JPH04114116A - Zoom lens - Google Patents

Abstract

PURPOSE:To realize a high power variation ratio and a large aperture ratio, to make the lens compact and inexpensive, and to obtain high aberrational performance by using a cemented lens of one negative lens and one positive lens as a 2nd group, and providing at least one aspherical surface, and satisfying specific conditions. CONSTITUTION:The 2nd group II mainly moves in power variation and at least a 1st group I moves so as to compensate image point movement resulting from the movement of the 2nd group; and the 1st group I consists of one negative lens and one positive lens and has at least one aspherical surface and the 2nd group II consists of the cemented lens of one negative lens and one positive lens and includes at least one aspherical surface. Then inequalities I - III hold. Here, phi1 is the composite refracting power of the 1st group (phi1<0), phi2 the composite refracting power of the 2nd group, phiP1 the refracting power of the most object side surface in the 1st group, and phiP2 the refracting power of the most object side surface. Consequently, the zoom lens which has the high power variation ratio and large aperture ratio and is made compact and inexpensive while having the high aberrational performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and particularly to a zoom lens that can be used in small cameras such as video cameras and electronic still cameras.

2. Description of the Related Art In recent years, due to the packaging of electronic components and improvements in integration rates, the volume and weight of lenses occupying the bodies of video cameras and the like have become relatively large.

The same can be said about cost.

Miniaturization, weight reduction, and cost reduction are absolute requirements for current video cameras and the like, and these requirements for lenses are increasing year by year.

In pursuit of miniaturization, weight reduction, and cost reduction, single-focal or bifocal lenses may be considered, but considering their attractiveness as a product, they are considered to be far inferior to zoom lenses. . For example, zooming and continuous framing during video recording cannot be achieved with single-focal or bifocal lenses.

On the other hand, if a zoom lens does not have a high variable power ratio, it will be less attractive as a product, but since a high variable power ratio and miniaturization are inherently contradictory items, a zoom lens with a high variable power ratio In order to achieve this, it is inevitable that the device will become larger.

Therefore, in order to create a zoom lens that achieves a good balance between high zoom ratio and compact size, it is necessary to create specifications that take into account optical design and current needs. For example, the zoom ratio is 6x and the aperture ratio is F/1.

4 to 1.6 zoom lenses are possible.

As such a conventional video camera lens, there is one described, for example, in Japanese Patent Laid-Open No. 1-120523. This is a 6x zoom lens with an FNO of 1.4, but since it is composed of 14 lenses, it reduces costs and
It cannot be said that weight reduction has been sufficiently achieved. Also,
An example of using an aspherical lens to reduce the number of lenses is described in JP-A-1-201614. This is a 6x zoom lens with FNO of 1.5 and the number of lenses is 8. However, this lens also has a positive first lens group, has a thick core, and cannot be said to have achieved sufficient weight reduction.

What the above conventional examples have in common is that the first group has positive refractive power.

In such a type of zoom lens, it is difficult to achieve sufficient reduction in size and weight.

Therefore, in view of this situation, the present invention has a high zoom ratio and a large aperture ratio, and is also compact (e.g., smaller and lighter), lower in cost (e.g., fewer lenses than conventional zoom lenses), and It is an object of the present invention to provide a zoom lens that achieves high performance in terms of aberrations.

In particular, the objective is to realize a bright zoom lens with a variable power ratio of about 6 times and an FNO of about 1.4 to 1.6 while maintaining high optical performance.

Meno In order to achieve the above object, the zoom lens of the present invention has the following features: A first group having negative refractive power in order from the object side.

A second group having a positive refractive power and a third group having a positive refractive power.
The second group mainly moves during zooming, and at least the first group moves to compensate for the resulting image point movement. The first group includes one negative lens and one positive lens. and includes at least one aspherical surface, the second group consists of a cemented lens of one negative lens and one positive lens, and includes at least one aspherical surface, the following conditions It is characterized by satisfying formulas ■～■.

0.5〈1φ, 1/φ2＜1.0 ・・・・・・■0
．． 2<φ'+/φ+<1.1 ・・・・・・■0
．． 5<φP2/φ2<1.0 ・・・・・・■However, φ,: Combined refractive power of the 1st group (φ1<0) φ2: Combined refractive power of the 2nd group φp1: Most of the 1st group Refractive power φP2 of the object side surface: This is the refractive power of the surface closest to the object side in the second group.

In the present invention, during zooming, the second group mainly moves on the optical axis to perform the zooming action. In addition, by providing the first group with negative refractive power, the inclination of off-axis incident light can be immediately reduced in the first group, the diameter of the front lens can be reduced, and aberration correction can be made. becomes easier.

Since both the first and second groups are each composed of two lenses, one positive lens and one negative lens,
The combination of positive and negative aberrations also allows for good correction of chromatic aberration. Furthermore, by introducing an aspheric surface into each group, the degree of freedom in monochromatic aberration correction can be greatly improved.

In addition, by making the second group a positive/negative cemented lens,
The second group tolerance can be made much looser.

6x zoom class, F/1.4 with a small number of lenses
In order to achieve high performance of ~1.6, the first and second groups
Conditional expression (■), which requires the power ratio of both groups to be appropriately given so that the groups satisfy the above conditional expressions (■) to (■), indicates the ratio of the refractive powers of the movable first and second groups. The movement locus of both groups, especially the first group, changes depending on this ratio. As the upper limit of conditional expression (2) approaches, the first group movement locus will be located closer to the object side at the telephoto end than at the wide end, and when the upper limit is exceeded, the amount of peripheral light at the telephoto end will decrease. Conversely, as the lower limit is approached, the lens will be located closer to the image side at the tele end than at the wide end.If the lower limit is exceeded, the amount of peripheral light at the wide end will decrease.

Even if either the upper limit or the lower limit of conditional expression (2) is exceeded, it is necessary to increase the diameter of the first group and the diameter of the second group in order to prevent a decrease in the amount of peripheral light, making it impossible to achieve compactness.

In order to further improve the performance, it is necessary to configure the shapes of the first group and the second group so as to satisfy the above-mentioned conditional expressions (1) and (2).

Conditional expression (2) indicates how much the negative refractive power of the surface of the first group closest to the object is to be distributed. When the negative refractive power is weakened below the lower limit, higher-order aberrations generated on the first image side surface become large, making it difficult to improve the performance. On the other hand, if the negative refractive power is increased beyond the upper limit, negative distortion and coma aberration will occur, and off-axis performance will deteriorate.

Conditional expression (2), like conditional expression (2), indicates to what extent the positive refractive power of the surface of the second group closest to the object is to be distributed. If you exceed the upper limit and give positive refractive power to the surface closest to the object,
The amount of spherical aberration generated in the second group becomes excessive, and the spherical aberration deteriorates negatively. On the other hand, when the value is below the lower limit, the amount of spherical aberration generated in the second group becomes insufficient, and the spherical aberration actually deteriorates.

To explain the third group more specifically, in order to ensure back focus while properly correcting spherical aberration, the third group includes a front group that starts from a surface convex to the object side and has negative refractive power as a whole; It is preferable to use a so-called reverse telephoto lens with a rear group having positive refractive power. Further, specifically, the front group is constructed of a positive meniscus lens and a negative lens in order from the object side, since the number of lenses is small and it is advantageous in terms of aberration correction.

At this time, it is preferable to satisfy the following conditional expressions (1) to (2).

1.0<l φA/φg<3.0 ・・・・・・■0
〈1φ,・f+＜O,S・・・・・・■0.5
<1/(φP3・fW)<1.3 ・・・・・・■ However, φS: Composite refractive power of the 3rd group fW: Composite focal length of the entire system at the wide end φ,: Front of the 3rd group Combined refractive power of the group (φn < O) φP3: This is the refractive power of the surface closest to the object side in the third group.

The third group, which follows the first and second groups, must form a good image of the convergent light beam emitted from the second group, but must also ensure sufficient back focus. Therefore, it is preferable to adopt a configuration that satisfies the conditional expression (2).

Conditional expression (2) indicates the refractive power ratio between the first group and the third group, and if the positive refractive power of the third group is increased so as to fall below the lower limit, sufficient back focus cannot be obtained.

Conversely, if we weaken the positive refractive power of the third group so that it exceeds the upper limit,
Spherical aberration at the wide end occurs in an amount greater than the allowable amount.

Also, although the magnitude of the back focus can be controlled by the magnitude of the negative refractive power of the front group of the third group, there is a trade-off relationship in that it becomes difficult to correct each aberration including spherical aberration. It is preferable to adopt a configuration that satisfies formulas (1) and (2).

If the negative refractive power of the front group in the third group is weakened by falling below the lower limit of conditional formula (■), sufficient back focus will not be obtained, and conversely, if the upper limit is exceeded, spherical aberration will occur beyond the allowable amount at the wide end. It ends up.

Conditional expression 〇 indicates the appropriate range of refractive power for the positive refracting surface at the front of the third group; if it falls below the lower limit, sufficient back focus will not be obtained, and if it exceeds the upper limit, the curvature of field at the wide end will decrease. Correct correction will not be possible.

Further, focusing of the lens system of the present invention is performed by the first group,
This can be done by extending a part of each of the second group or the third group, all of them, or the entire lens system. In particular, when focusing is performed by extending the first group, performance deterioration is small and there is almost no decrease in illuminance, so it is possible to easily perform close-up photography that is much closer than in the conventional example.

Furthermore, if the second group is mainly moved during zooming, and the first and third groups are moved to correct the resulting movement of the image point, the degree of freedom in correcting aberrations increases, and - Good aberration correction can be achieved.

Further, the rear group in the third group consists of one positive lens,
In order to correct aberrations, it is preferable that the third group has at least one open-valve spherical surface.

For aberration correction, the rear group in the third group is preferably composed of two positive lenses or one positive lens and one negative lens.

Alternatively, the rear group in the three groups is composed of one positive lens,
Moreover, if the third group has at least one open valve spherical surface, it is almost equivalent in terms of aberration correction to constructing the rear group of the three groups with two positive lenses or 61 positive and negative lenses. Despite this, the number of lenses is small and it is advantageous for cost reduction.

Su'l pull vinegar.

However, in each example, r+(i=1.2.3.,
, ) is the radius of curvature of the i-th surface counting from the object side, d: (
t = 1.2゜3, , ,) indicates the i-th axis top surface interval counting from the object side, N1 (i = 1, 2, 3, , , ),
ν+(i・1,2,3.,,,) is i counting from the object side
The refractive index of the second lens for the d-line.

In addition, f indicates the focal length of the entire system, and FNo indicates the open F-number.

In the examples, a surface with a radius of curvature marked with * indicates that it is an aspherical surface, and is defined by the following equation representing the shape of the aspherical surface.

2, where, be.

<Example 1>f"49.1~16.0~8.71 FNO=3.1
3~1.72~1.441] (Untan-JLIJ old)
Tadasu L! Eetama 1r2 24.920 r4 95.310 rs 29.216 re 16.551 rv* -45,879 re ■(Aperture re 8.771 r+s 9.531 r++ -60,954 r+2 8.024 r+3 34.26O r+4 pieces -12,556 r+5 00 r16 c.

1,400d, 0.900~27.799~61.198ds
1.300 N31.84666 ν323.8
2d65.500 N4 1.77250 ν,
49.77dv 41.439~8.709~1
．． 501d81.400d, 3.700Ns 1.78831 Shiro
47.32d+l+ 2.000 d++ 2.100 Ns 1.80741
νg 31.59d+21.500 dz33.100 N7 1.77250 Schiff 49.77d+44.000 dz55.000 Ns 1.45851 ν8
67.93 valve JLiTL only 1L r3: ε: 0.10000×10 A4=0.10582X 1O-4 AS”-0,27287X 1O-8 As=0.72531x IQ-1 @ r7: ε=O, 100OOX 10A ,=0.12
950X 1O-4 Aa=-0,87213X 10-" As=0.49808x 10-1@r, 4: ε: 0.10000x 10Aa=0.6
5008 x 10-' As = 0.12558
9~1.44~1.44ra 157.326 dj O,800~22.707~49.905r also 30.736 r7 umbrella -47,960 8,986 7,40O 1,77250 ν4 49.77 r++ 71. 786 7.556 19.342 dz 2.100 Na 1.80741
shi, 31.59d, 2 1.300 dz44.000 r+s dos 5.000 Ne (X) 弗]口一子JL: ε=O,100OOX 10 Aj=0.14041X 10-' Aa=-0.43336X 10 -" As = 0.15477 rIa: t = o, xooooox 10A, =
-0,44613X 10-' As=0.17339X 10-' As=-0.15460X 10-'<Example3> f=49.1~16.0~8.71 FNO=2.7
6～1.44～1.44Nenbeme 11ujUu1 糺L
! L Yusa 1 inch -54,563 dw 1.400 8.754 do 1.700 r+s -93,490 dz23.100 N7 1.77250 νt
49.77rl4 CX) d+-5,000Hm 1.45851r+s
■ Valve IC rl: t ; 0.10 (100X 10A4
= 0.70296
0.14625x 10-' A*knee 0.23242X10-' As=0.96446X 10-" rl*: t=0.10000X 10A4=
0.41519X10-'Ae"0.16121X10-'As=-0.12625X10-'<Example4> f=52.7-15.0-9.21 [LIL[L rl- 47,651 FNo=3.12~1.51~1.44JlfL!!
141 sentences ν8 67.93 dll, 300 N+ 1.77250 νI
49.7724.689 54.094 33.638 16.898 9, 624 rls 311.851 ds2.600 N2 1.84866 ν2 2
3.82da 1.200~29.302~54.0
68da 1.300 N3 1.84666
νa 23.82th 5.800 N-'1.
77250 ν, 49.77da 4.400
Ns 1.78831 ν547.32 dos 2.100 No 1.80741
Shiro 31.5926.187 d+22.900 N71.77250-16.4
47 dos 4.000 a (LJ 5.000 Ng 1.45851 Schiff 49.77 Shi, 67.93 Gei IJL YulL rs: t =O, 100OOX 10A4=
-0,91207X 10~5 Aa"0.14453X 10-" A@=-0,20791X 10-@ A+s=0.14465X 10-"A+r=-0,36568X10-" rs: t =0.100OOX 10A, =
0.17736x 1O-4 As=-0,27556X 10-' A*=0.47593x 10-@A+@knee 0.37627X 10-"A+2=0.1
1022X 10-+2 <Example 5> f=52.7~20.0~9.21 Fno=3.0
1 ~ 1.70 ~ 1.44 dishes 1 full inebriation'' 1 near!
Uni to 1r+* -51,286 d+ 1.300 N+ 1.77250 ν
+ 49.77ra 46.076 ds 1.200~19.290~53.514ra
m 36.362 ds 6.500 Ng 1.77250 V
s 49.77rlm1084.963 dos 2.200 Ng 1.80741 ν
, 31.59r14 QO dos 5.000 Ns 1.45851
νm 67.93r16 CX) Valve JJL barrier 1: rl: ε:0.10000X 10AJ=0
．． 66783X 1O-s Ae=-0, 12278X10-'As"0.10733X10" r4: ε=O, 100OOX 10A4"-0,
11800X 10-'As"0.74513X10-' A@=0.17201X 10-" rlI: e =O, 100OOX 10A4=
O, 10,487
7~1.73~1.44 Bloodside Sleeping Mill Lll-厘JLI 租 し ≧ A Σ A8 = -0, 25713X 1O-7 As = 0.10598X 10-' r5 : ε = O, 100OOX 10A,=-0,
11922x 10" A6=0.26552X 1O-7 A, = -0,12678X 1O-9 r12: ε=O, 100OOX 10A, = 0.1
1639X 1O-3 As =0.18013X 1O-5 As=-0,40812X 1 leaf 7 <Example 7> f=49.1~16.0~8.71 FNO=2.8
1~1.47~1.44a+a 4,000 O Valve IJL grandson IC: ε=0.100OOX 10 Aa=0.11613X 10-' (Aperture) A8=0.39696X 1O-5 A*=-0,20492X 10-'<Example8> f=49.1~16.0~8.71 FNo=3.2
3~1.71"-1,66 boat 1 (Motan-]uJn old"
Mori [Tsuru Eeki 1d + a 4.000 rI6 00 Ben] 1 [! ”C r2: ε=O, 100OOX 10A4 knee〇, 57576X 10-' Ae=-0.83774X 10-"A*"0.54205X10-"ry:A:"Q. 100OOX 10 A, = 0.12839x 10-' Aa = -0.31749XIO-" Aa mini-, 38646XIO-" r+4: E = O, 100OOX 10A, =
0.12862X 10-' d+s 4.0υO rI? ■ Valve"11L rl: s; 0.100OOX 10A4"
0.78186X 10-'As"-0,74125X10-' At=o, 80305X 10-@A+5=-0.25474X10-" Al2=-0,17950X 1O-13A+n=0.
10852X 1O-ISr6: ε=O, 100
OOX 10A4"0.15518X 10-' Ae=-0,13119X 10-' A*=0.27030X 10-'A+@;-0.10779X10-"Al2=-0,33512X10-" Al4=0.30443X 10 -” <Example 9> f=49.1~16.0~8.71 FNO=3.2
3~1.70~1.66 Yoshimiji*JLl; J0 Old 1 Tadarigou Eyuba 1r+a dos s, oo.

rl? valve! IL rl: ε=0.10000×1OA,=0.68
593x 10-' 1.45851 67.93 As=-0,85814X 10~7 A*=0.85286X 10-' /I+5=-0.28652X 10-"Al2=-0
,20131X 10-”Ala”0.11175X
10-”re: e:0.100OOX 10A4=0
．． 16035X 10-'Ae=-0.15696X10-' As=0.25272X 10-" A+@=-0, 31861X 10-th A++=-0,
29168X 1O-12A+a”0.20599X1
0"<Example10> f=49.1~16.0~8.71 F, O=3.3
3~1.76~1.44r1s ■ dos 5.000 No 1.45851rl
a 00 valve "1" grandchild IC rI: ε: 0.10000×10Aa=0.94
155X 10-' Aa knee 0.90178X 10-' As=0.11103X 10-"Alg"-0,36446
26090X 10-”Al4=0.15605X 1
O-16r6: ε=0.100OOX 1067
．． 93 ds 5.000 N4 1.77250 1)a
41.77A, = 0.23103
,47374X 1inch 12Ata=0.42745x
10-” r+a: ε:0.10000X 10Aa=0
．． 13102x 1O-3 Ae=0.11436X 10-' A*=0.98161X 10-' A+@=-0, 18319X 10-@A+2=-0,
25810X 1O-9A+, =-0,15523x
Lol@<Example 11> f=49.1~16.0~8.71 FNO=3.0
5-1.61-1.44 (L 1.300 N31
．． 83350 νs 21.0016.971 8, 419 rllll 131.545 r+2 24.226 r+a 23.135 ds 1.700 (Ls 4.000 rI6 c.

dos 5.000 Me 1.45851rI
7 oO valve] 1" grandson IC r,: ε=0.100OOX 10A,=0.87
651
,10888X10-" 67,93 A+4=0.82220X 10-" r6: ε=O,100OOX 10A,=0.1
6108
3425 X 10-I! <Example 12> f=49.1-16.0-8.71 FNO=3.3
3~1.70~1.86r+a 185.870 r+: t=o, 1ooooox 10A4"
0.10297X 10-' Ae=-0,35776x 1 leaf 7 km=0.40005x 1O-9 A+s"-0,42348X10-" A+2=-0,12176X 10-"A+ a =0
．． 23859 X 1 leaf l5ra: ε=o, t
oooox 10A4=0.14837X10-'Ae=-0,43859X10-" A*=0.10878X 10-" do 1.700 A+a=-0,48803X 10-"A+2=-0,
20039X 10-+2AI4”0.18676X
10-14 Next, conditional expression (■) in Examples 1 to 12 above
Table 1 shows the values of 1φA/φ2 in the equation (1) and φp, /φ in the conditional expression (2).

φp2/φ2 in conditional expression (■) in Examples 1 to 12 above
Table 2 shows the values of 1φA/φ3 in conditional expression 〇.

φo−fM in conditional expression (■) in Examples 1 to 12 above
1 and the value of 1/(φP3・fiI) in conditional expression
Shown in the table.

Table 2 Table 1 Table 3 Tables 1 to 12 are lens configuration diagrams corresponding to Examples 1 to 12, respectively, with arrows (1) and (2) in the figures.
) and (3) are the first group (1), the second group (II) and the third group
The movement of the group (I[[) from the telephoto end (T) to the wide end (W) is schematically shown.

In Examples 1 to 11, the closest to the object side of the third group (III),
In the twelfth embodiment, an aperture (A) is provided between the second group (II) and the third group (m). Also, at the end is a flat plate (P) that corresponds to a low-pass filter or face plate.
Aberrations are corrected with the lens inserted. In each embodiment, the diaphragm (A) and the flat plate (P) are fixed and do not move when zooming.

In Examples 1 to 11, when changing the magnification from the telephoto end (T) to the wide end (W), the second group (■) in charge of changing the magnification moves on the optical axis toward the image side, and In order to correct the movement of the image point, the first group (I) acts as a compensator and performs a U-turn movement on the optical axis, expanding toward the image side at the middle. Note that the third group (I[[) including the diaphragm (A) and the flat plate (P) is fixed and does not move.

In the twelfth embodiment, from the tele end (T) to the wide end (W
), the diaphragm (A) and the fourth group (IV) consisting of a flat plate (P) do not move, and the second group (IV), which is responsible for changing the magnification, does not move.
II) moves on the optical axis toward the image side. In order to compensate for the image point shift due to zooming, the first group (I) performed a U-turn movement in the middle and bulged toward the image side, and the third group (III) performed a U-turn movement in the middle and bulged toward the image side. Then, at the wide end, it will be located closer to the object than at the telephoto end.

In the first embodiment, the first lens group (I) moves in a U-turn and is positioned a little closer to the object side than the telephoto end at the wide end. In the second embodiment, the first lens group (1) moves in a U-turn and is positioned a little closer to the image side than the telephoto end at the wide end. In Examples 3 to 12, the first group (I) almost makes a U-turn, but at the wide end it is located slightly closer to the object side than at the telephoto end.

In Examples 1 to 3, the negative first group (I) consists of a biconcave negative lens and a positive meniscus lens convex to the object side,
The positive second group (II) consists of a negative meniscus lens concave to the image side and a biconvex positive lens, and the positive third group consists of an aperture (A),
It consists of a positive meniscus lens convex to the object side, a negative biconcave lens, a positive biconvex lens, and a flat plate (P). In addition, in Examples 1 and 2, only the second group (n) is a cemented lens,
In Example 3, the first group (I) and the second group (I[) are cemented lenses. Furthermore, in Examples 1 and 2, the first group (I
), the image side surface of the second lens in the second group (II), and the image side surface of the third lens in the third group (III) are aspherical surfaces. In Example 3, the first group (
The object side surface of the lens I), the image side surface of the second lens in the second group (n), and the image side surface of the third lens in the third group (III) are aspherical surfaces.

In Example 4, the negative first group (1) consists of a biconcave negative lens and a positive meniscus lens convex to the object side, and the positive second group (n) consists of a negative meniscus lens concave to the image side and a positive meniscus lens concave to the image side. It consists of a double-convex positive lens, with the positive third group being an aperture (A) and a positive meniscus lens convex toward the object side.

It consists of a negative meniscus lens that is concave on the image side, a positive biconvex lens, and a flat plate (P). In addition, the first group (I) and the second group (
n) is a cemented lens. Also, the second group in the first group (I)
The image-side surface of the lens, the image-side surface of the second lens in the second group (II), is an aspheric surface.

In Examples 5 and 6, the negative first group (I) consists of a biconcave negative lens and a positive meniscus lens convex to the object side, and the positive second group (n) consists of a biconcave positive lens and an object side. It consists of a negative meniscus lens with a concave side, and the positive third group is the aperture (A).
, a positive meniscus lens convex to the object side, a negative meniscus lens concave to the image side, a biconvex positive lens, and a flat plate (P). In Example 5, the first group (I) and the second group (I
F) is a cemented lens, and in Example 6, only the second group (n) is a cemented lens. In addition, in Example 5, the first
The object-side surface of the second lens in group (I), the object-side surface of the second lens in group (n), and the image side surface of the second lens in third group (III) are aspherical surfaces. In Example 6, the image of the object-side surface of the second lens in the first group (I), the object-side surface of the second lens in the second group (n), and the second lens in the third group (DI) The sides are aspherical.

In Example 7, the negative first group (I) consists of a positive meniscus lens convex to the image side and a negative biconcave lens, and the second positive group (n) consists of a negative meniscus lens concave to the image side and a negative meniscus lens concave to the image side. It consists of a biconvex positive lens, and the positive third group consists of an aperture (A), a positive meniscus lens convex to the object side, a biconcave negative lens, a biconvex positive lens, and a flat plate (P). In addition, the second group (I[
) is the only cemented lens. Furthermore, the image side surface of the first lens in the first group (I), the image side surface of the second lens in the second group (n), and the image side surface of the third lens in the third group (■) are , is an aspherical surface.

In Examples 8.10 and 12, negative first group (I)
consists of a biconcave negative lens and a positive meniscus lens convex to the object side, the positive second group (II) consists of a negative meniscus lens concave to the image side and a biconvex positive lens, and the positive third group (II) consists of a negative meniscus lens concave to the image side and a positive biconvex lens. m
) is the aperture (A), a positive meniscus lens convex to the object side, 2
It consists of a negative meniscus lens that is concave on the image side, a positive biconvex lens, and a flat plate (P). In Examples 8 and 12, the first group (I) and the second group (II) are cemented lenses. In Example 10, the first group (I) and the second group (II) are cemented lenses, and the third lens and fourth lens in the 183 group (III) are cemented lenses. Further, in Examples 8 and 12, the object side surface of the first lens in the first group (I) and the image side surface of the second lens in the second group (II) are aspherical surfaces. , the object-side surface of the first lens in the first group (I), the image-side surface of the second lens in the second group (II), and the image-side surface of the fourth lens in the third group (III). The surface is aspheric.

In Example 9, the negative first group (I) consists of a biconcave negative lens and a positive meniscus lens convex to the object side, and the positive second group (n) consists of a negative meniscus lens concave to the image side and a positive meniscus lens concave to the image side. It consists of a double-convex positive lens, with the positive third group being an aperture (A) and a positive meniscus lens convex toward the object side.

Concave negative meniscus lens on the image side, biconvex positive lens.

It consists of a negative meniscus lens concave on the object side and a flat plate (P). Note that the first group (I) and the second group (n) are cemented lenses. Further, the object-side surface of the first lens in the first group (I) and the image-side surface of the second lens in the second group (II) are aspherical.

In Example 11, the negative first group (I) consists of a biconcave negative lens and a positive meniscus lens convex to the object side, and the positive second group (I[) consists of a negative meniscus lens concave to the image side. It consists of a double-convex positive lens, and the positive third group is an aperture (A), a positive meniscus lens convex to the object side.

Concave negative meniscus lens on the image side, biconvex positive lens.

It consists of a positive meniscus lens convex to the object side and a flat plate (P). Note that the first group (I) and the second group (ff) are cemented lenses. Further, the object-side surface of the first lens in the first group (I) and the image-side surface of the second lens in the second group (n) are aspherical.

13 to 24 are aberration diagrams corresponding to Examples 1 to 12, respectively, in which (T) represents the focal length at the telephoto end, and (M) represents the intermediate focal length.

(W) shows the aberration at the focal length at the wide end.

In addition, the solid line (d) represents the aberration for the d-line, and the broken line (
SC) represents the sine condition. Furthermore, the dashed line (DI) and the solid line (
DS) represents astigmatism on the meridional plane and the sagittal plane, respectively.

In this way, the above example has a high variable power ratio of 6x and a large aperture ratio of Fl of 4 to 1.6, but it is a simple three-group system with only 7 to 8 elements in the entire system. Good aberration performance is achieved with a very small number of elements. Furthermore, the overall length and outer diameter of the front lens are much more compact than those of the conventional ones, and the desired objectives of the present invention are fully achieved.

JIBE1 As explained above, according to the present invention, it is possible to realize a zoom lens that has a high zoom ratio and a large aperture ratio, and is also compact, low cost, and has high aberration performance.

In particular, despite the small number of lenses (7 or 8), the zoom ratio is around 6x and the FNO is 1.
．． A zoom lens with a brightness of about 4 to 1.6 can be realized while maintaining high optical performance.

[Brief explanation of the drawing]

Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6,
FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 are lens configuration diagrams corresponding to Examples 1 to 12 of the present invention, respectively. Fig. 13, Fig. 14, Fig. 15, Fig. 16, Fig. 17,
Figure 18, Figure 19, Figure 20, Figure 21. Figure 22. FIGS. 23 and 24 are aberration diagrams corresponding to Examples 1 to 12 of the present invention, respectively.

Claims (1)

[Claims] (1) Consisting of, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power, and mainly during zooming. When the second group moves, at least the first group moves to correct the image point movement caused by the movement, and the first group consists of one negative lens and one positive lens, and at least one surface The second group is composed of a cemented lens of one negative lens and one positive lens, and includes at least one aspherical surface, and satisfies the following conditions. Zoom lens; 0.5<|φ_1|/φ_2<1.0 0.2<φ^P_1/φ_1<1.1 0.5<φ^P_2/φ_2<1.0 However, φ_1: of the first group Combined refractive power φ_2: Combined refractive power of the second group φ^P_1: Refractive power of the surface closest to the object in the first group φ^P
_2: Refractive power of the surface closest to the object side in the second group. (2) The third group is composed of, in order from the object side, a front group consisting of a positive meniscus lens and a negative lens and having a negative refractive power as a whole, and a rear group having a positive refractive power as a whole, and the following: The zoom lens according to claim 1, which satisfies the following conditions: 1.0<|φ_1|/φ_3<3.0 0<|φ_A・f_W|<0.8 0.5<1/ (φ^P_3・f_W)<1.3 However, φ_3: Composite refractive power of the third group f_W: Composite focal length of the entire system at the wide end φ_A:
Combined refractive power of the front group in the third group φ^P_3: This is the refractive power of the surface closest to the object side in the third group. (3) The rear group in the third group consists of one positive lens,
The zoom lens according to claim 2, wherein the third group has at least one aspherical surface. (4) The zoom according to claim 2, wherein the rear group in the third group consists of two positive lenses or one positive lens and one negative lens. lens. (5) The zoom lens according to claim 2, wherein the second group mainly moves during zooming, and the first group and the third group move to correct image point movement caused by the zoom lens. .