JPH05323193A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce variation in chromatic aberration due to zooming and to minimize the number of aspherical lenses. CONSTITUTION:The zoom lens is equipped with a front lens system 1 which consists of three lenses and has positive focal length, a variator system 2 which consists of three lenses and has negative focal length, an erector system 3 which consists of two convex and concave lenses, and a focusing system 4 which consists of two concave and convex lenses in order from the object side; and only one surface of the convex lens 10 of the erector system 3 on the side of an image plane 8 is made aspherical and conditions (a) -3X10<-3(1/nu1+f1)+(1/nu2+f2)<0 and (b) 0<(1/nu3+f3)+(1/nu4+f4)<2X10<-4> are satisfied, where f1 is the focal length of the convex lens 10 of the erector system 3, nu1 the Abbe number, f2 the focal length of the concave lens 11 of the erector system 3, nu2 the Abbe number, f3 the focal length of the convex lens 13 of the focusing system 4, nu3 the Abbe number, f4 the focal length of the convex lens 13 of the focusing system 4, and nu4 the Abbe number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in electronic photographing equipment such as video cameras.

[0002]

2. Description of the Related Art Conventionally, a zoom lens used in a small video camera is a front lens system including three lenses, a variator system including three lenses, and an erector including one lens in order from the object side. Many systems have a focusing system consisting of two lenses. In such a zoom lens, in order to reduce the number of lenses in the entire system,
Aspherical lenses are used for the erector system and the focusing system.

[0003]

However, in this zoom lens, since the erector system lens is composed of one lens, the variator system chromatic aberration is left uncorrected for the purpose of canceling the chromatic aberration generated in the erector system. Therefore, it is necessary to reduce chromatic aberration in the entire system. In such a method of correcting chromatic aberration, there remains a problem that chromatic aberration greatly changes due to zooming. Further, the aspherical lens is more expensive than a general lens, and it is desired to reduce the number of aspherical lenses used by more effectively using the aspherical lens. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zoom lens in which variation in chromatic aberration due to zooming is small and the number of aspherical lenses can be minimized.

[0004]

In order to achieve the above object, the present invention comprises, in order from the object side, a front lens system composed of three lenses and having a positive focal length, and a negative system composed of three lenses. Equipped with a variator system having a focal length of, an eclectic system composed of two convex and concave lenses, and a focusing system composed of two convex and concave lenses, and one or both surfaces of the convex convex lens of the focusing system are formed into an aspherical surface. , The convex lens has a focal length f ₁ , the Abbe number is ν ₁ , the eclectic concave lens has a focal length f ₂ , the Abbe number is ν ₂ , the focusing concave lens has a focal length f ₃ , the Abbe number is ν ₃ , and the focusing is When the focal length of the convex lens of the system is f ₄ and the Abbe number is ν ₄ , (a) −3 × 10 ⁻³ <(1 / ν ₁ · f ₁ ) + (1 / ν ₂
・ F ₂ ) <0 (b) 0 <(1 / ν ₃ · f ₃ ) + (1 / ν ₄ · f ₄ ) <2
It is characterized in that each condition of × 10 ^-4 is satisfied.

[0005]

According to the present invention, by constructing the erector system with two lenses, it is possible to reduce the occurrence of chromatic aberration in the erector system and it is also advantageous for correction of off-axis aberrations. It is not necessary to use an aspherical lens in the system, and by using an aspherical lens for only one convex lens in the focusing system, it is possible to reduce fluctuation in chromatic aberration due to zooming. In particular, when the condition (a) is satisfied, the axial chromatic aberration of the erector system is overcorrected, and the axial chromatic aberration is undercorrected to balance the correction in the focusing system, and the condition (b) is satisfied. As a result, correction of axial chromatic aberration of the focusing system becomes insufficient, and correction of lateral chromatic aberration becomes advantageous. In this invention, the focal length _{(c) -0.9 <(f 1} / f 2) of each lens of the erector system <- is satisfied 0.7 conditions, the light beam weak power Elekta system becomes divergent Gimi Therefore, the correction of spherical aberration in the focusing system will not be disadvantageous, and conversely, the power of the eclectic system will be strong and the light beam will not be converging to a disadvantage in curvature of field. The focal length of each lens of the focusing system _{(d) -6 <(f 3} / f 4) <- is satisfied second condition, the focusing system has a strong positive power, the spherical aberration correction and high Magnification becomes advantageous.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows the structure of a zoom lens for a video camera. This zoom lens includes a front lens system 1, a variator system 2, an eclectic system 3 and a focusing system 4 in order from the object side (left side in the figure), and a diaphragm 5 arranged between the variator system 2 and the eclectic system 3. Variator system 2
After focusing the light flux from, the focusing system 4 forms an image on an image plane 8 such as a CCD through a crystal filter 6 and a protective glass 7.

The front lens system 1 is composed of three lenses, has a positive focal length, and is fixed to the forefront. The variator system 2 has a variable magnification function, is composed of three lenses, has a negative focal length, and is movably provided between the front lens system 1 and the diaphragm 5. The erector system 3 is for making the divergent light parallel light, is composed of a convex lens 10 and a concave lens 11, and is fixed to the rear side of the diaphragm 5. The focusing system 4 has an image forming function, and is composed of a concave lens 12 and a convex lens 13, and has an erector system 3 and a crystal filter 6
It is provided so as to be movable between and. The convex lens 13 of the focusing system 4 is an aspherical lens in which only one surface on the image plane 8 side is aspherical.

In such a zoom lens, the focal length of the convex lens 10 of the erector system 3 is f ₁ , the Abbe number is ν ₁ , the focal length of the concave lens 11 of the erector system 3 is f ₂ , the Abbe number is ν ₂ , and the focusing system is When the focal length of the concave lens 12 of 4 is f ₃ , the Abbe number is ν ₃ , the focal length of the convex lens 13 of the focusing system 4 is f ₄ and the Abbe number is ν ₄ , (a) −3 × 10 ⁻³ <( 1 / ν ₁ · f ₁ ) + (1 / ν ₂
・ F ₂ ) <0 (b) 0 <(1 / ν ₃ · f ₃ ) + (1 / ν ₄ · f ₄ ) <2
The structure satisfies the conditions of × 10 ^-4 (c) -0.9 <(f ₁ / f ₂ ) <-0.7 (d) -6 <(f ₃ / f ₄ ) <-2.

The conditions (a) to (d) will be described below. The condition (a) relates to correction of axial chromatic aberration of the elector system 3. Under this condition (a), the axial chromatic aberration of the erector system 3 is overcorrected to balance with the correction of the focusing system 4 where the axial chromatic aberration is undercorrected. Outside this range, axial chromatic aberration cannot be corrected well. The condition (b) relates to correction of axial chromatic aberration in the focusing system 4. Under this condition (b), the axial chromatic aberration of the focusing system 4 is undercorrected, which makes it advantageous to correct the lateral aberration. If it deviates from this range, it becomes impossible to satisfactorily correct lateral chromatic aberration. The condition (c) relates to the power of the elector system 3. If it is below this range, the power becomes weak and the light flux becomes divergent, so that the correction of the spherical aberration in the focusing system 4 becomes disadvantageous. On the other hand, if it is more than this range, the power becomes strong and the light beam is concentrated, so that it is disadvantageous to the curvature of field. The condition (d) relates to the power of the focusing system 4. Focusing system 4
Has a strong positive power, and if it is less than this range, it is disadvantageous in the correction of spherical aberration. Conversely, if it is more than this range, the power of the focusing system 4 becomes weak, and the image plane position adjustment of the focusing system 4 and This results in a large amount of movement in the focusing operation, which is disadvantageous for increasing the magnification.

As described above, in this zoom lens, by constructing the erector system 3 with the convex lens 10 and the concave lens 11, it is possible to reduce the occurrence of chromatic aberration in the erector system 3 and to correct the off-axis aberration. Since it is also advantageous, it is not necessary to use an aspherical lens for the erector system 3, and by using an aspherical lens only on one surface of the convex lens 13 of the focusing system 4, it is possible to reduce variation in chromatic aberration due to zooming. The number of aspherical lenses can be reduced to the minimum, and the price can be reduced. Particularly, in this zoom lens, by satisfying the condition (a), the axial chromatic aberration of the elector system 3 can be overcorrected, and the axial chromatic aberration can be balanced with the correction by the focusing system 4, which is undercorrected. By satisfying the condition (b), the axial chromatic aberration of the focusing system 4 can be insufficiently corrected, and the lateral chromatic aberration can be advantageously corrected. Further, by satisfying the condition (c), the power of the eclectic system 3 is weak and the luminous flux becomes divergent, which is disadvantageous in correcting the spherical aberration in the focusing system 4, or conversely, the power of the eclectic system 3 is strong. It is possible to prevent the light flux from becoming too concentrated and disadvantageous to the curvature of field, and by satisfying the condition (d), the focusing system 4 has a strong positive power and correction of spherical aberration and Higher magnification can be advantageous.

Next, specific examples of this zoom lens are shown in Table 1.
Shown in. In Table 1, f is 7.18 to 27.5 mm and F _NO is 2.
0, the image circle is 6mmφ.

[Table 1]

Where R _i is the radius of curvature, D _i is the center thickness of each lens or the air gap, N _i is the refractive index at the d-line,
ν _i represents the Abbe number. Here, D ₅ , D ₁₀ , D ₁₅ , D ₁₉
Is a variable surface distance, and an example thereof is shown in Table 2.

[Table 2]

Further, the convex lens 13 of the focusing system 4
The expansion formula of the aspherical surface is: Z = cy ² / [1 + √ {1- (A ₁ +1) c ² y ² }] + A ₂ y ⁴ + A ₃ y ⁶ + A ₄ y ⁸ + A ₅ y ¹⁰ . However, Z is the amount of change in height at the central axis, c is the paraxial curvature, y is the height from the center, and A _i is the aspherical surface coefficient. The aspherical surface coefficient A _i is as shown in Table 3.

[Table 3]

Regarding the operation of such a zoom lens,
This will be described with reference to FIGS. 2 (A) to 2
(B) shows each system position at wide-angle, intermediate, and telephoto, and FIGS. 3 to 5 show spherical aberration and astigmatism at wide-angle, intermediate, and telephoto. Figure 2 at wide-angle
As shown in (A), the variator system 2 moves toward the front lens system 1 side and approaches, and the focusing system 4 moves to the middle of the elector system 3 and the crystal filter 6. Spherical aberration and astigmatism in this state have aberration curves as shown in FIGS. 3A and 3B, and it can be seen that the aberration characteristics are good. At the intermediate time, as shown in FIG. 2 (B), the variator system 2 moves to almost the middle of the front lens system 1 and the diaphragm 5, and the focusing system 4 becomes the middle of the elector system 3 and the crystal filter 6. To slightly move to the erector system 3 side.
The spherical aberration and astigmatism in this state have the aberration curves as shown in FIGS. 4A and 4B, and it can be seen that the aberration characteristics are good. Furthermore, when the lens is telephoto,
As shown in (C), the variator system 2 moves toward the diaphragm 5 side and approaches, and the focusing system 4 slightly moves from the middle of the elector system 3 and the crystal filter 6 toward the crystal filter 6 side. The spherical aberration and astigmatism in this state are shown in FIG.
The aberration curves are as shown in (A) and FIG. 5 (B),
It can be seen that the aberration characteristics are good.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows the structure of the zoom lens of the second embodiment. This zoom lens has the same configuration as that of the first embodiment except that the focusing system 4 is different. That is, the focusing system 4 is composed of the concave lens 12 and the convex lens 20, and is movably provided between the erector system 3 and the crystal filter 6. The convex lens 20 of the focusing system 4 is an aspherical lens whose both surfaces are aspherical. Also in this zoom lens, the focal length of the convex lens 20 is f4 and the Abbe number is ν
When set to 4, the structure satisfies the conditions (a) to (d) as in the first embodiment. Therefore, in such a zoom lens, in addition to the same effects as those of the first embodiment, in particular, both surfaces of the convex lens 20 of the focusing system 4 are formed as aspherical surfaces, so that the magnification is higher than that of the first embodiment. You can get high performance.

Table 4 shows a specific example of such a zoom lens. In Table 4, f is 7 to 56 mm, F _NO is 2.0, and the image circle is 6 mmφ.

[Table 4]

Where R _i is the radius of curvature, D _i is the center thickness of each lens or the air gap, N _i is the refractive index at the d-line,
ν _i represents the Abbe number. Here, D ₅ , D ₁₀ , D ₁₅ , D ₁₉
Is the variable surface spacing, and an example thereof is shown in Table 5.

[Table 5]

The convex lens 20 of the focusing system 4
The expansion formula of the aspherical surface of is exactly the same as that of the first embodiment,
The aspherical coefficient A _i is as shown in Table 6 unlike the first embodiment.

[Table 6]

Regarding the operation of such a zoom lens,
This will be described with reference to FIGS. 7A to 7
(B) shows each system position at wide-angle, intermediate, and telephoto, and FIGS. 8 to 10 show spherical aberration and astigmatism at wide-angle, intermediate, and telephoto. In the wide-angle state, as shown in FIG. 7A, the variator system 2 moves toward the front lens system 1 side and approaches, and the focusing system 4 moves to an intermediate position between the erector system 3 and the crystal filter 6. The spherical aberration and astigmatism in this state have the aberration curves as shown in FIGS. 8A and 8B, and it can be seen that the aberration characteristics are good. Further, in the intermediate state, as shown in FIG. 7 (B), the variator system 2 moves to almost the middle of the front lens system 1 and the diaphragm 5, and the focusing system 4 becomes the middle of the elector system 3 and the crystal filter 6. To slightly move to the erector system 3 side.
The spherical aberration and astigmatism in this state have aberration curves as shown in FIGS. 9A and 9B, and it can be seen that the aberration characteristics are good. Further, in the telephoto state, as shown in FIG. 7C, the variator system 2 moves to the diaphragm 5 side and approaches, and the focusing system 4 moves to the crystal filter 6 side and approaches. The spherical aberration and astigmatism in this state have the aberration curves as shown in FIGS. 10A and 10B, and it can be seen that the aberration characteristics are good.

[0020]

According to the first aspect of the present invention, by forming the erector system with two lenses, it is possible to reduce the occurrence of chromatic aberration in the erector system and it is also advantageous for the correction of off-axis aberrations. Therefore, it is not necessary to use an aspherical lens in the erector system, and the focusing system convex lens 1
By using the aspherical lens only for the number of lenses, it is possible to reduce the variation of the chromatic aberration due to zooming, reduce the number of the aspherical lenses to the minimum, and achieve the cost reduction. In particular, by satisfying the condition (a), the axial chromatic aberration of the elector system can be overcorrected, and the axial chromatic aberration can be balanced with the correction of the focusing system, which is undercorrected, and the condition (b) is satisfied. By satisfying the condition, correction of axial chromatic aberration of the focusing system becomes insufficient,
Correction of lateral chromatic aberration can be made advantageous. Claim 2
According to the invention, by satisfying the condition (c),
The power of the erector system is weak and the light beam becomes divergent, which is disadvantageous in correcting spherical aberration in the focusing system. Conversely, the power of the erector system is strong and the light beam becomes converging, which is disadvantageous in field curvature. By satisfying the condition (d), the focusing system has a strong positive power, and it is possible to advantageously correct spherical aberration and increase the magnification.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a zoom lens according to a first embodiment of the present invention.

2A and 2B show respective system positions when the zoom lens of FIG. 1 is used, FIG. 2A is a diagram showing each system position at a wide angle, FIG. 2B is a diagram showing each system position at an intermediate time, and FIG. The figure which shows each system position at the time of a telephoto.

FIG. 3 shows aberrations in the wide-angle state of FIG.
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

FIG. 4 shows aberrations in the intermediate state of FIG. 2 (B),
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

FIG. 5 shows aberrations in the telephoto state of FIG.
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

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

7A and 7B show respective system positions when the zoom lens of FIG. 6 is used, FIG. 7A shows respective system positions at a wide angle, FIG. 7B shows respective system positions at an intermediate time, and FIG. The figure which shows each system position at the time of a telephoto.

FIG. 8 shows aberrations in the wide-angle state of FIG.
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

FIG. 9 shows aberrations in the intermediate state of FIG. 6 (B),
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

FIG. 10 shows aberrations in the telephoto state of FIG. 6 (C),
(A) is a spherical aberration diagram, (B) is an astigmatism diagram.

[Explanation of reference numerals] 1 front lens system 2 variator system 3 erector system 4 focusing system 10 convex lens of erector system 11 concave lens of erector system 12 concave lens of focusing system 13 and 20 convex lens of focusing system

Claims (2)

[Claims] 1. A front lens system consisting of three lenses and having a positive focal length, a variator system consisting of three lenses and having a negative focal length, and a lens having two convex and concave lenses in order from the object side. An eclectic system and a focusing system composed of two concave and convex lenses are provided, and one or both surfaces of the convex lens of the focusing system is formed into an aspherical surface. The focal length of the convex lens of the erector system is f ₁ and the Abbe number is ν ₁ , The focal length of the concave lens of the erector system is f ₂ , the Abbe number is ν ₂ , the focal length of the concave lens of the focusing system is f ₃ , the Abbe number is ν ₃ , the focal length of the convex lens of the focusing system is f ₄ , When the number is ν ₄ , (a) −3 × 10 ⁻³ <(1 / ν ₁ · f ₁ ) + (1 / ν ₂
・ F ₂ ) <0 (b) 0 <(1 / ν ₃ · f ₃ ) + (1 / ν ₄ · f ₄ ) <2
A zoom lens characterized by satisfying each condition of × 10 ^-4 . 2. The focal length of each lens of the erector system and the focal length of each lens of the focusing system according to claim 1, wherein: (c) −0.9 <(f ₁ / f ₂ ) <− 0.7 (d) A zoom lens characterized by satisfying each condition of −6 <(f ₃ / f ₄ ) <− 2.