JPS62138817A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To increase the refracting power of each lens group and to shorten the overall length of a lens system by providing a distributed index lens in a specific shape. CONSTITUTION:The 1st lens group has a lens N which has negative refracting power and a lens PF which has positive refracting power and has its convex surface on an object side or lens PR which has positive refracting power and has its convex surface on an image-surface side on the object side. Then, the lens PF or PR is so constituted that the internal refractive index of at least one lens decreases gradually along the optical axis from the vertex of the convex surface of the lens L. The distribute index lens is used on at least either of the object-side or image-surface side of the negative lens in the 1st lens group to increase the refracting power of the 1st lens group and shorten the overall length, and aberration variation during power variation, specially, spherical aberration variation is compensated excellently.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a compact zoom lens, and in particular, to a lens system using a so-called refractive index distribution type lens having a predetermined shape in which the internal refractive index gradually changes in the optical axis direction. A lens-shutter camera that improves optical performance by being used on the one hand - A compact zoom lens with a short overall lens length (distance from the first lens surface on the object side to the imaging plane) that is effective in video cameras, etc. .

(Prior Art) In recent years, with the miniaturization of cameras such as lens shutter cameras and video cameras, there has been a demand for small-sized zoom lenses with short overall lens lengths. Also, lens 5 for lens shutter cameras, etc. Recently, even in the field of small cameras that do not require conversion, it has become desirable to install a zoom lens, and there is a demand for a short, compact zoom lens with a total lens length comparable to that of conventional single-focal-length lenses. .

A zoom lens that includes a standard angle of view (35 at a shooting angle of view of 2ω-47 degrees, and a focal length of f-50 when converted to a still camera), which is commonly used in lens shutter cameras, is disclosed in, for example, Japanese Patent Publication No. 49-29146. Many proposals have been made, including This type of zoom lens consists of two lens groups, a first lens group with negative refractive power and a second lens group with positive refractive power, in order from the object side, and the magnification is changed by changing the distance between both lens groups. The refractive power arrangement is in the order of negative and positive.

For this reason, the pack focus becomes long, which is preferable for a 7-lens camera, but the overall length of the lens tends to be too long for a lens shutter camera.

Therefore, the present applicant first applied for 4! ! ? Kaisho 57-201213
In the publication, the zoom lens has two lens groups, a first lens group with a positive refractive power and a second lens group with a negative refractive power, from the object side, and whose magnification is varied by changing the distance between both lens groups. I suggested a lens. This publication discloses a zoom lens that has a short back focus and a short overall lens length by adopting an arrangement of positive and negative refractive powers in order from the object side.

In this zoom lens, if the refractive power of both the first and second S lens groups is strengthened, the amount of movement of each lens group during zooming will be reduced, and the overall length of the lens can be further shortened. However, if the refractive power of the lens group is strengthened, aberration fluctuations due to zooming will increase1, and it will become difficult to properly correct this.

(Problems to be Solved by the Invention) The present invention provides at least two positive and negative refractive powers in order from the object side.
When changing magnification by changing the distance between both lens groups, the refractive power of each lens group, especially when the refractive power of the first and second lens groups is strengthened, causes aberrations to fluctuate during zooming. In particular, it is an object of the present invention to provide a compact zoom lens that satisfactorily corrects spherical aberration fluctuations using a gradient index lens and shortens the overall length of the lens.

(Means for solving the problem) It has at least two lens groups, a first lens group with positive refractive power and a second lens group with negative refractive power, in order from the object side, and from the wide-angle side to the telephoto side. In a zoom lens in which the distance between both lens groups is reduced during zooming, the first lens group includes at least one lens N with negative refractive power and a positive lens N with a convex surface facing the object side. A lens PF1 having a refractive power of The internal refractive index of the lens L is configured such that it gradually decreases along the optical axis from the apex of the convex surface of the lens L.

The features of this claimed invention are described in the Examples.

(Example) Figures 1 to 5 are numerical examples 1 to 5 of the present invention, respectively.
Lens IO? It is a front view. The figure and I are the first with positive refractive power.
Lens group 12 is a second lens group with negative refractive power, and when changing the magnification from the wide-angle end to the telephoto end, both lens groups are moved toward the object side while decreasing the distance between them. By adopting such a refractive power arrangement and a zoom type, the Fumei example is designed to shorten the overall lens length on the wide-angle side.

Then, by using a gradient index lens having the above-mentioned requirements on at least one of the object side or image side of the lens with negative refractive power in the first lens group, the refractive power of the first lens group is strengthened and the total length of the lens is reduced. The aberration fluctuations that occur during zooming (in particular, the spherical aberration fluctuations that occur at that time) are well corrected.

In the refractive index distribution of the gradient index lens in this embodiment, the refractive index gradually decreases from the apex of the convex surface of the lens L in the direction of the original axis.

By adopting such a shape, the spherical aberration caused by the convex surface can be corrected in a well-balanced manner as a whole by reducing the refractive index, especially in the peripheral area of the convex surface, while reducing the tendency for under-correction.

Now the absolute value of the refractive power of the convex surface is φ) The radius of curvature of the convex surface trs
Let N(x) be the refractive index when taking the Kg axis in the optical axis direction. That is, as the distance from the optical axis increases, the refraction i N (X) decreases and the refractive power of the convex surface weakens.

In particular, in this example, the refractive index N(:t) within the lens with respect to the distance X in the optical axis direction from the apex of the convex surface of the gradient index lens
The change in dN/dx t- is maintained appropriately and aberration correction is performed well overall.

Next, nine fundamental features of the gradient index lens in this example will be described. In this implementation row, the first lens group with negative refractive power is N, which is moved in the first lens group with positive refractive power as the darkness changes.
is provided, and various aberrations such as spherical aberration accompanying zooming are corrected within the first lens group. In addition, a positive refractive power of a predetermined strength is imparted to the first lens group to shorten the total length of the lens. At this time, at least one lens L having a convex surface facing in the opposite direction to the lens N is provided on the object side or the image side of the lens N having a negative refractive power, and the refractive power of this lens L and the refractive power of the lens N are provided. This maintains an appropriate relationship with the lens and reduces aberration fluctuations that occur when changing magnification.

However, in this example, if an attempt is made to further strengthen the refractive power of the convex surface of the lens L and to strengthen the refractive power of the first lens group to shorten the overall lens length, various aberrations, especially spherical aberrations, will occur on the convex surface of the lens L. It's coming. It is very difficult to properly correct this in the first lens group. Therefore, in this embodiment, the lens L is replaced by a gradient index lens #1 having the above-mentioned requirements, and various aberrations at this time are appropriately corrected.

Next, using spherical aberration as an example, the effect of the 9-gradient index lens on third-order aberration will be described.

Regarding the third-order aberration coefficient of the gradient index lens, P, J
, 5ands (Journal of the Optical Society of America J, O, S, A
Volume 60, No. 11, 1970, P1436)
Although it has been reported by many others, it will be expressed here based on the display symbols of Matsui's ``Lens Design Method, J (Kyoritsu Shuppan)''.

If the third-order aberration coefficient in a spherical system and a homogeneous medium is 1, the refraction term in the lens is IJl, and the refractive index distribution type lens transfer order is I, then y −ht'IN,,
......(A2)...-(A3) Here, I is the refraction term SI that occurs when the medium is homogeneous, and / is the refraction term SI that occurs when the medium is a homogeneous medium. The refraction term, {circle around (2)} is the order of transfer of aberrations that occur when light is refracted when it passes through the gradient index lens.

When there is a refractive index distribution in the optical axis direction, the refraction term is the refraction car 8
．． ．． Hato becomes. If the refractive index distribution in the optical axis direction is set at the vertex of the convex surface as the origin, then N(X) −N +N x+N x2+N5x3+ −
...... (A6) It is expressed as follows. Also, dN/dx is dN/dx-Nl + 2N2K + 3N3X2
+ ・=・・・・・・・・・(A7)

When the front or rear of the gradient index lens is a homogeneous medium, equation (A7) is introduced into equations (A2) and (A3). At the vertex of the convex surface, it divides by x-0, so dNo, / d
x-Nt At the exit surface of the lens L, the thickness of the lens L is d
Then, it is obtained by substituting x-d into equation (A7) (however, the value when the focal length 'i-IK of the wide-angle lens is normalized).

Than this becomes.

Equation (88) is the difference in the slope of the refractive index on the entrance side or exit side lens surface of the gradient index lens, and fk,! Since the slope of the distribution in a homogeneous medium is O, on the incident side and on the exit side... (AIO).

From equation (A9) and (AIO), if the slope N on the entrance side has a negative value, the spherical aberration tends to be overcorrected. If the inclination to is negative, spherical aberration tends to be overcorrected.

Therefore, if the above-mentioned gradient index lens is applied to the 1-concave lens in the first lens group, where spherical aberration tends to be under-corrected when the positive refractive power is strengthened, spherical aberration fluctuations during zooming can be controlled arbitrarily. 1. It becomes possible to easily achieve a compact zoom lens in which the overall length of the lens is shortened.

In particular, in this example, the refractive index change of the gradient index lens is 0.05 ((dN/dx) ・fW (5,0-...
...It is preferable to set as shown in (1) in terms of aberration correction.

When the upper limit of conditional expression (1) is exceeded and the refractive index difference within the lens becomes significant, it becomes easy to correct spherical aberration in the positive direction, but fluctuations in other aberrations, especially astigmatism, This is not preferable because the difference in distance becomes large.

Furthermore, when the lower limit of conditional expression (1) is exceeded and the refractive index difference decreases, it becomes insufficient to correct spherical aberration in the positive direction.

In addition, in this embodiment, the radius of curvature of the convex surface of the lens L is set to 0.25 (IRAl/fW(1,5・−・−+21
It is preferable to set it as follows because it is possible to efficiently impart a refractive index difference to the convex surface.

When the lower limit of conditional expression (2) is exceeded and the curvature of the convex surface becomes stronger, the difference in refractive index on the convex surface becomes sharper, and spherical aberration is well corrected, but other aberrations such as coma aberration It's not good because it happens a lot. On the other hand, if the upper limit is exceeded, it becomes difficult to satisfactorily correct spherical aberration in which the difference in refractive index on a convex surface is small.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side・N
i and νl are the refractive index and Abbe number of the glass of the first lens in order from the object side, respectively.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of light is assumed to be positive, Re paraxial radius of curvature, a + &
H"'65 Hkll 1 b2! "'When b4 is each aspherical coefficient, + Kame3I (6+a4■8+&5H10+bIH3+b2
It is expressed by the formula H5+b3H7+b4H9.

For example, the expression l'-D-OXJ means l'-10-XJ.

Also, the refractive index change of a gradient index lens is N(X) −No+N1x+N2x2+N5x3+ − when the X axis is taken in the optical axis direction.
It is expressed by the formula.

Numerical Example I F-1 to 1.889 FNO-1: 4.0 to 5.62
ω-62'~35.3°R1-0,420D 1-0.
06 N 1-N(X)R2-2-521D 2-
0.04 R3--0,537D 3-0.02 N 2-L8
0610 v2=40.9R4-0,475D
4-0.05 N 3-1.70154 v
3-41.2R5-0,825D 5-0.02 R6-1,555D 6-0.07 N 4-1.6
0311y 4-60.7R7--0.442
D 7-0.06R8-5, 821D 8-0.
02 NS-1,56384u 5-60.7
R9--0,80509-0.03-0.30.

RIO--0,639DIO-0,06N 6-1.7
5520 v 6-27.5R11-0,422
Dll-0,02R12--0,732012-0,0
3N? -1.65844 y 7-5 (19R1
3--L569 D13-0.13*R14gang-0
, 319D14-0.03 N 8-L6825
0 v 8 Lord 447R15 Maro-1,015 R14 surface Aspheric &1--5.32D-02, R2-9,94D-01,
R3-7, 94D+OO.

R4-1, 44) D+02, R5-Z16D+03
b,--3,57D-02,b2--4.23D+00
, b3--LOOD+01.

b4-6.970+01 Numerical Example 2 F-1~1.9 FNO=l:4.0~5.6 2ω
-6τ~3&R1-0,351D 1-0.07
N 1-N(X)R2-Z982 D 2-0.
03R3--0,530D 3=0.0IN
2-L80610 y 2-40.9R4-0
,511D 4-0.05 N 3-1.70154
C3-4L2R5-0,791D 5-0.01 R6-1598D 6-0.07 N 4-1
．． 60311 v 4-60.7R7--0.4
38 D7-0.05R8=4.591
D 8-0.03 N 5-L69680
y 5-5a5R9--0,920D 9-0.0
7~0.32R10=-0,578DIO-0,06N
6-1.75520 Jiro 27.5811--0
．． 406 Dll-0,03R12--0,737
D12-0.03 N 7-1.61484
ν 7-5L2R13--L464 D13-0
．． 12*R14=-0,300D14-0.02N
8-L68250 y 8-447R15--, L
OO9 R14 surface Aspherical surface a -1 λ32D-02, a -1,40D+00
, R3-1,53D+01.

a-177D+02, R5-L84D+03
bl-4560-02, b2--5.19D4-00
, b3--1.20D+01.

b4-1.24D+02 Numerical Example 3 F-1~1.9 FNO-1:40~5.62ω-6
τ~35,3°Rl=0.586 D 1-0.0
9 N 1=L617QOy 1=62.8R2-9
,117D 2-0.05 R3--L508 D 3-0.07 N
2-L85026 v 2-3Z3R4-2,
63204-0, 16 R5-0, 909D 5-L), 10 N 3-N (
x) R6--1.127 06-0.12~0.56R
7--0.866 D? -0,11N 4-1.7
2000 Shi4-43.7R8--0,573D
8-0.13*R9--0,404D 9-0.04
N 5-L61700 v 5-LL8RIO--
1303 R9 surface Aspherical surface al--L77D-01, R2-1, 4LD+OO, R
3--7,190+0Oa4-3-43D"02, R
5-L40D+02b□-Z72D-01, b2-a9
4D+00, b3-L25D+02b4”452D
+02 Numerical Example 4 F-1~1.9 F'N0-1:4.0-5.6 2
ω-6τ~35.3°R1-0,650o 1-0.
'06 N 1-N(X)R2-Z813
D 2-0.03R3--L521 D 3-0.
09 N 2-L71736 y 2-29.5R
4-4,60804-0,13 R5 14340 D 5-0.05 N 3-1
．． 64250 Shi3-58.4R6--0,622D
6 San0.12~0.56R7=-0,836D
7-0.08 N 4-1.71300 v 4-
548R8--0,535D 8-0.13*R9-
-0,419D 9-0.06 N 5-L6031
1 y 5-60.7RIO--1a088 89 surfaces Aspherical surface al--127D-01, R2-4020-01, a3
=9.75D+o01L4-146D+02, I
L5--1.50D+03b-6,64D-03,
b −”-5,57D+OO, b3--9.52D+
OL.

b4-4.4OL)+02 Numerical Example 5 F-1~1.9 F'N0-1:4.0~5.62ω
-62゛~35,3”R1-0,472D 1-0.0
6 N 1-N(X)R2-6,375D 2-0.
05 R3--0,540D 3-0.02 N 2-L8
0518 Shi2-25.4R4-1,777D 4-
0.04 R5--0,858D 5-0.05 N 3-1.
60311 Shi3-60.7R6--0.397
D 6-0.05R7=-1079D 7-0.03
N 4-1.58313 v 4-59.4R8-
-(L770 D 8-0.01R9= 1509
D 9-0.04 N S-1,56965y 5
-49.4RIO-4951DIO-0.07~0.3
5R11--α790 Dll-0,06N 6
-L75520 ν 6-27.5R12--0,
443D12-0.02R13--0,628013-
0,03N 7-L73400 Sheer 5L, 5R1
4--L315 D14-0.12*R1'5=-
0,338D15-0.03N 8-L785
90 y 8=442R16--0,982 R1S surface Aspherical surface a -6,84D-03, a -5,64D-01, a
3”-4,640+00.

a-6,23D+01, a5-5.830-
t-01bl--3, 68D-03, b2--L75D
+OO, b3-4.67D+01.

b4-1.871)+02 In Numerical Examples 1 and 2.5, the first lens group has five lenses with positive, negative, positive, positive and positive refractive powers in order from the object side, and the second lens uk has positive, negative refractive power. It is composed of three lenses with positive refractive power, and the first lens on the object side of the first lens group is a gradient index lens, which reduces spherical aberration on the wide-angle side, -low at the periphery of the screen, and low at the center of the screen. The introverted coma aberration is well corrected.

In particular, in Example 5, the curvature of field and the astigmatism difference are reduced over all the threads.

, fi value In Example 3.4, the first lens group is composed of three lenses with positive, negative, and positive refractive powers, and the second lens group is composed of two lenses with positive and negative refractive powers. The third lens from the object side of the first lens group is a gradient index lens, which satisfactorily corrects spherical aberration, especially at zoom positions intermediate from the wide-angle side.

In this embodiment, a plurality of lens groups that are fixed or move during zooming may be provided behind the second lens group to form a zoom lens with three or more lens groups.

(Effects of the Invention) According to the invention, by providing a gradient index lens with a predetermined shape in the lens group that constitutes a zoom lens, the refractive power of each lens group can be strengthened, and as a result, the total length of the lens can be shortened. Furthermore, it is possible to achieve a compact no-sum lens with high optical performance with little aberration variation, especially spherical aberration variation, due to zooming.

[Brief explanation of drawings]

1 to 5 are cross-sectional views of lenses of numerical examples 1 to 5 of the present invention, and FIGS. 6 to 10 are boar aberration diagrams of numerical examples 1 to 5 of the present invention, respectively. In the aberration diagrams, (J3) and (C) are the aberrations at the wide-angle end and the intermediate 1-telephoto end, respectively. 1 in the figure. I[ are the first and second lens groups, respectively, and f is the focal length.

Claims (1)

[Scope of Claims] (1) It has at least two lens groups, a first lens group with a positive refractive power and a second lens group with a negative refractive power, in order from the object side, and the change from the wide-angle side to the telephoto side. In a zoom lens in which the distance between both lens groups is reduced during magnification, the first lens group includes at least one lens N having a negative refractive power.
and a positive refractive power lens P_F with a convex surface facing the object side on the object side of the lens N, or a positive refractive power lens P_R with a convex surface facing the image surface side on the image surface side of the lens N. The internal refractive index of at least one of the lenses P_F and P_R is configured such that the refractive index gradually decreases from the apex of the convex surface of the lens L along the optical axis. A small zoom lens. (2) Based on the vertex of the convex surface of the lens L, when the length in the optical axis direction is x, the refractive index is N, and the focal length of the entire system at the wide-angle end is f_W, 0.05<|(dN/dx )×f_W|<5.0. The compact zoom lens according to claim 1, which satisfies the following condition: