JPH03259209A - Inner focus type small-sized zoom lens device - Google Patents

Abstract

PURPOSE:To shorten the overall length and to make the zoom lens device compact by composing a 5th group of four lens elements and moving a 3rd group toward a short-distance body when the lens system is put in focus on the body. CONSTITUTION:A 1st group with positive refracting power, a 2nd and the 3rd group which have negative refracting power, and a 4th and the 5th group which have positive refracting power are arranged and the 5th group consists of the four lens element, i.e. a positive lens which is nearly equal in curvature between both surfaces or larger in curvature on the object side than on the image plane side, a negative lens which is concave to larger curvature on the image plane side than on the object side, and two positive lenses; when the lens system is put in focus on the short-distance body, the 3rd group is moved toward the object and the conditions shown by inequalities I-III are satisfied. In the inequalities I-III, fII, fIII are the respective focal lenghts of the 2nd and 3rd groups, fW the focal length of the whole system on a wide-angle end, f10 the focal length of the 10th lens from the object side, and f8.9 the composite focal length of the 8th and 9th lenses. Consequently, the device can be reduced in size and weight.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a small zoom lens device using an inner focus method, and in particular, it is improved to shorten the overall length of the lens and realize a zoom ratio of 3 times or more. This invention relates to an inner focus compact zoom lens device.

(Prior Art and Problems to be Solved by the Invention) Zoom lenses for solid-state image pickup devices have conventionally been of a type in which focusing is performed in a first group, and an inner focus type in which an internal lens group is moved.

In the former type, focusing is performed by the first group, so the diameter of the first group becomes large and the first group accounts for more than half of the entire weight of the lens system, placing a heavy burden on the drive mechanism.

On the other hand, the latter inner focus type zoom lens has a lens system composed of, for example, four groups, and the zoom ratio is changed by moving the second group, and the defocus caused by zooming is corrected by moving the third group. It is.

Since the first group of this inner focus zoom lens is fixed, it is possible to attach special filters such as polarizing filters, and even if a conversion lens is attached to the first group to further increase magnification, the zoom ratio cannot be changed. Since the conversion lens does not rotate together, it has the characteristic that no extra load is placed on the lens drive system.

Since there is a demand for miniaturization in both video cameras and still cameras, it is necessary to keep the overall length of the lens system as short as possible even if the zoom ratio is increased.

On the other hand, aberrations are sufficiently corrected9. It is necessary to have excellent performance in practical use.

There have been many proposals for inner focus zoom lenses in order to make them smaller and lighter (for example, Japanese Patent Application Laid-open No. 62-206516, Japanese Patent Application Laid-open No. 63-44614, etc.), but they are small and lightweight with high magnification. Its total length was insufficient for the purpose of achieving this.

An object of the present invention is to meet the above-mentioned demands, and to provide an inner-focus compact zoom lens device that has excellent lens performance in practical use, is short in overall length, compact, and inexpensive, and can achieve a high magnification of about 3 times. There is a particular thing.

(Means for Solving the Problems) In order to achieve the above object, an inner focus type compact zoom lens device according to the present invention has, in order from the object side, a first group having a positive refractive power and a second group having a negative refractive power. group and third
The first group includes a fourth group and a fifth group having positive refractive power.

A zoom lens device in which the fourth group and the fifth group are fixed, and the second group is moved from the object side to the image side during zooming, and the third group performs focus shift correction and focusing due to the zooming,
The fifth lens group includes, in order from the object side, a positive lens with both surfaces having the same curvature or a convex surface with a stronger curvature than the image side facing the object side, and a negative lens with a concave surface having a stronger curvature than the object side facing the image side. Consisting of a total of 4 lenses, 2 positive lenses and 2 positive lenses.
Focusing on a short-distance object is performed by moving the third group toward the object, and the following conditions are satisfied.

0.9< f ■/fw <2.1 ... (1
)3.2 < f m /f w <6.5...
(2) 0.6 < l f , o/f 8.9 +
<0.9-(3) However, f, fm; Focal length of the second and third groups fW; Wide-angle end focal length of the entire system flo: Focal length of the 10th lens from the object side fa
, s: composite focal length of the 8th and 9th lenses from the object side (Example) The present invention will be described in more detail below with reference to the drawings.

FIG. 1 is a schematic diagram of a lens arrangement showing a first embodiment of an inner focus type compact zoom lens device according to the present invention.

In the figure, the left side is the object side, and the right side is the image plane side.

1 is a negative meniscus lens, 2 is a positive lens having a convex surface with a larger (stronger) curvature on the object side than on the image plane side, and these are bonded together. 3 is a positive lens having a convex surface on the object side and a concave surface on the image side.

The first group is composed of three lenses 1, 2, and 3, and is a fixed lens group having positive refractive power.

Also, 4 is a negative meniscus lens with a surface with a larger curvature facing the image plane side than the object side, and 5 is a biconcave negative lens.

6 is a positive meniscus lens with a surface having a larger curvature facing the object side than the image surface side.

The second lens group is composed of the three lenses 4, 5, and 6 mentioned above, and is a negative lens group that provides a zooming variable power effect.

Reference numeral 7 denotes a negative meniscus lens whose surface having a larger curvature than the image side faces the object side, and this lens element constitutes the third group.

This third group corrects the movement of the image plane due to the zooming action and also performs focusing.

Further, 8 is a biconvex lens, 9 is a positive lens with a convex surface with a larger curvature than the image side facing the object side, 10 is a negative lens with a concave surface with a larger curvature than the object side facing the image side, and 11 is a biconvex lens. , 12 is a positive meniscus lens with a surface having a larger curvature than the image side facing the object side.

The fourth group is constituted by the lens 8 mentioned above.

The fifth group is composed of lenses 9, 10, 11 and 12, and is a fixed lens group with positive refractive power.

An optical member (beam splitter) 13 and an aperture (auto iris) 15 are included between the fourth group and the fifth group. Furthermore, a low-pass filter 14 is inserted in front of the image plane 16.

To change the zoom ratio, the second lens group is moved to the right in the figure, while the third lens group is moved to perform correction and focusing by the zoom action. .

Next, find the radius of curvature, thickness, and refractive index of both sides of each lens.

Numerical examples of the Atsube number and the distance between the lens and the aperture are shown below.

R, 68,589d.

R233,056d2 R, -397,208 da R422,905d- Rs 47.31 ds Re 34.109 ds R78,84d.

Re -66,165d8 R1125,03ds R+o 14.1B2 d+.

R++ 28.13 6++ RI2-10.96 d+z R+3-19.886 6.3 R1453,7296+< R+5-36.792 (Ls l, 2 n, =1.80518 25.47.4
n, = 1.62041 60.30.15
n, = 1.0 5 n, = 1.62041 6OJ Book I
n5=1.0 1 ns =l 69680 55.54.7
n, = 1.0 0.8 n, = 1.69680 55.50, 15
ns = 1.0 2.2 n1o = 1.84666 23.9 lines 2
n++=1.0 1 n,,=1.48749 70.1 book 3
n,3=1.0 2.4 n,,=1.74320 49JO,5n
+s=1.0 R,,oo d,6 R,700d,.

R+s oOdos RlB 10.372 d, 9 R20-129, 1186z.

R21-40,033d2, R2□ 8.2 dz2 R2324,277da3 R2445,149dza R2S 10,162 d2s R2628,948d2s R27°' d27 2600 n1s=1.51633 64.1 n+t =1.0 n+e=1.0 n1s =1.74320 49.3 n2. =1.0 n,,"1.80518 25.4 n, 2=1.0 n234.69680 55.5 n2.=1.0 n2s=1.69680 55.5 n2s=1.0 nz7=1. 51633 49.3 Focal length of zoom lens f = 9J F,, = 1.4 However, book 1; 0.8 ~ 14,928 book 2; 18.493 ~ 6.4 book 3; 2.635 ~ 0.6 ~26 R1-28: Radius of curvature of each lens surface d1-3.: Surface spacing 11-2.: Refractive index of each lens or air d: Appe number d: Variable distance dl between lenses 3 and 4: Variable distance d13 between lenses 6 and 7: Variable distance between lenses 7 and 8 FIG. 3 is a schematic diagram of a lens arrangement showing a second embodiment of an inner focus type compact zoom lens device according to the present invention.

In the figure, lenses 21 to 32 are lenses 1 to 1 of the first embodiment.
Similarly, the beam splitter 33° and low-pass filter 34 correspond to those of the first embodiment.

Although the thickness of the lenses is different from the first example by 9 intervals and the value of the refractive index is different, when focusing on the lens shape, the lens 31
The noticeable difference is that the thickness of the lens 32 has become thinner, and the image plane side of the lens 32 has become flat.

The radius of curvature, thickness, refractive index, Abbe number of both surfaces of each lens, and the number chain side of the distance between the lens and the aperture are as follows.

R, 58, 127 R,33,056 R31967,252 R, 24,011 R555,967 R, 35,373 R, 8, 84 Re -44,461 R, 41,831 R,, 15,175 R1□　26.583 R12-11,447 R,, -20,88 R,, 79,479 R, 5-29,454 R16l RI 7 0゜ d, 1.2 d2 6.55 ds　O,O d4 4.98 d5 Book 1 61 d74.7 do 018 d, 0,1 dl. 2.12 dll book 2 121 dl3 Book 3 dll 2J7 dlso,=5 d, s6.0 do71.545 νd n, 4.84666 23.88 n2 = 1.62041 60.27 n3 = n=　=1. e2o4160.27 ns=1.0 n64,71300 53.98 n, = 1.0 na”1.71300 53.98 n, = 1.0 n1o=1.84666 23.88 01□=1.0 nlz=1.48749 70.15 1+s=1,0 n14=1.74320 49.37 n+s=1.0 n 1s=1.51633 64.15n,,=1.0 R+a ■ dl8 R+s 10.58 dl5 R2 (+-54,505d2゜ R2□ -26,208d21 R228,275d2z R2130, 118d2s R24-80,92dzt R2S 10.544 d2s R26(X) d26 R2,oo d27 R28o.

1,955 4.63 0.96 0.85 1.09 1.55 0.15 6.55 n+s=1.0 n,s=1.80400 46.65 02°=1.0 n,,=1 .84666 23.88 n,,=1.0 0.3=1.72342 37.95n2*=1.0 0.5=1.62041 60.27026=1.0 n,,=1.51633 64. 15 Focal length of zoom lens f = 9J ~ 26F,, = 1.4 However, book 1; 0.8 ~ 14,875 book 2; 18.844 ~ 6.127 zero 3; 1.858 ~ 0.5 5th The figure is a schematic diagram of a lens arrangement showing a third embodiment of an inner focus two-compact zoom lens device according to the present invention.

In the figure, lenses 41 to 52 are lenses 1 to 1 of the first embodiment.
Similarly, the beam splitter 53 and the low-pass filter 54 correspond to those of the first embodiment.

Similar to the second embodiment, the first embodiment refers to the thickness of the lens.

Although the spacing and refractive index values are different, when focusing on the lens shape, the thickness of the lens 51 is thinner, the image plane side of the lens 52 is flat, and the curvature of both convex surfaces of the lens 49 is the same. Although the curvature of the biconcave surfaces of No. 50 is larger on the image plane side, the noticeable difference is that the difference in curvature has become smaller.

Numerical examples of the radius of curvature, thickness, refractive index, Abbe number of both surfaces of each lens, and the distance between the lens and the aperture are as follows.

(Margin below) R, 58,378 R233,624 R, 1585,877 R, 25,028 R349,42 R626,844 R, 8,347 R, -46J71 R, 28,685 R,, 14,682 R1,36,018 R,, -11,961 R,, -21,753 R,,44,471 R, 5-46,882 R,, o.

R,, o.

R,, o.

R,, 35,822 dl 1.2 d25.77 d30.15 d4 4.1 d5 Book 1 d, 1 d7 4.57 do O,8 ds　O,1 Lo2J2 d,, *2 dl21 dl3 Book 3 dl42.31 1Lso, 5 dll 6 dl71.5 a+s1.5 dll 4.51 νd n, = 1.84666 23.88 n2 = 1.60311 60.7 n, = 1.0 n, = 1.69680 55.62 ns=1.0 n64, 69680 55.62 n7=1.0 n-=1.71300 53.98 n9=1.0 n+o”1.84666 23.88 n1□=1.0 n+z”1.56732 42.83 n,,=1. O n,,=1.80400 46.65 1+s=1.0 n,,=1.51633 64.15 01□=1.0 n+s=1.0 n1s=1.77250 49.57 R2o-35,822dz.

R21-23,145dz+ R2221,912d＊□ R2349,251dz3 R2,-32,127d24 R2515,81 (Ls R26oOd26 R27ood2゜ R211o.

0.41 0.85 0.57 2.21 0.15 2.84 2.43 n2o=1.0 nz, =1.84666 23.88 nz2=1.0 nz3=1.80400 46.65 n24= 1.0 n2s=1.77250 49.57 n2a=1.0 n,=1.51633 64.15 Focal length of zoom lens f=9.3~26Fx0=1.
4 However, Book 1: 0.8 ~ 16.326 Book 2: 19.231 ~ 5.252 Book 3: 2.047 ~ 0.5 The zoom lens device according to the present invention realizes miniaturization and weight reduction, and also reduces each aberration. In order for this to be sufficiently corrected, the following conditions must be met.

First, it is necessary to have a relationship of 0.9<lfn/fw<2.1-(1). Note that fn and fm are the second group.

The focal length of the third group, fw, indicates the wide-angle end focal length, respectively.

Equation (1) is a conditional expression regarding the focal length of the second group, and in this type of lens system, if the focal length of the second group is long,
There is a property that the focal length of the first group becomes long.

This is a condition for keeping the amount of movement of the second group within the optimum range during zooming. When the upper limit value is greater than 2.1, the amount of movement of the second group increases, the overall length increases, the diameter of the front lens of the first group increases, and compactness is lacking. If the value is smaller than the lower limit of 0°9, the refractive power will be strong and the amount of movement will be small, but the amount of aberration variation in the zoom section will be large, making it difficult to correct the aberrations with other lens groups.

Next, 3.2 < f m / f w <6.5・
...(2) must be satisfied.

This equation (2) relates to image plane movement correction during zooming and the focal length of the third group for use as a focus lens. If the upper limit value of 6.5 is exceeded, the amount of movement required to correct the image plane movement due to zooming and the amount of movement when focusing increases, and the diameter of the front lens in the first group increases, resulting in a lack of compactness. It turns out.

On the other hand, if the value is smaller than the lower limit of 3.2, the amount of movement becomes small, so that the focus control mechanism during telephoto becomes complicated, resulting in a lack of mass productivity and increasing the negative Petzval of the zoom section.

Furthermore, 0.6<lf. /f a,s 1<0.9・
...Condition (3) must be met. If the upper limit value of this equation is greater than 0.9, the aberrations that remain after zooming, especially coma aberration, become so large that they cannot be corrected completely. When the value becomes smaller than the lower limit of 0.6, the negative Petzval increases.

Next, in the configuration of the fifth group, the lens closest to the object (the first
．． In the second and third embodiments, lenses 9 and 29 are used, respectively.
and 49) have the same or larger curvature on both sides, and the second lens (lenses 10, 30 and 50 in the first, second and third embodiments, respectively) has the same or larger curvature. By orienting the large surface toward the image plane,
Spherical aberration and coma aberration can be suppressed.

The fourth group and the fifth group normally have two and five elements, but these are reduced to one and four elements, respectively, to make them more compact and to correct aberrations.

Further, the second group can correct coma aberration and astigmatism by separating the two lenses on the image side.

FIGS. 2, 4, and 6 show the characteristics of spherical aberration, astigmatism, and distortion at wide-angle, standard, and telephoto positions. Figures 2, 4 and 6 are respectively shown in Figure 1. Second
and corresponds to the third embodiment.

In each figure, T is the characteristic of the meridional image plane, and S is the characteristic of the sagittal image plane. As is clear from these characteristic diagrams, each aberration is suppressed in a well-balanced manner, and it is clear that the lens has excellent performance in practical use.

(Effects of the Invention) As explained above, the present invention configures the lens systems of the first group to the fifth group as described above, and satisfies formulas (1) to (3). Therefore, it has the following effects.

In the conventional example, the fourth group had two elements and the fifth group had five elements, but in the present invention, the fourth group has one element and the fifth group has four elements, while correcting aberrations. It can be configured more compactly than other zoom lenses.

Therefore, according to the present invention, it is possible to realize a small inner focus type zoom lens device with a short overall length, which has sufficient aberration correction, has excellent performance in practice, and has a zoom ratio as high as about 3 times.

[Brief explanation of drawings]

1, 3 and 5 respectively show a first embodiment of an inner focus type compact zoom lens device according to the present invention. Second
and FIG. 7 is a schematic diagram of a lens system showing a third example. Figures 2, 4 and 6 are respectively shown in Figure 1. Characteristic diagrams corresponding to the second and third embodiments, wide angle. FIG. 4 is a diagram showing spherical aberration, astigmatism, and distortion in standard and telephoto conditions. 1-12.21-32.41-52...Lens 13.
33.53...beam splitter 14.3.4.54
...Low pass filter 15.35.55...Aperture 16.36.56...Image plane

Claims (1)

[Claims] A first group having a positive refractive power, a second group and a third group having a negative refractive power, and a fourth group and a fifth group having a positive refractive power are arranged in order from the object side. The first, fourth, and fifth groups are fixed, and during zooming, the second group is moved from the object side to the image side, and the focus shift correction and focusing due to the zooming are performed by the third group.
In a zoom lens device that uses groups, the fifth group includes, in order from the object side, a positive lens with a convex surface facing the object side whose curvatures are the same on both sides or whose curvature is stronger than the image side, and a concave lens whose curvature is stronger than the object side. consists of a negative lens facing the image plane side and two positive lenses in total, and focusing on a short distance object is performed by moving the third group toward the object side. An inner focus compact zoom lens device that satisfies the following conditions. 0.9<|f_II/fw|<2.1...(1)3.2
<|f_III/fw|<6.5...(2)0.6<|
f_1_0/f_8_,_9|<0.9...(3) However, f_II, f_III; Focal length of the second and third groups fw; Wide-angle end total system focal length f_1_0; Focal length f_8_,_9; Composite focal length of the 8th and 9th lenses from the object side