JP2541264B2 - Compact zoom lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a compact zoom lens suitable for, for example, a lens-sitter camera and the like, and particularly to a compact zoom lens having excellent short-distance imaging performance. It is a thing.

[Conventional technology]

In recent years, small cameras with lens shutters have become more and more automated, and automatic focus adjustment, automatic film loading, date imprinting device, built-in flash, etc. have become common specifications, and the user base has become quite wide. Recently, many products equipped with a multifocal lens have been provided, and those equipped with a zoom lens have also appeared, and the range of use has been expanded further.

The simplest zoom lens suitable for miniaturization of this type is a telephoto two-group zoom lens including a first lens group having a positive focal length and a second lens group having a negative focal length. It is a lens. Since this lens type has less back focus limitation than a lens for a single-lens reflex camera, it is a type suitable for shortening the back focus to some extent and downsizing.

[Problems to be solved by the invention]

By the way, the following three types of methods (1) to (3) are known as the focusing methods of the conventional telephoto type two-group zoom lens.

(1) A focusing method in which the entire lens system is moved as a unit.

(2) A focusing method in which the second lens group having a negative focal length is moved.

(3) A focusing method in which the first lens group having a positive focal length is moved.

Among these, in the methods (1) and (2), the amount of movement of the lens system required for focusing differs greatly at the wide-angle end and the telephoto end. This complicates the focusing device of the zoom lens, such as the automatic focusing mechanism. Also, a large and heavy lens group must be moved, which is not suitable for downsizing and cost reduction of the entire camera.

On the other hand, the method (3) is a focusing method generally used in zoom lenses, and has an advantage that the amount of movement of the lens system required for focusing can be made substantially equal at each focal length from the wide-angle end to the telephoto end. Therefore, the focusing device, especially the automatic focusing mechanism can be simplified, and at the same time, the size and cost of the entire camera can be reduced. For example, it is known from JP-A-60-170816. ing.

However, in this focusing method which has been known so far, in order to achieve a high zoom ratio and a compact size, the first lens group must be configured to have relatively strong power.

Therefore, tolerances such as eccentricity tend to be strict,
There is a risk of increasing costs.

Further, in the short-distance focusing state on the wide-angle side, meridional image plane curvature toward the object side and coma occur, and the image forming performance is significantly deteriorated, so that a sufficiently satisfactory image quality cannot be obtained.

Therefore, the present invention solves such a problem by a configuration adopting a novel focusing method, draws out a good short-distance focusing performance from the wide-angle end to the telephoto end, and is compact while achieving high magnification and simple. The main purpose of the present invention is to provide a zoom lens that can achieve cost reduction with its configuration.

[Means for solving problems]

The present invention comprises, in order from the object side, a first lens group G ₁ having a positive focal length and a second lens group G ₂ having a negative focal length, wherein the first lens group G ₁ and the second lens group G ₁ the inter-group distance between the lens group G ₂ by relatively changing the zoom lens to perform zooming, the first lens group G ₁ has a stop, the narrowed Riyori object group before having disposed positive focal length side G _F , having a rear group G _R arranged on the image side of the diaphragm and having a positive focal length, having the front group G _F , wherein the front group G _F is a lens with a concave surface facing the object side. It has at least one component and is basically configured to move the front group G _F to the object side for focusing.

In such a lens configuration, f _w is the focal length at the wide-angle end of the zoom lens, and f ₁ is the first lens group G ₁
, F _F is the focal length of the front lens group G _F , f _R is the focal length of the rear lens group G _R , and R is the object side of the lens component arranged with the concave surface facing the most object side in the front lens group G _F. Assuming that the radius of curvature is, (1) 0.5 <f ₁ / f _w <0.9 (2) 2.0 <f _R / f _F <5.0 (3) −1.7 <R / f _w <−0.4 It is a thing.

[Work]

In general, a telephoto type zoom lens adopting a method of focusing by moving the first lens group G ₁ toward the object side has a first lens group G ₂ in order to correct a positive distortion aberration generated in the second lens group G ₂ . By forming a lens surface with a concave surface facing the object side in one lens group, negative distortion is generated, and the distortion is corrected by balancing these aberrations.

However, as shown in FIG. 1A, the focusing method for moving the first lens group G ₁ toward the object side is concave toward the most image side in the first lens group G ₁ particularly when short-distance focusing is performed at the wide-angle end. The oblique rays g, h in the near-distance focused state, which are incident on the lens surface D arranged with the lens facing, are the oblique rays e, f in the infinity focused state.
It tends to diverge compared to.

For this reason, with respect to the lens surface D arranged with the concave surface facing the most object side in the first lens group G ₁ , the incident angle i of the oblique ray g on the upper side in the short-distance focused state is in the infinity focused state. It becomes larger than the incident angle j of the upper oblique ray e. As a result, the upper oblique ray g in the short-distance focused state is refracted more downward than the upper oblique ray e in the infinity focused state, so that inward coma occurs.

On the other hand, the incident angle 1 of the lower oblique ray h in the near-distance focused state is lower than the lower oblique ray f in the infinity focused state.
Is smaller than the incident angle k of. As a result, the lower oblique ray h in the near-distance focused state is refracted upward relative to the lower oblique ray f in the infinity focused state, so that an outward coma aberration occurs. To do.

Further, in this short-distance focusing state, the image plane due to the off-axis meridional oblique ray moves in the negative direction, and the image plane is curved.
When the zoom lens is downsized and the zoom ratio is increased, the short-distance imaging performance is significantly deteriorated.

Further, since the present invention performs focusing to extend the front lens group G _F , it has the same tendency of aberration as described above with reference to FIG. 1A. Accordingly, the present invention first by dividing the first lens group to the front group G _F and the rear group G _R, the focusing method of changing the inter-group distance between the front group G _F and the rear group G _R, essentially power arrangement It has a structure that can improve the degree of freedom.

In order to counteract such aberrations, the present invention is to weaken the refractive power of the front group G _F, by employing a configuration in which fed a large front group G _F at the time of focusing, a short distance focusing such as described above Aberrations that deteriorate the imaging performance in this state are corrected in a well-balanced manner, achieving outstandingly improved short-distance focusing performance, high magnification, and compactness.

The principle of the present invention will be specifically described below. First, as described above, by making the refractive power of the front lens group G _F in the present invention basically weak, the extension amount of the front lens group G _F at the time of focusing becomes large. Then, when the front group G _F is extended to the object side for focusing, the concave surface is arranged toward the most object side in the front group G _F with the amount of extension, as shown in FIG. 1B. The off-axis meridional oblique ray m incident on the lens surface D enters the lens surface D as an oblique ray n having a higher incident height.

Therefore, as the incident height of the off-axis meridional oblique ray incident on the concave lens surface D increases, the incident angle of the off-axis meridional oblique ray incident on the concave lens surface D increases, and as a result, The effect of the oblique rays being refracted downward becomes greater.

That is, as the amount of extension of the front lens group G _F increases, the height at which the off-axis meridional oblique rays are incident on the concave lens surface D increases, and therefore the strong refractive power in the peripheral portion of the concave lens surface D is received. , This off-axis meridional oblique ray is largely refracted downward.

Therefore, the off-axis meridional oblique light beam has a large effect that the lower ray is refracted downward relative to the central ray, which is the central ray, and inward coma occurs. On the other hand, the effect that the upper ray is refracted downward relative to the principal ray is small, and outward coma is generated. Further, the off-axis meridional image plane moves in the positive direction.

As described above, the present invention, by canceling the former aberrations described above based on FIG. 1A in a well-balanced manner by the latter aberrations described above based on FIG. 1B, causes aberration fluctuations at short distances, mainly. It achieves excellent short-distance focusing performance by keeping the field curvature and coma aberration fluctuations to a minimum.

 The conditions of the present invention will be described in detail below.

First, the conditions (1) and (2) are effective in suppressing the range of the focal length of the first lens group G ₁ suitable for the focusing method adopted by the present invention and the aberration variation in the short-distance focused state. It defines the range of the focal length between the group G _F and the rear group G _R.

When the value exceeds the upper limit of the condition (1), the refractive power of the first lens group G ₁ becomes small, and it becomes difficult to achieve compactness and high magnification. Regarding the focusing performance, it is not necessary to use the front group G _F feeding method because good focusing performance can be obtained even if the feeding method of the first lens group G ₁ is adopted. Dare, using the focusing method for feeding the front group G _F, the amount of movement becomes excessively large in the front group G _F, the positive curvature of field great to occur particularly when focusing on a nearby. On the other hand, when the value goes below the lower limit of the condition (1), it is advantageous for downsizing and high magnification of the zoom lens, but it becomes difficult to correct various aberrations.

Above the upper limit of the condition (2), the amount of movement of the front group G _F in the focusing system by feeding the front group G _F is not significantly increased compared to the case of the feeding of the first lens group, in order that, the front group The effect of extending G _F is weak, and negative field curvature occurs in a short-distance focused state, which is not preferable. On the contrary, if the lower limit of the condition (2) is exceeded, the amount of movement of the front group G _F becomes too large in the case of focusing by the front group G _F extension.
The effect of the extension of the front lens group G _F becomes excessive, and positive field curvature occurs in a short-distance focused state, which is not preferable.

The condition (3) relates to this concave surface of the lens component arranged with the concave surface facing the object side most in the front lens group G _F , and is most suitable for the focusing method and the aberration correction by the extension of the front lens group G _F adopted in the present invention. 3 illustrates a range of suitable concave shapes.

First, when the lower limit of the condition (3) is exceeded, the negative distortion aberration generated on the concave lens surface becomes small, and the positive distortion aberration generated on the second lens group G ₂ cannot be completely corrected. On the other hand, when the value exceeds the upper limit, the coma generated on the concave lens surface becomes so large that it becomes difficult to correct it.

〔Example〕

Examples according to the present invention will be described below. Each of the examples has a focal length of 36 to 78 mm and an F number of 3.6 to
It is a compact zoom lens with a brightness of about 7.8 and an angle of view of 60 to 30 °.

The first embodiment, the second embodiment, the fifth embodiment, the sixth embodiment and the seventh embodiment all have the same lens configuration as that of the first embodiment shown in FIG. The third embodiment and the fourth embodiment have lens configurations as shown in FIG.

The values of specifications of the first to seventh examples are listed below. 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 lens surface spacing, Abbe is the Abbe number, and n is the refractive index for the d line (λ = 587.nm). .
In addition, FN is an F number, 2A is an angle of view, D0 is an object distance from the first lens surface, and β is a short-distance photographing magnification.

The condition corresponding values in the above-described first to seventh embodiments according to the present invention are shown in the following condition corresponding value tables.

Focusing in the first embodiment, the second embodiment, the fifth embodiment, the sixth embodiment, and the seventh embodiment changes the air gap between the 11th surface and the 12th surface of the lens to change the front group G _F. It is extended to the object side. Further, in focusing in the third and fourth examples, the air gap between the eighth surface and the ninth surface of the lens is changed, and the front group G _F is extended to the object side.

Aberration diagrams of the first to seventh examples of the present invention are shown in order in FIGS. 4 to 17, respectively.

FIG. 4, FIG. 6, FIG. 8, FIG. 10, FIG. 10, FIG. 12, FIG. 14 and FIG. 16 are aberration diagrams in the infinity in-focus condition in Embodiments 1 to 7, and FIG. , FIG. 7, FIG. 9, FIG. 11, and FIG.
FIG. 15, FIG. 15 and FIG. 17 show aberration diagrams in the near focus state (600).

For comparison with the conventional zoom lens, FIGS. 18 to 24 show the focusing of the first lens group G ₁ based on the lens data of the first to seventh embodiments of the present invention. An aberration diagram for a close-range in-focus state (600) when the performing method is adopted is shown.

In these aberration diagrams, A is a half screen in the infinity focused state, B is the object height, FN is the F number, Y is the image height, and H is the incident height in the near distance focused state. Regarding the point aberration diagram, the broken line is a meridional screen,
The solid line is shown as the sagittal image plane.

In these aberration diagrams, (a) is the shortest focal length state at the wide-angle end, (b) is the intermediate focal length state,
19C shows various aberrations in the longest focal length state with the telephoto end.

In addition to comparing the optical performance of the conventional lens system that employs the focusing method that extends the first lens group G ₁ with the present invention,
When the optical performance of the present invention itself is evaluated, as is apparent from each aberration diagram, the present invention shows that various aberrations are from the wide-angle end to the telephoto end,
Further, it can be seen that the correction is extremely excellent from the infinity in-focus state to the short-distance in-focus state. Therefore,
According to the present invention, it is possible to realize a compact zoom lens having excellent zooming performance and a zoom ratio of 2 times or more.

〔The invention's effect〕

As described above, according to the present invention, the compact shape is maintained with a simple configuration, the zoom ratio is more than 2 times, and the aberration is favorably corrected from the wide-angle end to the telephoto end, and further from the infinity in-focus state to the close-range in-focus state. It is possible to realize a zoom lens capable of ensuring a corrected and excellent imaging performance.

[Brief description of drawings]

FIG. 1A is a diagram showing the principle of occurrence of aberrations in a short-distance focus state in the focusing system for moving out the first lens group G ₁ , FIG. 1B is a diagram showing the principle of the focusing system of the present invention, and FIG. 2 is 1st Example, 2nd Example, 5th Example,
FIGS. 4A to 17 are lens configuration diagrams showing the lens configurations of the sixth and seventh examples, FIG. 3 is a lens configuration diagram showing the lens configurations of the third example and the fourth example, and FIGS. (C) is a diagram showing various aberrations of the first to seventh embodiments of the present invention,
For comparison with the present invention, FIGS. 18 (a) to 24 (c) adopt the feeding method of the first lens group G ₁ based on the lens data of the first to seventh embodiments of the present invention. FIG. 9 is a diagram of various types of aberration in a short-distance focused state (600) when the image is taken. [Explanation of main parts] G _F …… front group (G ₁ …… first lens group) G _R …… rear group (G ₁ …… first lens group) G ₂ …… second lens group S …… diaphragm

Claims (1)

(57) [Claims] 1. A first lens unit having a positive focal length in order from the object side.
It is composed of a lens group G ₁ and a second lens group G ₂ having a negative focal length, and zooming is performed by relatively changing the group distance between the first lens group G ₁ and the second lens group G _2. In the zoom lens to be performed, the first lens group G ₁ has a diaphragm, a front group G _F arranged on the object side of the diaphragm and having a positive focal length, and a positive focal length arranged on the image side of the diaphragm. A rear group G _R, and the front group
G _F has at least one lens component with a concave surface facing the object side, the front group G _F is moved to the object side for focusing, and f _w is the focal length at the wide-angle end of the zoom lens, and f ₁ is the focal length of the first lens group G ₁ , f _F is the focal length of the front lens group G _F , f _R is the focal length of the rear lens group G _R , and R is the concave surface facing the most object side in the front lens group G _F. Assuming that the radius of curvature of the arranged lens component on the object side is (1) 0.5 <f ₁ / f _w <0.9 (2) 2.0 <f _R / f _F <5.0 (3) −1.7 <R / f _w <− Compact zoom lens characterized by being constructed to satisfy 0.4.