JPS6344615A - Compact zoom lens for video camera - Google Patents

Abstract

PURPOSE:To obtain a lightweight, compact zoom lens by specifying the relation between the resultant refracting power of the 4th group and the resultant refracting power of the rear group of the 5th group. CONSTITUTION:The 1st group I is a fixed positive lens group, the 2nd group II is a negative lens group which moves for variable power at the time of zooming, and the 3rd group III is a negative lens group which is used even for focusing while an image plane is made constant at the time of zooming; and the 4th group IV is a fixed positive lens group composed of two positive lenses IV-1 and IV-2 which make divergent luminous flux from the 3rd group III sort of convergent and the 5th group V consists of the front group VA and rear group V5B. The front group consists of a positive lens VA-1 having a high-refractive-index surface on an object side and a negative lens VA-2 having a high-refractive-index surface on the object side, and the rear group is a three-element positive lens group consisting of a positive lens VB-1, a negative meniscus lens VB-2 having a convex surface on the object side, and a positive lens VB-3 having a high-refractive-index surface on the object side. Then, there is a diaphragm between the 4th group IV and the 5th group V and meets requirements shown by inequalities I.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a zoom lens for a video camera that detects defocus and performs 7 focusing. I do.

In recent years, the number of electrical components in video cameras has rapidly increased, so that the volume of the lens, ff11, occupying the main body of the video camera has become relatively large. Moreover, the same is not true for the cost, and the cost of the entire system increases due to the lenses.

Therefore, the current video camera lens is 1lffiffi.
It is desired that the device be compact and inexpensive.

Conventionally, as a lens for a video camera, a four-group zoom lens with positive, negative, and negative groups is known. As shown in Japanese Patent Application Laid-open No. 93423, this zoom type normally performs 7 orcasing in the 7th lun's group, so the positive lun's group has a large diameter and occupies the weight and volume of the 6th or more of the entire system. . It is clear that if focusing is done in this way, it will not be possible to make the lens any lighter or more compact than it is now. Therefore, in order to reduce the volume of the B111 of the Luns group, part of the variator, the funbensator, the master lens, and the Mako 1
There is a way to perform 7 orcasing using earth -n.

However, according to this method, the amount of extension of the 7-ocusing changes as the focal length changes due to zooming, so a complicated drive system is generally required and the configuration is difficult. However, in recent years, it has become possible to control this feeding wind with a relatively simple configuration and with high precision using an autofocus unit and its drive system.

It is also possible to introduce into a video camera a configuration similar to the one in which multiple components move during zooming, which is often used in recent zoom lenses, etc., but the configuration is complicated and costs increase accordingly. Moreover, the following problems arise.

First, in the type that has separate moving parts before and after the aperture, the automatic aperture (auto iris) used in video cameras is a much larger member compared to the outer diameter of the lens, so the lens groups before and after it are linked. In order to move the lens, the interlocking member must be very large, and even if the glass part of the lens can be made smaller, the lens barrel structure will become larger, and as a result, it will be difficult to use a compact lens. This makes it unsuitable for video lenses.

In addition, there are also types in which the first group moves during zooming.
When compared with the type where the group is immobile when zooming, Pt5
The parts that link the movement of the first group and other moving parts, such as the front with the cam groove, become extremely hot, and even if the positive outer diameter becomes smaller, if you consider it including the mirror m, it will become larger. This makes it impossible to achieve compactness, making it unsuitable as a video camera lens.

The purpose of the present invention is to provide a zoom lens for a video camera that performs a 7-occupation with a camcorder, is lightweight, compact, inexpensive, and has good aberration control, and is particularly used for auto 7↑-cus. .

The present invention will be explained in detail below.

A type with moving multi-components like the Moeki is not suitable as a zoom lens for video cameras, so the moving components during zooming are produced by the second group (variator), which has negative refractive power, and the second group (variator), which also has negative refractive power. Limited to the powerful Pt53 group (Funbenseta). In addition, in order to simplify the 7-span lens structure, a convencator that moves even during zooming is used.As is clear from FIGS. 1 to 5, in the lens group according to the present invention, the first group (1) is fixed positive lens group,
The second group (II) is a negative lens group that moves to change the magnification during zooming, the third n (III) is a negative lens group that keeps the image plane constant during zooming and is also used for focusing, and the fourth group (IV) is a negative lens group that moves to change the magnification during zooming. Two positive lenses (
A fixed positive lens group consisting of IY-1, IIV-2), the fifth group (V) is divided into a front group (■^) and a rear group (V[l),
A positive lens whose front group has a strong refractive surface facing the object side (V8-1
) and a negative lens (V^-2) with a strong refractive surface facing the object side.
The rear group consists of a positive lens (VB-1), a negative meniscus lens (VD-2) with a convex surface facing the object side, and a positive lens (VI3-3') with a strong refractive surface facing the object side. It is a positive lens group consisting of three elements, and the ttS4 group (IV)
There is an aperture between the lens and the fifth group (V). Further, the present invention is characterized by satisfying the following conditions.

(1) 1.18<φ■/φV [l<2.0 However, φ! v: composite refractive power of the fourth group, φvB: Combined refractive power of the 5th group and rear group It is.

Note that the refractive power of the Pt5s rear group (VO) is 7T, which determines the refractive power of the 5th group (master lens).
The value obtained by connecting the refractive power of the fourth group (IV) to the refractive power of the fifth group and rear group (VO) remains constant regardless of the range of change in focus and -χ distance of individual zoom lenses of different types. It can be considered as

The type that focuses with the variator (3rd group) has a larger axial air gap between the variator (2nd group) and the variator than the 7 focus type with the 1st group, so the 77 occal magnification of the zoom section is smaller. , the same F
If NO, the focal length of the fifth group (master lens) will become longer.

Moreover, for this reason, the Petzval sum for the entire system shifts to a negative value. In particular, in this type of lens system, the Petzval sum tends to be negative, making it difficult to correct aberrations. Also, because the focal length and α distance of the master lens become longer, the diameter of the aperture becomes larger for lenses with the same FNO.As mentioned above, it is desirable that the automatic aperture (auto iris) of a video camera be as small as possible. . Therefore, by increasing the refractive power of the fourth group and making the light beam enter the aperture as a convergent beam, the aperture diameter can be reduced. In addition, if the refractive power of the second group is increased, the Petzval sum will move positively and aberrations will be corrected better.
/? -/7 The sludge becomes shorter and the total length becomes shorter. In addition, the height of the light flux passing through the master lens becomes lower,
As a result, the master lens can be made smaller.

Condition (1) is a condition for increasing the refractive power of the fourth group. If the refractive power of the fourth group exceeds the lower limit of condition (1) and becomes smaller, the light beam incident on the aperture will not be converged sufficiently, As a result, the aperture diameter cannot be made small, and the optical system cannot be made lighter and more compact while maintaining the brightness of FNo and high optical performance that the present invention aims to achieve, and aberrations cannot be sufficiently corrected. , On the other hand, when the upper limit of condition (1) is exceeded, residual aberrations, especially coma aberration, become excessive,
It will not be corrected in the later optical system.

It is desirable that the lens according to the present invention further satisfy the following conditions.

(2) 0.13< l φII X d
ll<0.20φ■: Combined refractive power of the third group d■: This is the axial air distance between the second and third groups at infinity at the telephoto end.

This condition shows the relationship between the refractive power of the Funben Setter and its delivery space in the case of 7-ocusing with the Funben Setter. If the upper limit of condition (2) is exceeded, the shortest shooting distance near the telescope will become longer than the actually required shooting distance, and
Also, if the value of condition (2) exceeds the upper limit, the first lens of the tSI group and M[fi of the aperture will change, and the marginal ray near the middle will be This makes it difficult for the lens to pass through, and the effective diameter of the first lens group becomes smaller.In addition, the 77-square magnification becomes smaller, leading to an unnecessarily large size of the fourth Pt55 lens group.

Note that the effective diameter of the first group is determined by the outermost marginal ray near the middle. This is to ensure that the illuminance due to the most off-axis light beam does not become insufficient when the aperture is set to the minimum aperture.

In order to make it easier for this light flux to pass through the diaphragm, the present invention reduces the positive power of the object-side surface of the first lens of the first group, and increases the positive refraction of the object-side surface of the second lens of the second group. By reducing the power and increasing the negative refractive power of the image-side surface, the light beam incident from a high position is prevented from being refracted too much. That is, consideration is given to decreasing the positive refractive power and increasing the negative refractive power at a high point where the light beam enters the lens.

As a result, the diameter of the first group is sufficiently small compared to the entire system, and the ratio of the weight and volume of the first group to less than 50% is extremely compact.
Compared to the conventional optical system with the same specifications shown in Publication No. 3, the effective diameter of the first group is reduced by about 15% and the weight by about 18%, making it extremely lightweight and compact. [It is possible to provide a zoom lens for a video camera that is compact, inexpensive, has well-corrected aberrations, and has extremely high contrast at low frequencies transmitted through a low-pass filter.

Examples of the present invention are shown below, in which r1, r2, r,
... is the radius of curvature of the lens surface counted from the object side, d
l, d2, d, ... are on-axis intervals counted from the object side,
N2, N, . . . are the refractive indexes of the lenses counted from the object side, and λl, λ7, λ, . . . are the Abbe numbers of the lenses counted from the object side. B indicates a beam splitter, 1F indicates a low-pass filter, and P indicates a face plate.

fjSl, Figures 2.3.4.5 and 1.2.3 of the present invention, respectively.
．． FIG. 4.5 is a configuration diagram of a lens in a long focal length state according to Example 4.5. FIG. 6.7.8 is an aberration diagram of the lens according to the first embodiment of the present invention under conditions of 16-point distance, wide focal length, and short focal length. 9.10.11 respectively show the long focal length of the lens according to the second embodiment of the present invention;
It is an aberration diagram of the lens in a state where the focal length is wide, u j and the point i is separated by y. Figures 12, 13, and 14 each show Pt of the present invention.
FIG. 53 is an aberration diagram of the lens according to Example 53 in long focal length, intermediate focal length, and short focal length states; 15th.
16 and 17 are aberration diagrams of the lens according to the fourth embodiment of the present invention in the long focal length, intermediate focal length, and short focal length states, respectively. 18, 19, and 20 are aberration diagrams of the lens in the long focal length, intermediate focal length, and short focal length states, respectively, according to the fifth embodiment of the present invention.

(Left below) Example 1 f=9.25-52.5 FNO,=
1.65-2.09 2al=48.32-9.03
Radius of curvature Distance between top surfaces of shafts Refractive index (Nd) Dispersion (νd) [82 lines 816 lines d1□wheel 9.2'3 1.0, 24,338
1.59322.0 13.583 10,
035 3,27052.5 21.270
4.117 1.500 Zenri 102. G
24 φ■/φVB=1.5131φI I
X dll=0.150 Example 2 f=8.7~4
9.7 FNO, /1.22~1.78 2ω=
51.00~9.54 Radius of curvature Axis spacing Refractive index (Ntl) Dispersion (νd) r d
5 d+, J12 8.7 1,0 2
4.710 1.84620 13.45
9 10,477 3.02649.7
21,661 4.2 1.700 Zenri 114.218 φ■/16 VB=1.2
191φI I X dII =0.14:1 Example 3 f=9.25-52.5 FNO,/1.
65~2.08 2ω=, 148.32~9.03 Radius of curvature Axial spacing Refractive index (Nd) Dispersion (
I'd) f ds book dl. Book
+4+2o9.25 0.999 2
4,262 1,65622.0 13
．． 551 10.05f+ :1.3
152.5 21.217 4.2
1.5 Zentai 102.671 φ■/φB
=1.5791φIll Xd■=0.155 Example 4 r=to, 3~58.2 FNO,/
1.85~2.52 2ω=43.89~8.15 Radius of curvature Axial distance Refractive index (NJ) Molecule eL (
νd) F&+: d,,5.5 N,!
1,51680 ν+s 84.12r
ds book d. Book + Itz car 10
+3 1+0 20.064
5.20324.0 12.804 7
,229 6.23458.2 20.
167 4,6 1.5 total length 104
．． 169 φ■/φB"1.2461φ■+
x dll=o, 147 Example 5 f=10.2-58.2 FNO,/
1.65-2.29 2Q+ =43.89-8. I
! i24.0 12.009 6.909
(i, 20958.2 +8.9
27 4.5 1.7 Zentai IO
2,747φ■/φv ++= 1.24h1φIll
l X d [l=0.160

[Brief explanation of drawings]

Figures 1.2.3.4.5 and 1.2.3.4 of the present invention, respectively.
．． FIG. 5 is a diagram illustrating the configuration of a lens with different focal lengths according to five different examples. 6.7.8 are aberration diagrams of a lens according to a PtSi embodiment of the present invention in the target focal length, intermediate focal length, and short focal length conditions, respectively. Figures 9, 10, and 11 are diagrams showing the convergence of the lens in long focal length, intermediate focal length, and short focal length states, respectively, according to the second embodiment of the present invention. 12, 13, and 14 respectively show long focal length, intermediate focal length, and ! of the lens according to the third embodiment of the present invention. , -1. FIG. 3 is an aberration diagram of a lens in distance, tilt angle, and distance states. Section 15.1
Figure 6.17 shows lens configurations j, ii, 1. according to the fourth embodiment of the present invention, respectively. ' They are aberration diagrams of the lens at sky distance, intermediate focal length, and short focal length states. 18, 19 and 20 respectively show a long focal length lens according to the fifth embodiment of the present invention;
This is the aberration 1 of the lens in the state of intermediate focus, t-distance, and short focal length. I... 1st group ■... 2nd group ■... 3rd group ■... ff14i IV-1, l'V-2...
Positive lens ■... 5th group VA... Pt4s group front group VA-1... Positive lens V
^-2...Negative lens VB...Fifth group rear group V[l-1...Positive lens VB
-2...Negative meniscus lens V[l-3...Positive lens Applicant: Minolta Camera Co., Ltd. Figure 1 Figure 2 Figure 4 Figure 5 Figure J! 57. 1, collection 1
Distortion zu 0 single face acquisition positive Ie pull non-point role destination 1
74/j5 figure Fm, = 2.2 de Fm, -/, 65 death, 81 plow

Claims (1)

[Claims] 1. The first group is a fixed positive lens group, the second group is a negative lens group for changing magnification that moves during zooming, and the third group is a lens group that keeps the image plane constant during zooming and performs focusing. The fourth group is a fixed positive lens group consisting of two positive lenses to convert the divergent upward beam emitted from the third group into a slightly convergent beam, and the fifth group is a front group. -Divided into a rear group, the front group consists of two lenses: a positive lens with a strong refracting surface facing the object side, and a negative lens with a similarly strong refracting surface facing the object side.
The rear group is a positive lens group for image formation consisting of three elements: a positive lens, a negative meniscus lens convex to the object side, and a positive lens with a strong refractive surface facing the object side. A compact zoom lens for a video camera, which has an aperture between the lenses and satisfies the following conditions: However, φIV: composite refractive power of the 4th group, φVB: composite refractive power of the 5th group and rear group. Power. 2. A compact zoom lens for a video camera according to claim 1 that satisfies the following conditions: 0.13<|φIII|×dII<0.20, where φIII: composite refractive power of the third group; dII: On-axis distance between the second and third groups at infinity at the telephoto end.