JPH06138390A - Zoom lens - Google Patents

Abstract

PURPOSE:To brighten an F-number about twice on a wide angle side, to obtain a change ratio of magnification of about three times, and to enlarge a back- focal distance by changing the magnification while moving a second and a third lens groups, and specifying a satisfied condition. CONSTITUTION:A third lens group has action for changing mainly a role and magnification of a master lens, and a second lens group has action for supplementing the action for changing the magnification, and also, compensating a focal deviation caused by a change of the magnification. In such a state, from an object side, a first positive lens group, a second negative lens group and a third positive lens group are arrayed in order, and by moving a second lens group and a third lens group, the magnification is changed, and also, conditions shown by expressions I-IV are satisfied. In the expressions I-IV, fw, fi, (z), ft and z3 denote a focal distance of a short focus side of the whole system, a focal distance of an i-th lens group (i=1, 2, 3), a change ratio of the magnification of the whole system, a focal distance of a long focus side of the whole system, and a change ratio of the magnification of a third lens group, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in small video cameras, electronic still cameras and the like.

[0002]

2. Description of the Related Art In recent years, a CCD has been provided as a light receiving element.
Small video cameras and electronic still cameras having screens of 1/2 inch and 1/3 inch have been developed.

The photographing lens used in this type of camera is a small-sized (bright) zoom lens having a small F number.

As a conventional compact zoom lens, a retrofocus type two-group zoom lens having a negative first lens group is known.

[0005]

However, in the retrofocus type two-group zoom lens, when the F number is set to about 1: 2, the lens diameter of the rear group becomes large and high-order spherical aberration occurs.

As a zoom lens having a small F number, a positive first lens group, a negative second lens group as a variator, a negative third lens group as a compensator, and a positive fourth lens as a master lens. There is known a 4-group type zoom lens configured by arranging groups.

However, in the four-group type zoom lens, the entire lens system is large, and in particular, the front lens diameter is large.

Further, in a conventional zoom lens having a three-group structure, focusing is performed by moving either the first lens group or a part of the third lens group (master lens group) in the optical axis direction. However, when focusing with the first lens group, if the shortest shooting distance is shortened,
The amount of movement and the diameter of the lens group increase. Further, when focusing is performed by a part of the third lens group, variation of aberration becomes large.

[0009]

OBJECT OF THE INVENTION This invention has an F number of 1: on the wide angle side.
An object of the present invention is to provide a zoom lens which is bright as about 2 and has a magnification change ratio of about 3 times and a large back focus.

Another object of the present invention is to provide a zoom lens which can shorten the shortest shooting distance without increasing the lens diameter and has a small aberration variation during focusing.

[0011]

A zoom lens according to the present invention comprises at least three lens groups arranged in the order of positive, negative, and positive from the object side, and moves a second lens group and a third lens group. To change the magnification, and
The following conditions (a) to (d) are satisfied.

(A) 0 <fw / f1 <0.25 (b) -0.9 <fw / f2 <-0.4 (c) 0.3 <fw / f3 <0.8 (d) 0.7 <logz3 / logz <1.0 However, fw is The focal length on the short focus side of the entire system, fi is the i-th
The focal length of the lens group (i = 1,2,3), z is the change ratio of the magnification of the entire system (z = ft / fw), ft is the focal length on the long focus side of the entire system, z3
Is the magnification change ratio of the third lens group (z3 = m3t / m3w), m3t
Is a lateral magnification on the long focal side of the third lens group, and m3w is a lateral magnification on the short focal side of the third lens group.

[0013]

EXAMPLES Examples of this zoom lens will be described below.

The zoom lens of the present invention employs a new zoom system and focusing system which are intermediate between those of the conventional retrofocus type two-group zoom lens and the four-group type zoom lens.

The zoom method adopted by the present invention and the conventional 4
Compare with group type zoom method. In either method, the second and third lens groups move. However, in the conventional method, the second lens group has a function of mainly changing the magnification, and the third lens group has a function of compensating a focus shift due to the change of the magnification. On the other hand, according to the method of the present invention, the third lens group mainly has a role of a master lens and an action of changing the magnification, the second lens group complements the action of changing the magnification, and the focus by changing the magnification is It has a function of compensating for the deviation.

In the zoom lens of the embodiment, a positive first lens group, a negative second lens group, and a positive third lens group are arranged in this order from the object side, and the second lens group and the third lens group are arranged. The magnification is changed by moving and, and the following conditions
Satisfies (a) to (d).

(A) 0 <fw / f1 <0.25 (b) -0.9 <fw / f2 <-0.4 (c) 0.3 <fw / f3 <0.8 (d) 0.7 <logz3 / logz <1.0 However, fw is The focal length on the short focus side of the entire system, fi is the i-th
The focal length of the lens group (i = 1,2,3), z is the change ratio of the magnification of the entire system (z = ft / fw), ft is the focal length on the long focus side of the entire system, z3
Is the magnification change ratio of the third lens group (z3 = m3t / m3w), m3t
Is a lateral magnification on the long focal side of the third lens group, and m3w is a lateral magnification on the short focal side of the third lens group.

The condition (a) defines the power of the first lens group. When the value goes below the lower limit of the condition (a), the power of the first lens group becomes negative, and the lens diameter of the rear group increases, so that a bright zoom lens having an F number of about 1: 2 cannot be obtained. On the other hand, when the value exceeds the upper limit, the power of the first lens group increases, the effect of changing the magnification of the second lens group increases, and the fluctuation of aberration when changing the magnification increases.

The condition (b) defines the power of the second lens group. When the value goes below the lower limit of the condition (b), the negative power becomes large, and the aberration when the magnification is changed fluctuates. On the other hand, when the upper limit is exceeded, the lens becomes large.

The condition (c) defines the power of the third lens group. When the value goes below the lower limit of the condition (c), the power of the third lens group becomes small, so that the movement amount of the third lens group for changing the magnification becomes large and the total length of the lens becomes large. On the other hand, when the value exceeds the upper limit of the condition (c), the power becomes large and the fluctuation of the aberration when changing the magnification becomes large.

The condition (d) defines that the action of changing the magnification of the third lens unit should be made larger than that of the second lens unit.
When the value goes below the lower limit of the condition (d), the effect of changing the magnification of the second lens group increases, and it becomes difficult to correct aberrations. On the other hand, when the value exceeds the upper limit, only the third lens group has the effect of changing the magnification, so that the rate of changing the magnification cannot be increased.

By satisfying these conditional expressions at the same time, it is possible to obtain a compact zoom lens having a magnification change ratio of about 3 times and a small F number.

In order to obtain a more compact zoom lens, it is preferable that the following conditions (e) and (f) are satisfied.

(E) -1 <m2 <0 (f) m3t <-1 <m3w where m2 is the lateral magnification from the short focal side to the long focal side of the second lens group.

The conditions (e) and (f) define the lateral magnification of the second lens group and the third lens group. By satisfying these conditions, it is possible to reverse the moving direction of the second lens group when changing the magnification, with the intermediate focal length as a boundary. Further, since the third lens group moves to the object side almost in proportion to the increase in the focal length, a more compact zoom lens can be obtained.

Further, in order to secure a space for providing an element such as a beam splitter between the image plane and the lens, it is preferable to satisfy the following condition (g).

(G) 1.5 <fBw / fw where fBw is an air-equivalent back focus (excluding the plane-parallel plate) on the short focus side of the entire system.

In each embodiment described later, the value of fBw is expressed by the following equation. fBw = d20 + d21 / n21 where d20 is the distance from the final lens to the plane-parallel plate, d
21 and n21 are the thickness of the plane-parallel plate and the refractive index of the d-line.

The condition (g) defines the back focus.
By satisfying this condition, it is possible to secure a space for providing a plurality of elements such as a beam splitter between the lens and the image plane.

The stop is arranged in front of the third lens group or in the third lens group. When the diaphragm is provided in front of the third lens group, the front lens diameter can be reduced. Further, when the diaphragm is provided in the third lens group, it is possible to more effectively prevent the ghost caused by the imaging surface and the surface of the master lens when the light flux is stopped.

Further, it is desirable that the second lens group having a large power has the focusing function. If this is given to the first lens group having a small power, the peripheral light amount becomes insufficient.

At this time, it is desirable to satisfy the following condition (h).

(H) 0.0 <logz2 / logz <0.3 where z2 is the zoom ratio of the second lens group (z2 = m2t / m2w), m2
t is the lateral magnification on the long focus side of the second lens group, and m2w is the lateral magnification on the short focus side of the second lens group.

The condition (h) defines the magnification changing action of the second lens group. By satisfying this condition, it is possible to reduce the difference in the amount of extension for focusing at each focal length.

For example, the extension amount (X) at the shortest shooting distance of 0.2 m (distance from the object to the image plane) in Embodiment 1 described later is X = 1.14 and f = 12.0 when the focal length f is f = 6.15. When X = 1.51, and when f = 17.5, X = 1.57. In Example 2,
When f = 6.15, X = 1.01, when f = 12.0, X = 1.22, and when f = 17.5, X = 1.21.

Further, in the third embodiment, the shortest shooting distance is 0.
Even when the size is as small as 1 m, the difference in the amount of X = 2.95-3.06 and the amount of feeding can be suppressed to only about 0.1 mm.

In order to secure a long back focus, it is desirable to further satisfy the following conditions (i) and (j).

(I) 1.0 <dw / ft <2.0 (j) 2.1 <fBw / fw <3.5 where dw is the distance between the second lens unit and the third lens unit on the short focus side.

The condition (i) defines the distance between the second and third lens groups. When the value goes below the lower limit of this condition, the fluctuation of the aberration during zooming becomes large in order to secure a long back focus. On the other hand, if the upper limit is exceeded, the total lens length becomes long and the lens diameter of the front lens group becomes large.

The condition (j) defines the back focus in a narrower range than the condition (g) described above.

[0041]

Example 1 FIG. 1 shows a lens configuration of a zoom lens according to Example 1. Specific numerical configurations are shown in Tables 1 and 2. In the table, FNO. Is F number, f
Is the focal length, ω is the half angle of view, r is the radius of curvature, d is the lens thickness or air spacing, n is the refractive index at d-line (588 nm), and ν is the Abbe number.

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

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

Second Embodiment FIG. 5 shows a lens configuration of a zoom lens according to a second embodiment. Specific numerical configurations are shown in Tables 3 and 4. 6, 7, and 8 show various aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

Third Embodiment FIG. 9 shows the lens configuration of a zoom lens according to a third embodiment. Specific numerical configurations are shown in Tables 5 and 6. 10, 11, and 12,
Various aberrations are shown at the wide-angle end, the intermediate focal length, and the telephoto end, respectively.

[0049]

[Table 5]

[0050]

[Table 6]

[0051]

Fourth Embodiment FIG. 13 shows the lens configuration of a zoom lens according to a fourth embodiment. Specific numerical configurations are shown in Tables 7 and 8. 14, 15, and 16
Shows aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively.

[0052]

[Table 7]

[0053]

[Table 8]

[0054]

Fifth Embodiment FIG. 17 shows the lens arrangement of a zoom lens according to the fifth embodiment. Specific numerical configurations are shown in Tables 9 and 10. 18, 19, and 20.
Shows aberrations at the wide-angle end, the intermediate focal length, and the telephoto end, respectively.

[0055]

[Table 9]

[0056]

[Table 10]

Table 11 shows the relationship between the above-mentioned knowledge of complaints and the examples.

[0058]

Table 11 Conditional Expression Example 1 Example 2 Example 3 Example 4 Example 5 fw / f1 0.104 0.090 0.086 0.094 0.096 fw / f2 -0.62 -0.63 -0.65 -0.59 -0.58 fw / f3 0.43 0.47 0.45 0.40 0.45 logz3 / logz 0.79 0.88 0.88 0.76 0.765 m2 -0.22 ~ -0.18 ~ -0.17 ~ -0.21 ~ -0.22 ~ -0.28 -0.21 -0.20 -0.27 -0.29 m3w -0.47 -0.49 -0.50 -0.45 -0.43 m3t -1.07 -1.24 -1.25 -1.00 -0.98 fBw 12.83 12.75 12.85 16.36 16.23 fBw / fw 2.09 2.07 2.09 2.64 2.25 logz2 / logz 0.21 0.12 0.12 0.24 0.235 dS / ft 1.17 0.97 1.12 1.33 1.16

[0059]

As described above, according to the structure of the present invention, the F number is as bright as about 1: 2 on the wide-angle side and has a zoom ratio of about 3 in spite of the three-group structure. It is possible to provide a compact and high-performance zoom lens suitable for a small video camera or electronic still camera.

[Brief description of drawings]

FIG. 1 is a lens system configuration diagram at a wide-angle end of a zoom lens according to a first example.

FIG. 2 is a diagram of various types of aberration at the wide-angle end of the zoom lens according to the first example.

FIG. 3 is a diagram of various types of aberration at the intermediate focal length of the zoom lens according to the first example.

FIG. 4 is a diagram of various types of aberration at the telephoto end of the zoom lens according to the first example.

FIG. 5 is a lens system configuration diagram at a wide-angle end of a zoom lens according to a second example.

FIG. 6 is a diagram of various types of aberration at the wide-angle end of the zoom lens according to the second example.

FIG. 7 is a diagram of various types of aberration at the intermediate focal length of the zoom lens according to the second example.

FIG. 8 is a diagram of various types of aberration at the telephoto end of the zoom lens according to the second example.

FIG. 9 is a lens system configuration diagram at a wide-angle end of a zoom lens according to a third example;

FIG. 10 is a diagram of various types of aberration at the wide-angle end of the zoom lens according to the third example.

FIG. 11 is a diagram of various types of aberration at the intermediate focal length of the zoom lens according to the third example.

FIG. 12 is a diagram of various types of aberration at the telephoto end of the zoom lens according to the third example.

FIG. 13 is a lens system configuration diagram at a wide-angle end of a zoom lens according to a fourth example;

FIG. 14 is a diagram of various types of aberration at the wide-angle end of the zoom lens according to the fourth example.

FIG. 15 is a diagram of various types of aberration at the intermediate focal length of the zoom lens according to the fourth example.

FIG. 16 is a diagram of various types of aberration at the telephoto end of the zoom lens according to the fourth example.

FIG. 17 is a lens system configuration diagram at a wide-angle end of a zoom lens according to a fifth example;

FIG. 18 is a diagram of various types of aberration at the wide-angle end of the zoom lens according to the fifth example.

FIG. 19 is a diagram of various types of aberration at the intermediate focal length of the zoom lens according to the fifth example.

FIG. 20 is a diagram of various types of aberration at the telephoto end of the zoom lens according to the fifth example.

Claims (10)

[Claims] 1. A first lens group having a positive focal length and a second lens group having a negative focal length in order from the object side.
At least three lens groups including a third lens group having a positive focal length are arranged, and zooming is performed by moving the second lens group and the third lens group, and the following condition (a): A zoom lens characterized by satisfying conditions (d). (a) 0 <fw / f1 <0.25 (b) -0.9 <fw / f2 <-0.4 (c) 0.3 <fw / f3 <0.8 (d) 0.7 <logz3 / logz <1.0 However, fw is The focal length on the short focus side, fi is the focal length of the i-th lens group (i = 1,2,3), z is the zoom ratio (z = ft / fw) of the whole system, and ft is the whole system. The focal length on the long focus side, z3 is the zoom ratio of the third lens group (z3 = m3t / m3w), m3t is the lateral magnification on the long focus side of the third lens group, and m3w is the short magnification of the third lens group. The lateral magnification on the focal side. 2. The zoom lens according to claim 1, wherein the following conditions (e) and (f) are satisfied. (e) -1 <m2 <0 (f) m3t <-1 <m3w where m2 is the lateral magnification from the short focal side to the long focal side of the second lens group. 3. The zoom lens according to claim 1, wherein the following condition (g) is satisfied. (g) 1.5 <fBw / fw where fBw is the air-focused back focus (excluding the plane-parallel plate) on the short focus side of the entire system. 4. The zoom lens according to claim 1, wherein the first lens group is fixed during zooming. 5. The zoom lens according to claim 1, wherein a diaphragm is provided closer to the object side than the third lens group, and the diaphragm is moved integrally with the third lens group during zooming. 6. The third lens group includes, in order from the object side, a positive 3a lens group and a positive 3b lens group, and a diaphragm is provided farther from the object side than the 3a lens group. ,
The zoom lens according to claim 1, wherein the diaphragm is moved integrally with the third lens group during zooming. 7. A first lens group having a positive focal length and a second lens group having a negative focal length in order from the object side.
At least three lens groups including a third lens group having a positive focal length are arranged, and the second lens group and the third lens group are moved to perform zooming,
A zoom lens characterized by focusing by a lens group. 8. The zoom lens according to claim 7, wherein the following condition (h) is satisfied. (h) 0.0 <logz2 / logz <0.3 where z2 is the zoom ratio of the second lens group (z2 = m2t / m2w), m2t is the lateral magnification on the long focus side of the second lens group, and m2w is the It is the lateral magnification on the short focus side of the two lens groups. 9. The first lens group is fixed during zooming and focusing.
Zoom lens described in. 10. The zoom lens according to claim 1, wherein the following conditions (i) and (j) are satisfied. (i) 1.0 <dw / ft <2.0 (j) 2.1 <fBw / fw <3.5 where fw is the focal length of the entire system on the short focus side, and dw is the second lens group and the third lens on the short focus side. The inter-group distance to the group, ft is the focal length of the whole system on the long focus side, and fBw is the back focus (excluding the plane-parallel plate) when converted to air on the short focus side.