JPH0688940A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To obtain a compact zoom lens suitable for a video camera, etc., including a wide angle in a variable power area, having a variable power ratio of six, F number of about 1.4-2.0, a few number of component lenses and compact in the total length and the front lens diameter. CONSTITUTION:This lens comprizes, in order from an object side, a first positive lens component remaining fixed at the time of varying the power, a second negative lens component moving for varying the power, a third positive lens component remaining fixed at the time of varying the power and a fourth positive lens component for compensating time movement of a focal position occurred at the time of varying the power, the second lens component is composed of a first negative lens having a high power surface faced to the image side, a second biconcave lens and a third positive lens in order from the object side and an air lens is arranged between the second and the third lenses. If necessary, a fifth lens component having comparatively lower refractive power on the image side of the fourth lens component is arranged while being fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a compact zoom lens which is suitable for a video camera or the like and has a wide variable angle with a high zoom ratio.

[0002]

2. Description of the Related Art Hitherto, as a bright and highly variable zoom lens used in a video camera or the like, Japanese Patent Laid-Open No. 62-24
As disclosed in Japanese Patent Application Laid-Open No. 213 and Japanese Patent Application Laid-Open No. 63-123009, it is composed of four lens components having positive, negative, positive, and positive refracting powers in order from the object side. While keeping the third lens component fixed, the second lens component is moved in one direction to perform zooming, and the fourth lens component is moved back and forth to correct the variation in the focal position due to zooming. Things are known.

The angle of view at the wide-angle end of these zoom lenses is
In the case of the one described in JP-A-62-24213, the angle is about 46.2 degrees, and
In the case described in the publication, the angle is about 50.2 degrees. If a wider-angle lens is used, the front lens becomes too large in this type of zoom lens. Further, in this type of zoom lens, the movement amount of the fourth lens component for correcting the image plane position due to zooming is relatively large,
If the entire system is reduced in order to make the lens system compact, there is a drawback in that it is not possible to sufficiently correct the variation in aberration due to zooming.

[0004]

The present invention is suitable for video cameras and the like, has a wide angle of view of about 55.0 degrees at the wide-angle end, a zoom ratio of about 6 times, and an F number of 1.4 to. The objective of the present invention is to obtain a zoom lens of about 2.0, which has a small number of components and is compact in both the overall length and the front lens diameter but does not include the above-mentioned drawbacks.

[0005]

The zoom lens of the present invention basically has a positive refractive power in order from the object side.
The first lens component that remains fixed during zooming, has a negative refractive power, the second lens component that moves back and forth for zooming, that has a positive refractive power, that remains fixed during zooming A certain third lens component is composed of a fourth lens component having a positive refracting power and correcting the movement of the focal position due to zooming. The second lens component has a strong concave surface on the image side in order from the object side. It is composed of a negative first lens, a biconcave second lens, and a positive third lens, and an air lens is arranged between the second lens and the third lens. This second lens component moves from the object side to the image side when zooming from the wide-angle side to the telephoto side.

It is desirable that the light beam incident on the fourth lens component be substantially afocal. Further, in the zoom lens of the present invention, focusing is preferably performed by the fourth lens component, but may be performed by the first lens component or the third lens component.

The zoom lens of the present invention is specifically
The first lens component includes at least one positive lens and at least one negative lens, the third lens component includes at least one positive lens, and the fourth lens component includes at least one positive lens and at least one lens. Including the negative lens of, the following conditions are satisfied. 4.0 <f ₁ /fw<4.7 (1) 0.2 <| f ₂ | Fw / (fwZ) <0.4 (2) 1.8 <f ₄ /fw<2.5 (3) However, fw: focal length at wide-angle end of the entire system fi: combined focal length of i-th lens component Fw: F-number at wide-angle end Z: zoom ratio

Further, in some cases, a fifth lens component having a relatively weak refractive power and fixed during zooming is placed on the image side of the fourth lens component.

Furthermore, it is desirable to introduce an aspherical surface satisfying the following conditions into the fourth lens component or the fifth lens component. 0.001 <FwΣΔi / fw <0.03 (4) where Δi is the difference in the optical axis direction between the aspherical surface at the maximum effective diameter on the i-th refracting surface and the reference spherical surface having the vertex curvature radius, The case where the aspherical surface is displaced toward the image side as the distance from the optical axis is positive is defined as positive. Σ is the sum for all aspherical surfaces in the fourth lens component and the fifth lens component.

More specifically, in the zoom lens of the present invention, the first lens component is composed of, in order from the object side, a negative meniscus lens and a positive lens having a convex surface directed toward the object side.
It is composed of a positive doublet and a positive meniscus lens having a convex surface facing the object side, the third lens component is one positive lens, and the fourth lens component is, in order from the object side,
It is desirable that at least one positive lens having a strong convex surface facing the image side, at least one pair of negative lens, and doublet of the positive lens are included, and the following conditions are satisfied. n ( ₁ p)> 1.55 (5) n ( ₂ n)> 1.65 (6) ν ( ₂ n) −ν ( ₂ p)> 20.0 (7) where n ( ₁ p): Average value of refractive index of positive lens in first lens component n ( ₂ n): Average value of refractive index of negative lens in second lens component ν ( ₂ n): Abbe of negative lens in second lens component Average number ν ( ₂ p): The average Abbe number of the positive lens in the second lens component.

[0011]

In the basic construction of the zoom lens of the present invention, the second lens component includes at least two negative lenses because the second lens component has a sufficient refracting power and zooming is performed. This is to reduce the amount of movement to reduce the front lens diameter. Further, by disposing the air lens between the biconcave second lens and the positive third lens, the light ray can be repelled by the second lens and the height of the light ray incident on the third lens can be increased. As a result, the height of the light beam incident on the second lens component can be kept low, and the front lens diameter can be made more compact. Moreover, as the angle of view becomes wider, it becomes difficult to balance the spherical aberration over the entire range from the wide-angle end to the telephoto end, and the field curvature becomes over, but between the second lens and the third lens. By providing the air lens, it is possible to avoid the above deterioration of performance.

At least one negative lens is included in each of the first lens component and the fourth lens component having a positive refractive power, and at least one positive lens is included in the second lens component having a negative refractive power. This is because the axial chromatic aberration and the chromatic aberration of magnification are sufficiently corrected in the entire region of zooming. The third lens component having positive refracting power does not necessarily include a negative lens, but by over-balancing the color correction of the fourth lens component, even if this is omitted, the chromatic aberration of the entire system will be reduced. You can make corrections.

By making the light beam incident on the fourth lens component substantially afocal, it is possible to reduce aberration fluctuations due to movement of the component due to zooming. Further, when focusing is performed by moving the fourth lens component toward the object side, it is possible to reduce variation in aberration due to movement of the component due to focusing.

The condition (1) relates to an appropriate value of the focal length of the first lens component, and is in a range particularly effective for widening the angle.
If the upper limit is exceeded, the diameter of the front lens will increase and the meridional image plane will become over, making it difficult to widen the angle. If the lower limit is not satisfied, it will be advantageous for widening the angle, but it will be difficult to correct spherical aberration at the telephoto end. become.

The condition (2) relates to the proper value of the focal length of the second lens component, and when the absolute value of the focal length becomes large beyond the upper limit, it is advantageous for aberration correction, but from the first lens component to the third lens component. The length up to the lens component increases, and a compact lens system cannot be obtained. If the lower limit is not satisfied, the above-described configuration makes it impossible to correct aberration fluctuations associated with zooming, particularly distortion and coma aberrations, and the negative distortion at the wide-angle end becomes excessive.

Condition (3) relates to the focal length of the fourth lens component, and if the lower limit is not satisfied, the length from the front of the fourth lens component to the image pickup surface tends to be short, which is advantageous for shortening the overall length. However, the angle of view of the entire fourth lens component becomes large, and the height at which the light flux incident on the screen corner passes through the first lens component becomes high, leading to an increase in the front lens diameter. When the upper limit is exceeded and the focal length becomes long, not only the total length of the lens system becomes long, but also the diaphragm diameter for obtaining a predetermined aperture becomes large.

The condition (4) is the fourth lens component and the fifth lens component.
Regarding the sum of the amount of aspherical deformation in the effective diameter of each lens surface for all aspherical surfaces in the lens component, if the lower limit is not satisfied, negative distortion will be corrected at the wide-angle end if the entire system is made compact. However, if it exceeds the upper limit, it is effective in correcting distortion, but the field curvature becomes excessive over the entire zoom range.

The condition (5) relates to the refractive index of the positive lens which constitutes the first lens component. If the condition is not satisfied, it becomes difficult to correct the spherical aberration over the entire zoom range.

The condition (6) relates to the refractive index of the negative lens constituting the second lens component. If the condition is not satisfied, it becomes difficult to correct the negative distortion aberration at the wide angle end under the above configuration.

The condition (7) relates to the difference in the Abbé number between the negative lens and the positive lens constituting the second lens component. If the condition is not satisfied, the variation of chromatic aberration during zooming, especially the variation of chromatic aberration of magnification becomes large. At the wide-angle end, the short-wavelength imaging point tends to shift too much in the direction in which the image height is small and in the telephoto side in the direction in which the image height is large.

[0021]

EXAMPLES Examples of the zoom lens of the present invention will be shown below. In the table, f is the focal length of the entire system, 2ω is the angle of view, F is the F number, fB is the back focus, R is the radius of curvature at the apex of each refractive surface, D is the distance between the refractive surfaces, and N is the d-line of the lens material. Is the refractive index, and vd is the Abbe number for the d-line of the single lens material. In addition, the aspherical shape has κ as the conic constant,
Ai is an aspherical surface coefficient, and Pi is a power of the aspherical surface.

[Equation 1] Where x is the origin of the aspherical vertex and coordinates from the object side to the image side along the optical axis h: Coordinates of which the aspherical vertex is the origin and perpendicular to the optical axis r: Paraxial radius of curvature of the aspherical surface Represents

The first to third embodiments have a fixed fifth lens component. Placing the fifth lens component, which remains fixed during zooming, on the most image side is extremely effective in compactly constructing a high zoom lens having a zoom ratio of about 6 times. In the first and second examples, the refractive power of the fifth lens component is positive. In this type of zoom lens,
The diaphragm is placed in front of the third lens component or the fourth lens component, but when the rear part of the diaphragm is shortened in order to make the entire system compact, the exit pupil position becomes extremely close to the image plane. It tends to be. When placing a solid-state image sensor such as a CCD on the image pickup surface, if the exit pupil position is too close to the image pickup surface, the effect of color filters and on-chip lenses on the image pickup surface causes
A color shift is likely to occur with respect to the peripheral light flux, and the amount of peripheral light is likely to decrease due to an apparent change in aperture ratio. But the fifth
If the refractive power of the lens component is set to be positive and the lens component is placed relatively close to the image plane, the exit pupil position can be located further away, and the above-mentioned problems can be improved.

On the contrary, in the third embodiment, the refracting power of the fifth lens component is made negative. In this case, the telephoto ratio of the combined system of the fourth lens component and the fifth lens component can be made small, so that the total length of the lens system can be made shorter than in the case where the fifth lens component is not provided. In addition, if the zoom system is made compact, it tends to be difficult to correct the negative distortion aberration generated in the second lens component at the wide-angle end, but by disposing the fifth lens component having negative refractive power, Since such an effect can be partially canceled, the overall length of the zoom system and the front lens diameter can be reduced as compared with the conventional one.

The fifth lens component has a relatively weak refractive power, and unlike the other lens components, it is placed near the image plane regardless of zooming, so that the focus position changes due to environmental changes such as temperature and humidity. Since the number is small, it can be configured by a plastic lens (marked with * in the table) as in the embodiment.

The fourth embodiment does not have a fixed fifth lens component. By introducing an aspherical surface into the fourth lens component, the number of constituent lenses is reduced.

The numerical values corresponding to each condition in each embodiment are as follows. Third Embodiment Second Embodiment In the first embodiment the fourth embodiment _{f 1 / fw 4.40 4.36 4.34 4.30} | f 2 | Fw / (fwZ) 0.295 0.294 0.295 0.297 f ₄ / fw 2.25 2.11 2.18 2.02 Fw ΣΔi / fw 0.0144 0.0146 0.0224 0.0089 n ( ₁ p) 1.65 1.65 1.65 1.65 n ( ₂ n) 1.73 1.73 1.73 1.73 ν ( ₂ n) −ν ( ₂ p) 23.8 23.8 23.8 23.8

Example 1 f = 6.18 to 36.18 F = 1.44 to 2.00 2ω = 54 ° 58 'to 9 ° 14' Variable spacing f A B C D 6.18 0.79 15.79 4.10 4.72 15.04 8.37 8.21 3.20 5.62 36.18 14.21 2.38 7.00 1 0.82 Subsystem focal length First lens component f (1-5) = 27.176 Second lens component f (6-11) =-7.412 Third lens component f (12-13) = 27.371 Fourth lens component f (14-18) = 13.904 Fifth lens component f (19-22) = 140.931 Aspherical coefficient / power number 12th surface κ = −0.60880 × 10 A1 = 0.29549 × 10 ⁻³ P1 = 4.0 A2 = −0.70126 × 10 ⁻⁵ P2 = 6.0 A3 = 0.12627 × 10 ⁻⁶ P3 = 8.0 A4 = −0.12357 × 10 ⁻⁸ P4 = 10.0 20th surface κ = 0.24569 × 10 ² Maximum effective diameter 4.932 A1 = 0.33329 × 10 ⁻³ P1 = 4.0 A2 = −0.43227 × 10 ⁻⁶ P2 = 6.0 A3 = 0.15415 × 10 ⁻⁶ P3 = 8.0 A4 = 0.15413 × 10 ⁻⁹ P4 = 10.0

Example 2 f = 6.14 to 36.01 F = 1.44 to 2.00 2ω = 55 ° 16 'to 9 ° 18' Variable spacing f A B C D 6.14 0.79 15.79 4.10 4.72 15.10 8.37 8.21 3.20 5.62 36.01 14.21 2.38 7.00 1 0.82 Subsystem focal length First lens component f (1 to 5) = 26.779 Second lens component f (6 to 11) = −7.356 Third lens component f (12 to 13) = 32.080 Fourth lens component f (14-18) = 12.980 Fifth lens component f (19-22) = 227.999 Aspheric coefficient / power number 12th surface κ = −0.41997 × 10 A1 = 0.37125 × 10 ⁻³ P1 = 4.0 A2 = −0.69701 × 10 ⁻⁵ P2 = 6.0 A3 = 0.12554 × 10 ⁻⁶ P3 = 8.0 A4 = −0.12374 × 10 ⁻⁸ P4 = 10.0 20th surface κ = 0.24569 × 10 ² Maximum effective diameter 5.038 A1 = 0.33329 × 10 ⁻³ P1 = 4.0 A2 = −0.43227 × 10 ⁻⁶ P2 = 6.0 A3 = 0.15415 × 10 ⁻⁶ P3 = 8.0 A4 = 0.15413 × 10 ⁻⁹ P4 = 10.0

Example 3 f = 6.16 to 36.01 F = 1.44 to 2.00 2ω = 55 ° 02 'to 9 ° 16' Variable spacing f A B C D 6.16 0.79 15.79 4.10 4.72 15.10 8.37 8.21 3.20 5.62 36.01 14.21 2.38 7.00 1 0.82 Subsystem focal length First lens component f (1-5) = 26.72
8 2nd lens component f (6-11) = -7.37
9 3rd lens component f (12-13) = 31.92
7 4th lens component f (14-18) = 13.43
5 Fifth lens component f (19-22) =-141.886
2 Aspheric surface coefficient / power number 12th surface κ = −0.72884 × 10 A1 = 0.19203 × 10 ⁻³ P1 = 4.0 A2 = −0.65563 × 10 ⁻⁵ P2 = 6.0 A3 = 0 .12859 × 10 ⁻⁶ P3 = 8.0 A4 = −0.12311 × 10 ⁻⁸ P4 = 10.0 20th surface κ = 0.24569 × 10 ² Maximum effective diameter 5.008 A1 = 0.33329 × 10 ^-3 P1 = 4.0 A2 = -0.43227 × 10 ^-6 P2 = 6.0 A3 = 0.15415 × 10 ^-6 P3 = 8.0 A4 = 0.15413 × 10 ^-9 P4 = 10.0

Example 4 f = 6.18 to 36.01 F = 1.44 to 2.00 2ω = 55 ° 40 'to 9 ° 16' Variable spacing f A B C D 6.18 0.79 15.79 4.10 8.06 15.11 8.37 8.21 3.20 8.96 36.01 14.21 2.38 7.00 5 .16 Focal length of subsystem First lens component f (1 to 5) = 26.579 Second lens component f (6 to 11) = −7.432 Third lens component f (12 to 13) = 35.575 Fourth lens component f (14 to 18) = 12.514 Aspheric coefficient / power number 12th surface κ = −0.28311 × 10 A1 = 0.73539 × 10 ⁻³ P1 = 4.0 A2 = −0. 87 125 × 10 ⁻⁵ P2 = 6.0 A3 = 0.16093 × 10 ⁻⁶ P3 = 8.0 A4 = −0.10542 × 10 ⁻⁸ P4 = 10.0 18th surface κ = −0.38661 × 10 Maximum effective diameter 5.008 A1 = 0.37554 × 10 ⁻⁴ P1 = 4.0 A2 = 0.87734 × 10 ^-6 P2 = 6.0 A3 = 0.31965 × 10 ^-8 P3 = 8.0

[0031]

As can be seen from the above embodiments and aberration diagrams, the zoom lens of the present invention has a wide angle of view of about 55.0 degrees, a zoom ratio of about 6 times, and an F number of 1. 4-
About 2.0, the number of components is small, the overall length and the front lens diameter are compact, but the aberration is well corrected in the entire zoom range,
The zoom lens is suitable for video cameras and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a zoom lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a second embodiment of the zoom lens according to the present invention.

FIG. 3 is a sectional view of a zoom lens according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a fourth embodiment of the zoom lens according to the present invention.

FIG. 5 is an aberration diagram of the first embodiment of the zoom lens according to the present invention.

FIG. 6 is an aberration diagram of a second embodiment of the zoom lens according to the present invention.

FIG. 7 is an aberration diagram of a third embodiment of the zoom lens according to the present invention.

FIG. 8 is an aberration diagram of a fourth embodiment of the zoom lens according to the present invention.

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[Procedure amendment]

[Submission date] September 7, 1993

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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[Figure 6]

[Figure 7]

[Figure 8]

Claims (2)

[Claims] 1. A first lens component having a positive refracting power and remaining fixed during zooming, and a second refracting lens having a negative refracting power and moving back and forth for zooming in order from the object side. A lens component, a third lens component that has a positive refractive power and remains fixed during zooming, and a fourth lens component that has a positive refractive power and corrects movement of the focal position during zooming. The second lens component is composed of, in order from the object side, a negative first lens having a strong surface facing the image side, a biconcave second lens, and a positive third lens. A zoom lens characterized in that an air lens is arranged between the lenses. 2. The zoom lens according to claim 1, further comprising a fifth lens component, which has a relatively weak refractive power and is fixed during zooming, on the image side of the fourth lens component.