JPH02153311A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To reduce the weight of the zoom lens and to make the lens compact by providing a 1st lens group consisting of a negative and a positive lens which are arranged separately in order from the object side and 2nd-4th lens groups including at least two positive and negative lenses and satisfying a special condition. CONSTITUTION:The 1st lens group G1 consists of the negative and positive lenses which are arranged separately in order from the object side. The 2nd-4th lens groups G2-G4 each have at least two negative and positive lenses and the respective lens group is moved to the object side while the group interval be tween the 1st lens group G1 and 2nd lens group G2 is increased and the group interval between the 3rd lens group G3 and 4th lens group G4 is decreased to vary the power from the wide-angle end to the telephoto end. Further, this constitution satisfies conditional expressions (1) and (2). Consequently, an about 3 times variable power ratio is secured and the lens is reduced in weight and cost and made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a compact, high-performance zoom lens with a small number of lenses.

(Prior art) In recent years, as this type of zoom lens,
This is proposed in Japanese Patent No. 6523, and this basically consists of a 1171st lens group with positive refractive power, a second lens group with negative refractive power, and a front group and a rear group with positive refractive power. Third
It consists of a lens group, and during zooming from the wide-angle end to the telephoto end, at least the 1171st lens group and the front and rear groups in the third lens group are moved from the image side to the object side.

This lens system was very advantageous in terms of compactness.

In addition, Japanese Patent Application Laid-Open No. 57-5012 and Jikai [1g57
In Japanese Patent No. 29024, a lens is proposed in which the 1171st group is composed of two negative and positive lenses, thereby achieving compactness and cost reduction.

(Problems to be Solved by the Invention) However, although the zoom lens proposed in JP-A-63-66523 has a relatively large number of lens elements, it is said to be sufficient in terms of aberration correction. hard. For this reason, it has not been sufficient in terms of cost reduction and performance improvement.

Also, JP-A-57-5012 and JP-A-57-2
Although the zoom lens proposed in Publication No. 9024 is designed to be compact and reduce costs by minimizing the number of lens elements, it does not correct chromatic aberration in each lens group, resulting in poor performance. I wasn't satisfied with that. Moreover, since the second lens group is constructed with a relatively small refractive power, the diameter of this lens becomes large, and it is difficult to say that it is sufficient in terms of compactness.

Therefore, the present invention solves all of the above problems and provides a high-performance zoom lens that is lightweight, compact, and cost-effective by having a small number of lenses, and has a zoom ratio of approximately 3x. is intended to provide.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group having a negative refractive power. a third lens group G having positive refractive power; and a fourth lens group G having positive refractive power.
4, the second lens G! is composed of two lenses in which a negative lens and a positive lens are separated and arranged in order from the object side, and the second lens G! Each of the lens groups from the fourth lens group 64 is as follows:
It has at least two lenses, a negative lens and a positive lens, and the distance between the first lens group G1 and the second lens group G2 is expanded, and the third lens group G and the fourth lens group G9
The lens group is moved toward the object side while reducing the distance between the groups, thereby changing the magnification from the wide-angle end to the telephoto end.

This configuration satisfies the following conditions.

(1) 4.5≦l rl/ (t l ≦7.5
(2) 1.2≦1fzn/fzl≦1.6 However, [1; Focal length of the 1171st group.

f2: Focal length M of the second lens group.

f, 4: Combined focal length of the third lens group and the fourth lens at the wide-angle end.

Further, in order to satisfactorily correct aberration fluctuations due to zooming and obtain excellent imaging performance, it is desirable to satisfy the following conditions.

(3) α1 ≦1 However, α: is the angle between the optical axis and the paraxial ray from an object point at infinity on the axis that enters the lens surface closest to the object of the fourth lens group at the wide-angle end, In the ray tracing formula, the initial value is α1
-Olh, = f, (focal length M of the entire system at the wide-angle end).

(Function) In general, in a zoom lens having a positive/negative/positive/positive configuration, the 1171st group is composed of two positive lenses and one negative lens, and among them, the specifications such as those of the present invention, In other words, even in a zoom lens having an angle of view of 58° or more at the wide-angle end and a variable power ratio of 2.7 or more, the 117th
One group was usually composed of three positive, positive and negative lenses.

For this reason, in such a zoom lens, even if the second to fourth lens groups are configured with the minimum number of lenses, not only will the 1171st lens group become thicker, but the lens diameter will also become thicker. Since the weight of the system also increases, it is not possible to sufficiently reduce the size, weight, and cost of the lens system.

Therefore, by configuring the 1171st group with two negative and positive lenses, not only can you reduce the number of large lenses by one, resulting in a significant weight reduction, but you can also make the 1171st group thinner, which reduces the lens diameter. Reduce the filter size (you can
Overall, significant cost reductions can be achieved.

However, if the 1171st group is forcibly constructed of two negative and positive lenses, the fluctuations in field curvature and astigmatism that occur with zooming will be large, making it difficult to correct aberrations.

Therefore, the present invention first focuses on
In order to realize a zoom lens having lens groups, the first
The refractive power of the 171st group is configured to be small to reduce the load on aberration correction. As will be explained later, by making full use of the movement of each lens group during zooming and reducing the load on the 1171st group during zooming, a good aberration balance is achieved for the lens system as a whole. .

Note that if the two negative and positive lenses are placed separately in the first lens group, various aberrations will be reduced even though the number of lenses is smaller than when the two negative and positive lenses are cemented together. Improve the degree of freedom in the correction of the 1171st
Since the principal point of the group can be moved to the image side, the 117th
It is possible to provide an advantageous configuration in which a distance between the first lens group and the second lens group can be ensured.

As described above, when the 1171st lens group is configured with a small refractive power, the degree of convergence of the light rays passing through this group becomes weak, whereas the second lens group receives a large diverging effect, resulting in overcorrection of various aberrations. Become.

Therefore, if the refractive power of the second lens group is further increased, it is advantageous for making the lens system more compact, but it becomes more difficult to correct aberrations.

On the other hand, if the refractive power of the second lens group is made weak, it is advantageous in terms of aberration correction, but as the second lens group becomes thicker, the lens diameter increases, and The amount of movement of the second lens group during magnification is large (as a result, it is difficult to ensure a distance between the moving groups, and as a result, it is not possible to obtain a large zoom ratio).

In this way, when the 1171st lens group is configured with weak positive refractive power, in order to ensure a large zoom ratio while making the lens system compact and good aberration correction, the second lens group must be used as a normal lens. It is necessary to have a different configuration.

Therefore, first of all, the second lens group of the present invention has a relatively large number of lenses for good aberration correction, but by configuring this lens group to have strong refractive power, it can be made substantially more compact. has been achieved.

Next, a variable power system for the zoom lens of the present invention having the 1171st lens group with a weak refractive power and the second lens group with a strong refractive power as described above will be described.

Normally, in a zoom lens having a positive/negative/positive lens configuration, when changing magnification, the first lens group is moved to the object side while the second lens group is fixed or moved to the image side. While increasing the composite magnification of the lens and the second lens, the movement of each lens group is reduced to achieve compactness.

However, with the lens configuration of the present invention, that is, the lens configuration having the 1171st group consisting of two lenses with weak refractive power and the second lens group with strong refractive power, the degree of freedom in aberration correction with respect to zooming is There aren't many.

Therefore, by using the normal magnification method as described above, the 117th
If the combined magnification ratio of the first lens group and the second lens group is increased, aberrations occurring in both lens groups cannot be sufficiently corrected.

Therefore, in the present invention, when changing magnification, the 1121st lens group is moved toward the object side, while the second lens group is moved toward the object, contrary to the usual method. By lowering the combined magnification ratio of the first lens group and the second lens group, the load on aberration correction for the magnification change of both lens groups is reduced.

Instead of lowering the combined magnification ratio of the 1121st lens group and the second lens group, by moving the third lens group and the fourth lens group relatively largely toward the object side, The composite magnification ratio is increased.

Therefore, by using such a variable power system, it is possible to obtain a substantially large variable power ratio while maintaining a good aberration balance for the lens system as a whole.

Note that if the 1121st group is configured with a small refractive power as described above, the amount of movement of the 1121st group during zooming will be large, but the configuration in which the overall length at the wide-angle end is extremely small makes it highly portable. A compact zoom lens can be realized.

As described above, by making maximum use of the movement of each lens group during zooming, the 1121 lens has weak positive refractive power.
Despite the lens configuration having a second lens group having a strong negative refractive power, a large zoom ratio can be achieved while maintaining a good aberration balance as a whole lens system.

Next, the above conditions (1) and (2) will be explained in detail. Conditions (1) and (2) define the optimum distribution of refractive power in each lens group.

Condition (1) defines the optimum ratio of refractive powers between the 1121st lens group and the second lens group. There are two possible cases in which the lower limit of condition (1) is exceeded:

+al When the focal length of the first lens group is very small.

Mountain) When the focal length of the second lens group is very long.

First, the focal length of the 1121st group becomes very small.
In the case of t, if the 1121st group is composed of two positive and negative lenses, a large amount of negative spherical aberration will occur, and it will not only be difficult to correct it with the second lens group having negative refractive power. The above-mentioned curvature of field and astigmatism occur due to variable magnification, and furthermore, it becomes difficult to correct lower coma aberration. Therefore, when attempting to correct aberrations well, the result is that the first
This is not preferable because it becomes difficult to configure the 121st group with two elements, which goes against the purpose of the present invention.

Also, the focal length of the second lens group becomes extremely large)
In this case, although the aberrations generated in the second lens group itself can be suppressed to a small level, the principal ray with the maximum angle of view that enters the second lens group is incident at a higher position farther from the optical axis, so This is not preferable because the effective diameter of the second lens group increases, leading to an increase in the size and cost of the lens system. Moreover, the amount of movement of the second lens group for changing the magnification is large (as a result, it becomes difficult to secure the group spacing for changing the magnification).

Conversely, the following two conditions exceed the upper limit of condition (1).
Two cases are possible.

(When the focal length of the C1 first lens group is very long.

(When the focal length of the dl second lens group is very small.

Therefore, first of all, the focal length of the 1121st group becomes very large (in the case of EL, although the aberrations generated in the first lens group itself can be suppressed to a small value, the focal length of the maximum angle of view incident on the 1121st group The effective diameter of the 1121st group increases because the light ray enters at a higher position farther away from the optical axis.Furthermore, because the amount of movement of the 1121st group due to zooming increases, the maximum angle of view at the telephoto end increases. The principal ray also enters at a higher position, which is not preferable because it leads to an increase in the size of the lens system and a significant increase in cost.

Also, the focal length of the second lens group becomes very small (d
In the case of i, the negative refractive power of the second lens group is large (as a result, the light rays incident on this group are subject to a large diverging effect, and are particularly affected by downward coma aberration, field curvature, and non-conformity due to zooming. Not only does the variation in point aberration increase, but it also becomes difficult to correct spherical aberration.For this reason, in order to perform good aberration correction, it is necessary to increase the number of elements in this group, which results in an increase in the size of this group. This not only results in a cost increase but also goes against the purpose of the present invention.

Next, condition (2) defines the optimal ratio between the combined refractive power of the third and fourth lens groups and the refractive power of the second lens group at the wide-angle end.

If the lower limit of condition (2) is exceeded, the combined focal length of the third lens group and the fourth lens group at the wide-angle end becomes small, which is advantageous for compactness, but it also reduces field curvature, astigmatism, and upward On the other hand, if the upper limit of condition (2) is exceeded, the combined focal length of the third and fourth lens groups at the wide-angle end becomes difficult to correct and obtain good imaging performance. Although this is advantageous for correcting aberrations, the overall length of the lens becomes thick, which is undesirable because it increases the size of the entire system.

Further, the present invention is configured such that a paraxial ray from an object point at infinity on the axis that enters the lens surface of the fourth lens group closest to the object at the wide-angle end satisfies condition (3) as shown below. This is very effective for suppressing fluctuations in field curvature and astigmatism due to relative movement between the third and fourth lens groups during zooming.

(3) α8 ≦1 However, α-: This is the angle between the optical axis and the paraxial ray from an object point at infinity on the axis that enters the lens surface of the fourth lens group closest to the object at the wide-angle end. In the ray tracing formula, the initial value is α1
=0, h, =fw (focal length of the entire system at the wide-angle end).

Here, α8 is the value multiplied by the refractive index of the object-side medium immediately in front of that surface in the paraxial ray tracing formula at the wide-angle end. That is, the initial value α9,h of the light beam incident on the first surface closest to the object is α+ ”O, b+ =fw, and the value is determined by the following equation.

α to '1 α section + h test φ test α direct 19 α Sumire hll++ -hx ell' d ('However,
αI3NIIUK α, 'MiNl'Ul+' = J+1 Ug++φ Ward
= (Ng' Ng)/rme w' ” d
g'/N y'rk; Radius of curvature of the second surface.

hk: Incidence height of the first surface.

φK = plane layer rupture power at the top of the first plane.

UK: The angle of the paraxial incident ray on the surface with respect to the optical axis.

dl: Vertex distance between the first surface and the (k+1)th surface.

Nll, Ni1-1: Refractive index for d-line.

Regarding the above paraxial tracking formula, for example, see Yoshiya Matsui's ``
It is detailed on pages 19-20 of ``Lens Design Method'' (Kyoritsu Shuppan).

Condition (3) will be explained in detail below.

If the paraxial ray from the object point at infinity on the axis, which is incident on the object side of the fourth lens group, is relatively parallel to the optical axis so as to satisfy condition (3), the Even if the distance between the third lens group and the fourth lens group is changed, field curvature and astigmatism can be adjusted in a well-balanced manner while minimizing fluctuations in spherical aberration.

In other words, under light beam conditions that satisfy condition (3), the movement ratio of the third lens and the fourth lens group should be set so as to obtain the best image surface characteristics in each focal length condition. This makes it possible to reduce the burden of correcting field curvature and astigmatism in the first and second lens groups, and minimizes the number of elements in the entire lens system, making it compact and high-performance that reduces costs. This makes it possible to realize a zoom lens with a wide range of functions.

However, outside the range of condition (3), the paraxial ray from the object point at infinity on the axis that enters the fourth lens group becomes more convergent or more divergent, so that the fourth lens group When the lens is extended toward the object side, the fluctuations in spherical aberration become so large that they cannot be ignored compared to the fluctuations in field curvature and astigmatism associated with zooming, resulting in a decrease in imaging performance. If you try to maintain the imaging performance associated with the increase in magnification, the burden of aberration correction on the first lens group and the second lens group will increase, making it difficult to configure the first lens group with two positive and negative lenses. The system cannot be made more compact.

Furthermore, in order to suppress fluctuations in spherical aberration due to zooming to a smaller value and achieve higher performance, it is desirable to configure the lens to satisfy -0, 5≦α0≦0.2.

Further, in order to achieve sufficient aberration correction and improve performance while maintaining a compact shape, it is desirable to configure the lens to satisfy the following conditions.

(5) n, -n, ≧0.1 (6) ν, - Schiff ≧25 r, -r.

r, -rc (9) 5B”≦2ω0≦78′″However, f2: Focal length of the second lens group.

fo: Focal length of the entire system at the wide-angle end.

fT: Focal length of the entire system at the telephoto end.

n,1: refractive index for the d-line of the negative lens in the 1171st group.

n, H The refractive index for the d-line of the positive lens in the first lens group.

C; Atsube number of the negative lens in the first lens group.

C: Atsube number of the positive lens in the first lens group.

r,: radius of curvature of the object side of the negative lens in the 1171st group.

",: Radius of curvature of the image side surface of the negative lens in the 1171st group.

r(+Radius of curvature of the object side of the positive lens in the first lens group.

r4: Radius of curvature of the image side surface of the positive lens in the 1171st group.

2ω@: Angle of view at the wide-angle end of the lens system.

The above conditions (4) to (9) will be explained in detail below.

Condition (4) defines the optimal focal length so that the second lens group has the optimal refractive power.

If the lower limit of condition (4) is exceeded, it becomes difficult to correct field curvature, astigmatism, coma, etc., and conversely, if the upper limit of condition (4) is exceeded, it becomes disadvantageous to compactness. Furthermore, if the configuration satisfies the following conditions, it will be more advantageous for compactness and good aberration correction.

Condition (5) defines the optimum difference in refractive index between the negative and positive lenses in the 1171st group. If this condition is not met, the Petzval sum becomes too small and the balance between field curvature and astigmatism is lost, making it difficult to perform good correction. In addition, it is more preferable that this condition is 0.16 or more.

Condition (6) is a condition for performing appropriate achromatization in the 1171st group. Outside of this condition, variations in axial and off-axis chromatic aberrations due to zooming become large, making it difficult to obtain good performance.

Condition (7) defines the appropriate shape of the negative lens in the 1171st group. If the lower limit is exceeded, not only will the entire lens system become larger, which is contrary to the purpose of the present invention, but it will also become difficult to correct spherical aberration on the telephoto side. On the other hand, if the upper limit is exceeded, the principal point of the negative lens in the 1171st group tends to move toward the object, making it difficult to secure the distance between the 1171st group and the second lens group, and furthermore, the image It becomes difficult to correct surface curvature and coma aberration.

Condition (8) defines the appropriate shape of the positive lens in the 1171st group. If the lower limit is exceeded, it becomes difficult to correct field curvature and coma aberration, and conversely, if the upper limit is exceeded, it becomes difficult to correct spherical aberration on the telephoto side.

Condition (9) defines an appropriate angle of view at the wide-angle end of the lens system, and if the lower limit is exceeded, the cost will increase if the lens of the present invention is realized.

On the other hand, if the upper limit is exceeded, it becomes difficult to correct aberrations when the 1171st group consists of two negative and positive lenses, and therefore good aberration correction cannot be obtained.

The entire lens system of the present invention includes the 1171st lens group with two negative and positive lenses, the second lens group with four negative, negative, positive and negative lenses, and the third lens group with three positive, positive and negative lenses. If the fourth lens group is composed of two positive and negative lenses, a compact zoom lens with high performance equivalent to 35105mm for a 3511-lens reflex camera can be realized.

In this case, in a preferred specific configuration of the present invention, in order from the object side, the first lens group G includes a negative meniscus lens Lll with a convex surface facing the object side, and a surface with a strong curvature facing the object side. The second lens group G has a positive lens L1□ directed toward the
A negative lens L□ with a surface of strong curvature facing the image side, a negative lens Ltx, and a positive lens L0 with a surface of strong curvature facing the object side.
and a negative lens Lf4, the third lens group G has a positive lens □ and LxN, and a negative lens L33 with a surface of strong curvature facing the object side, and the fourth lens group G4 has , a biconvex lens L4, and a negative lens L4 with a surface of strong curvature facing the image side! It is good to have the following.

Further, it is desirable that the present invention is configured to further satisfy the following conditions.

r, −r・ However, r: radius of curvature of the object side surface of the negative lens located closest to the image side of the fourth lens group.

",: The radius of curvature of the image side surface of the negative lens located closest to the image side of the fourth lens group.

Condition (10) defines the appropriate shape of the negative lens located closest to the image side of the fourth lens group.

If the lower limit of this condition is exceeded, it becomes difficult to correct upper coma aberration, field curvature, etc. On the other hand, if the upper limit is exceeded, it becomes difficult to secure the back focus necessary for an eye reflex camera. Furthermore, it is more preferable that the upper limit of this condition (10) is 0.2.

Furthermore, by adopting a configuration that incorporates an aspherical lens, the present invention can be more advantageous in correcting field curvature, astigmatism, and coma aberration during zooming. however,
If an aspherical lens is introduced into the first lens group, the lens diameter becomes large, which increases the cost. Therefore, it is preferable to introduce an aspherical lens into the second lens group or the fourth lens group.

In this case, it is desirable that the aspherical lens introduced satisfies the following conditions.

-1^5-sl: Difference in the optical axis direction between the aspheric surface at the outermost edge of the effective diameter and a reference spherical surface having a predetermined apex radius of curvature.

f@: Focal length of the entire system at the wide-angle end.

The above condition (11) defines an appropriate amount of displacement from the aspherical surface to the reference spherical surface along the optical axis direction. If the lower limit of this condition is exceeded, it becomes difficult to effectively correct field curvature, astigmatism, and coma, and conversely, if the upper limit is exceeded, manufacturing becomes difficult.

Furthermore, on the lens surface through which the off-axis light flux passes through a position with a high effective diameter, that is, on the object side of the negative lens located closest to the image side of the fourth lens group, there is a negative refractive power in the peripheral area as described above. It is most effective to provide an aspherical surface that increases the strength.

(Example) The zoom lens shown in each example of the present invention has a variable power ratio of 3.
About double, 36. It has a focal length of 0 to 102.0, and the lens configuration in the first embodiment of the present invention is shown in FIG. In both the second and third embodiments, the first
It has the same configuration as the first embodiment shown in the figure, and the second embodiment
, the lens configurations of the third embodiment are shown in FIGS. 3 and 5, respectively.

Here, in FIGS. 1, 3, and 5, the top part shows the shortest focal length state BW (wide-angle end), the middle part shows the intermediate focal length state M, and the bottom part shows the longest focal length state T (telephoto end). As shown in the figure, zooming from the wide-angle end to the telephoto end in each example is achieved by increasing the distance between the first and second lens groups while increasing the distance between the third and fourth lens groups. This is done by moving each group toward the object so as to reduce the distance between the groups.

In addition, the specific configuration of each embodiment is shown in each figure (Figures 1 and 3).
As shown in Figure 5), from the object side, there are two lenses: a negative meniscus lens Lll with a convex surface facing the object side, and a positive meniscus lens L+t with a surface of strong curvature facing the object side. The 1171st group G1, the negative lens LSI whose surface with strong curvature faces the image side, and the negative lens Lz! A second lens group G consists of four lenses: a positive lens L23 with a surface of strong curvature facing the object side, and a negative lens Lx4.
2 and a positive lens l-11 with a surface of strong curvature facing the object side.
A third lens group G includes three lenses: a biconvex lens Let, and a negative lens Lff3 with a surface of strong curvature facing the object side.

The fourth lens group G4 consists of two lenses: a biconvex lens 1 and a negative lens L4z with a surface of strong curvature facing the image side.

However, in the first embodiment as shown in FIG. 1, a positive lens L having a surface of strong curvature faces the object side in the second lens group
23 and a negative lens L0 are bonded together, and in the third embodiment as shown in FIG. 5, the negative lens L in the second lens group. and a positive lens L0 with a surface of strong curvature facing the object side are bonded together.

Further, in each embodiment, the object side surface of the negative lens L4t, which is located closest to the image side of the fourth lens group G4 and has a surface of strong curvature facing the image side, has an aspherical surface.

Below, the values of the specifications of the first to third embodiments are shown in Tables 1 to 3, respectively.
Listed in Table 3. In the table, the leftmost number represents the order from the object side, r is the radius of curvature of the lens surface, d is the distance between lens surfaces,
The refractive index n and the ambe number ν are the d-line (λ-587.6r+s
+).

In addition, the height of the aspherical surface mentioned above from the optical axis is h, and the height h from the optical axis is
The distance between the tangent plane of the apex of the aspheric surface is X, the conic constant is k, and the 2nd, 4th, 6th, 8th, and 10th aspheric coefficients are A2, Aa, and A, respectively. Aa, A,
When the paraxial radius of curvature is r, it is expressed by the following aspherical equation.

In the table below, E-' in the value of the aspherical coefficient representing the aspherical shape represents to-''.

B r 41.1118 50.7129 61.6971 AI= 3.4705 [! '-10, A+o=-1,
2903E-12A, = 3.1596E-10,A
1. =-1,72291! -122ω+ 64.4°~ 23.2 " 63.657 42.190 43.184 563.710 ?9.205 16.708 1102.137 15.207 56.374 -27.660 402.262 51.652 264 .945 27.835 20.251 -61.876 23.825 56.688 -879.212 39.440 f 36.0000 d 4 0.5651 dll 10.7393 d16 13.0528 B f 43.3706 1.60 2.00 7.50 (variable) 23.0 55.6 1.86074 1.69680 1.00 46.8 3.60 1.00 56.4 3.50 25.5 2.20 1.80 60. 0 (variable) 3.00 45.9 0, 10 6.80 ?0.4 1.30 25.5 (variable) 1.76684 1.50137 1.80458 1.64000 1.54814 1.48749 1.80458 4.60 4.75 1.30 (Bf) 60.0000 20.7?91 6.0194 9.4124 55.2232 45.9 33.9 1.54814 1.80384 102.0000 37.7267 2.0167 6.1216 69.6535 19th side k -1,0O00 [!÷00, A4 = -3,4183B-05, A, = 6.4795E-11, Am -0,0000 p,, = -4,0211E -08 A1゜--5,5995[!-13 Table 4 below lists numerical values corresponding to the conditions of the present invention.

1]-0LLLL However, r4 rc r@
It is r@. In addition, the amount of displacement along the optical axis direction from the aspheric surface to the reference spherical surface in the above conditional expression regarding the aspheric surface is as follows: the effective diameter φ of the first to third embodiments is 17
．． This is the value at the time of 8.17.6.19.0.

The lenses in each example are constructed with an extremely small number of 11 lenses, and the first lens group is constructed with two lenses, resulting in a shape that is extremely advantageous for cost reduction and weight reduction. There is. Furthermore, the total length (distance from the first surface to the image plane) at the wide-angle end of the first to third embodiments is 10
9.51.109.69.112.98, it is extremely compact, so it can be seen that it is highly portable.

Figures 2, 4, and 6 respectively show various aberration diagrams of the first to third embodiments of the present invention, and (A) in the various aberration diagrams shows the shortest focal length state (wide-angle end). , (B) is the intermediate focal length state, and (C) is the longest focal length state! a (telephoto end). Here, d in each aberration diagram is dv
A (λ=587.6na), g is g&'A (λ=43
5.8 nm), and the broken line in the astigmatism diagram represents the meridional image plane, and the solid line represents the sagittal image plane.

From the comparison of each aberration, it can be seen that the lens maintains a compact shape, has a variable magnification ratio of about 3x, and has excellent imaging performance from the wide-angle end to the telephoto end.

It should be noted that focusing in the present invention is preferably performed by moving the third lens group and the fourth lens group toward the image side.

(Effects of the Invention) As described above, according to the present invention, the 1171st group can be configured with two lenses while ensuring a variable magnification ratio of about 3x and a long bank focus, resulting in a significant cost reduction. It is also possible to achieve a compact zoom lens that is lightweight, portable, and easy to operate.

In addition, in terms of aberration correction, in particular field curvature and coma aberration are extremely well corrected, making it possible to realize a high-performance compact zoom lens with excellent imaging performance from the wide-angle end to the telephoto end. .

[Brief explanation of the drawing]

FIGS. 1, 3, and 5 respectively show the first to fourth embodiments of the present invention in order.
FIG. 7 is a lens configuration diagram of a third embodiment and a diagram showing a variable power system of the present invention. Figure 2 (A), Figure 4 (A), Figure 6 (A)
1 and 2 respectively represent various aberration diagrams in the shortest focal length state (wide-angle end) of the first to third embodiments of the present invention. Figure 2 (
B), FIG. 4(B), and FIG. 6(B) respectively show various aberration diagrams in the intermediate focal length state of the first to third embodiments of the present invention. Figure 2 (C), Figure 4 (C), Figure 6 (
C) shows various aberration diagrams at the longest focal length M (telephoto end) of the first to third embodiments of the present invention, respectively. (Description of main parts) G1 - 1171st group 6, - 1171st group Gz'' - 1st lens group G4 - 11 - 1st lens group

Claims (1)

[Claims] 1) In order from the object side, a first lens group G_1 having a positive refractive power, a second lens group G_2 having a negative refractive power,
In a zoom lens having a third lens group G_3 having a positive refractive power and a fourth lens group G_4 having a positive refractive power, the first lens group G_1 includes a negative lens and a positive lens in order from the object side. Consisting of two lenses arranged separately, each lens group of the second lens G_2 to the fourth lens G_4 has at least two lenses, a positive lens and a negative lens, the first lens While increasing the group distance between the group G_1 and the second lens group G_2 and reducing the group distance between the third lens group G_3 and the fourth lens group G_4,
A compact zoom lens, characterized in that the lens groups are moved toward the object side to change the magnification from a wide-angle end to a telephoto end, and the zoom lens satisfies the following conditions. (1) 4.5≦|f_1/f_2|≦7.5 (2) 1.
2≦|f_3_4/f_2|≦1.6, however, f_1: focal length of the first lens group. f_2: Focal length of the second lens group. f_3_4: Combined focal length of the third lens group and the fourth lens at the wide-angle end. 2) A compact zoom lens according to claim 1, which satisfies the following conditions. (3) |α_w|≦1 However, α_w is the angle between the optical axis and the paraxial ray from the axially infinite object point that enters the lens surface of the fourth lens group closest to the object at the wide-angle end. This is a value obtained by setting the initial values in the axial ray tracing formula to α_1=0 and h_1=f_w (focal length of the entire system at the wide-angle end).