JPH03237420A - Zoom lens for video camera - Google Patents

Abstract

PURPOSE:To miniaturize respective lens groups and to shorten the whole length of a zoom lens system consisting of five components of positive, negative, positive, and positive lenses by setting up 2nd and 4th lens groups as movable lens groups at the time of zooming, dividing the 5th lens group into the pre-group and the post-group, and providing 5th lens group with specific lens constitution. CONSTITUTION:The zooming lens system consists of the 1st lens group I having positive refractive power, the 2nd lens group II having negative refractive power, the 3rd lens group III having negative refractive power, the 4th lens group IV having positive refractive power, and the 5th lens group V having positive refractive power, and at the time of zooming, the 1st, 3rd and 5th lens groups I, III, V are fixed. The 5th lens group V is divided into the pre-group and the post group, the pre-group consists of two lenses, i.e. a positive lens turning its strong refractive face to the object side and a negative lens turning its strong refractive face to the object side and the post group consists of two lenses, i.e. a negative meniscus lens turning its convex face to the object side and a positive lens turning its strong refractive face to the object side. Consequently, the residual aberration of out-axis light flux whose aberration correction is difficult can be effectively corrected is difficult can be effectively corrected on a spherical face, the number of lenses can be reduced, the system can be made compact, and the whole length of the system can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compact high-power zoom lens mounted on a video camera.

E. Prior Art] In recent years, progress has been made in the miniaturization of integrated video cameras;
As camera bodies have become smaller, video lenses have also become smaller, but the rate at which camera bodies have become smaller is:
Second, lens systems are not getting smaller.

2. Description of the Related Art A four-component zoom lens (positive, negative, negative, positive) is conventionally known as a lens for a video camera. In general, the front group is extended, and the first lens group is large, making it unsuitable for downsizing.
Therefore, as in Japanese Patent Publication No. 63-44614.44615, there is an attempt to reduce the size by using the third lens group as both a convencator and a focusing lens. However, in this type of lens, it is necessary to have a focusing lens on the object side of the diaphragm, and to widen the distance between the variator of the second lens group and the third lens group for focusing. As a result, the Petzval sum becomes negative, making it difficult to correct aberrations. In addition, the overall length becomes longer, and the focal length of the master of the fourth lens group becomes longer. A longer master means a longer overall length and a larger effective diameter of the master, so overall miniaturization was not sufficient.

In addition, the applicant has already filed the patent application No. 63-2.
There is a five-component zoom lens with positive, negative, negative, positive and negative components as shown in No. 01556.201557. This is because the second lens group and the third lens group are a variator and a convencator, respectively.
Focusing is performed by the fourth lens group. However, even with this type of lens, there is a focusing lens on the object side of the diaphragm, and the third lens group moves during zooming, making the mechanical system complicated and making it difficult to miniaturize the system as a whole.

[Question 8 to be solved by the invention: As in point 2, miniaturization is not sufficient with the conventional III-power. Here, the present invention provides a lens structure capable of realizing a super-T type lens that has been desired in recent years.

Summary of this invention] Two configurations of the present invention will be explained below.

The present invention: a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with negative refractive power, and a third lens group with positive refractive power. During zooming, the first lens group, the third lens group, and the fifth lens group are fixed. Furthermore, by using the second lens group as a variator for zooming, and the fourth lens group as a focusing lens and a venter for image point correction, the lens drive unit can be configured to the minimum required level. Mechanism can be simplified. This method of using both a focusing lens and a convencator contributes to reducing the size of the entire lens system including the lens drive mechanism system rather than reducing the size of the lens system. Another advantage of this configuration is that by fixing the third lens group, the distance between the variator of the second lens group and the third lens group can be narrowed, which prevents the Petzval sum from becoming too negative in the direction of 1. Furthermore, the objective is to prevent the focal length of the master of the fifth lens group from becoming longer and the effective diameter from increasing. In addition, the negative third
By increasing the degree of divergence of the luminous flux in the lens group, the degree to which the amount of movement of the fourth lens group is effective for back focus is increased. As a result, the amount of movement of the fourth lens group for image point correction and focusing can be reduced.

In addition, by fixing the aperture between the second and third lens groups, it is possible to bring the most off-axis beam closer to the optical axis at a medium focal length, and the first lens It is also possible to reduce the effective diameter of the group. Furthermore, the aperture can be placed between the third lens group and the fourth lens group, and in this case, the telescend link characteristics of the lens system are improved.

The fifth lens group is divided into a front group and a rear group. The front group consists of two lenses: a positive lens with a strong refractive surface facing the object side and a negative lens with a strong refractive surface facing the object side. It consists of two lenses: a negative meniscus lens convex to the side and a positive lens with a strong refractive surface facing the object, and it is desirable to have at least one aspherical surface in the rear group of the fifth lens group. , residual aberrations of off-axis light beams that are difficult to correct can be satisfactorily corrected using an aspheric surface, and furthermore, it is possible to reduce the number of lenses and shorten the overall length. Further, by satisfying the following conditional expression, the advantages of the present invention can be reliably achieved.

0.39<1 middle 3/monkey 111<0.96...(1) ψ
5B/ψ41<1.02...(2) 0.06<1D3
*Monkey 31<0.21...(3)0.04<t, 4
*vs <o, ts... (4) However, middle 3: middle refractive power of the third lens group 4: refractive power IP5 of the fourth lens group: middle refractive power of the fifth lens group 5B=fifth lens group Refractive power of the rear group D3: Axial air distance between the third and fourth lens groups L4: Maximum movement amount of the fourth lens group during zooming when the object distance is infinite (1) 2 is satisfied This allows the amount of back focus for the entire system to be appropriate. If this upper limit is exceeded, the fourth
The refractive power of the lens group becomes too weak and the hack focus becomes longer than necessary.

Furthermore, if the lower limit is below, the refractive power of the fourth lens group will become too strong, and the amount of aberration produced in the fourth lens group will also be too large, making it difficult to correct it with the fifth lens group. In addition, equation (1) is a conditional equation that defines the degree to which the amount of movement of the fourth lens group is effective for hack focusing, and by satisfying (1) (2), the amount of movement of the fourth lens group moves for image point correction and focusing. The amount of movement becomes an appropriate value.

Equation (2) is a conditional expression that stipulates that the huck focus is not longer than necessary at the rear principal point position of the fifth lens group.

If the refractive power of the fourth lens group becomes too weak by exceeding the upper limit of equation (2) above, the back focus λ will be extended more than necessary.

Equation (3) centers the distance between the third and fourth lens groups, and if this upper limit is exceeded, the distance between the third and fourth lens groups becomes too wide and the Petzval sum becomes negative. This makes performance correction difficult. Furthermore, if the correction is forced, the number of lenses required for aberration correction will increase. Conversely, if the lower limit is exceeded, the third lens group and the fourth lens group
Since the distance between the lens groups becomes too narrow, it is not possible to secure enough space for the fourth lens group to move for image point correction and focusing.

Equation (4) is a conditional expression for keeping the amount of movement of the fourth lens group at an appropriate value in order to reduce the size of the entire system.

Note that, considering that the fourth lens group performs focusing, in order to maintain an appropriate amount of movement, it is more desirable that conditional expression (1) falls within the following range.

0.39< i 'P3/'P41 <0.70...
(1) Furthermore, the third lens group can be formed by one lens having negative refractive power. If the zoom ratio or required performance further increases, by cementing the third lens group, it is possible to reduce the number of lenses and shorten the overall length while maintaining even better performance.

(Example) Examples of the present invention are shown below.
．． ...Ln is the lens number counted from the object side, rl
, r2. ..., rn is the radius of curvature of the lens surface counted from the object side, di, d2. ..., dn is the axial air distance counted from the object side, Nl.

N2. ..., Nn is the refractive index of the lens counted from the object side, and C1. C2. ..., rn indicates the number of lenses counted from the object side, and conditional expressions (1) to (4)
The values for each example are shown in Table 2.

Figures 1 to 6 show the constituent countries of Examples 1 to 6, respectively.In Figure 0, the last flat plate is, in order from the object side, a beam splitter for a focus detection device, a low-pass filter, and a face plate. That's quite a bit.

In the examples, the surface marked with * indicates that it is an aspheric surface,
The shape of the aspheric surface is expressed as follows. (The aspheric coefficients of each example are summarized in Table 1.

) Section 1.2.3.4.5.6. The figure shows Example 1.2.3.
4.5.6. The configuration diagram is shown below. 7th degree 8, 9. 1
0. 11. Figure 12 shows examples 1, 2゜3, 4.5
．． 6. In the aberration diagrams, <s> indicates the short focus side, <M> indicates the medium focus side, and <L> indicates the long focus side.

-V...1st to 5th lens groups, respectively.

↓ Jofushu et al. However, co = reference curvature ε; Parameter of quadratic surface Ai + i-th order aspheric coefficient Y: Height from optical axis X: Optical sleeve direction deviation from reference curved surface at height Y [ [Effects] According to the present invention, while maintaining good optical performance, it is possible to significantly downsize the lens group and shorten the total length of the lens system compared to the conventional method.

[Brief explanation of drawings]

Example 1 Lens number f = 0 to 30.0 to 8.8 Radius of curvature Axis spacing FNO-2, 3 to 1.6 to 1.6 Refractive index (Nd) Number of 7 (νd) Example 2 and space number f -52,5-30,0-9,2 Curve 1 radius Axis top surface spacing FNO = 2.2 ~ 1.6 ~ 1.6 Refractive index (Nd) A7 (νd) Σd = Chest, 059 ~ 84. □□□～枳, O59Σd Tomiaki, 059 ~84.059 ~84. (!59 Example 3 Example meeting Lens number r = 52.5 ~ 11.0 - '1.2 Vertical observation Axis top surface distance FNO = 2.4 ~ 1.6 ~ 1.6 Refraction 1d) 7 fhe (νd) Lens number f -52, 5-311, O-9, 2 Radius of curvature Axis spacing FNO = 2.2 to 1.6 to 1.6 7-digit number of refractive index (g) (νω Σd = 77 .734 ~ sword, 734 ~77.734 Σd sword. 347 ~ n, 347 ~ 77.347 Example 5 Example 6 S1 bow f-shell 0-16.0-6.7 Curvature ladle 1 L Collapse distance F\O = 1.6 ~ 12 ~ 12 [Fold - $ "O + d)? 1, l1k (ν, i) Lens number f- mark, 4 ~ 12.0 - 6.4 Radius of curvature Axis top surface distance FNO = 2.3 ~ 1.6 ~ 1.6 771st order of refractive index ω (νω Id-72, 393 ~ 72.393 ~ 72.393E
d-79.928 〜79.928 〜T9.0EB 1st table Shadow octopus detail 1st figure I[II[11SJ 2nd figure 2nd table conditions! For each expansion 3rd figure 4th figure (,-) ■ shi-hitori no qno shi-1,--no nmrv v ■ ■ 5th figure■ m■ ■ ■ m■ ■ Figure 8 Ma, i button U Hiru Sei Yi condition non, φ! 5! and all songs 〃 Kimen U shakyumi thorn o incident'' Do, 4. Figure □Additional point positive power l convergence negative 46, aberration 1 convex%

Claims (1)

[Claims] (1) In order from the object side, a first lens group with positive refractive power that is fixed during zooming, a second lens group that has negative refractive power and is movable during zooming, and a negative refractive lens group that is movable during zooming. The third lens group has strong power and is fixed when zooming, and the fourth lens group has positive refractive power and is movable when zooming.
A zoom lens consists of a lens group and a fifth lens group that has positive refractive power and is fixed during zooming. (2) The fifth lens group is
Divided into a front group and a rear group, the front group consists of a positive lens with a strong refractive surface facing the object side and a negative lens with a strong refractive surface facing the object side.
2. The zoom lens according to claim 1, wherein the rear group comprises two lenses: a negative meniscus lens convex toward the object side and a positive lens with a strong refractive surface facing the object side. (3) The zoom lens according to claim (2), wherein the fourth lens group moves on the optical axis during focusing. (4) The zoom lens according to claim (3), which satisfies the following conditional expression: 0.39<|Ψ3/Ψ4|<0.96 |Ψ5B/Ψ4|<1.02 0.06<|D3*Ψ3| <0.21 0.04<L4*Ψ5<0.15 However, Ψ3: Refractive power of the third lens group Ψ4: Refractive power of the fourth lens group Ψ5: Refractive power of the fifth lens group Ψ5B: Fifth lens group Refractive power of the rear group D3: Axial air distance between the third and fourth lens groups L4: Maximum amount of movement of the fourth lens group during zooming when the object distance is infinite (5) To the fifth lens group The zoom lens according to claim 4, wherein at least one aspherical surface is used. (6) Claim (
5) The zoom lens described above. (7) The zoom lens according to claim (6), wherein the aperture is placed between the second lens group and the third lens group. (8) At least one lens in the first lens group or the fourth lens group
The zoom lens according to claim 7, wherein the surface is an aspherical surface.