JPS6187119A - Small zoom lens - Google Patents

Abstract

PURPOSE:To compensate aberration efficiently over the whole screen by constituting the 2nd lens group of the 2-1th lens having concave surfaces on both the sides and the 2-2th meniscus-like lens turning its convex surface to the image side and having negative refractive force which are arranged successively from the object side. CONSTITUTION:The 2nd lens group is constituted of two negative lenses, i.e. the negative lens having concave surface on both the sides and the negative meniscus lens turning its concave surface to the object side which are arranged successively from the object side. Since the negative meniscus lens is improved in refractive force without increasing the curve of the image surface and the 1st lens of the 2nd lens group forms concave surfaces on its both sides, two negative lenses of the 2nd lens group take partial charge of negative refractive force each other and both the radiuses of curvature are moderate, so that the generation of a curve on the image surface is reduced at the generation of aberration. Consequently, a small zoom lens reducing the variation of the curve on the image surface due to variable power and efficiently compensating the aberration over the whole screen can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a small zoom lens, and in particular to a small zoom lens K[ It is something to do.

Recently, with the miniaturization of lens shutter cameras, video cameras, etc., there has been a demand for a zoom lens with a short overall lens length. Even in the field of hut cameras where lenses cannot be changed, such as Yatta cameras, it is desired to attach a zoom lens, and there is a demand for a small zoom lens with the same length as the conventional single focal length lens. There is.

Zoom lenses that include a standard angle of view (35fII2, fII2 at a shooting angle of view of 2ω-47 degrees, focal length of about 50mm when converted to a still camera) that are commonly used in lens shutter cameras are, for example, those disclosed in Japanese Patent Publication No. 49-29146. Many have been proposed.

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 magnification is varied by changing the distance between both lens groups. However, because the lens has a negative and positive refractive power arrangement in order from the object side, the puck focus is relatively long, which is a desirable configuration for a single-lens reflex camera, but the overall lens length tends to be too long for a lens shutter camera. there were.

The present applicant previously disclosed in %1 Publication No. 57-201213 that the lens is composed of two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, in order from the object side. We proposed a compact zoom lens that changes the magnification by changing the distance between the two. In this publication, since a positive and negative refractive power arrangement is adopted in order from the object side, a zoom lens with a relatively short pack focus and a short overall lens length is achieved.

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

The main feature of a compact zoom lens to achieve this purpose is that it has two lens groups, the first lens group with positive refractive power and the second lens group with negative refractive power, in order from the object side. In a zoom lens that performs magnification by changing the distance between both lens groups, the second lens group T has both lens surfaces concave in order from the object side, and the second lens has a convex surface facing the image plane side. This lens is composed of a meniscus-shaped 2-2 lens with negative refractive power.

Next, we will describe the structure and operation of a small, uninvented zoom lens.

FIG. 1 shows the refractive power arrangement of an embodiment of the present invention. In the figure, (4) is the zoom position at the wide-angle end, and (B) is the zoom position at the telephoto end.
shows. In the same figure, fI is the detail of the first lens with positive refractive power, fII is the second lens group with negative refractive power, and both lenses are moved toward the gold object side while decreasing the distance between both lens groups. The magnification is being changed. With such a refractive power arrangement, this embodiment achieves a zoom lens with a short pack focus and a minimum overall lens length at the wide-angle end.

In the present invention, by setting the lens shape of the second lens group fII as described above, the curvature of field from the center of the screen to the periphery K is reduced over the entire zoom range, thereby obtaining good optical performance. In other words, the second lens group is composed of two lenses with negative refractive power, and the sum is made so that no lens with positive refractive power is included, preventing the Petzval sum from increasing in the negative direction and completely changing it. Variations in field curvature are minimized over the magnification range.

The second lens group is composed of two negative lenses, including a negative biconcave lens in order from the object side, and a negative meniscus lens with its concave surface facing the object side. The lens has a strong refractive power, and the curvature of field does not become large.Since the first lens in the second lens group is biconcave and has a large negative refractive power, the two lenses in the second lens group have a strong negative refractive power. Since the lenses share negative refractive power with each other, the radius of curvature of both lenses becomes loose, and the occurrence of aberrations, particularly curvature of field, is reduced.

The object of the present invention is achieved by satisfying the above structural requirements, but in order to achieve even better aberration correction, the focal length of the second-second lens is t-/II2, and the zoom at the wide-angle end is When the focal length of the entire system at the position is 't-fw, -tt s < 7fII2, 2//W < -Lo
It is preferable to satisfy the following condition: ・−・・−(fII2). □The conditional expression il+ is for reducing the fluctuation of the field curvature during magnification and obtaining a flat image surface, and the conditional expression ( When the refractive power of the second-second lens becomes stronger beyond the upper limit of fII2, the Petzval sum increases in the negative direction,
The field curvature tilts toward the positive direction. If the lower limit is exceeded, the refractive power of the 2-2nd lens becomes too weak, and the negative refractive power is distributed to the 2-1st lens too much, resulting in large fluctuations in coma aberration and curvature of field due to zooming. This is not desirable because it becomes , Furthermore, in the present invention, when the radius of curvature of the object-side lens surface of the 2-2 lens is RfII2, 3, -LO(Rna 77w(-0,2...--
It is preferable that the condition +21 is satisfied.

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

Moreover, if the lower limit is exceeded, inward coma aberration at the wide-angle end increases, which is not preferable.

In the present invention, in order to reduce the curvature of field as well as the lens shape of the 2nd-2nd lens described above, it is necessary to reduce the curvature of the field on the image side of the 2nd-balanced lens by 1,0 (R,2 //w(15,0・−・−−−−−+
It is preferable to set the condition so as to satisfy the condition 31. If the upper limit of conditional expression (3) is exceeded, the image plane will be over-corrected, and if the lower limit is exceeded, the image plane will be under-corrected.

Furthermore, in the present invention, various aberrations due to zooming, especially spherical aberration,
To achieve a compact zoom lens with less variation in coma aberration and efficient magnification change, the focal lengths of the first and second lens groups are F, F2, first lens group, !, respectively. - When the amount of movement of the second lens group during full zooming is S and S2, respectively - L 5 < F, /F, <-α6 ...
...(4)0.4(S□/S2<α9 ・
It is preferable to satisfy the condition (5).

Conditional expression (4) is used to maintain a well-balanced refractive power of the first and second lens groups, reduce aberration fluctuations due to zooming, and perform zooming efficiently, so the lower limit of conditional expression (4) is roughly set. If the refractive power of the first lens group is exceeded and the refractive power of the first lens group becomes weaker, the pack focus becomes longer and the total lens length becomes longer, making it difficult to achieve a compact zoom lens. Aberration and 14 in the screen
Conditional expression (5) is for efficiently changing the magnification under conditional expression (4), and when the upper limit of conditional expression (5) is exceeded, If the amount of movement of the first lens group increases, the total length of the lens at the telephoto end will become too long.
It becomes difficult to obtain a predetermined variable power ratio of 9, in which the lens group and the second lens group move in parallel. Moreover, if the lower limit is exceeded, the amount of movement of the second lens group is too large compared to the first lens group, and as a result, it interferes with the first lens group, which is not preferable.

Further, in the present invention, based on conditional expression (4), when the focal length of the second balance is /I[1, R4< /III/fr12 (:xo -・-
- It is preferable to set the second-balance and the refractive power of the second-second lens so as to satisfy the condition (6).

If the lower limit of conditional expression (6) is exceeded and the refractive power of the 2nd-balance becomes weaker, the share of the negative refractive power of the 2nd-2nd lens becomes too large, resulting in a large amount of coma aberration at the wide-angle end, and conversely the lower limit If the refractive power of the second balance becomes too strong beyond this value, the amount of variation in astigmatism and curvature of field will increase 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, the lens surfaces of the 2-2 lens are made into aspherical surfaces whose negative refractive power increases as the lens periphery vcvs<. It is preferable to do so. 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 K, 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. In the value implementation sequence R
i is on the object side! Il[K radius of curvature of the iJth lens surface, DiFi the thickness and air gap of the first lens from the object side, Ni and yl are the refractive index and Atsube number of the glass of the first lens from the object side, respectively. It comes out.

Numerical Example I F'-100-150 FNO-1: 4.5-5.
6 2ω-5&gi~37.9°R1-67, 41D 1
-464 N 1-L 77250 C1-49.
6B>219.45 D2-9.56R3--50
,60D3-185 N2-L71?36 y2-
29L5R4-30216゜56 D←10.13R
5--20fII2, 8D 5-= 130 N
3-L 62041 y 3-60.3R6-
-53,72D6-1. 93R7-18191D 7- 4.0ON 4-1
．． 62280 ν 4 57. OR9--345
,88D 9=5.0o N 5-1.62
280v 5-57.0RIO-41&42
DID-20, 28RfII2, Ceramic-3 & 57
Dll- & 75 N 6-L 61
800 ν 641λ4R12--7L24 Numerical Example 2 F-100~150 FNO-1:45~翫6 2
ω-56, t~37. G R1-1a12 Di-
464N1-1.77250 y1m9.6R2
-209,0202 Glue 9.55 R3--5α31 D 3= L 81 N
2=L 71736 v 2-29.584-
148 & 17 D←io, 03R5--291
6305-125N 3-L 62280y
3-57.0R6--5451D←199 R7-20(L 97D?-401N4-L
62280 C4-57. OR8 wheel -9194
D B-4α43 ~l&35 R9=30132 D 9=5. , Go
N5-L 62280 v hs7.0
RIO-52 & 61 DIG-2a 39RfI
I2, --3 & 92 Dll-175N 6-
1.61800 ν ←6λ4R12−−7λ7
7 Numerical Example 3 F-100~150 FNO-1:45~5.62ω
-5ba~a7. rR1-6&05 D1=460
N1-L77250 yl-49,6
R2-197, 30D 2- & 44R3--5α8
1 03= L 83 N 2-L 71
736y 229.5R4-107&42
D 4-9.91R5--25134D 5- &
12 N B-1622 (fund) C3→7.0R6
-493D 6- Z 06 R7= 18 & 50 D? -410N 4-
L 62230 v 4-5 & 2R8--9
& 82 D e-4α42~1a33 R9-289,08D 9- & 00 N
S-L 62280 ν 5-57.0RIO-
57&23 DIG-20,72RfII2, =
-3 & 47 Dll - & 75 N f
yL 61800 y 6-6L 4R12--7
λ22 Numerical Example 4 F-100~150 FNO-1:45~&6 2(
II-56JS” ~ 37.G R1-6L30 D
i-&66 N1=L77250 yl
→9.6R2-10 & 92 D 2-6.34R
3-446D 3-& 51 N 2-L 7173
6 Shi2-29.5R4I-16JL fII2,
D 4-16.98R5-10 & 06 D
S-235N 3”L 83400y 3-
37.2R← 3L 59 D 6-5.63
N 4 torture L 77250 ν ←49,
6R7--9-87D 7-41. 55~17.47 R8--316,03D 8- & Go
N 5 Maro 1.62041 ν 5-60.3R9
-436,8009-1&62 R10=-3487010-&75 N
6-L 61800 y &=644all--
60,53 Numerical Example 5 F-Zoo~150 FNO=1:45~5-6 2
ωw5ha~37. G R1-56.89 Di-156
N1-L77250 yl=4t6R2-87,24
D2-6.94 R3P-6! L 73 D 3-185 N 2-
L 71736 ν or 2 Kai 5R4-15437D 4
-1 & 99 R5-9163D! y-132N5=L83400
y3-37.216-29.57 D←&77
N 4”L77250 v←49.6・R
7-10497D 7-41.61~17.53 88--325.22 D 8p= & Go
N5=L62041y5-6α
3R9-43a 04 D 9-1 & 75RIO
--3λ91 DIO-& 75 N 6-L 6
2041 Jiro 6α3RfII2, --5&03 Numerical Example 6 F-100~150 FNO-1:45~&62ωShizu56Jf~37.9°R1-6410Di-&99
N1-L77250 Shi1-4 & 6R2-74 &
86 02-418 R3--8L 83 D 3- a 60 N 2
-L 71736 Shi2-2 tension 5R4-15L 10
D 4-15.19R5-109,22D S=
421 N 3-L 69680
y 3-56.5R6--7&62D
6-41. fII2, ~17.02 R7--31460 D 7- 5.00
N ←1.62280 ν 4-57.0R
8-469,22D 8-16.75R9--30,4
4D 9-175 N S-1,618■ 5-6 & 4RIO--49,51 Numerical Example 7 F-100~150 FNO-1:4.5~&62ω
-5α~37.9°R1-7λ09 Di-49
2Nu meeting L 77250 ν 1-49.6R2
-15λ37 D 2 6.39R 106.0
0 D 3- a 01 N > L? 7250
C2→Kai6R←58L 51 D 4-4.60R
5= -77, 83D 5p 496 N 3wL
75520 y 3=27.5R6-12L63
D 6-1a 63R7-fII2, 6,2607-
2 to 84 N 4-L 77250 y
4=49.6R8--7432D 8-37. 77-1fu69 R9-279,20D 9 embroidery 5. Go N 5
-L 62280 ν 5-57.0RIO-4
80,26DIO-17,64all--31,53D
ll-fu75 N 6-L 62280 Jiro 5
7.0g1z--sα

[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 cross-sectional views of lenses of numerical embodiments 1, 4, and 6.7 of the present invention, and FIGS. 6 to 9 are aberration diagrams of numerical embodiments 1, 4, 6.70 of the present invention, respectively. It is. In the figure (~ indicates the wide-angle end, (B) indicates the telephoto end. S and C indicate the sine condition, 6M indicates the meridional image plane, ΔS indicates the sagittal image plane, d indicates the d-line, and g indicates the g-line.

Claims (3)

[Claims] (1) In 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 object side, and zooms by changing the distance between both lens groups. ,
The second lens group is composed of, in order from the object side, a 2-1 lens whose both lens surfaces are concave, and a 2-2 lens with a meniscus-shaped negative refractive power whose convex surface faces toward the image plane side. A small zoom lens. (2) When the focal length of the 2-2nd lens is f_II_2 and the focal length of the entire system at the wide-angle end zoom position is f_W, the condition -1.75<f_II_2/f_W<-1.0 is satisfied. A compact zoom lens according to claim 1, characterized in that: (3) A claim that satisfies the following condition: -1.0<R_II_3/f_W<-0.2, where the radius of curvature of the object-side lens surface of the second-second lens is R_II_3. The small zoom lens described in item 2.