JPS6187120A - small zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a small zoom lens, and more particularly, to a small zoom lens with a short overall lens length (distance from the first lens surface to the image forming surface) that is useful in 41iK lens shutter cameras, video cameras, etc. It is something.

Recently, with the miniaturization of lens shutter cameras, video cameras, etc., there has been a demand for compact zoom lenses with short overall lens lengths. Particularly in the field of small cameras such as lens shutter cameras that do not require lens replacement, it is desired to attach a zoom lens, and there is a demand for a small zoom lens with a length comparable to that of conventional single focus lenses.

Many zoom lenses, including the standard angle of view commonly used in lens-shutter cameras (focal length of about M50M when converted to a 35m still camera at a shooting angle of view of 2ω-47 degrees), have been proposed in many ways, including Japanese Patent Publication No. 49-29146. has been done. This type of zoom lens consists of a first lens group with negative refractive power and a second lens group with positive refractive power in order from the object side.
It is composed of two lens groups and the magnification is changed by changing the distance between both lens groups, but because the refractive power is arranged in order from the object side to negative and positive, the pack focus is relatively long and it can be used as a single-lens reflex camera. is a preferable configuration, but the overall length of the lens tends to be too long for a lens shutter camera. We have proposed a compact zoom lens that is composed of two lens groups, the second lens group having negative refractive power, and whose magnification is varied by changing the distance between both lens groups. In this publication, since a positive and negative refractive power arrangement is adopted in order from the object side, the pack focus is relatively short and a zoom lens with a short overall lens length is achieved.

An object of the present invention is to provide a compact zoom lens that reduces field curvature among the various aberrations of the zoom lens proposed in the same publication, and achieves good aberration correction over the entire screen.

The main feature of the compact zoom lens for achieving the purpose of the present invention is that it has two lens groups, in order from the object side: a first lens group with positive refractive power and a second lens group with negative refractive power. In a zoom lens in which magnification is changed by changing the distance between both lens groups, the second lens group has a meniscus-shaped second lens group with a convex surface facing the object side from the object side and having a negative refractive power. It is composed of a lens and a meniscus-shaped 2-2 lens with a negative refractive power whose convex surface faces the image plane side.

Next, the structure and operation of the small claw zoom lens of the present invention will be described.

FIG. 1 shows the refractive power arrangement of an embodiment of the present invention. In the same figure, (N is the zoom position at the wide-angle end, (B) is the zoom position at the telephoto end)
- Show. In the figure, fl is the first lens group with positive refractive power, and fII is the second lens group with negative refractive power, and the magnification is changed by moving both lens groups toward the object side while decreasing the distance between them. It is carried out. With such a refractive power arrangement tK, as shown in this embodiment, a zoom lens with a short pack focus and a minimum overall lens length at the wide-angle end is achieved.

The present invention is achieved by setting the lens shape of the 5@2 lens of II as described above, so that the lens shape of the 5@2 lens of II is set as described above.
The body surface curvature from the center to the periphery is reduced to achieve good optical performance. In other words, the second lens group has a negative refractive power of 2
The lens is constructed with a positive refractive power lens, which prevents the Petzval sum from increasing in the negative direction and reduces fluctuations in field curvature over the entire magnification range.

In addition, the aberrations of each lens in the second lens group are minimized because the structure is symmetrical to the object side: a negative meniscus lens with a convex side facing the object side, and a negative meniscus lens with a concave side facing the object side. They have the effect of canceling each other out, making it possible to suppress the amount of aberration generated.

The object of the present invention is achieved by satisfying the above-mentioned comparison condition t-, but in order to achieve even better aberration correction, the focal length mtf of the second-second lens, the wide-angle end When the focal length of the total ■2 system at the zoom position is fw, -2-0<fa□/fw<-0,8...
...(1) It is preferable to add the condition t'' @.

Conditional expression (11 is for minimizing the variation in body curvature during magnification and obtaining a flat image surface, and the upper limit of conditional expression (1)) is directly exceeded and the refractive power of the 2nd-2nd lens becomes stronger. The Petzval sum increases in the negative direction, and the curvature of field falls in the positive direction.Also, when the lower limit value is exceeded, the refractive power of the 2nd-2nd lens is weak. This is not preferable because the coma aberration and the fluctuation of the four image planes due to the 9-tone action, which has a large contribution to the image, become large.

Furthermore, in the present invention, the second -
When the curvature of the lens surface on the object side of the two lenses is R113, -1,o (RI[3/fW <-α15 -・-・
-.f2) is preferably satisfied.

When the upper limit of conditional expression (2) is exceeded, the curvature of field at the zoom position increases in the positive direction, especially at the wide-angle end, and the fluctuations in the curvature of field due to zooming become large.

Moreover, exceeding the 1-direction limit is undesirable because inward coma aberration at the wide-angle end increases.

In the present invention, in order to reduce the lens shape of the 2-2 lens as described above and the 1-quadrant curvature, it is necessary to
(When the FJjJ ratio radius tR■2 of the lens surface on the surface side, o, s < R112/ fW (s, o
It is preferable to set the condition so as to satisfy the condition (3).0 If the upper limit of conditional expression (3) is exceeded, the image plane will be over-corrected, and the lower limit 1lI1. On the other hand, if the value exceeds 1, the image plane becomes under-corrected.

Furthermore, in the present invention, various aberrations due to zooming, especially spherical aberration,
In order to achieve a compact zoom lens that minimizes fluctuations in coma aberration and efficiently changes magnification, the focal lengths of the first and second lens groups should be adjusted to F, F2, $Luns group and second lens, respectively. When the amount of movement of the group λ 1 ゛ in full magnification is S□ and S2, respectively, -L5 (F1/F2(-0, 6... -... (4
)0.4(S□/S2(0,9......(5
) is preferably satisfied.

Conditional expression (4) is used to maintain a good balance of refractive power between the first and second lens groups, reduce aberration fluctuations due to zooming, and perform zooming efficiently.The lower limit of conditional expression (4) is 1.
i! If the refractive power of the first lens group is exceeded and the refractive power of the first lens group becomes weaker, the back focus becomes longer and the total lens length becomes longer, making it difficult to achieve a compact zoom lens.If the upper limit is exceeded, the total lens length becomes shorter. Spherical aberration and coma aberration often occur in the middle of the screen.

Conditional expression (5) is for efficient scaling under conditional expression (4).
When the amount of movement of the lens group increases, the total length of the lens at the telephoto lens becomes too long, and the first and second lens groups move almost in parallel, making it difficult to obtain a predetermined variable power ratio. Moreover, if the lower limit is exceeded, the amount of movement of the ^22 lens will be too large compared to the first lens group, and as a result, it will interfere with the first lens group, which is not desirable.

In addition, the present invention provides that, under conditional expression f, 11, when the point distance t of the second rune is fIll, zO<fII□/fII□<λ8...
6) It is preferable to set the refractive power of the second lens so that the following condition is added by 7jijj.

If the upper limit 11i of conditional expression (6) is exceeded and the refractive power of the second lens becomes weaker, the share of the negative refractive power of the two lenses becomes too large, resulting in a large amount of coma aberration at the wide-angle end. If the no-fracting power of the second lens becomes too strong, the amount of variation in astigmatism and curvature of field increases during zooming.

In the present invention, the first lens group is sequentially positive, negative,
4 lenses of positive and positive refractive power or 4 lenses of positive, negative, negative and positive refractive power or 4 lenses of positive, positive, negative and positive refractive power or 4 lenses of positive, negative and positive refractive power Preferably, it is composed of three lenses.

In the present invention, in order to obtain better optical performance over the entire screen, at least 1% of the lens surfaces of the 2nd-2nd lens should be shaped so that the negative refractive power increases toward the lens periphery. Preferably, it is spherical. This makes it possible to further reduce fluctuations in the field curvature towards the under-corrected side, particularly at the intermediate portion of the zooming.

In the present invention, focusing is preferably performed by extending the entire lens system because it reduces fluctuations in aberrations, but it may also be performed by moving only the first lens group or the second lens group. According to this, the lens barrel becomes simple.

As described above, according to the present invention, it is possible to reduce aberration fluctuations due to zooming, particularly fluctuations in field curvature, achieve excellent aberration correction over the entire screen, and achieve a compact zoom lens.

Next, numerical examples of the present invention will be shown. R in numerical dog example
i is on the object side! In order of ll, the radius of curvature of the 14th L/lens surface, Di is the thickness and air gap of the 1st lens from the object side, Ni and ν1 are the refractive index of the glass of the IRKth lens from the object side, respectively. This is Atsbe's number.

Numerical Example I F-4α0-60. OFNO-1: 4.5-6.6
2ω-56J'~37,9°R1=2456
D 1-L 50 N 1-L 71736
y 1-29.5R2-89, 3802-1
,94 R3-17,11D 3-1.94 N 2-L 7
1736 v 2-29. SR4-70,4704
-1,86 R5 7 & 96 D 5-1.90 N 3-1
．． 62041 C3-60.38←-17,9606
-λ14 R7 15 & 30 D 7- 169
N 4-1.62041 ν 4-60.3R
8--3&73 08-16.28~&65 R9= 9a 12 D 9-! 00
N! PL 62280 v 5-57.0
RIO-46,89DIO-& 82 R11--15,68Dll-L 50 N 6-L
62280 Jiro 57.0R12-3λ19 a value Example 2 F-4αG-60, OFNO-1: 4.5-5.62ω
-56,8″~37.9°R1 electric 26.96
D 1■ 1.76 N 1-L 77250
ν 1-49.6R2-80,80D2-&64 R3--19,9703-1,13N 2-L 717
36 C2-29. SR4--62), 0704
-λ replacement R5--85,5705-1,44N 3-1.620
41 Shi3-60.3R6--2), 39D 6ru α76 R7-69, 68D 7-1.60 N 4-L
62280 Shi4-57.0R9=271.54
D9=100N S-1,62
280v 5=57.0RIO-67,61010-
8,43 R11--15,29Dll-1,50N 6-1.6
1800 ν 6-6λ4R12--30,55 Numerical Example 3 F=40.0-60. OFNO-1:45-5.6 2
61-36.8°~37.9'P, 1-26.86
01-L 71 N 1-L 77250 Si1
-49.6R2-72,660>'160 R3= -19,9503PL 14 N 2-L
71736 v >29. SR4--235,93
04-404 R5--85,37D 5- 1.46 N
3-L 62041 ν 3-60.3R6-
-2),4606-0,77 R7 6485 D? -1,58N 4-
162041 ν 4-60.3R8--4a
98 0 &-15.47 ~ Parent 8 R> 25α49 D 9-2.00
NS-162280ν 5-57.0RIO-6a1
8 DIG-Plate 48R11 Thin-1 & 11 D
ll■L (fund) N 6-L 61 帥0 Jiro 6
14R12--9,85 Numerical Example 4 F-40,0 to 60. OFNO-1: 4.5-5.6
2ω-561f~37.9°R1-2) LO2D 1-
L89 N 1-L77250y
1-4SL6R2-8&80 D2-4 (2nd R3--2α32 0 3- 1.30
N 2-L 71736 ν 2 29.5R
← 59fu13 D 4-409R! F-114
51D 5= 1.17 N 3-L 62280
v 347. OR6 Akebono -2λ51 D 6
-L 07R7-7L 24 D 7-1
．． 75 N 4-L 62280 ν
4-57.0R8--3& 19 D 8-1&
55-5.91 Rh? 7L 10 D'fi L Go N
5=L 62280v 5-57.0RIG-79
,70DIO-& 36 R11--1& 46 Dll-1,50N 6
-1.61800 ν 6-6&4R12--3
G, 98 Numerical Example 5 F-4α0-6Q, OFN() 1:45-5.6 2
m-56g -37,9'R1-2)63υ 1-1
．． 58 N 1-L 77250 ν
1-49.6R>: 16.42 D 2-2
．． 70R3--2 & 22 D 3- L 15
N 2-1.71736 C 2-29L 5
R4--5a 05 D 4-7.48R5-37
,73D 5- α92 N 3-L 834
00 v 3-37.2R&-a 11.81
D fy SL 30 N 4-L
77250y 4-49.6R7--40
．． 69 07 layer 1&OOR8-116,26D 8
-100 N S-1,62041ν 5-6
0.3R9-5L7a D 9- &32RIO-
-1 & 78 DIO-L 50 N
6-L 61800 y 6-614R11--
25,78 Numerical Example 6 F-40,0-60,OFNO-1:45~&62ω-
567~37.9°R1=2&39D
1-2.38 N 1-1.77250
v 1-49.6R2-297,6402-L
78 R3--33,49D 3- L 16 N 2-dimensional L
71736 Shi2-29.5R4-5&38
D 4-7.55R5-4LO8D5orL 19
N 3-1.69680 Shi3-5 & 5R6--3
3.27 0 +l & 7G~6. O6 R7-19 (L 24 D 7- L 00
N4-L 62280y
4=57.0R8 Fog 6 (1,03D 8-7.10 R9=-112)D 9-1.50 N 5”1
．． 61800y 5=63.4RIO--20
,80 Numerical Example 7 F-40, (1-60, OFNO-1: 4.5-5.6
2a+-565~37.9"R1-24,9601-
1,93N 1-L 77250 Si1-49.6
R2-39,8902-Z58 R3~ 48.11 03- 1.92
N 2-1.77250 ν 2-49.
6R4--413,7104-1,77 R sea 30.19 D 5-λ02 N 3-1.
75520 Shi3-27.5R6=5&56
D6 self 6.72R7-49,41D? -1,10N
4-L 77250 ν 4-49.6R8
--30,9208-1193 ~4.30 R9= 40L 97 D 9- Z QON
5=L 62280y 5-57.0RIO-
7L 15 DIO-7, 10R11= -11
65Dll-L 50N 6-L 62280
v 6-57.0R12--2), 84

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the refractive power arrangement in one embodiment of the present invention, and FIG.
5 to 5 are lens cross-sectional views of numerical examples 1, 5, and 6.7 of the present invention, and FIGS. 6 to 9 show various aberrations of numerical examples 1, 5, and 6.7 of the present invention, respectively. It is a diagram. In the figure, (A) shows the wide-angle end, and (B) shows the telephoto end. S and C are sine conditions, 6M is the meridional image plane, △S is the sagittal image plane, ddd line, and g is the g line.

Claims (3)

[Claims] (1) A zoom lens that has two lens groups, a first lens group with positive refractive power and a second lens group with negative refractive power, in order from the real side, and changes the magnification by changing the distance between both lens groups. In,
The second lens group includes, in order from the object side, a meniscus-shaped 2-1 lens with negative refractive power with its convex surface facing the object side, and a meniscus-shaped 2-1 lens with negative refractive power with its convex surface facing the image plane side. A compact zoom lens characterized by being composed of two lenses. (2) When the focal length of the 2-2 lens is f_1_2 and the focal length of the entire system at the wide-angle end zoom position is f_W, the following condition is satisfied: -2.0<f_II_2/f_W<-0.8 A compact zoom lens according to claim 1, characterized in that: (3) The scope of the claim is characterized in that, when the radius of curvature of the object-side lens surface of the 2-2 lens is R_II_3, the condition -1.0<R_II_3/f_W<-0.15 is satisfied. The small zoom lens described in item 2.