JPH0247617A - Zoom lens - Google Patents

Abstract

PURPOSE:To realize the X8 zoom of high picture quality and high performance compactly without increasing the cost by composing a 3rd group of a negative single lens which has its large-curvature surface on the object side and satisfying specific conditions. CONSTITUTION:A 2nd group consists of three lenses, i.e. a negative lens which has a large-curvature surface on the object side, a biconcave lens, and a positive lens which has a large-curvature surface on the object side and is arranged while a certain space is left in order from the object side, and a 3rd group consists of the negative single lens having the large-curvature surface on the object side. Then inequalities I-IV hold. In the inequalities I-IV, psiI, psiII, and psiIII are the refracting power values (reciprocal of focal length) of the 1st-3rd groups, fr and fw are the composite focal length values of the whole system at the telephoto end and wide-angle end, and dAIR is the on-axis gap between the 2nd negative lens and positive lens in the 2nd group. Consequently, the X8 zoom lens of high picture quality and high performance is constituted compactly without increasing the cost.

Description

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

In recent years, the cost of electronic components for video cameras, etc. has been reduced. Although miniaturization has been achieved at a considerable speed, it is difficult to say that the lens systems that meet this trend have made as much progress as electronic components, and in terms of cost.

Weight aspect. In terms of size, etc., the ratio of lenses to the camera body is increasing year by year. Furthermore, in recent years, very high-resolution image sensors have come into use for consumer use, and the optical performance of the lens itself is now required to be higher than that of conventional lenses. Therefore, in order to satisfy high performance, lens systems have become more complex and larger, reducing costs. There are also movements that go against the trend of downsizing.

Conventionally, a 6x zoom lens was developed by, for example, Japanese Patent Application Laid-Open No. 60-2609.
A 13 to 15 sheet configuration, such as that shown in No. 12, was common. However, even with this configuration, it is difficult to say that it satisfies recent demands for high resolution.

Furthermore, although a 6x zoom lens is becoming established as a standard specification for video cameras, an 8x zoom lens is often used in high-end video cameras that are one rank higher. In order to realize an 8x zoom lens, complexity and size are unavoidable, which also requires cost reduction. This goes against the grain of compactness. For example, an example of an 8x zoom lens is disclosed in Japanese Patent Application Laid-Open No. 60486818, but it usually has a configuration of 14 to 16 lenses, making it considerably larger than a 6x zoom lens.

Therefore, in order to achieve the high image quality 8x zoom lens that has been attracting attention recently, a complex configuration of about 15 or more elements is required.
Furthermore, the lens had to be considerably larger than a 6x zoom lens.

The present invention aims to achieve a compact 8x zoom lens with high image quality and high performance at the same cost as a conventional 6x zoom lens. The aim is to achieve this with about 14 sheets.

Main team ■Mold! In order to achieve the above object, the zoom lens according to the present invention includes, in order from the object side, a first group having a positive refractive power. 2nd group with negative refractive power, 3rd group with negative refractive power. 4th group with positive refractive power. It consists of a total of five groups, including a fifth group with positive refractive power, and during zooming, the second group moves significantly on the optical axis and mainly has a variable power function. The resulting movement of the image point is corrected by movement of the third or fifth group. Focusing is performed on the first group or the third group. Or by either group 5.

More specifically, the first group consists of, in order from the rostral side, a negative meniscus lens with a convex rostral side, a positive lens with a strong surface facing the rostral side or a combination thereof, and a lens with a strong surface facing the rostral side. The second group consists of three positive lenses facing toward the image side, and the second group consists of a negative lens with a strong surface facing the image side from the rostral side, a biconcave lens, and a strong surface facing the rostral side placed with a certain amount of space. The third group consists of a single negative lens with a strong surface facing toward the incisal side. The fourth group consists of one or two positive lenses, making the divergent light beam after the third group almost afocal, and the fifth group consists of five lenses, three positive lenses and two negative lenses. Become.

The major feature here is that the second group is of a three-separate type, negative, negative, and positive. In recent years, it has become mainstream to have this second group composed of three elements, one negative, one negative and one positive. This laminated type makes it easy to increase the refractive power of the second group and is advantageous for compactness, but in wide zoom lenses as wide as 8x, aberration fluctuations due to zooming are large and high performance is achieved. In order to do this, we either have to accept the increased cost of making it a 4-piece structure, or have the third group made of two pieces pasted together, or we have to go to extreme 1.
It was necessary to choose between weakening the refractive power of the 2.3 group and accepting an increase in size. On the other hand, according to the configuration of the present invention, which has a three-element configuration, it is possible to reduce aberration fluctuations in the entire zoom range while maintaining compactness. The reason for this is the combination of the opposing surfaces of the second negative lens and positive lens in the second group, which corrects spherical aberration and field curvature to a higher degree than the bonded type over the entire zoom range. Because you can. An example of selecting this type is the one shown in Japanese Patent Publication No. 62-29769, which has a 6x zoom and consists of 13 to 15 images, but in terms of performance, The high performance required here has not been achieved.

Here, in order to achieve high-performance 8x zoom with 13 to 14 images, the following conditions must be satisfied.

■ 3.8 <19', l fT < 6.5
However, steam〈0■1. l<inertia fT <1.7 ■ 1.1<l to l/ψi <1.8 However, cage〈0■ 0.05<dA+t/9<0.40 where, %
+9'l+% is the refractive power (reciprocal of the focal length) of the first to third groups, and fT and fW are the telephoto end.

This is the combined focal length of the entire system at the wide end. d^I1
1 is the axial distance between the second negative lens and the positive lens in the second group.

Now, in order to achieve a high performance 8x zoom lens with a small configuration of 3 elements in the 1st group, 3 elements in the 2nd group, and 1 element in the 3rd group,
Particular attention must be paid to spherical aberration, curvature of field, and chromatic aberration while zooming.

The goal is to keep it from changing as much as possible. In order to satisfy these requirements, the selection of a zoom solution is an important issue. Therefore, the conditions for limiting the zoom solution to some extent are (1) to (2).

Conditions (1) and (2) indicate the appropriate range of refractive power of the second group and the first group. The stronger each of these is, the more advantageous it is to compactness, but if the upper limit is exceeded, the effect will be almost gone, and conversely, the amount of higher-order aberrations will increase dramatically, making it impossible to correct flare etc. . On the other hand, if the lens is weakened below the lower limit, the amount of higher-order aberrations generated will be reduced, but the overall length will increase and the diameter of the front lens will also increase, making it impossible to satisfy the demand for compactness.

Condition (2) indicates the refractive power range of the third group as a relative ratio to the refractive power of the first group, and is particularly important when the third group is a compensator lens group. The 1st ° 2nd group is the condition ■,
When the range (2) is set, if the third group is not within the range (2), the locus of movement of each group during zooming will exceed the range in which the various aberrations mentioned above can be properly corrected. Specifically, below the lower limit, fluctuations in spherical aberration and field curvature due to zooming become large; on the other hand, above the upper limit, fluctuations in chromatic aberration increase, and furthermore, the Petzval sum becomes largely negative over the entire region, resulting in Surface curvature worsens over the entire area.

If the first to third groups are set within the appropriate range of conditions ■ to ■,
Due to the effect of the appropriate zoom solution and the opposing surfaces (air lens) of the second negative lens and positive lens of the second group,
In particular, due to the synergistic effect of suppressing variations in spherical aberration and curvature of field to a sufficiently small level, it is possible to suppress variations in various aberrations and generation of higher-order aberrations to a sufficiently small level. The system disclosed in Japanese Patent Publication No. 62-29769 does not select this appropriate zoom solution, and therefore remains unsatisfactory in terms of performance.

Condition ■ is a condition for realizing the effect of this air lens.It means that if the air lens is brought closer than the lower limit, the effect will be weakened, and conversely, if it is moved further away than the upper limit, the air lens Although the effect of the lens increases, the Petzval sum tends to shift significantly to the negative side, deteriorating the image surface properties.

Next, the fourth group will be described. The fourth group includes the above-mentioned 1-
In combination with the third group, one biconvex lens is sufficient. However, when particularly high performance is required, two positive lenses may be used.

When it is composed of one glass, it is preferable to use a glass with a high refractive index within the range shown in condition (2).

■ nw>1.57 Here, ) is the refractive index of the fourth group single lens at the d-line. If this is constructed with a single piece of low refractive index glass, spherical aberration cannot be corrected sufficiently.

Next, the fifth group will be described. The fifth group is an important lens group responsible for final image formation. It is desirable that this fifth group has a configuration similar to that of Japanese Patent Laid-Open No. 61-93423 filed by the present applicant. In other words, the front group consists of two lenses: a positive lens with a surface that is stronger toward the incisal side than the incisal side, and a negative meniscus lens that also has a surface that is stronger toward the incisal side, and a positive lens that is placed with a certain amount of space between them. It consists of a total of five lenses: a negative meniscus lens with a strong surface facing the image side, and a positive lens with a strong surface facing the incisal side. In such a configuration, it is particularly desirable to satisfy the following conditions.

■ 1.1<ψD11/ψIF<1.9 However, ψ1=
□, ψ□=upper two n, -1 r IIP r Dll
■ Wake-rb>0.12 Here, ψ, 2. ψ indicates the refractive power of the strong negative refractive surface of each of the two negative lenses in the fifth group, and the refractive index for the d-line of the rostral negative lens and the image side negative lens is nl + nD
The radius of curvature on the rostral side of the former and on the image side of the latter is rlP, respectively.
+ Indicated by rllll. In addition, positive and C indicate the average values of the respective refractive indexes (d-line) of the negative lens and positive lens in the fifth group, respectively.

Condition (2) indicates the ratio of the refractive powers of the two strong refractive surfaces of the two negative lenses in the fifth group, and these two surfaces mainly correct spherical aberration, curvature of field, coma, distortion, etc. but,
Depending on the distribution of refractive power to both surfaces, the correction status of each aberration differs. In other words, if a strong refractive power is applied to the image side to the extent that it exceeds the upper limit, it will be advantageous for correcting off-axis aberrations such as field curvature and distortion, but the outermost light of spherical aberration will be significantly positively shifted. It is easy to do this, and the contrast decreases significantly near the axis.

Also, the back focus becomes too short.

On the other hand, if the lower limit is exceeded and the refractive power is concentrated on the incisal side, spherical aberration can be easily corrected, but off-axis field curvature and distortion will be insufficiently corrected.

Condition (2) indicates that it is desirable that the refractive index of the positive lens constituting the fifth group is lower than that of the negative lens. This is because when the 8x zoom class is configured with a positive/negative/positive/positive type, the Benz-Pearl sum tends to become large and negative, and the image plane properties tend to deteriorate. Therefore, it is necessary to make the P,Tupard sum sufficiently small by making a difference in the refractive index of the positive lens and the negative lens to the extent that condition (2) is satisfied.

By satisfying each of the above-mentioned conditions, the total system has only 13 to 14 sheets, which is a small number of sheets.
It can achieve a higher-performance 8x zoom over the entire screen than previous models. Although the present invention has been described only when two components move during zooming, the present invention applies even if the zoom format has three or more moving components, as long as it has a positive/negative/negative/positive/positive configuration. can be used.

Based on the present invention (Examples are shown below). Here, Example 1
~6, the 1st group is focusing, the 2nd group is a variator (magnification change), and the 3rd group is a compensator (image plane correction)
In Example 7, the second group is a variator, and the third group is a compensator and a focusing device. Furthermore, in the example, a 10x zoom lens was realized according to the present invention.

Here, in each example, rl+r2. ... is the radius of curvature of each lens surface, and dl+d! +... is the surface spacing,
N+, N2... are the refractive indexes of each lens for the d-line; C2. ...indicates the Atsube number.

Incidentally, in any of the embodiments, it is possible to perform focusing with the fifth group, and by slight modification, the fifth group can also be used as a compensator.

<Example 1> f = 66.3-37.0-8.7 F, l. =2.
03~1.75~1.75rzb-1(6,)til concave fl spacing d.

d+3 death 28.455 3.800 1.500 Middle 23.708 3.797 6.249 wide 1.001 27.625 5.129 5.500 with times fl S ll d, co Re 28.461 3.800 1, 500 dollar 23.713 3.793 6.255 Y de 1.000 27.656 5.105 <Example 2> f=66.3~37.0~8.7 F. =2.04-1.75-1.75 <Example 3> f=66.3~37.0~8.7 F,,=2.03~1 75-1.75 1, btlU N+9 1,'/l'/Jb ν i9.4i Time J 1st floor Middle wide S 28.325 23.602 1.000 <Example 4> r=66.3~28.0~8.7 d.

3,800 3.845 27.607 1,500 6.178 5.018 F ,, =2.02~1.75~1.75d17ZZ
, 0UIJ Nxw ■, bibbu νz? b4. lυ Middle wide d with concave fl.

29.112 21.107 1.000 <Example 5> f=66.3~28.0~8.7 d eye 3.800 6.189 28.434 d eye 1.500 7.116 4.978 FNO=2.00~1.75~1.75 concave fl attached Tere Middle wide 29.337 21.251 1.000 <Example 6> l1 3.700 6, 282 28.747 l1 ko 1.600 7.104 4.890 s　222.349 f=66.3~28.0~8.7 FNO=2.08~1.75~1.75 fl interval te 25.239 3.700 1,900 Middle 18.381 5.643 6.815 Y de T,oo.

24.344 5.495 <Example 7> f = 66.3 ~ 37.0 ~ 8.7 FNO = 2.02 ~ 1.75 ~ 1.75 r Go O Concave fl spacing tele middle wide 27.740 23 .225 1,000 7.100 7.768 30.539 1.400 5.247 4.701 <Example 8> f = 78.0-42.0-8.3 F8° = 2.12-1. 75~1,75d s,oo
.

1.51680 h 64.20 24.124 d+o 3.3υU 1.7! II bυ ν10 ct, bυ wide 1.000 29.741 6.2
59r26th JLfil Kumashi 31.400 Middle 26.800 d.

4.100 2.727 1 , 500 7.473 Next, FIGS. 1 to 4 show the schematic configurations at the telephoto end of each of the above embodiments, of which FIG. Correspondingly, FIG. 2 shows Example 6, and FIG. 3 shows Example 7.
and FIG. 4 correspond to the example date. For the second group (II) and the third group (I[[), the first
In the figure, the movement from the telephoto end (T) to the wide end (W) is schematically shown by arrow lines (1) and (2). Group 5 (
(3) shown in front of V) represents a diaphragm, and a flat plate (4) placed behind the fifth group (V) is a flat plate corresponding to a low-pass filter or a face plate.

5 to 12 are aberration diagrams corresponding to each of Examples 1 to 8, in which (a) is the telephoto end, (b) is the intermediate focal length, and (
c) represents various aberrations at the wide end. Also, solid line (d)
represents the aberration for the d-line, and the dotted line (SC) represents the sine condition. Further, the dotted line (DM) and the solid line (DS) represent astigmatism on the meridional plane and the sagittal plane, respectively.

[Brief explanation of the drawing]

FIGS. 1, 2, 3, and 4 are lens configuration diagrams corresponding to each embodiment of the present invention, and FIGS.
8, 9, 10, 11, and 12 are aberration diagrams. Darkness

Claims (1)

[Claims] (1) In order from the object side, the first group has a positive refractive power, the second group has a negative refractive power, the third group has a negative refractive power, and the third group has a positive refractive power. Consists of a total of 5 groups: the 4th group and the 5th group with positive refractive power.When zooming, the magnification is changed by the movement of the 2nd group on the optical axis, and the resulting image point movement is transferred to the 3rd or 5th group. In a zoom lens that corrects by moving the second
The group consists of three elements, in order from the object side: a negative lens with its strong surface facing the image side, a biconcave lens, and a positive lens with its strong surface facing the object side, placed with some space from the biconcave lens. death,
A zoom lens characterized in that the third group is composed of a negative single lens with a strong surface facing toward the object side, and the zoom lens satisfies the following conditions. 3.8<|ψ_II|f_T<6.5 However, ψ_II<0
1.1<ψ_ I f_T<1.7 1.1<|ψ_III|/ψ_ I <1.8 However, ψ_I
II<00.05<d_A_I_R/f_W<0.40 where (ψ_I, ψ_II, ψ_III are the first to third
In the refractive power of the group (reciprocal of the focal length), f_T and f_W are the combined focal lengths of the entire system at the telephoto end and wide end, respectively. d_A_I_R is the axial distance between the second negative lens and the positive lens in the second group. (2) In order from the object side, the first group consists of a negative meniscus lens with a convexity toward the object side, a positive lens with a strong surface facing the object side or a combination thereof, and a positive lens with a strong surface facing the object side. The fourth group is composed of one or two positive lenses, and the fifth group is composed of three positive lenses and two negative lenses, a total of five lenses. A zoom lens according to claim 1. (3) Place the fifth group in order from the object side, with a certain amount of space between the front group, which consists of two lenses: a positive lens with a strong surface facing the object side, and a negative meniscus lens with a strong surface facing the object side. It is characterized by a rear group consisting of three elements: a positive lens with a strong surface facing the image side, a negative meniscus lens with a strong surface facing the image side, and a positive lens with a strong surface facing the object side. A zoom lens according to claim 2. (4) The zoom lens according to claim 3, wherein the fifth group satisfies the following conditions. 1.1<ψ_D_R/ψ_B_P<1.9 However, ψ_B_P=(n_B-1)/r_B_P, ψ_D_R=(1-n_D)/r_D_R@n_N@-
@n_P@＞0.12 Here, ψ_B_P and ψ_D_R indicate the refractive power of the strong negative refractive surfaces of the two negative lenses in the fifth group, and the d-line of the object side negative lens and the image side negative lens. Each refractive index for n
The radius of curvature on the object side of the former and the radius of curvature on the image side of the latter are represented as r_B_P and r_D_R, respectively. Also, @n_
N@ and @n_P@ each indicate the average value of the refractive index (d-line) of the negative lens and positive lens in the fifth group.