JPH0460509A - Zoom lens - Google Patents

Abstract

PURPOSE:To improve the optical performance of the zoom lens consisting of a five lens elements while shortening its overall length by composing the 1st lens element of one single lens with negative refracting power and one single lens with positive refracting power. CONSTITUTION:The 1st lens element consists of the negative meniscus lens which has its convex surface on the object side and biconvex single lens and the 2nd lens element consists of a negative meniscus lens which has its convex surface on the object side and a negative doublet composed of a biconcave lens and a positive lens. Further, the 3rd lens element is one biconvex lens which is fixed depending upon power variation, the 4th lens element is a doublet of at least a negative meniscus lens and a positive lens, and the 5th lens element is composed of at least a single lens having relatively weak refracting power. Consequently, aberration variation is reduced and the diameter of the lens is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and particularly to a zoom lens suitable for video cameras, electronic still cameras, and the like.

(Prior Art) Recent video cameras are required to be compact and lightweight, as well as to have high image quality.In response, compact and high-resolution image sensors are also attracting attention. In addition, along with this, there is a demand for a high-performance zoom lens with a variable power ratio of about 6, a small number of lenses, and a compact overall length and front lens.

Conventionally, as a zoom lens, as seen in Japanese Unexamined Patent Publications No. 62-24213 and No. 63-123009, four lenses have refractive powers of positive, negative, positive, and positive in order from the object side.
Consisting of lens components, the first lens component and the third lens component are fixed during zooming, the second lens component is moved in one direction to perform zooming, and the fourth lens component is moved back and forth. There are known devices that correct for fluctuations in focal position due to zooming. In this type of zoom lens, the amount of movement of the fourth lens component for correcting the image plane position during zooming is relatively large, and if the entire system is downsized in pursuit of compactness, aberrations due to zooming may occur. This method has the disadvantage that it is not possible to sufficiently compensate for fluctuations in .

In addition, an aspherical zoom lens with a reduced number of lenses is known, as seen in Japanese Patent Application Laid-Open No. 2-39011, but currently, when an aspherical lens is made of glass, the lens Even if the number of sheets can be reduced, the cost is high. Further, using an aspherical lens in the moving group is not necessarily preferable in consideration of performance deterioration due to eccentricity.

Furthermore, if a zoom lens is made smaller, it is necessary to shorten the focal length, which inevitably shortens the back focus. In video cameras, electronic still cameras, and the like, a short back focal length is inconvenient because it is necessary to insert a low-pass filter or an infrared cut filter between the rear end of the lens and the imaging surface.

(Problems to be Solved by the Invention) The present invention is suitable for video cameras and electronic still cameras that have a small number of constituent elements, are compact in overall length and front element, have sufficient back focus, and have a variable magnification ratio of about 6. An object of the present invention is to provide a suitable zoom lens.

(Means for solving the problem) In order to achieve the above object, the zoom lens of the present invention has the following features:
In order from the object side, it is composed of one single lens with negative refractive power and one single lens with positive refractive power.The first lens component has positive refractive power and is fixed during zooming, and the negative refractive a second lens component that has power and changes magnification by moving on the optical axis;
A third lens component that has positive refractive power and is fixed when changing the magnification; a fourth lens component that has positive refractive power and corrects the movement of the focal position due to changing the magnification by moving the second lens component; and a fourth lens component that is fixed when changing the magnification. It is characterized by being composed of a positive or negative fifth lens component.

The second lens component moves on the optical axis from the object side to the image side from the wide-angle end to the telephoto end. Furthermore, it is desirable that the light beam incident on the fourth lens component be substantially afocal.

Focusing in the present invention may be performed by the first lens component, and more preferably by the fourth lens component.

Specifically, in the present invention, the first lens component is composed of a negative meniscus lens with a convex surface facing the object side and a biconvex single lens, and the second lens component is a negative meniscus lens with the convex surface facing the object side. and a negative doublet consisting of a biconcave lens and a positive lens, the third lens component is a biconvex lens that is fixed depending on the magnification, and the fourth lens component is composed of at least a negative meniscus lens and a positive lens. It is a doublet, and the fifth lens component is composed of at least a single lens having relatively weak refractive power. Further, unlike the other lens components, the fifth lens component is placed near the image plane, so there is little variation in the focal position due to environmental changes such as temperature and humidity, so it can also be configured with a plastic lens. In addition, in order to maintain optical performance, a fixed third lens component is used when changing the magnification.
Preferably, each final lens component has at least one aspherical surface.

(Function) In the zoom lens of the present invention, the first lens component is composed of two lenses, a negative meniscus lens and a biconvex lens from the object side, and the air gap between the lenses is mainly due to spherical aberration from the intermediate focal length to the telephoto end. It also has the effect of suppressing fluctuations in coma aberration. This reduces the weight of the first lens component,
Lower costs can be expected. Furthermore, when an aspherical lens is used, it is possible to improve optical performance while reducing the number of lenses and even shortening the overall length.

The second lens component is composed of a negative meniscus lens with its convex surface facing in order from the object side, and a negative doublet consisting of a biconcave lens and a positive lens. While suppressing the increase in size of the entire system due to zooming, it is possible to reduce fluctuations in aberrations, especially fluctuations in distortion and astigmatism, caused by zooming. Furthermore, by appropriately selecting the refracting power, the amount of movement for changing the magnification can be reduced and the diameter of the front lens can be reduced.

The third lens component is a fixed positive single lens that changes magnification and has positive refractive power.

It becomes possible to reduce the burden of aberration correction on the fourth lens component. Furthermore, it is advantageous to use an aspheric surface on at least one surface of this lens system in terms of correcting spherical aberration.

The fourth lens component consists of at least a negative meniscus lens and a positive lens, and the concave surface on the image side of the negative lens has the function of correcting negative distortion generated in the second lens component. Further, when focusing is performed using the fourth lens component, it is preferable that the fourth lens component is composed of a bonded lens consisting of at least one set of a positive lens and a negative lens, taking into account the influence of decentering on optical performance deterioration.

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

The first and fourth lens components with positive refractive power each include one negative lens, and the second lens component with negative refractive power includes one positive lens over the entire zoom range. This is to sufficiently correct chromatic aberration and chromatic aberration of magnification. The reason why it is not necessary to include a negative lens in the third lens component having positive refractive power is that the chromatic aberration in the fourth lens component can be canceled out by overextending it.

Chromatic aberration in the entire system can be corrected to the extent that it does not pose a practical problem.

In the basic configuration of the present invention, placing the fifth lens component that is fixed at the time of zooming closest to the image side is extremely effective in constructing a compact high-power zoom lens with a zoom ratio of about 6. . In the zoom lens of the present invention, the diaphragm is placed in front of the third lens component, but if you try to make the entire system compact and shorten the area behind the diaphragm, the position of the diaphragm will change relative to the imaging plane. They tend to be extremely close. CC on the imaging plane
When installing a solid-state image sensor like D, if the exit pupil position is too close to the imaging surface, the color filter and on-chip lens on the imaging surface may cause color shift with respect to the peripheral light flux, or the apparent aperture ratio may change. The amount of peripheral light tends to decrease due to changes in the amount of light. However, if the refractive power of the fifth lens component is positive and it is placed relatively close to the imaging plane, the exit pupil can be positioned further away, and the above-mentioned problems can be improved.

In addition, when the refractive power of the fifth lens component is negative, the telephoto ratio of the composite system of the fourth lens component and the fifth lens component can be made smaller, so the lens The total length of the system can be shortened. Furthermore, when trying to make a zoom system compact, negative distortion generated in the second lens component tends to be difficult to correct at the wide-angle end. Because this effect can be partially canceled out, the overall length of the zoom system and the diameter of the front lens can be made smaller than in the past.

In the zoom lens of the present invention, in order to reduce aberration fluctuations due to zooming and focusing and to reduce the lens diameter, '1' 4 + Atsube's number of the glass material of the positive lens in the first lens component: 2 Abbe number f4 of the glass material of the negative lens in the lens component: Focal length fo of the fourth lens component: Focal length fX at the wide-angle end of the entire lens system: Focal length F at the telephoto end of the entire lens system F-number Z at the wide-angle end : Magnification ratio fl-3" Combined focal length from the second lens component to the third lens component at the telephoto end n2-: Average value of the refractive index of the negative lens in the second lens component Shea of the second lens component Average value of the Atsube number of the negative lens ν2°: Atsube number n3+ of the positive lens in the second lens component
Refractive index Δ of the positive lens in the third lens component: When the amount of deformation at the effective radius position of the first aspherical surface from the object side, f+/f1-. 1<0.5 (1)0
．． 4<f, /f,<1.0 (2)
0.25<If21Fw/(FwZ)<0.5
(3) n, >1.6 (
4) v2--v2゜):2o (
5) 1.7<n11-<3.0 (
6) v+〉45. C<35 (
7) 0.001<F, VΣ△j/fw<0.05
It is preferable to satisfy (8). However, ΣΔ1 is the sum of the amount of deformation.

Conditional expression (1) relates to the combined refractive power of the first to third lens components at the telephoto end. When focusing is performed using the fourth lens component, the amount of focusing movement becomes large at the telephoto end, so aberration fluctuations due to focusing are significant. If the combined focal length of the first to third lens components is within the specified range, the light beam incident on the fourth lens component can be made almost afocal, and fluctuations in spherical aberration due to focusing can be reduced.

If the upper limit of this range is exceeded, the spherical aberration will vary greatly in the negative direction, which is not preferable.

Conditional expression (2) concerns the focal lengths of the first and fourth lens components, and since conditional expression (1) makes the light beam incident on the fourth lens component almost afocal, the entire system becomes extremely telephoto. In order to obtain a long back focus for the entire system without causing distortion, it is desirable to make the focal length of the fourth lens component a little longer and the focal length of the first lens component a little shorter. If the upper limit is exceeded, the back focus distance can be lengthened, but the refractive power of the first lens component becomes too large, and convergent spherical aberration and coma aberration at the telephoto end worsen. If the lower limit is exceeded, sufficient focus cannot be ensured, or the refractive power becomes large, resulting in insufficient correction of spherical aberration at the wide-angle end, which is undesirable.

Conditional expression (3) concerns the appropriate value of the refractive power of the second lens component, and if the absolute value of the focal length increases beyond the upper limit, it will be advantageous in terms of aberration correction, but from the first lens component to the third lens component. (If the lower limit of 1° is exceeded, aberration fluctuations due to zooming, especially distortion and coma aberration fluctuations, cannot be corrected with the simple configuration described above.) This results in excessive negative distortion at the wide-angle end.

Conditional expression (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 with the above-described configuration.

Conditional expression (5) concerns the difference in Abbe number between the negative lens and the positive lens that constitute the second lens component.If one condition is violated, the fluctuation of chromatic aberration during zooming, especially the fluctuation of lateral chromatic aberration, increases, and the image height at the wide-angle end increases. On the telephoto side, the short-wavelength imaging point tends to shift too much in the direction of larger image height.

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

Conditional expression (7) relates to the Atsube number of the lenses constituting the first lens component, and when changing the magnification, the fixed first lens component is configured with two lenses, negative and positive, in order from the object side. If the upper and lower limits of are exceeded, magnification aberration will occur on the over side and correction will be difficult, which is undesirable. More preferably, in order to cancel out the chromatic aberrations of the positive lens and the negative lens, it is desirable that the difference in Abbe number between the glass materials be %', V->15.

At least one of the aspherical surfaces of the fixed lens component is related to a reference spherical surface having its on-axis radius of curvature as the radius of curvature,
For a surface with a convex reference spherical surface, it is an aspherical surface that has a deformation amount in the direction of convexity from the center of the refractive surface toward the periphery, and for a surface with a concave reference spherical surface, the center of the refractive surface Negative distortion occurs in the second lens component, which is an aspherical surface that is deformed in a direction concave toward the periphery and has a strong negative refractive power when trying to construct a compact zoom system. It is effective to satisfy the first conditional expression (8) in correcting.

(Example) An embodiment of a zoom lens according to the present invention will be shown below.

In the example, plastic lenses are used as the fifth lens component, and these lenses are marked with this mark. Plastic lenses generally have a change in refractive index due to environmental changes such as temperature and humidity, but in the embodiments of the present invention, by appropriately selecting the refractive power of the plastic lens, fluctuations in the focal position due to changes in refractive index can be suppressed. I'm suppressing it.

Plastic lens materials include PC (polycarbonate) and PMMA (polymethyl methacrylate).
etc. The refractive power of these materials changes nonlinearly with temperature. Data on changes in refractive index due to temperature are shown below.

PCPMMA Standard refractive index (20°C) 1.583 1.492 Refractive index (50°C) 1.5788 1.4884 The aspherical shape in the example is expressed by the following formula.

However, each symbol in the formula is as follows.

C: Paraxial curvature of the aspheric surface h: Height from the optical axis: Conic constant φ: Amount of deformation of the aspheric surface measured from the apex of the aspheric surface in the optical axis direction (including the amount of displacement due to the spherical surface). Each symbol is R
is the radius of curvature of each refractive surface, D is the interval between refractive surfaces, N is the refractive index of the lens material, ν is the Abbe number, f is the focal length of the entire lens system, 2ω is the angle of view, and F is the F number. .

Various values are shown below.

f+/f□~.

f4/f1 f　21　Fw/(FwZ) V, −ν2+ n, fT; FwΣ△4/fyu (Example 1) f near, 10-40.54 2ω: 48.2'~8.3a Example 1 Example 2 -0.29 -0.17 2.84 2,64 0.351!　　　　0.325 28.75 2g, 90 2.25 2,27 0.02935 0.01288 F: 2.00~3.2O N.

5] 39.513 0.70 1.69680 55.5 fA B 7.10 0.80 15.2016.72
8.17 7.8340.54 14.2
0 1.80f□(Na 1-4) =29.
543f, (Nn10-11)=27.766f,
(No. 1518) = 85.559 Aspheric coefficient 10th surface K = -0,11250x 102A1=
-0,18342x 10-' A2=-0,24323x 10-' A3= 0.22978 x 10-"A4=-0,3
0553x 10-" K = 0.73337xlO A1 = -0,14132X 10-" A2 = 0.31909 X 10-'A3 = 0.1
1989 X 10-'A4= 0.3]577X10
-13 f2(No 5-9) =-6,989f 4(Nn
12-14) = 20.155 15th side 8.70 4.34 2.28 P1= P2; P3= P4= P1= P2= P3= P4= 7.12 11.48 13.55 4.0 6. 0 8, O IO00 (Example 2) NQ f near, 10 ~ 40.99 2ω: 48.07' ~ 8.18°: 2.00
~3.2O A 7.10 0.80 17.13 8.17 40.99 14.20 25.50 8.13 2.10 7.17 3.77 4.13 5.78 9.17 8.82 f (NQ I~4) = 27.241f3 (No
lO~11) = 28,263f s (Nn15
1g) = -84,803 Aspheric coefficient 10th surface f2 (bulk 5 to 9) = -6,660 f, (Nα12 to 14) = 18.732 15th surface K = -0,23522X 102 A1 = -0 , 83191
2478 8,0 A4= 0.29472X10-” P4= 10
．． 0 (Effects of the Invention) As seen in the examples and aberration diagrams, the zoom lens of the present invention is compact, has a variable power ratio of about 6 times, has a small number of lenses of about 9, and is fully variable. This lens achieves well-balanced aberration correction over the magnification range, making it particularly suitable for video cameras, electronic still cameras, and the like.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the zoom lens of the present invention,
The sectional view of the second embodiment, FIGS. 3 and 4 are aberration curve diagrams of the first embodiment and the second embodiment, respectively. Diagram

Claims (2)

[Claims] (1) In order from the object side, the first lens component has positive refractive power and is fixed when changing magnification, the second lens component has negative refractive power and changes magnification by moving on the optical axis, and the positive A fourth lens component has a positive refractive power and corrects the movement of the focal point due to the movement of the second lens component, and when the magnification is changed, the fourth lens component has a positive refractive power and is fixed when changing the magnification. A zoom lens composed of a fixed fifth lens component, characterized in that the first lens component is composed of one single lens with negative refractive power and one single lens with positive refractive power. zoom lens. (2) In the zoom lens according to claim (1), the third
At least 1 in each of the lens component and the fifth lens component.
A zoom lens characterized by having an aspheric surface that is larger than a surface.