JPH0413109A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To make the zoom lens compact and to decrease aberrational variation by giving relatively low negative refracting power to a 5th lens element which is fixed at the time of power variation. CONSTITUTION:A 1st lens element consists of one positive tablet composed of a negative meniscus lens and a biconvex lens and a positive meniscus lens which is convex to the object side in order from the object side and a 2nd lens element II consists of a negative lens which has a large-curvature surface on the image side and a negative tablet composed of a biconcave lens and a positive lens in order from the object side and a 3rd lens element III is one positive lens or a positive tablet composed of one positive lens and a negative meniscus lens; and a 4th lens element IV includes at least a negative lens having a large-curvature surface on the image side and one positive lens in order from the object side and the 5th lens V is composed of a single negative lens which has relatively weak refracting power. Consequently, the zoom lens is made compact, various aberrations are compensated excellently, and variation of the various aberrations due to power variation is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and in particular to a compact, bright, and high variable power zoom lens suitable for video cameras and the like.

(Prior art) As seen in Japanese Patent Application Laid-open No. 62-24213 and Japanese Patent Application Laid-Open No. 63-123009, as a bright, high-power zoom lens used in video cameras, etc.
Consists of four lens components having positive, negative, positive, and positive refractive powers in order from the object side, including a variable magnification middle barrel lens component and a third lens component.
The lens component remains fixed, the second lens component is moved in one direction to change the magnification, and the fourth lens component is moved back and forth to compensate for fluctuations in the focal position due to the change in magnification. Are known.

(Problems to be Solved by the Invention) In this type of zoom lens, the amount of movement of the fourth lens component for correcting the image plane position accompanying zooming is relatively large, and in order to make the lens system compact, the entire system As the lens size is reduced, there is a drawback that variations in aberrations caused by zooming cannot be sufficiently corrected.

The purpose of the present invention is to use a camera suitable for video cameras and the like, with a variable magnification ratio of about 6 times and an F number of about 1.4 to 2.0.

It is an object of the present invention to provide a zoom lens having a small number of lenses, compact in overall length and front lens diameter, and free from the above-mentioned drawbacks.

(Means for Solving the Problem) Basically, the zoom lens of the present invention has, in order from the object side, a positive refractive power, a first lens component that remains fixed during zooming, and a negative refractive power. A second lens component that has a positive refractive power and moves back and forth to change the power, a third lens component that has a positive refractive power and remains fixed during the change of power, and a third lens component that has a positive refractive power and moves back and forth as the power changes. It is composed of a fourth lens component that corrects movement of the focal position, and a fifth lens component that remains fixed during zooming, and the fifth lens component is characterized by having a relatively weak negative refractive power.

The second lens component moves from the object side to the image side when changing the magnification from the wide-angle side to the telephoto side.

It is preferable that the light beam incident on the fourth lens component be substantially afocal.

In the zoom lens of the present invention, focusing is performed at the fourth lens.
Although it is preferable to use a lens component, it is also possible to use a first lens component or a third lens component.

Specifically, in the zoom lens of the present invention, the first lens component includes at least one positive lens and at least one negative lens, and the second lens component includes at least two negative lenses and at least one positive lens. The third lens component includes at least one positive lens, the fourth lens component includes at least one positive lens and at least one negative lens, and the fifth lens component includes at least one negative lens. , satisfies the following conditions.

0.25<IfiFw/(fwZ)<0.4
(1) 1.8< f , / f w<2.5
(2) However, fl is the combined focal length of the second lens component, fw is the focal length of the entire system at the wide-angle end, and F- is F at the wide-angle end.
The number 2 is the variable power ratio.

It is desirable to introduce an aspherical surface into the fourth lens component or the fifth lens component, and at least one of them is
For a surface whose curvature radius is the radius of curvature on its axis, and whose surface is convex, it is an aspheric surface that has deformation in the direction from the center of the refracting surface to the periphery, and the surface of the genera is aspheric. For a concave surface, it is an aspherical surface that has a deformation amount in the direction of concaveness from the center of the refractive surface toward the periphery,
When the amount of deformation at the effective radius position of the j-th aspherical surface in order from the object side is Δ1, and the above direction is taken as a positive direction, 0.001<FwΣΔt/ f w<O', 02'
(3)6 However, Σ is the sum of all aspherical surfaces in the fourth lens component and the fifth lens component.3 In the zoom lens of the present invention, more specifically, the fourth lens component is , consisting of, in order from the object side, a pair of positive doublets consisting of a negative meniscus lens and a biconvex lens, and a positive meniscus lens with the convex facing toward the object side, and the second lens component is, in order from the object side, It consists of a negative lens with a strong surface facing the image side, and a negative doublet consisting of a biconcave lens and a positive lens, and the third lens component is one positive lens or one positive lens and a negative meniscus lens. The fourth lens component includes at least a negative lens with a strong surface facing the image side and one positive lens in order from the object side, and the fifth lens component has a relatively weak refractive power. It is desirable that the lens be composed of a negative single lens having

n2->1.6 (4) Ya, -
1ν2. >2C) (5)n, ・f
D>1.8 (6) However, n2-: Average value of the refractive index of the negative lens in the second lens component vz-: Average value of the Abbe number of the negative lens in the second lens component vz+: Second lens component Atsbe number n of the positive lens inside:
It is the refractive index of the positive lens in the third lens component.

The fifth lens component has a relatively weak negative refractive power, and
Unlike other lens components, since it is placed near the image plane regardless of magnification, there is little variation in the focal position due to environmental changes such as temperature and humidity, so it can also be constructed from a plastic lens.

(Function) In the basic configuration of the zoom lens of the present invention, placing the fifth lens component closest to the image side, which remains fixed during zooming, makes it possible to make a high-power zoom lens with a zoom ratio of 6x in a compact size. It is extremely effective in configuring In particular, by making the refractive power of the fifth lens component negative, the telephoto ratio of the composite system of the fourth lens component and the fifth lens component can be made smaller, so the total length of the lens system is longer than that of the case without the fifth lens component. can be shortened. Furthermore, when attempting to construct a zoom system compactly, it tends to be difficult to correct negative distortion generated in the second lens component at the wide-angle end.

This is because such an effect can be partially canceled by placing a fifth lens component with negative refractive power.

The overall length of the zoom system and the diameter of the front lens can be made smaller than before.

By making the light flux incident on the fourth lens component substantially afocal, changes in aberration due to movement of this component due to zooming can be reduced. Furthermore, when focusing is performed by extending the fourth lens component toward the object side, aberration changes due to movement of the fourth lens component due to focusing can be reduced.

At least one negative lens is provided in each of the fourth lens component and the fourth lens component having positive refractive power.

The reason why the second lens component having negative refractive power includes at least one positive lens is to sufficiently correct axial chromatic aberration and lateral chromatic aberration in the entire range of magnification. Although the third lens component with positive refractive power does not necessarily include a negative lens, by overbalancing the color correction of the fourth lens component, the chromatic aberration of the entire system can be corrected even if this component is omitted. can do.

゛The reason why the second lens component includes at least two negative lenses is that the second lens component has sufficient refractive power.
This is to reduce the amount of movement required for zooming and to make the diameter of the front lens compact.

Condition (1) concerns the appropriate value of the focal length of the second lens component; if the absolute value of the focal length exceeds the upper limit and becomes large, it is advantageous in terms of aberration correction, but the length from the first lens component to the third lens component increases, making it impossible to obtain a compact system.If the lower limit is exceeded, with a simple configuration such as the one described above, it becomes impossible to correct aberration fluctuations associated with zooming, especially fluctuations in distortion and coma, and Negative distortion becomes excessive.

Condition (2) relates to the focal length of the fourth lens component, and if the lower limit is exceeded, the length from the front of the fourth lens component to the imaging surface tends to become shorter, which is advantageous for shortening the overall length. The angle of view of the entire fourth lens component becomes larger, and the height at which the light beam incident on the corner of the screen passes through the first lens component becomes higher, leading to an increase in the front lens system. When the focal length exceeds the upper limit and the focal length becomes longer, not only does the overall length of the lens system become longer, but also the aperture diameter to obtain a predetermined aperture becomes larger.

In the specific configuration of the zoom lens of the present invention, the first lens component includes, in order from the object side, a positive doublet consisting of a negative meniscus lens and a biconvex lens, and a positive meniscus lens with the convex side facing the object side. It is composed of
This is mainly to suppress fluctuations in spherical aberration and coma aberration from the intermediate focal length to the telephoto end. The positive meniscus lens on the image side is configured almost abranatically with respect to the axial light beam, and also has the effect of correcting negative distortion generated in the second lens component having strong negative refractive power.

The second lens component is composed of, in order from the object side, a negative lens with a strong surface facing the image side, and a negative doublet consisting of a biconcave lens and a negative lens. While suppressing the increase in size of the entire system due to thickening, it is possible to reduce fluctuations in aberrations associated with zooming, especially fluctuations in distortion and astigmatism.

The third lens component is composed of one positive lens, but by making it a positive doublet consisting of a positive lens and a negative meniscus lens, it is easy to correct axial chromatic aberration over the entire zoom range. Become. Furthermore, when the aperture ratio is large, the degree of freedom due to the increased number of surfaces can be used mainly for correcting spherical aberration. When the third lens component is composed of one positive lens, it is advantageous to use an aspheric surface on at least one surface of this lens in terms of correcting spherical aberration.

The fourth lens component includes at least a negative lens with a strong surface facing the image side and at least one positive lens in order from the object side, but the strong concave surface on the image side of the negative lens occurs in the second lens component. It has the function of correcting the negative distortion that occurs.

Regarding a geneatrix surface that has at least one of the aspheric surfaces in the fourth lens component or the fifth lens component as its radius of curvature on its axis, from the center to the periphery of the refractive surface for a surface where the generatrix surface is convex. It is an aspherical surface that has a deformation amount in the direction of convexity toward the periphery, and for a surface with a concave genera, an aspherical surface that has deformation amount in the direction of concaveness from the center of the refractive surface toward the periphery. This is effective in sufficiently correcting the negative distortion generated in the second lens component having strong negative refractive power when attempting to configure the zoom system compactly.

Condition (3) concerns the sum of the aspherical deformation amounts at the effective diameter of each lens surface for all the aspherical surfaces in the fourth and fifth lens components. , it becomes difficult to correct negative distortion at the wide-angle end, and if the upper limit is exceeded, it is effective in correcting distortion, but the curvature of field becomes excessive over the entire zoom range.

Condition (4) relates to the refractive index of the negative lens constituting the second lens component, and if this condition is violated, it becomes difficult to correct negative distortion at the wide-angle end under the above configuration.

Condition (5) relates to the difference in Abbe number between the negative lens and the positive lens that constitute the second lens component.If the condition is violated, the fluctuation of chromatic aberration during zooming, especially the fluctuation 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 of larger image height, and at the telephoto end, in the direction of smaller image height.

Condition (6) relates to the refractive index of the positive lens constituting the third lens component, and if the condition is violated, it becomes difficult to correct spherical aberration over the entire zoom range.

(Example) Examples of the present invention will be given below.

In some of the examples, plastic lenses are used, and these lenses are marked with an asterisk. Plastic lenses generally have a change in refractive index due to changes in environmental temperature, but in the embodiments of the present invention, by optimally combining the refractive powers of each plastic lens, changes in the focal position due to changes in refractive index can be prevented. is suppressed. As the plastic lens material, PC (polycarbonate), PMMA (polymethyl methacrylate), etc. are used. The refractive power of these materials changes linearly with temperature. The data is shown below.

PCPMMA Reference refractive index (20° C.) 1.583 1.492 Refractive index (at 50) 1.5788 1.4884 The definition of the aspheric coefficient in the example is as follows.

C: paraxial curvature of aspheric surface represents.

In addition, each symbol in the table is as follows: R is the radius of curvature of each refractive surface, D is the distance between the refractive surfaces, N is the refractive index of the lens material, C is the Abbe number, f is the focal length of the entire lens system, and 2ω is the image angle, F is the F number, and fB is the back focus.

Example 1 f=7.20~40.99 F: 1.64~
2.402ω=51.4'~8,84' fs=
2.0RD N v B However, X: Coordinate from the object side to the image side along the optical axis with the apex of the aspherical surface as the origin h: Eleventh surface perpendicular to the optical axis with the apex of the aspherical surface as the origin K = A4 = A, = A, = A1. = 18th surface aspherical coefficient -1,94404 -4,57908X 1O-s 8.90194 X 10-" -5,39124x 10-" 1.23222 .3 11th surface Aspheric coefficient Effective radius 5.OK = -1,
07994 K = A, = A, = A, = ALo= Variable interval -3,11174x 10 -7,81744X 10-' 4.95831 X 10-' -2,91924x to-" 2.94816X 10-" f a 7.20 1.0 23.04 11.2 40.99 15.4 f□=29.404 f4=14.654 16.4 6.2 2.0 f2=-7,96O f,=-528, 527 c d 5.24 4.67 4.45 5,46 8.42 1.49 f3=30.138 Example 2 f = g, go~49.98 =2.0~2.6 2ω=51. 546~8.86″ f, = 1.80 Sea A4 = A, = A, = 80. = 18th surface K = A4 = A, = A, = A1° = -4,49354X10-' 9.15906 x lo-"-5,38924x10-'1.23222xIO-" Aspheric coefficient Effective radius 6,0 -3.58728 x 10 -5.38150 X 10-' -1,59535X 10-7 -4.29237 x 10 -' 3.53996 7255 f2=-8,253 f,=-81,908 c d 8.5150 6.6236 7.3787 7.7599 11.9425 3.1961 f,=32.+86 Example 3 f=8.80~50 .00 F: 2.0~2.6 2ω=54.66°~9.40' fB==1.8O 19'' 11114.111 2.00 18] -50,791 1,50 1,51633 64, 1 Page 11 K = A, = AG = A, = 80. = 18th surface K = A, = AG = A, = A1゜ = Variable interval 8.80 27.01 50.00 Aspheric coefficient Effective radius -2,11982 -4,49777x 1O-s 9.14945 X 10- @ -5,38926X 10-9 1.23222 X 10-10 Aspherical coefficient Effective radius 1.33922 X 10 -4.18551 83427 x 10-11 5.0 5.0 1.0354 11.3604 15.8099 17.50 7.175 2.7255 7.2151 6.0712 10.6739 7.9296 9.0735 4.4708 f1=29 .982 f4=17.471 f2=-8,234 f,=-76,932 f,=32,662 14-30,549 Example 4 f=9.27~52.80 2ω=49.2″ ~8.4゜F: 1.44~1.98 fB=4.78 19th surface Aspheric coefficient Effective radius K = -7,58103X 10-' 21st surface Aspheric coefficient Effective radius = -1,69524 Variable interval 9.27 19.50 52.80 8.029 5.929 8.050 25.600 12.700 1.000 1.100 14.000 25.700 8.3 7.6 1.185 3.300 11.692 f1=48.09 f2=-12,51f3=3
9.58f4=20.94 f5=-1344,
01 Values in each example are as follows.

Example 1 Example 2 Example 3 Example 4f21h/
(fwZ) 0.318 0.330 0.
294 0.341f4/fw 2.04
1.95 1,99 2.269Σ△1/
fw O,00530,01580,00780
,0083v,-ν2. 2g, 65 25.7
25.7 28.65n347 2.17
3 2.400 2.400 2.036 (Influence of the invention) As shown in each example and its aberration diagram, the zoom lens of the present invention has a variable power ratio of about 6 and an F number of 1.4 to 2. ．．
Although it is bright and has a high zoom ratio of about 0, it is compact, various aberrations are well corrected, and fluctuations in various aberrations due to zooming are extremely small, making it suitable for video cameras and the like.

[Brief explanation of the drawing]

FIG. 1 is an optical layout diagram showing the basic configuration of the zoom lens of the present invention, and FIGS. 6,7.8
．． FIG. 9 is a diagram of aberration curve #i of the above-mentioned 1.2.3.4 embodiment.

Claims (1)

[Claims] In order from the object side, the first lens component has a positive refractive power and remains fixed during zooming, the second lens component has a negative refractive power and moves back and forth for zooming, and the positive A third lens component has a refractive power and remains fixed when changing the magnification, a fourth lens component has a positive refractive power and corrects movement of the focal position due to changing the magnification, and a fourth lens component has a positive refractive power and remains fixed when changing the magnification. A zoom lens comprising a certain fifth lens component, the fifth lens component having a relatively weak negative refractive power.