JP2010175581A - Zoom lens and electronic device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lower the cost of a lens. <P>SOLUTION: When the radii of curvature of front and rear lens surfaces of a fourth lens 4, a fifth lens 5 and a sixth lens 6 of a second group lens G2 are L4R1, L4R2, L5R1, L5R2, L6R2, respectively, and the refractive indexes in e-line and substantially at 547 nm of a second lens 2 and a third lens 3 are L5n, L6n, they are related to each other by expressions: 14<¾L4R1¾/L4R2<17... (1); 10<(¾L4R1¾+¾L5R1¾+L6R2)/(L4R2+L5R2)<15... (2); and L5n+L6n≥3.6... (3). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an inner focus or rear focus type zoom lens, and more particularly to a small and high zoom lens with a short overall lens length used in a video camera or a broadcast camera.

  The configuration of the conventional four-group lens is as follows.

  That is, a first group lens, a second group lens, a third group lens, and a fourth group lens arranged in order with respect to the light entering direction are provided, and the position of the second group lens is defined as an image plane. The zoom is adjusted from the wide-angle end to the telephoto end.

  In recent years, in a small zoom lens with a short zoom lens length and a high zoom ratio used for a video camera or a broadcast camera, in order to achieve this zoom function with a high magnification, the radius of curvature of the second lens group is reduced and the refractive power is reduced. A method has been proposed in which the entire lens is reduced in size by reducing the amount of movement in the optical axis direction for zooming (for example, Patent Document 1 below).

  In addition, there has been proposed an optical system that reduces the overall size by making the light beam substantially afocal with the third lens group (for example, Patent Document 2 below).

Furthermore, there are some which use an image sensor with a small effective area of the light receiving surface to achieve downsizing (for example, Patent Document 3 below).
JP 2001-116999 A JP 2004-279489 A JP 2005-173313 A

  The problem in the conventional example is that the cost of the lens becomes high.

  That is, in the above-described conventional example, the radius of curvature of the lens has to be reduced in order to achieve a high-magnification zoom function, so that the yield of mass production is reduced, resulting in an increase in cost.

  Therefore, the present invention aims to reduce the cost of the lens.

In order to achieve this object, the present invention is a zoom lens including a first lens group to a fourth lens group in order from the front side with the light entering direction in front. The fourth lens having the above positive lens, the first lens having a positive refractive power, a movable structure, consisting of three lenses, both concave from the front, and negative lenses. 5th lens, the 2nd group lens which has the 6th lens which is a positive lens, and 2 lenses, both sides are convex on the front side, and the 7th which has an aspherical surface in at least one of these both sides A third lens unit having a lens and an eighth lens that is a negative meniscus lens having a strong concave surface on the rear side; a movable structure; both surfaces are convex; and at least one surface of both surfaces Fourth lens unit having an aspheric lens And the curvature radii of the front and rear lens surfaces of the fourth lens, the fifth lens, and the sixth lens of the second group lens are L4R1, L4R2, L5R1, L5R2, and L6R2, respectively. 14 <| L4R1 | / L4R2 <17 (1) where the refractive indices of the lens and the third lens at the e-line, approximately 547 nm, are L5n and L6n.
10 <(| L4R1 | + | L5R1 | + L6R2) / (L4R2 + L5R2) <15 (2)
L5n + L6n ≧ 3.6 (3)
In this way, the intended purpose is achieved.

As described above, the present invention is a zoom lens including the first lens group to the fourth lens group in order from the front side with the light entering direction as the front side, and includes two or more positive lenses. A first lens unit having a positive refractive power, a movable structure, consisting of three lenses, and in order from the front, both surfaces are concave surfaces, a negative lens, a fourth lens, a fifth lens, A second lens unit having a sixth lens, which is a positive lens, and two lenses, and on the front side, both surfaces are convex, and a seventh lens having an aspheric surface on at least one of both surfaces, and the rear On the side, a third lens unit having an eighth lens, which is a negative meniscus lens with a strong concave surface, and a movable structure, both surfaces are convex, and at least one of these surfaces has an aspheric surface A second group lens having a lens having the second lens; The curvature radii of the front and rear lens surfaces of the fourth lens, the fifth lens, and the sixth lens are L4R1, L4R2, L5R1, L5R2, and L6R2, respectively, and the second lens and the third lens. When the refractive index at e-line, approximately 547 nm is L5n, L6n,
14 <| L4R1 | / L4R2 <17 (1)
10 <(| L4R1 | + | L5R1 | + L6R2) / (L4R2 + L5R2) <15 (2)
L5n + L6n ≧ 3.6 (3)
Is to satisfy the following conditions.

  That is, in the present invention, the radius of curvature of the fourth lens, the fifth lens, and the sixth lens of the second group lens is increased, and the thickness of the fourth lens and the fifth lens of the second group lens is increased. Therefore, mass production is facilitated, and as a result, the yield of mass production is improved, so that the cost of the lens can be reduced.

  As described above, according to the present invention, while adopting the inner focus and rear focus types, the entire lens system is downsized, and the large aperture of FNo. When the ratio and the zoom ratio are increased by 10 times or more, the lens configuration and refractive power of each lens group are set optimally to cover the entire zoom range from the wide-angle end to the telephoto end, and from the object at infinity to the very close range. It is possible to achieve a zoom lens in which aberration is well corrected over the entire object distance to the object and high optical performance is achieved. Therefore, it is possible to provide a zoom lens that is suitable for a video camera and a digital still camera, yet has a high magnification and is compact, high performance, and low cost.

(Embodiment 1)
1, 4, and 7 are sectional views of numerical examples 1 to 3 of the rear focus type zoom lens according to the present invention, and FIGS. 2 and 3 are numerical examples 1, 5, and 6, respectively. Example 2, FIGS. 8 and 9 are graphs showing various aberrations of Numerical Example 3. FIG. In the aberration diagrams, FIGS. 2, 5, and 8 show the wide-angle end, and FIGS. 3, 6, and 9 show the telephoto end. FIG. 10 shows a numerical example of the conditional expression in the present invention.

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

  The zoom lens according to the first embodiment of the present invention includes four lens groups. In FIG. 1, the left side of the drawing is a light entry direction, and the light entry direction is hereinafter referred to as the front side. In order from the side, there are a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4.

  The first group lens G1 has a function of condensing when capturing an image of a subject. In FIG. 1, the first lens 1 is a negative lens for capturing light from a front side at a wide angle. And two or more positive lenses, a second lens 2 for condensing and a third lens 3.

  The second group lens G2 has a structure that is movable from the front to the rear with respect to the optical axis of the light. The lens configuration includes three lenses, and both surfaces are concave in order from the front. The fourth lens 4, the fifth lens 5, and the sixth lens that is a positive lens, and has a function of scaling the image of the subject.

  The third lens group G3 is composed of two lenses. The seventh lens 7 has a convex surface on the front side and an aspheric surface on at least one of the both surfaces, and a strong concave surface on the rear side. And an eighth lens 8 that is a negative meniscus lens directed to the lens, and corrects the aberration of the scaled image received from the second group lens G2, thereby making the image afocal, By changing the light into parallel light, a fourth group lens G4, which will be described later, has a function of making the movable range for focusing as small as possible. The above-mentioned aspherical surface has a non-constant curvature on the surface, for example, the curvature near the center of the surface is small and the curvature increases toward the outer edge, that is, the vicinity of the center is gentle and becomes steep as it goes to the outer edge. It ’s like that.

  The fourth lens group G4 has a structure that is movable from the front to the rear with respect to the optical axis of the light. The lens configuration is such that both surfaces are convex, and at least one of these surfaces has an aspheric surface. It has a ninth lens 9 and has a function of focusing the image.

  In FIG. 1, the aperture stop 10 is located between the second group lens G2 and the third group lens G3, and although not shown, generally a wing-like opening is freely possible. This mechanism system has a function of making it easy to correct the aberration of the light of the third group lens G3 by adjusting the amount of light by adjusting the aperture amount.

  Further, although not shown, there is a filter 11 between the fourth group lens G4 and an image sensor located behind the fourth group lens G4, and generally has a structure in which a crystal and a glass member are bonded together. The image sensor has a function as a filter for cutting off infrared rays or the like that become noise.

Now, the curvature radii of the front and rear lens surfaces of the fourth lens 4, the fifth lens 5, and the sixth lens 6 of the second group lens G2 are L4R1, L4R2, L5R1, L5R2, and L6R2, respectively. When the refractive indexes at the e-line of the fifth lens 5 and the sixth lens 6 at approximately 547 nm are L5n and L6n,
14 <| L4R1 | / L4R2 <17 (1)
10 <(| L4R1 | + | L5R1 | + L6R2) / (L4R2 + L5R2) <15 (2)
L5n + L6n ≧ 3.6 (3)
By determining the radii of curvature of the front and rear lens surfaces of the fourth lens 4, the fifth lens 5, and the sixth lens 6 that satisfy the above three expressions, The fourth lens 4, the fifth lens 5, and the sixth lens 6 have large radii of curvature, and the fourth lens 4 and the fifth lens 5 of the second lens group have a large thickness. As a result, the yield of mass production is improved, so that the cost of the lens can be reduced.

  In the figure, G1 is a first group lens, G2 is a second group lens, G3 is a third group lens, and G4 is a fourth group lens. Reference numeral 10 denotes an aperture stop, which is disposed in front of the third group lens G3. An equivalent glass 11 such as a cover glass of the image sensor or a low-pass filter is a glass block such as a face plate or a filter. In this embodiment, when zooming from the wide-angle end to the telephoto end, the second group lens G2 is moved to the image plane side as indicated by an arrow 12, and the image plane variation accompanying the zooming is convex to the fourth group lens G4 toward the object side. It is corrected by moving while having a trajectory. Further, a rear focus type is employed in which the fourth group lens G4 is moved on the optical axis for focusing. The solid line curve 13 and the dotted line curve 14 of the fourth lens group G4 shown in the figure are the image planes when zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. The movement locus for correcting the fluctuation is shown. The first group lens G1 and the third group lens G3 are fixed during zooming and focusing, but may be moved for zooming or aberration correction. In the present embodiment, the fourth group lens G4 is moved to correct image plane fluctuations accompanying zooming, and the fourth group lens G4 is moved to perform focusing.

  In particular, as shown by the curves 13 and 14 in the figure, the zoom lens is moved so as to have a convex locus toward the object side upon zooming from the wide-angle end to the telephoto end. As a result, the space between the third group lens G3 and the fourth group lens G4 is effectively used, and the overall length of the lens is effectively shortened. Next, features of the lens configuration will be described sequentially.

  Conditional expression (1) is for increasing the refractive power of the second lens group G2 and reducing the size. Without satisfying this condition, if the refractive power is increased by reducing the radius of curvature, the negative Petzval sum increases, not only when good imaging is not obtained, but deviates from the manufacturable radius of curvature, An optical system may not be realized.

  Conditional expression (2) is for reducing the size of the entire system and realizing high zoom ratio. With respect to the radius of curvature pursuing mass production efficiency of the fourth lens R2 that can be manufactured, the curvature radius L4R1 on the front side of the fourth lens takes a value that satisfies the conditional expression (2), so that the state of each aberration is also good. Thus, an optical system with a wide angle of view and a high zoom ratio can be realized.

  Conditional expression (3) indicates that when the curvature radius L4R2 on the rear side of the fourth lens and the curvature radius L5R2 on the rear side of the fifth lens are made to be curvatures that can be manufactured, the curvature radius L4R1 on the front side of the fourth lens, By taking the values of the curvature radius L5R1 on the front side of the fifth lens and the curvature radius L6R2 on the rear side of the sixth lens so as to conform to the conditional expression, the power of the second lens group G2 is kept constant and negative. An optical system capable of obtaining good imaging characteristics without increasing the Petzval sum can be configured.

  By this conditional expression, the refractive power of the second group lens G2 and the amount of movement of the second group lens G2 accompanying the zooming to obtain a desired zoom ratio can be in an optimum relationship, exceeding the upper limit value of the conditional expression (3). If the desired zoom ratio cannot be obtained and the lower limit is exceeded, aberration fluctuations due to zooming increase, which is not appropriate. Therefore, not only the image surface is over (overcorrected), but also the sensitivity is increased, and the focus and the image are liable to occur.

The curvature radii of the object side (front side) and image side (rear side) lens surfaces of the seventh lens 8 and the eighth lens 8 constituting the third group lens G3 are L7R1, L7R2, L8R1, and L8R2, respectively. and when,
3 <| L7R2 | / L7R1 <5 (4)
2 <L8R1 / L8R2 <3 (5)
By satisfying the following condition, the third lens unit G3 has a positive lens 7 having a convex surface facing the object side and a meniscus having a convex surface facing the object side. The fourth lens group G4 is arranged from the positive ninth lens 9 whose convex surfaces are convex so that the entire lens system is miniaturized and various aberrations are good. It is corrected to.

  In particular, the third group lens G3 is a so-called telephoto type, the principal point position of the third group lens G3 is moved to the object side, and the actual distance between the third group lens and the fourth group lens is shortened to reduce the size. . When the lens shape of the seventh lens 7 in the third lens group G3 satisfies the conditional expression (4) and the lens shape of the eighth lens 8 satisfies the conditional expression (5), the optical total length is short and a good result is obtained. Image characteristics and zoom ratio can be ensured.

  If the upper limit of conditional expression (4) is deviated, the refractive power of the negative seventh lens 7 of the third group lens G3 becomes weak, and it becomes difficult to achieve downsizing by making the third group lens G3 a telephoto type. come. If the lower limit is exceeded, the refractive power increases, but each aberration deteriorates and a good image cannot be obtained.

  If the upper limit value of the conditional expression (5) is deviated, the principal point position of the third group lens G3 moves to the object point side, and the distance between the third group lens G3 and the fourth group lens G4 cannot be sufficiently secured, which is close. When shooting, focusing becomes difficult. Moreover, if it deviates from the lower limit, the refractive power becomes weak, and miniaturization cannot be achieved. As a result, while satisfying these conditions, the afocal property of the on-axis marginal ray exiting the third lens group G3 is maintained while ensuring the optimal back focus, and coma and field curvature are corrected well. A compact zoom lens is realized.

  The rear focus type zoom lens that is the object of the present invention can be achieved by satisfying the above-mentioned various conditions, but it can be improved over the entire zoom range and the entire object distance while further reducing the size of the entire lens system. In order to obtain optical performance, it is preferable to satisfy at least one of the following conditions.

  The object-side, image-side lens surface of the seventh lens 7 and the object-side lens surface of the ninth lens 9 are made up of aspherical surfaces whose positive refractive power decreases from the lens center toward the periphery. It is that. With this configuration, the chromatic aberration of the third group lens G3 and the fourth group lens G4 is suppressed satisfactorily, and spherical aberration and coma aberration are corrected well. These aspheric surfaces may be plastic lenses. Also, other lenses may be made of plastic.

  The first group lens is composed of a meniscus negative first lens 1 having a convex surface facing the object side, a positive second lens 2 having convex surfaces on both lens surfaces, and a positive third lens 3 having a convex surface facing the object side. The second lens group G2 is composed of three lenses, the meniscus negative fourth lens 4 having a convex surface facing the object side, the negative fifth lens 5 having concave both lens surfaces, and the positive sixth lens 6 The fifth lens and the sixth lens are cemented. As a result, aberration fluctuations accompanying zooming are corrected satisfactorily.

  The fourth group lens G4 is moved so as to correct the image plane variation accompanying the movement of the second group lens G2 during zooming and perform focusing. At this time, in order to suppress aberration fluctuations due to focusing, particularly chromatic aberration fluctuations, both lens surfaces are composed of a convex positive ninth lens 9 and a minimum unit of one lens.

  In the lens system of the present invention, since the second group lens G2 is a negative lens group, a zoom lens of 10 times or more is configured by satisfying conditional expressions (1), (2), and (3).

  Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are respectively the i-th lens in order from the object side. Refractive index and Abbe number of glass. In the numerical examples, the last two lens surfaces are glass blocks such as face plates and filters. Table 1 shows the relationship between the above-described conditional expressions and numerical values in the numerical examples. The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, and K, A, B, C, and D are aspherical coefficients, respectively. When

なる式で表している。

It is expressed by the following formula.

  2 and 3 are aberration diagrams of the numerical value example 1 at the zoom position at the wide-angle end and the telephoto end. The zoom lens according to Numerical Embodiment 1 is configured based on the data in Table 1.

また表２に物点が無限位置の場合のズーミングによって可変な空気間隔を示す。

Table 2 shows the air spacing that is variable by zooming when the object point is at an infinite position.

また表３に本実施例１のズームレンズの非球面係数を示す。

Table 3 shows the aspheric coefficients of the zoom lens of Example 1.

図２、図３では非点収差図におけるΔＳはサジタル像面を表し、ΔＴはタンジェンシャル像面を表す。また球面収差図においては、ｅ線とｇ線の球面収差を表す。また歪曲収差図も合わせて、これらの収差図からわかるように収差の小さい良好な光学性能を実現することができる。

2 and 3, ΔS in the astigmatism diagram represents a sagittal image plane, and ΔT represents a tangential image plane. In the spherical aberration diagram, the spherical aberration of the e-line and the g-line is shown. In addition, it is possible to realize good optical performance with small aberration as can be seen from these aberration diagrams together with the distortion diagrams.

4 is a cross-sectional view of a main part of Numerical Example 2 of the rear focus zoom lens according to the present invention, and FIGS. 5 and 6 are aberration diagrams at the zoom positions at the wide-angle end and the telephoto end of Numerical Example 2. FIG.
The zoom lens of Numerical Example 2 is configured based on the data in Table 4.

また表５に物点が無限位置の場合のズーミングによって可変な空気間隔を示す。

Table 5 shows the air spacing that is variable by zooming when the object point is at an infinite position.

また表６に本実施例２のズームレンズの非球面係数を示す。

Table 6 shows the aspheric coefficients of the zoom lens of Example 2.

図５、図６では非点収差図におけるΔＳはサジタル像面を表し、ΔＴ はタンジェンシャル像面を表す。また球面収差図においては、ｅ線とｇ線の球面収差を表す。また歪曲収差図も合わせて、これらの収差図からわかるように収差の小さい良好な光学性能を実現することができる。

5 and 6, ΔS in the astigmatism diagram represents a sagittal image plane, and ΔT represents a tangential image plane. In the spherical aberration diagram, the spherical aberration of the e-line and the g-line is shown. In addition, it is possible to realize good optical performance with small aberration as can be seen from these aberration diagrams together with the distortion diagrams.

  FIG. 7 is a cross-sectional view of the main part of Numerical Example 3 of the rear focus type zoom lens of the present invention, and FIGS. 8 and 9 are aberration diagrams at the zoom positions at the wide-angle end and the telephoto end of Numerical Example 3. The zoom lens of Numerical Example 3 is configured based on the data in Table 7.

また表８に物点が無限位置の場合のズーミングによって可変な空気間隔を示す。

Table 8 shows air intervals that can be changed by zooming when the object point is at an infinite position.

また表９に本実施例３のズームレンズの非球面係数を示す。

Table 9 shows the aspheric coefficients of the zoom lens of Example 3.

図８、図９では非点収差図におけるΔＳはサジタル像面を表し、ΔＴはタンジェンシャル像面を表す。また球面収差図においては、ｅ線とｇ線の球面収差を表す。また歪曲収差図も合わせて、これらの収差図からわかるように収差の小さい良好な光学性能を実現することができる。

8 and 9, ΔS in the astigmatism diagram represents a sagittal image plane, and ΔT represents a tangential image plane. In the spherical aberration diagram, the spherical aberration of the e-line and the g-line is shown. In addition, it is possible to realize good optical performance with small aberration as can be seen from these aberration diagrams together with the distortion diagrams.

  Table 10 shows numerical examples of the first to third embodiments.

1 is a configuration diagram of a zoom lens according to a first embodiment of the present invention. FIG. 5 is a diagram illustrating spherical aberration, astigmatism, and distortion at the wide angle end in the zoom lens according to the first exemplary embodiment of the present invention. FIG. 5 is a diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end in the zoom lens according to the first exemplary embodiment of the present invention. Configuration diagram of a zoom lens according to a second embodiment of the present invention FIG. 6 is a diagram illustrating spherical aberration, astigmatism, and distortion at the wide angle end in the zoom lens according to the second exemplary embodiment of the present invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end in the zoom lens according to the second exemplary embodiment of the present invention. Configuration diagram of a zoom lens according to Example 3 of the present invention FIG. 10 is a diagram illustrating spherical aberration, astigmatism, and distortion at the wide angle end in the zoom lens according to the third exemplary embodiment of the present invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end in the zoom lens according to the third exemplary embodiment of the present invention.

G1 1st group lens G2 2nd group lens G3 3rd group lens G4 4th group lens 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 7th lens 8 8th 8 lens 9 9th lens 10 Aperture 11 Equivalent glass of image sensor cover glass, low-pass filter, etc. 12 Movement of the second group lens during zooming 13 Movement of the fourth group lens during focusing at infinity shooting 14 Short distance Movement of the fourth lens group during focusing

Claims (6)

A zoom lens composed of a first lens group to a fourth lens group in order from the front side, with the light entering direction being the front side, having two or more positive lenses, and having a positive refractive power A first lens unit having
A movable structure, consisting of three lenses, and in order from the front, both surfaces are concave, a fourth lens that is a negative lens, a fifth lens, and a second lens group that has a sixth lens that is a positive lens;
It consists of two lenses, with a convex surface on the front side, a seventh lens having an aspheric surface on at least one of the both surfaces, and a meniscus negative lens with a strong concave surface on the rear side. A third lens group having an eighth lens that is
A fourth structure lens having a movable structure and having convex surfaces on both surfaces and a lens having an aspheric surface on at least one of the both surfaces;
The curvature radii of the front and rear lens surfaces of the fourth lens, the fifth lens, and the sixth lens of the second group lens are L4R1, L4R2, L5R1, L5R2, and L6R2, respectively. 14 <| L4R1 | / L4R2 <17 (1) where the refractive index of the third lens at the e-line, approximately 547 nm, is L5n and L6n.
10 <(| L4R1 | + | L5R1 | + L6R2) / (L4R2 + L5R2) <15 · (2)
L5n + L6n ≧ 3.6 (3)
A zoom lens characterized by satisfying the following conditions: When the curvature radii of the front and rear lens surfaces of the seventh lens that is the front lens of the third lens group and the rear eighth lens are L7R1, L7R2, L8R1, and L8R2, respectively.
3 <| L7R2 | / L7R1 <5 (4)
2 <L8R1 / L8R2 <3 (5)
The zoom lens according to claim 1, wherein the following condition is satisfied. The lens surface on the front side of the seventh lens constituting the third group lens and / or the lens surface on the front side of the fourth group lens has a shape in which the positive refractive power decreases from the lens center to the peripheral portion. 2. The rear focus zoom lens according to claim 1, wherein the zoom lens is an aspherical surface. 6. The rear focus zoom lens according to claim 1, wherein the first group lens includes two or more positive meniscus lenses and one negative meniscus lens. The rear focus type according to any one of claims 1 to 5, wherein the first lens group has a three-lens configuration, and two or more of the three lenses use optical glass having an Abbe number of more than 50. Zoom lens. An electronic apparatus comprising the zoom lens according to claim 1.

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