view at the wide-angle end is about 64 to 72, the zoom ratio is about 3.5, the zoom ratio is about 3.5, and the aberration is well corrected. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a paraxial refractive power arrangement of a zoom lens according to the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 according to the present invention.

FIG. 3 is a diagram illustrating various aberrations of Numerical Example 1 according to the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 2 according to the present invention.

FIG. 5 is a diagram showing various aberrations of Numerical Example 2 relating to the present invention.

FIG. 6 is a lens sectional view of a numerical example 3 according to the present invention.

FIG. 7 is a diagram illustrating various aberrations of Numerical Example 3 relating to the present invention.

FIG. 8 is a lens sectional view of a numerical example 4 according to the present invention.

FIG. 9 is a diagram illustrating various aberrations of Numerical Example 4 relating to the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group L5 Fifth group dd line g g line S. C Sine condition ΔS Sagittal image plane ΔM Meridional image plane SP stop

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-136014 (JP, A) JP-A-2-167520 (JP, A) JP-A-3-85509 (JP, A) JP-A-7- 151975 (JP, A) JP-A-7-27979 (JP, A) JP-A-7-199070 (JP, A) JP-A-7-146441 (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 G02B

Claims (3)

(57) [Claims] 1. A first group having a positive refractive power , in order from the object side,
The fifth lens unit includes a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a negative refractive power. Denotes the distance between the lens units i and i + 1 at the wide-angle end.
iw, the distance between the i-th lens unit and the (i + 1) -th lens unit at the telephoto end is Di
t, the focal lengths of the entire system at the wide-angle end and the telephoto end are Fw,
If the focal length of the entire system is Ft, the interval between the first and second lens groups at the zoom position where the focal length of the entire system is (Fw · Ft) ^1/2 is D1m ,
When the focal length of the group is f5 and the lateral magnification at the wide-angle end is β5w , D1w <D1m D1t <D1m D2w> D2t D3w <D3t D4w> D4t 0.45 <| f5 / fw | <1.5 1.2 < A zoom lens satisfying a condition of β5w <1.7 . 2. When the combined focal length of the first, second and third lens groups at the wide-angle end is φ _123W and the focal length of the second lens group is f2 , 0.3 <fw · φ _123W < _1.20. 3. The zoom lens according to claim 2, wherein the following conditional expression is satisfied: 0.6 <| f2 / fw | <3.0. 3. A camera comprising the zoom lens according to claim 1.