JP2947473B2 - Compact high-magnification zoom lens system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact high-magnification zoom lens system suitable for a camera having no restriction on back focus, for example, a lens shutter.

Furthermore, the present invention relates to the focusing and the aperture position of the zoom lens system.

2. Description of the Related Art Japanese Patent Application Laid-Open Nos. 56-128911 and 57-2012 describe zoom lenses for cameras having no restrictions on back focus.
A positive-leading two-component zoom lens composed of two components, positive and negative, in order from the object side such as No. 13 is known. Further, a three-component zoom lens disclosed in Japanese Patent Application Laid-Open Nos.
Various types of component zoom lenses have been proposed.

However, most of these zoom lenses have a relatively small zoom ratio, and a zoom ratio of 3
A zoom lens that surpasses has not been realized.

On the other hand, a relatively compact zoom lens for a single-lens reflex camera having a zoom ratio exceeding 3 is disclosed in Japanese Patent Application Laid-Open Nos. Sho 54-30855 and 55-156912, and Japanese Patent Application Laid-Open No. 57-169716 by the present applicant. Although various proposals have been made, the overall length of the lens system (the length from the front surface of the lens closest to the object side to the film surface) is large due to the constraints of the back focus.

Conventionally, most zoom lenses employ a front-group moving-out method in which the moving distance of focusing is constant for the same photographing distance in order to avoid complication of the mechanical mechanism of focusing. However, if the front-group moving-out method is adopted in the zoom type of the positive refractive power component leading type including the wide angle range, the front lens diameter becomes large in order to secure the illuminance ratio of the outermost periphery of the screen during close-up shooting.

On the other hand, in Japanese Patent Application Laid-Open No. 58-144332 by the present applicant, a condition in which the focusing movement amount for the same photographing distance is constant regardless of the focal length of the lens even in the extending method other than the front group extending method is presented. In recent autofocus cameras, the above-mentioned restrictions on focusing have been greatly eased. Conversely, in an autofocus camera, in order to make the drive system for focusing as compact as possible, it is desirable that the focusing lens group be lightweight and move a small amount.
Not enough has yet been realized.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact, high-performance, high-magnification zoom lens system suitable for a camera having no restrictions on back focus.

Further, the present invention provides a high-magnification zoom lens system that achieves a compact focusing drive system in an autofocus camera and high performance in close-up shooting by focusing with a relatively lightweight lens group. It is the purpose.

A further object of the present invention is to provide a zoom lens system in which the zoom ratio is increased while the zoom formation is simplified as compared with JP-A-60-57814.

Further, an object of the present invention is to provide a compact and high-performance high-magnification lens capable of moving the focusing and the aperture with the same driving source, and having sufficiently considered downsizing of the camera body and simplification of the mechanism. A zoom lens is provided.

Overview of the Present Invention A zoom lens system according to the present invention that achieves the above object has a first positive lens unit [I] and a second positive lens unit in order from the object side, as shown in the cross-sectional views of FIGS. The first positive lens group [L] includes a lens group [II] and a third negative lens group [III], and is used for zooming from the shortest focal length end (hereinafter referred to as S side) to the longest focal length end (hereinafter referred to as L end). I]
And the third negative lens group [III] moves from the image side to the object side, and the second positive lens group [II] moves during zooming. As a result, when zooming from the S end to the L end, As the air gap between the second lens groups increases, the air gap between the second and third lens groups decreases, and the second positive lens group [II] moves from the image side to the object side during focusing on a nearby object. While moving, the diaphragm is disposed closest to the object side or the image side of the second positive lens group [II], and is located in either the second positive lens group [II] or the third negative lens group [III]. It has an aspherical surface.

By arranging the second lens group [II], which is a focusing lens group, and the diaphragm in the same lens group as in the above-described configuration, the second lens group [II] and the diaphragm are shared by the same drive source. It is possible to do. In addition, by disposing the diaphragm closest to the object side or the image side of the focusing lens group, it is not necessary to move the diaphragm during focusing, so that the driving force required for focusing may be relatively weak. On the other hand, if the diaphragm is arranged in the focusing lens group, the driving force required for focusing needs to be relatively strong, and the eccentricity of the front and rear groups that sandwich the diaphragm in the focusing lens group will increase. Because of the large size, it is difficult to achieve high mounting accuracy. Therefore, by arranging the second lens group [II] and the diaphragm in the same lens group, it is possible to sufficiently reduce the size of both the lens system and the camera body or to simplify the mechanism.

Further, in the zoom lens system according to the present invention, it is desirable that the following condition is satisfied.

Here, L ₂ : the distance from the vertex of the most object side lens surface of the second positive lens group [II] at the S end to the film surface L ₂ ′: the most image side of the second positive lens group [II] at the S end Distance _L from the vertex of the lens surface to the film surface _L : Focal length of the entire system at the L end.

Conditional expression (1) defines the thickness of the second lens group [II] with respect to the focal length ( _L ) of the entire system at the L end. Since the stop is located closest to the object side or the image side of the second lens group [II], it is difficult to match the luminous flux around the screen with the stop over the entire zooming area if the upper limit is exceeded. And vignetting around the screen when narrowing down. In addition, the lower limit of the second lens group [I
If the thickness of [I] becomes too thin, even if the second lens group [I
Even if an aspherical surface is used in [I], it becomes difficult to satisfactorily correct aberrations and fluctuations during zooming, in particular, a balance between spherical aberration and coma.

Further, in the zoom lens system of the present invention, it is preferable that the following condition is further satisfied.

Where: _L : Focal length of the whole system at L end _S : Focal length of the whole system at S end Β _L2 : lateral magnification of the second lens unit [II] at the L end β _S2 : lateral magnification of the second lens unit [II] at the S end β _M2 : intermediate focal length This is the lateral magnification of the second lens group [II] in the state (hereinafter referred to as M state).

The conditional expressions (2) and (3) are conditions for defining the moving amount of focusing at each focal length in focusing using the second lens group [II].

In Japanese Patent Application Laid-Open No. 58-1443312, in order to keep this amount of extension constant regardless of a change in the focal length, It has been shown that the value of P indicated by needs to be substantially constant regardless of the change in the focal length. However, where, _A is the combined focal length of the lens group on the object side of the focusing lens unit, the beta _F is the lateral magnification of the group focusing lens.

In the present invention, since the second lens group [II] is a focusing lens group, the value Pi of P at an arbitrary focal length is Becomes

If Pi is constant in the entire zooming region, the amount of extension of the second lens group [II] is substantially constant regardless of the change in the focal length. Therefore, if the value of Pi is compared for each focal length, it becomes a comparison of the focusing movement amount for each focus processing.

Conditional expression (2) defines the ratio of the focusing movement amount at the S end to the focusing movement amount at the L end, and similarly, conditional expression (3) defines the focusing movement in the M state with respect to the focusing movement amount at the L end. It defines the ratio of the quantities. If the upper limits of conditional expressions (2) and (3) are exceeded, the focusing movement amount at the S end and the M state becomes too large compared to the focusing movement amount at the L end.

On the other hand, if the lower limit is exceeded, the focusing movement amount in the S end and the M state becomes too small compared to the L end, and in any case, the focusing movement amount is corrected by the camera body according to each focal length. In recent autofocus cameras, the restriction on the correction means has been greatly eased, but an excessively large moving amount ratio complicates the correction means and makes the camera body This hinders compactness and simplification.

Further, in the zoom lens system according to the present invention, it is preferable that the following condition is further satisfied.

Here, Δd _L , Δd _S , and Δd _M are focusing movement amounts from the infinity shooting state to the closest shooting state at the L end, the S end, and the M state, respectively.

Conditional expressions (4) and (5) represent L in the second lens group [II].
The ratio of the focusing movement amount in the end, S end, and M states is L
End, S end, and the focal length in the M state.
This is a focusing condition that includes compactness and simplification of the camera body together with conditional expressions (2) and (3). Problems that occur when the upper and lower limits of conditional expressions (4) and (5) are exceeded are the same as those described in conditional expressions (2) and (3).

If the maximum photographing magnification does not exceed β = 1/10 at the time of the closest photographing, it cannot be said that the focusing method is sufficiently practical.

Further, the zoom lens system according to the present invention has an aspheric surface in the second lens group [II], which is a focusing lens group,
It is desirable to satisfy the following conditions.

However, X: displacement of the optical axis direction at a height Y from the optical axis represented by the following formula _{X = X 0 + A 4 Y} 4 + A 6 Y 6 + A 8 Y 8 + A 10 Y 10 + ... X 0: lower The shape of the sphere used as a reference for the aspheric surface expressed by the formula A: Aspherical surface coefficient C ₀ : Curvature of the spherical surface as a reference of the aspherical surface N: Refractive index on the object side of the aspherical surface N ′: Refractive index on the image side of the aspherical surface

The condition (6) is that if the surface to which the aspherical surface is applied has a positive refractive power, the aspherical surface has a surface shape whose positive refractive power becomes looser as the distance from the optical axis of the lens increases. If the surface has a negative refractive power, it indicates that the surface has a negative refractive power that increases as the distance from the optical axis of the aspherical lens increases. In the vicinity of the optical axis which has little influence on the spherical aberration, even if the condition (6) is deviated by only a small amount, the condition substantially falls under the present invention. Accordingly, while the second lens group [II] as a whole has a strong positive refractive power, the aspherical surface provided therein satisfies the condition (6), so that it is relatively loose at a position away from the lens optical axis. It can have refractive power.
Accordingly, the on-axis light beam passes through a relatively high position in the second lens group [II] and the off-axis principal ray passes through a relatively low position. By applying the method to the lens group [II], it is possible to satisfactorily correct spherical aberration and fluctuation of coma during zooming.

In addition, in the present invention, the second lens group [II]
Aberration fluctuations that occur when the second lens group [II] is moved from the image side to the object side during focusing from infinity photography to closest photography, since the off-axis principal ray passing through the lens is at a relatively low position. And maintain excellent aberration performance.

In addition, by having an aspheric surface in the third lens group [III], it becomes possible to satisfactorily correct positive distortion at the L end and fluctuation of coma during zooming.

Furthermore, in the present invention, it is desirable that the following conditions are also satisfied.

Here, FM is the screen diagonal length.

The condition (7) is a condition for maintaining the compactness of the entire system while measuring the enlargement of the zoom ratio. If the upper limit of the condition (7) is exceeded, the overall length becomes long, and the compactness aimed at by the present invention is maintained. Becomes difficult. On the other hand, when the value goes below the lower limit of the condition (7), the back focus becomes short when the zoom ratio becomes large, and the diameter of the third lens group [III] increases or the second lens group [II] and the third lens group [III] increase. Lens group [III]
Becomes extremely thin, and the degree of freedom for correcting aberration fluctuations during zooming is reduced. When the degree of freedom is reduced, in a zoom lens including a wide angle and a relatively large zoom ratio as in the present invention, even if the aberration is corrected at the S end and the L end, particularly the spherical aberration in the M state is obtained. And it is difficult to correct the curvature of field.

Condition (8) is a condition for maintaining the compactness of the entire system while maintaining high performance under condition (7).
If the thickness of the second lens group [II] increases beyond the condition (1), it becomes difficult to realize a compact optical system. Conversely, when the value goes below the lower limit of the condition (8), it becomes difficult to correct aberration fluctuations during zooming, particularly spherical aberration and coma in a well-balanced manner, even if an aspheric surface is used for the second lens group [II].

Further, in the present invention, it is desirable that the following conditions be satisfied in addition to the above conditions (1) to (8).

However, where, f ₂ is the focal length of the second lens group (II).

The condition (9) appropriately defines the refractive power of the second lens group [II]. When the refractive power of the second lens group [II] becomes weaker than the upper limit of the condition (9), the third lens group is reduced. The on-axis luminous flux incident on [III] becomes high, the back focus becomes long, and the compactness is easily impaired. Conversely, if the refractive power of the second lens group [II] becomes too strong below the lower limit of the condition (9), the aberration generated in the second lens group [II] becomes large, and the spherical aberration at the S end in particular decreases. It is difficult to make a sufficient correction, and the back focus is too short. Therefore, it is not preferable to secure sufficient image plane illuminance at the S end because the diameter of the third lens group [III] becomes large.

Further, in the zoom lens system according to the present invention, it is desirable to satisfy the following conditions.

(11) 0.08 <| ₃ / _L | <0.45 (12) 0.25 <(D _L12 −DS ₁₂ ) / _S <0.60 where D _L12 : axial distance between the first and second lens groups at the L end D _S12 : axial distance between the first and second lens groups at the S end β _L3 : lateral magnification of the third lens group [III] at the L end β _S3 : lateral magnification of the third lens group [III] at the S end It is.

Condition (10) regulates the zooming effect of the third lens group [III]. If the upper limit of the condition (10) is exceeded, the refractive power of the third lens group [III] becomes stronger or the third lens group [III] becomes stronger. The amount of movement of the group [III] increases, and in the former case, it becomes impossible to realize the third lens group [III] with a relatively simple configuration. In the latter case, aberration fluctuations during zooming become large and the total length at the L end becomes long. Therefore, it is difficult to make the whole system including the lens barrel compact. If the lower limit of the condition (10) is exceeded, the burden on the second lens unit [II] for zooming will be too strong.

The condition (11) defines the refractive power of the third lens unit [III], and exceeds the upper limit of the condition (11).
When the refractive power of [I] becomes weak, the amount of movement of the third lens group [III] becomes large in order to obtain a predetermined zoom ratio, and it becomes difficult to make the entire system compact including the lens barrel configuration. When the value goes below the lower limit of the condition (11), the third lens unit [II
When the refractive power of [I] increases, the aberration generated in the third lens group [III] increases, and it becomes difficult to sufficiently correct distortion and fluctuation of coma during zooming.

Further, the condition (12) defines a change in the distance between the first lens unit [I] and the second lens unit [II] due to zooming. If the upper limit of the condition (12) is exceeded, aberration due to zooming will be satisfied. It becomes difficult to satisfactorily correct fluctuations, especially spherical aberration and coma,
Since the distance between the lens groups is too large, the diameter of the front lens or the diameter of the rear lens is too large to secure a sufficient image plane illuminance at the outermost periphery of both surfaces, and it is difficult to ensure compactness. If the lower limit of the condition (12) is exceeded, the change in the distance between the two lens units during zooming will be small, making it difficult to increase the zoom ratio.

Further, in the present invention, it is desirable to satisfy the following conditions in processing the aspherical surface.

(13) Nd ₂ <1.6 νd ₂ <60 where Nd ₂ is the refractive index of the lens having an aspheric surface in the second lens group [II], and νd ₂ is the refractive index of the lens in the second lens group [II]. This is the Abbe number of a lens having a spherical surface. By using a plastic lens that satisfies the condition (13) for the lens having an aspherical surface, it is possible to save a great deal of labor in a processing step, which is preferable in manufacturing.

In the present invention, a specific configuration of each lens group is preferably as follows.

The first lens group [I] includes at least one positive lens and one
By including the negative lenses, the first lens unit [I] is given a relatively strong refractive power, and the amount of movement of the first lens unit [I] due to zooming can be suppressed as small as possible. In addition, since the third lens group [III] includes at least one positive lens and one negative lens, chromatic aberration during zooming, particularly chromatic aberration of magnification, can be corrected with good balance. During zooming, the first lens group [I] and the third lens group [III] move together and the second lens group [II] also moves separately, so that each lens group is separated. This is advantageous in terms of the lens barrel configuration as compared with the configuration in which the lens barrel is moved.

Although the present invention is basically a zoom lens system composed of three groups, even if a component having a relatively weak refractive power fixed to the most image side is added, the constitutional requirements of the present invention are essentially deviated. Never.

Examples Examples of the present invention will be described below. In each embodiment, r ₁ is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th axial distance in order from the object side, and ni and νi are the i-th lens in order from the object side. Are the refractive indices and Abbe numbers, and the surface marked with (*) is an aspheric surface. Tables 1 and 2 show values for each condition of each embodiment.

[Brief description of the drawings]

FIGS. 1 and 2 are sectional views showing lens arrangements at the shortest focal length end (S end) and the longest focal length end (L end) of the zoom lenses according to the first and second embodiments of the present invention, respectively.
FIG. 6 shows the shortest focal length end <S>, the intermediate focal length <M>, and the longest focal length end <
FIG. 7 is an aberration diagram showing various aberrations at an object distance of L> at infinity. I: First lens group II: Second lens group III: Third lens group F: Focusing lens group S: Aperture

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-184916 (JP, A) JP-A-61-52620 (JP, A) JP-A-62-78522 (JP, A) JP-A-63-1982 161423 (JP, A) JP-A-1-307715 (JP, A) JP-A-2-50117 (JP, A)

Claims (3)

(57) [Claims] 1. A zoom lens system comprising: a first positive lens group, a second positive lens group, and a third negative lens group, in order from the object side, and the first positive lens group when zooming from the shortest focal length end to the longest focal length end. And the third negative lens unit move from the image side to the object side, and the second positive lens unit moves during zooming. As a result, when zooming from the shortest focal length end to the longest focal length end, the first positive and second negative lens units are moved. As the air gap between the lens groups increases, the air gap between the second positive and third negative lens groups decreases, and when focusing on a nearby object, the second positive lens group moves from the image side to the object side. A diaphragm disposed on the most object side or the most image side of the second positive lens group, having an aspheric surface in the second positive lens group, and satisfying the following conditions: Magnification zoom lens system; Here, L ₂ is the distance from the vertex of the lens surface closest to the object side of the second positive lens group in the shortest focal length state to the film surface. L ₂ ′ is the lens surface of the second positive lens group closest to the image in the shortest focal length state. Distance from the vertex to the film surface L: focal length of the entire system at the longest focal length end X: displacement position in the optical axis direction on the aspheric surface in the second positive lens at the optical axis height Y represented by the following equation _{X = X 0 + a 4 Y} 4 + a 6 Y 6 + a 8 Y 8 + a 10 Y 10 + ... X 0: spherical shape of which the second aspherical criteria in aspheric in positive lens represented by the following formula A: Aspherical surface coefficient C ₀ : Curvature of the spherical surface serving as a reference for the aspherical surface in the second positive lens N: Refractive index on the object side of the aspherical surface in the second positive lens N ′: Aspherical surface in the second positive lens This is the refractive index on the more image side. 2. The zoom lens system according to claim 1, further satisfying the following condition: Where L: focal length of the whole system at the longest focal length end S: focal length of the whole system at the shortest focal length end In defined as an intermediate focal length βL of the entire system _2: the longest focal length lateral magnification of the second lens group at the end .beta.S _2: shortest focal length lateral magnification of the second lens group at the end .beta.M _2: in the intermediate focal length This is the lateral magnification of the second lens group. 3. The zoom lens system according to claim 2, further satisfying the following condition: Here, ΔdL, ΔdS, and ΔdM are the focusing movement amounts from the infinity shooting state to the closest shooting state at the longest focal length end, the shortest focal length end, and the intermediate focal length, respectively.