JP2506744B2 - Zoom lens - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for a video camera, and it is possible to reduce the number of lenses by optimizing the lens arrangement, curvature, and selection of glass materials, and to achieve a zoom ratio that achieves size and weight reduction. It provides a 6x high performance zoom lens.

2. Description of the Related Art In recent years, operability and mobility have been emphasized in video cameras, and in response to such demands, the size of image pickup devices of 1/2 inch has become mainstream. Along with this, there is a strong demand for compact, lightweight and high-performance zoom lenses. Further, there is a strong demand for cost reduction, and there is an urgent need to realize a zoom lens in which the number of constituent elements is reduced while maintaining high performance. The conventional zoom lens for video cameras has a zoom ratio of 6 and an F number of about 1.4, and each group constituting the variable power unit has three focusing units, three variator units, one compensator unit, and a relay lens. Many of them have 7 to 9 parts.

Problems to be Solved by the Invention In the case of a zoom lens, generally, the larger the zoom ratio, the longer the total lens length, which hinders miniaturization. Furthermore, in the case of a zoom lens for a video camera, the exit pupil position must be a certain distance or more from the image plane to prevent color shading, and a lens system with a long back focus is required because a crystal plate etc. is placed in front of the image plane. In order to realize a high-performance zoom lens with an F-number of about 1.4 and a zoom ratio of about 6 times, a large number of spherical lenses of 14 to 15 were indispensable. Also, small size
Increasing the refracting power of the variator portion to achieve weight reduction makes it difficult to correct aberrations. Furthermore, increasing the aperture ratio and reducing the number of lenses are not preferable for aberration correction.

Means for Solving the Problems The zoom lens according to the present invention has a first group as a focusing having a positive refractive power in order from the object side, and a zoom lens having a negative refractive power and moving along the optical axis. And a third group as a compensator section for keeping the image plane that fluctuates due to the movement of the variator section at a fixed position from the reference plane, and the first, second and third groups. It consists of a relay lens system connected to a variable power system,
The first group is composed of a single lens having a negative refracting power in order from the object side, and subsequently is composed of two single lenses having a positive refracting power, and the second group is composed of a single lens having a negative refracting power and a cemented lens. The third is composed of a single lens of negative refracting power, and the relay lens system is a single lens of positive refracting power, a single lens of negative refracting power, then two single lenses of positive refracting power, and then It is composed of a single lens of negative refractive power and a single lens of positive refractive power with a relatively large air gap, and the fourth lens of the relay lens system is a positive meniscus lens with a convex surface facing the object side. Therefore, the following conditions are satisfied.

(1) −1.3f _w <f ₂ <−1.1f _w (2) 0.9f ₁ <f _c <1.15f ₁ (3) 1.3f _w <r ₂₀ <2.4f _w (4) N ₁₃ <1.65 where f _w is the focal length of the entire system at the wide-angle end, f ₁ and f ₂ are the focal lengths of the first group and the second group, respectively, and f _c is the focal length of the third lens counted from the object side of the first group, r ₂₀ is the radius of curvature of the 20th lens surface counting from the object side, N ₁₃ is the 13th
The th lens refractive index is shown.

Action The present invention has the above-mentioned configuration, that is, by utilizing the spherical shape, selecting an appropriate lens type, and lens material.
Despite the small number of sheets, it achieves a large aperture ratio of F number 1.2, downsizing and weight reduction, and excellent aberration correction.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the zoom lens of the present invention. In FIG. 1, 1 is a first group, 2 is a second group, 3 is a third group, 4 is a fourth group, and 5 is an equivalent glass plate corresponding to a crystal filter or a face plate of an imaging device.

In order to make the zoom lens compact, it is crucial to increase the power of each group, and particularly to increase the power of the second group 2 (variator) that performs zooming. The condition (1) is a conditional expression that regulates the power of the second lens group, and gives a strong power, but is within a range in which good aberration can be realized due to the balance of the shape of each lens group. When the condition deviates from the lower limit, the size can be made compact, but the radius of curvature of the concave surfaces and other surfaces facing each other in the second lens group becomes small, which makes it difficult to correct aberrations. If the upper limit is exceeded, aberration correction will be easy, but the lens system will become large, which is not preferable.

The condition (2) is a conditional expression for making the first group 1 compact. Generally, in the zoom lens, the comprehensive range of the screen is defined by the effective diameter of the first group 1. When the effective diameter of the first group 1 is determined in consideration of the mounting error of the image pickup element and the like, the effective diameter of the first group 1 can be made smaller as the entrance pupil is closer to the object side. The condition (2) is a range in which the effective diameter of the first lens unit 1 can be reduced and good aberrations can be realized. When the condition deviates from the lower limit, the principal point of the first group 1 becomes closer to the image plane side,
Since the entrance pupil approaches the object side, the effective diameter of the first group 1 can be reduced, but the radius of curvature of the third lens of the first group 1 is reduced, which makes it difficult to correct aberrations. If the condition deviates from the upper limit, it is easy to correct the aberration, but this is not preferable because the effective diameter of the first lens unit 1 becomes large.

The fourth lens of the relay lens system has a strong positive refracting power in order to make the relay lens system compact, and serves as a meniscus lens convex to the object side in order to maintain a good aberration correction state. Condition (3) is the radius of curvature of the lens on the object side.
It defines r ₂₀ . If the condition exceeds the lower limit, it is advantageous for correcting spherical aberration, but it is difficult to correct off-axis aberrations because the angle of incidence of off-axis upper rays on the lens surface becomes large. Exceeding the upper limit is advantageous for correcting off-axis aberrations, but spherical aberration is undercorrected.

The condition (4) is a condition for keeping the Petzval sum favorable. If the condition exceeds the upper limit, the Petzval sum becomes large and it becomes difficult to correct the field curvature.

 An example of satisfying these conditions is shown below.

In the table, r ₁ , r ₂ , ... are the radii of curvature of each surface of the lens counted from the object side, d ₁ , d ₂ , ... are the wall thickness or air gap between the lens surfaces, and n ₁ , n ₂ , ... is the refractive index of each lens for d-line, ν
₁ , ν ₂ , ... are Abbe numbers for the d-line.

(Example 1) f = 9.231~53.166 F / NO = 1.245~1.769 r 1 = 58.712 d 1 = 1.20 n 1 = 1.80518 ν 1 = 25.5 r 2 = 29.699 d 2 = 2.219 r 3 = 55.806 d 3 = 3.55 n ₂ = 1.58913 ν ₂ = 6.12 r ₄ = -646.386 d ₄ = 0.2 r ₅ = 27.520 d ₅ = 7.20 n ₃ = 1.58913 ν ₃ = 61.2 r ₆ = -142.650 d ₆ = (* 1) r ₇ = -65.877 d ₇ = 0.90 n ₄ = 1.83400 ν ₄ ＝ 37.2 r ₈ = 15.632 d ₈ ＝ 2.420 r ₉ ＝ −39.498 d ₉ ＝ 0.90 n ₅ ＝ 1.72000 ν 50.3 r ₁₀ ＝ 11.579 d ₁₀ ＝ 3.50 n ₆ ＝ 1.84666 ν ₆ ＝ 23.9 r ₁₁ = 122.700 d ₁₁ = (* 2) r ₁₂ = -35.795 d ₁₂ = 0.90 n ₇ = 1.72250 ν ₇ = 49.6 r ₁₃ = 239.650 d ₁₃ = (* 3) r ₁₄ = 403.407 d ₁₄ = 3.48 n _{9 = 1.67790, ν 8 = 55.5 r} 15 = -28.487 d 15 = 2.80 F 16 = 32.734 d 16 = 1.00 n 9 = 1.84666 ν 9 = 23.9 r 17 = 19.395 d 17 = 1.24 r 18 = 28.487 d 18 = 4.74 n 10 _{= 1.58913 ν 10 = 61.2 r 19} = -57.379 d 19 = 0.20 r 20 = 14.691 d 20 = 5.00 n 11 = 1.72000 ν 11 = 50.3 r 21 = 28.707 d 21 _{9.81 r 22 = 21.168 d 22 =} 1.00 n 12 = 1.84666 ν 12 = 23.9 r 23 = 8.143 d 23 = 2.96 r 24 = 12.616 d 24 = 4.75 n 13 = 1.58913 ν 13 = 61.2 r 25 = -22.440 d 25 = 1.00 r ₂₆ ＝ ∞ d ₂₆ ＝ 6.70 n ₁₄ ＝ 1.51633 ν ₁₄ ＝ 64.1 r ₂₇ ＝ ∞ The air spacing that can be changed by zooming is shown by the following values.

f 9.2311 31.0322 53.1657 (* 1) 1.5000 17.9000 22.0600 (* 2) 20.9667 3.3875 4.0164 (* 3) 4.8326 6.0118 1.2229 f ₁ : 41.047 f ₂ ; -11.949 f _w : 9.2751 f _c : 39.78 (Example 2) f = 9.238 〜53.250 F / NO ＝ 1.250〜1.772 r ₁ ＝ 58.712 d ₁ = 1.20 n ₁ = 1.80518 ν ₁ ＝ 25.5 r ₂ ＝ 29.699 d ₂ ＝ 2.219 r ₃ ＝ 55.806 d ₃ ＝ 3.55 n ₂ ＝ 1.58913 ν ₂ ＝ 61.2 r _{4 = 646.386 d 4 = 0.2 r} 5 = 27.520 d 5 = 7.20 n 3 = 1.58913 ν 3 = 61.2 r 6 = -142.650 d 6 = (* 1) r 7 = -65.877 d 7 = 0.90 n 4 = 1.83400 ν 4 ＝ 37.2 r ₈ ＝ 15.632 d ₈ ＝ 2.420 r ₉ ＝ －39.498 d ₉ ＝ 0.90 n ₅ ＝ 1.72000 ν ₅ ＝ 50.3 r ₁₀ ＝ 11.579 d ₁₀ ＝ 3.50 n ₆ ＝ 1.84666 ν ₆ ＝ 23.9 r ₁₁ ＝ 122.700 d ₁₁ ＝ _{(* 2) r 12 = -35.795} d 12 = 0.90 n 7 = 1.72250 ν 7 = 49.6 r 13 = 239.650 d 13 = (* 3) r 14 = 403.407 d 14 = 3.48 n 8 = 1.67790 ν 8 = 55.5 r 15 _{= -28.487 d 15 = 2.80 r 16} = 38.623 d 16 = 1.00 n 9 = 1.84666 ν 9 = 23.9 r 17 = 21.467 d ₁₇ = 1.24 r ₁₈ = 32.254 d ₁₈ = 5.74 n ₁₀ = 1.49700 ν ₁₀ ＝ 81.6 r ₁₉ ＝ −97.301 d ₁₉ ＝ 0.20 r ₂₀ ＝ 20.585 d ₂₀ ＝ 5.00 n ₁₁ ＝ 1.7200 ν ₁₁ ＝ 50.3 r ₂₁ ＝ 128.906 d ₂₁ = 18.02 r ₂₂ = 16.020 d ₂₂ 1.00 n ₁₂ = 1.84666 ν ₁₂ ＝ 23.9 r ₂₃ ＝ 8.46 d ₂₃ = 1.38 r ₂₄ ＝ 10.268 d ₂₄ ＝ 4.75 n ₁₃ = 1.58913 ν ₁₃ ＝ 61.2 r ₂₅ ＝ −43.159 d ₂₅ ＝ 1.0 r ₂₆ ＝ ∞ d ₂₆ ＝ 6.70 n ₁₄ ＝ 1.51633 ν ₁₄ ＝ 64.1 r ₂₇ ＝ ∞ The variable air spacing by zooming is shown by the following values.

f 9.2313 31.0259 53.1437 (* 1) 1.5000 17.9000 22.0600 (* 2) 20.9667 3.3875 4.0164 (* 3) 4.8326 6.0118 1.2229 f ₁ : 41.07 f ₂ ; -11.949 f _w : 9.2751 f _c : 39.78 Effect of the invention Thus, under the lens configuration and conditions of the present invention, the F number is about 1.
2. A compact and lightweight high-performance zoom lens with a zoom ratio of about 6 times was created.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a zoom lens according to an embodiment of the present invention, FIGS. 2, 3, and 4 are various aberration diagrams of Embodiment 1, FIG. 5, FIG. 6, and FIG. In the various aberration diagrams of Example 2, the spherical aberration diagrams, the solid line indicates the spherical aberration for the d-line, the dash-dotted line indicates the g-line, the solid line indicates the sagittal field curvature, and the dotted line indicates the meridional field curvature. Show. 1 ... 1st group, 2 ... 2nd group, 3 ... 3rd group, 4 ... 4th group, 5 ... Glass plate.

Claims (1)

(57) [Claims] 1. A first group as a focusing section having a positive refracting power and a second group as a variator section having a negative refracting power and changing the magnification by moving on the optical axis in order from the object side. And a third lens unit as a compensator unit that keeps the image plane, which varies according to the movement of the variator unit, at a fixed position from the reference plane, and a relay lens connected to the variable power system formed by the first, second and third lens units. The first lens group is composed of a single lens element having a negative refracting power in order from the object side, followed by two single lens elements having a positive refracting power, and the second lens group is a negative lens element. The third lens group is composed of a single lens having a refractive power and a cemented lens, the third lens group is composed of a single lens having a negative refractive power, and the relay lens system is a single lens having a positive refractive power, a single lens having a negative refractive power, and then 2 A single lens with positive refractive power,
After that, it is composed of a single lens of negative refractive power and a single lens of positive refractive power with a relatively large air gap, and the fourth lens of the relay lens system has a positive refractive power with a convex surface facing the object side. It is a meniscus lens, and the focal length of the entire system at the wide-angle end is f _w , and the focal lengths of the first group and the second group are f ₁ , respectively.
f ₂ and the focal length of the third lens from the object side of the first group is f _c , the radius of curvature of the _20th lens surface from the object side is r ₂₀ , and the 13th lens The refractive index of N
A zoom lens that satisfies the following conditions when set to ₁₃ : -1.3f _w <f ₂ <-1.1f _w 0.9f ₁ <f _c <1.15f ₁ 1.3f _w <r ₂₀ <2.4f _w N ₁₃ <1.65