JPH0614136B2 - Large aperture zoom lens - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact large-aperture zoom lens suitable for a photographing zoom lens, particularly for a photographing device using an electronic image pickup tube or a solid-state image pickup device as an image pickup device.

2. Description of the Related Art An electronic image pickup tube is used as an image pickup device, and a zoom lens is almost used as a lens for a photographing device using a solid-state image pickup element. These zoom lenses are brighter than F / 2.0 and have a zoom ratio of 3x or more, which is superior to steel camera lenses that use a 35mm Leica size film, but is compact. It was never considered in terms of gender and cost. However, recently, a photographing device using a popular electronic image pickup device has begun to appear, and its optical system is also required to be compact and cost effective. Therefore, there is a growing need for a zoom lens in which the diameter of the front lens group is small and the total length is short, and the number of constituent lenses is small for this type.

Since this type of lens system has a strong character as one element of the system, there are restrictions on the back focus length, gravity restrictions for autofocus and power zoom with low power consumption, and the normal first lens system. It is preferable to use a rear focus instead of the group focus, a relay system that reduces the number of lens groups to be moved during zooming, and lengthens the back focus.

There are many zoom lenses for photography that have a brightness of F / 2.0 or more and a zoom ratio of 3 or more, but they are compact (the overall length is short and the front lens diameter is small) and cost-effective (especially No high-performance zoom lens has yet been known that satisfies all of the requirements for the number of lens components) and the length of the back focus, and can sufficiently cope with an increase in the number of pixels of image pickup devices in the future. In particular, no attempt has been made to improve the performance while keeping the back focus at 0.9 times or more the geometric mean f _S of the shortest focal length f _W and the longest focal length f _T of the zoom lens.

The need for a lens with a long back focus arises from the need to insert various optical members between the rear end of the lens and the imaging surface, but as the screen size becomes smaller and the focal length of the lens system becomes shorter, the back focus f _B The need to increase the ratio of f _S to f _S increases. Japanese Patent Sho 55-40
No. 852, Japanese Patent Publication No. 48-32387, and other zoom lenses having a small number of constituents are known, but these prior art examples do not take into consideration a short back focus or a long length.

Further, in the conventional example, even during autofocus, focusing is performed while driving the front lens group having a large diameter and heavy weight.
By adopting a rear focus that drives a lens group having a small diameter and a light weight to focus on this, an auto focus with low power consumption becomes possible. As a zoom lens using this method, the one described in JP-A-57-78513 is known. However, although the autofocus of this system has the above-described merits, Example 1 is not preferable in terms of performance because the variation of aberrations at the time of focusing at a short distance, especially the variation of astigmatism is large. Is F /
It is a dark lens at 5.6. As described above, this conventional example satisfies the requirement that the back focus is 0.9 times or more of f _S at F / 2.0 or more as described above, and further, the aberration variation at the time of focusing at a short distance, especially the spherical aberration, It does not meet certain conditions for reducing the fluctuation of coma.

Outline The zoom lens of the present invention has the following lens structure in order to secure a brighter back focus than F / 2 at a zoom ratio of 3 or more in a total angle of view of 15 ° to 45 ° and to reduce the number of constituent lenses. . That is, in order from the object side, the first group having a positive focal length, a variable power system including a variator having a negative focal length and a compensator having a negative focal length, and a relay system are provided. The system consists of a front lens group and a rear lens group, and the front lens group is composed of, in order from the object side, a positive lens, a positive lens with a strong convex surface facing the object side, and a negative lens with a strong concave surface facing the object side. The rear lens group includes a negative lens and at least two positive lenses, the first lens group is fixed, and the rear lens group of the relay system is extended toward the object side along the optical axis to move to a near object. It is a lens system that performs focusing and satisfies the following conditions (1) to (3).

(1) −0.3 <f _W / f _A <0.2 (2) 0.14f _IV <D <0.5f _IV (3) 1.5f _IV <l <2.2f _IV where f _W is The shortest focal length of the entire system, f _A is the composite focal length from the first group to the front group of the relay system, f _IV is the focal length of the relay system, D is the air distance between the front group and the rear group of the relay system, and l is It is the distance from the object side surface of the negative lens in the front lens group of the relay system to the image side surface.

The zoom lens of the present invention can perform focusing on a short-distance object point by moving the first group I toward the object side. However, in this focusing method, vignetting tends to increase as the object point at a closer distance is focused, and in order to prevent this, the diameter of the first group I must be increased. When autofocusing is performed using the first group I having such a large diameter and heavy weight, the torque of the drive motor becomes large and the power consumption becomes large.

The zoom lens of the present invention is a front lens group of the relay system (fourth lens group) IV.
It is also possible to employ a method of performing focusing by feeding the group IV _b after using an air space between the IV _a and the rear group IV _b to the object side along the optical axis. However, this focusing method tends to have large aberration fluctuations when focusing on a short-distance object point, and is particularly difficult to apply to a zoom lens that is brighter than F / 2.0, such as the zoom lens of the present invention.

In the present invention, and the focusing method according to the group feeding after said up front group IV _a is formed substantially afocal relay system from the first group I to be applicable without aberration fluctuations. Furthermore the combined focal length f of the match also contemplated that the back focus than 0.9F _s from the first group I to the front group IV _a relay system
_A must satisfy the above condition (1).

If the lower limit of this condition (1) is exceeded, spherical aberration at the near object point will be overcorrected, and if the upper limit is exceeded, spherical aberration will be undercorrected and the back focus will be 0.9 _fs or more. Becomes difficult.

Further, the zoom lens of the present invention can be made lightweight at low cost by making the relay system (fourth group) a small number of elements such as 6 or 7. Further, with this configuration, it becomes easy to secure a sufficient back focus when various optical members are inserted between the rear end of the lens and the image plane. Moreover, aberrations, particularly spherical aberration and coma, can be corrected well even if the back focus is lengthened with such a small number of lenses. In other words, the negative lens is arranged on the most image side of the front group IV _a of the relay system, and the divergent action is given to the light beam to lengthen the back focus. This negative lens also contributes to the correction of spherical aberration at the same time, but if the positive lens in front of this negative lens has a strong curvature on the image side, it has a strong positive refractive power and a strong negative refractive power. Since the light beams are closely aligned with each other, the light beams continue to receive the contradictory actions in a short time, which makes it difficult to correct the spherical aberration. Therefore, it is desirable that the positive lens has a shape having a strong convex surface on the object side.

Also it is possible to lengthen the back focus by setting the air distance D between the front lens group IV _a and the rear group IV _b of the relay system in the range of the condition (2).

When the distance D becomes 0.14f _IV or less beyond the lower limit of this condition (2), in order to lengthen the back focus, the power of the front group and the rear group of the relay system IV must be increased.
Aberration is aggravated, which is not preferable. In addition, the interval D is 0.15
If it is f _IV or more, the total length of the lens system tends to be long.

Although long back focus by to have a strong divergence on the object-side surface of the negative lens of the front group IV _a relay system as described above, the spherical aberration when the divergence is too strong, the correction of coma Becomes difficult. Therefore, in the zoom lens of the present invention, the distance from the position of the object-side surface of the negative lens to the rear focal point of the lens system satisfies the above condition (3).

If the lower limit of this condition (3) is exceeded, the divergence of the object-side surface of the negative lens will become too strong, making it difficult to correct aberrations. If the upper limit is exceeded, the overall length of the lens system will become long.

Further, in the zoom lens according to the present invention, in order to reduce the fluctuation of the astigmatism at a short distance, the rear group IV _b of the fourth group
Since it is desirable that the positive lens component on the most object side of the lens be concentric with respect to the pupil, the image side surface of this lens is a convex surface having a strong curvature. This is also advantageous for spherical aberration correction of a large aperture zoom lens that is brighter than F / 2. It is also advantageous for correction of spherical aberration that the object-side surface of the positive lens component closest to the image side is a convex surface having a significantly stronger curvature than the image-side surface.

It is another object of the present invention to provide a high-performance zoom lens which has a certain level of performance for the current electronic image pickup device in view of the future. To meet this requirement, we did the following:

First, the relay system of the fourth group IV was made to satisfy the following conditions (4) and (5).

(4) n _IVn > 1.78 (5) ν _IVap <ν _IVbp where n _IVn is the average refractive index of the negative lenses of the fourth lens group IV, ν
_IVap average of Abbe's numbers of the positive lens of the front group IV _a of the fourth group,
ν _IVbp is the average of the Atsube numbers of the rear group IV _b of the fourth group.

The largest factor in the occurrence of high-order aberrations such as spherical aberration and coma is that the radius of curvature of the negative lens of the relay system is generally small. Therefore, it is better to increase the refractive index of these negative lenses. If the condition (4) is not satisfied, the radius of curvature of the negative lens becomes too small and the high-order aberration is generated.

The condition (5) is for correcting lateral chromatic aberration.
If this condition is not satisfied, axial chromatic aberration can be corrected, but lateral chromatic aberration is insufficiently corrected.

Next, the zoom units from the first group I to the third group III are arranged in the following order from the object side. In other words, the first group I is composed of a positive lens component formed by cementing a negative meniscus lens and a biconvex lens, and a positive meniscus lens component of a single lens.
II is a negative lens component consisting of a single lens, and a negative lens component consisting of a cemented biconcave lens and a positive lens.
III includes one negative lens component. It is desirable that the following conditions (6) to (11) are satisfied.

(6) 2.5f _W <f _I <3.5f _W (7) −1.2f _W <f _II <−0.8f _W (8) 1.7 <n ₄ (9) 0.05 <n ₆ − n ₅ (10) 1.6 <n ₅ (11) 13 <ν ₅ −ν _{6 where} f _I and f _II are the focal lengths of the first lens group I and the second lens group II, respectively.
₄ is the refractive index of the negative lens component of the second group II, n ₅ and n ₆ are the refractive indices of the biconcave lens and the positive lens of the negative lens component of the second group II cemented together, and ν ₅ and ν ₆ are the negative values It is the Abbe number of the biconcave lens and the positive lens of the lens component.

Condition (6) of the above conditions defines the focal length of the first lens group I. If the upper limit of this condition is exceeded, the total length of the zoom portion will tend to be long, and if the lower limit is exceeded, the radius of curvature of each surface will be small. In order to secure the required luminous flux, the lens thickness must be increased, which is not preferable. In addition, it becomes difficult to correct aberrations, especially spherical aberration and coma.

The condition (7) defines the focal length of the second lens group II. If the upper limit is exceeded, it is desirable to shorten the total length of the zoom section, but the aberration fluctuation during zooming tends to be too large.
If the value goes below the lower limit, the total length of the zoom section becomes long.

If the conditions (8) to (10) are not satisfied, the aberration variation during zooming becomes large.

Of these conditions, conditions (8) and (10) both increase the refractive index of the negative lens in the second lens group, increase the radius of curvature of these lenses, and mainly reduce the occurrence of spherical aberration. Even if the second lens group II moves, the aberration does not change. Therefore, if these conditions are not satisfied, the aberration variation will be large.

The condition (9) is provided so that the cemented surface of the cemented negative lens component in the second lens group I has an aberration correcting action.
If the difference in the refractive index of both lenses of this negative lens component is small,
When it goes out of (9), the correction effect of this lens component becomes weak,
It must be corrected with another lens.

The condition (11) relates to chromatic aberration, and if the lower limit of this condition is exceeded, the variation of chromatic aberration during zooming tends to be large. That is, as the wavelength changes from wide to tele, axial chromatic aberration is undercorrected at shorter wavelengths, and lateral chromatic aberration is overcorrected.

Embodiments Embodiments of the present invention described above will be described below.

Example _{1 f = 14~24.25~42 r 1 = 73.7446} d 1 = 1.1600 n 1 = 1.80518 ν 1 = 25.43 r 2 = 29.0371 d 2 = 7.3000 n 2 = 1.62280 ν 2 = 57.06 r 3 = -142.5789 d 3 = _{0.1700 r 4 = 29.7376 d 4 =} 5.6000 n 3 = 1.62012 ν 3 = 49.66 r 5 = 187.5263 d 5 = 0.6000~8.158~13.563 r 6 = 761.2471 d 6 = 1.0400 n 4 = 1.73400 ν 4 = 51.49 r 7 = 12.6032 d _{7 = 3.9500 r 8 = -19.9311 d} 8 = 1.0400 n 5 = 1.69350 ν 5 = 53.23 r 9 = 14.4310 d 9 = 3.1000 n 6 = 1.84666 ν 6 = 23.88 r 10 = -537.6964 d 10 = 14.1628~4.601~3.099 r _{11 = -23.9031 d 11 = 1.0000 n} 7 = 1.69680 ν 7 = 55.52 r 12 = -49.2275 d 12 = 2.7690~4.810~0.854 r 13 = 83.5278 d 13 = 2.6697 n 8 = 1.73400 ν 8 = 51.49 r 14 = -26.0628 d ₁₄ = 0.6362 r ₁₅ = ∞ (aperture) d ₁₅ = 2.0000 r ₁₆ = 22.6910 d ₁₆ = 3.1050 n ₉ = 1.69680 ν ₉ = 55.52 r ₁₇ = 205.0173 d ₁₇ = 1.2990 r ₁₈ = -23.8698 d ₁₈ = 1.0000 n ₁₀ = 1.84666 ν ₁₀ ＝ 23.88 r ₁₉ ＝ -199.2548 d ₁₉ ＝ 8.6005 r ₂₀ ＝ 152.2247 d ₂₀ = 1.0000 n ₁₁ ＝ 1.80518 ν ₁₁ ＝ 25.43 r ₂₁ ＝ 26.2448 d ₂₁ 1.9319 r ₂₂ ＝ 120.3715 d ₂₂ ＝ 4.7975 n ₁₂ = 1.56873 ν ₁₂ ＝ 63.16 r ₂₃ ＝ -19.9767 d ₂₃ ＝ 0.1342 r ₂₄ ＝ 23.9392 d ₂₄ ＝ 4.6311 n ₁₃ ＝ 1.48749 ν ₁₃ ＝ 70.15 r ₂₅ ＝ -72.0532 l / f _IV ＝ 1.826, D / f _IV ＝ 0.346, f _W / f _A = 0.057 n _IVn = 1.82592, ν _IVap −ν _IVbp = -13.15 f _I / f _W = 2.717, f _II / f _W = -0.851, n ₄ = 1.73400, n ₆ −n ₅ = 0.15316, n ₅ = 1.69350 ν ₅ −ν ₆ = 29.35, f _B = 0.95f _S Example 2 f = 14 to 24.25 to 42 r ₁ = 73.4599 d ₁ = 1.1600 n ₁ = 1.80518 ν ₁ = 25.43 r ₂ = 29.7582 d ₂ = 7.3000 n ₂ = 1.62280 ν ₂ ＝ 57.06 r ₃ ＝ -143.3946 d ₃ ＝ 0.1700 r ₄ ＝ 29.8304 d ₄ ＝ 5.6000 n ₃ ＝ 1.62012 ν ₃ ＝ 49.66 r ₅ ＝ 193.5783 d ₅ ＝ 0.6000〜8.068〜13.415 r ₆ ＝ -249.6054 d ₆ = 1.0400 n _{4 1.73400 ν 4 = 51.49 r 7 =} 13.4290 d 7 = 3.9500 r 8 = -22.3190 d 8 = 1.0400 n 5 = 1.69350 ν 5 = 53.23 r 9 = 13.6545 d 9 = 3.1000 n 6 = 1.84666 ν 6 = 23.88 r 10 = 395.1326 _{d 10 = 13.8889~4.363~3.225 r 11 = -29.6120} d 11 = 1.0000 n 7 = 1.69680 ν 7 = 55.52 r 12 = -74.5434 d 12 = 3.0371~5.106~0.854 r 13 = 103.8661 d 13 = 2.6656 n 8 = 1.72916 ν ₈ = 54.68 r ₁₄ = -26.8147 d ₁₄ = 0.5983 r ₁₅ = ∞ (diaphragm) d ₁₅ = 2.0000 r ₁₆ = 24.1544 d ₁₆ = 3.7803 n ₉ = 1.69680 ν ₉ = 55.52 r ₁₇ = 586.5944 d ₁₇ = 1.2984 r _{18 = -21.4118 d 18 = 1.0000 n 10} = 1.84666 ν 10 = 23.88 r 19 = -175.5530 d 19 = 6.6556 r 20 = 78.7259 d 20 = 1.0000 n 11 = 1.80518 ν 11 = 25.43 r 21 = 33.7443 d 21 = 1.9815 r 22 _{= -76.7912 d 22 = 3.8000 n 12} = 1.48749 ν 12 = 70.15 r 23 = -17.6494 d 23 = 0.1342 r 24 = 51.5682 d 24 = 3.0000 n 13 = 1.48749 ν 13 = 70.15 r 25 = -54 .5234 d ₂₅ = 0.1500 r ₂₆ = 33.6811 d ₂₆ = 3.7439 n ₁₄ = 1.48749 ν ₁₄ = 70.15 r ₂₇ = 306.4734 l / f _IV = 1.907, D / f _IV = 0.284, f _W / f _A = -0.078 n _IVn = 1.82592, ν _IVap −ν _IVbp = -15.05 f _I / f _W = 2.696, f _II / f _W = -0.844, n ₄ = 1.73400 n ₆ −n ₅ = 0.15316, n ₅ = 1.69350, ν ₅ −ν ₆ = 29.35, _{f B} = 0.95f _S example _{3 f = 14~24.25~42 r 1 = 73.1407} d 1 = 1.1600 n 1 = 1.80518 ν 1 = 25.43 r 2 = 29.2813 d 2 = 7.3000 n 2 = 1.62280 ν 2 = 57.06 r ₃ = -142.5699 d ₃ = 0.1700 r ₄ = 29.4855 d ₄ = 5.6000 n ₃ = 1.62012 v ₃ = 49.66 r ₅ = 188.5203 d ₅ = 0.6000 to 8.038 to 13.370 r ₆ = -2148.9531 d ₆ = 1.0400 n ₄ = 1.73400 ν ₄ = 51.49 r ₇ = 12.7344 d ₇ = 3.9500 r ₈ = -19.2458 d ₈ = 1.0400 n ₅ = 1.69350 ν ₅ = 53.23 r ₉ = 1.4976 d ₉ = 3.1000 n ₆ = 1.84666 ν ₆ = 23.88 r ₁₀ =- _{336.4032 d 10 = 14.0324~5.201~2.643 r 11 =} -21. 0833 d ₁₁ = 1.0000 n ₇ = 1.9680 ν ₇ = 55.52 r ₁₂ = -51.2968 d ₁₂ = 2.3119 to 3.735 to 0.854 r ₁₃ = 103.8053 d ₁₃ = 2.6678 n ₈ = 1.72916 ν ₈ = 54.68 r ₁₄ = -34.5149 d ₁₄ = 0.6169 r ₁₅ = ∞ (aperture) d ₁₅ = 2.0000 r ₁₆ = 52.1018 d ₁₆ = 3.3386 n ₉ = 1.69680 ν ₉ = 55.52 r ₁₇ = -58.1766 d ₁₇ = 0.1500 r ₁₈ = 30.8549 d ₁₈ = 3.0000 n ₁₀ = 1.9680 ν _{10 = 55.52 r 19 = 90.7813 d} 19 = 1.3000 r 20 = -24.0593 d 20 = 1.0000 n 11 = 1.84666 ν 11 = 23.88 r 21 = -184.3586 d 21 = 5.8297 r 22 = 136.6332 d 22 = 1.0000 n 12 = 1.80518 ν _{12 = 25.43 r 23 = 27.4732 d} 23 = 1.9396 r 24 = 178.2704 d 24 = 4.7972 n 13 = 1.56873 ν 13 = 63.16 r 25 = -19.8353 d 25 = 0.1342 r 26 = 27.9084 d 26 = 4.6096 n 14 = 1.48949 ν 14 _{= 70.15 r 27 = -64.6149 l /} f IV = 1.860, D / f IV 0.255, f W / f A = 0.110 n IVn = 1.82592, ν IVap -ν IVbb = -11.415 f I / f W = 2.685 _{f II / f W = -0.840,} n 4 = 1.73400 n 6 -n 5 = 0.15316, n 5 = 1.69350, ν 5 -ν 6 = 29.35, f B = 0.95f S provided that r _1, r _2, ... lens Radius of curvature of each surface, d ₁ , d ₂ , ...
Is the wall thickness and air gap of each lens, n ₁ , n ₂ , ... Is the refractive index of each lens, ν ₁ , ν ₂ , ... Is the Abbe number of each lens, and f _B is the back focus focus.

Example 1 of the above examples has the lens configuration shown in FIG. That is also the rear group IV _b in the front group IV _a is a negative lens having a strong concave surface on the positive lens and the object side having a strong convex surface facing the positive lens and the object side in order from the object side in the fourth lens group IV Negative It is composed of a lens, a positive lens, and a positive lens.
The aberrations in the wide, standard and tele states of this embodiment are as shown in FIGS. 4, 5 and 6, respectively.

Example 2 has a lens configuration shown in FIG. The fourth group IV of this embodiment, a front group IV _a of a negative lens having a strong concave surface on the positive lens and the object side having a strong convex surface facing the positive lens and the object side, a negative lens and a positive lens element and a positive lens It is composed of a group IV _b after consisting positive lens. The aberration conditions in the wide, standard and tele states of this embodiment are as shown in FIGS. 7, 8 and 9, respectively.

Further, Example 3 has a lens configuration shown in FIG.
The fourth lens group IV of this embodiment is composed of a positive lens, a positive lens, a positive lens having a strong convex surface facing the object side, and a negative lens having a strong concave surface facing the object side, _a negative lens and a positive lens. It is composed of a group IV _b after the more positive lens. The aberrations in the wide, standard and tele states of this embodiment are as shown in FIGS. 10, 11 and 12, respectively.

Each of the above embodiments are both possible to perform Yotsute Fuokashingu to feed the group IV _b after the fourth group to the object side. Feed amount of the group IV _b after time the Fuokashingu was rows summer on a nearby object point at this method is as follows.

The aberrations of the respective examples at that time are shown in FIGS.
This is as shown in FIGS. 15, 16 to 18 and 19 to 21.

EFFECTS OF THE INVENTION The zoom lens of the present invention has a small number of components, a short overall length, and a zoom ratio of 3, F with an angle of view of 15 ° to 45 ° while securing a sufficiently long back focus of 0.9 f _S or more. / 2.
It is 0, has high performance, and is sufficiently compatible with an image pickup device having a large number of pixels. Also, a rear focus that is F / 2.0 and is light in weight with very little variation in aberration is possible.

[Brief description of drawings]

1 to 3 show Embodiments 1 to 3 of the present invention, respectively.
4 to 6 are aberration curve diagrams of the object point at infinity of Example 1, FIGS. 7 to 9 are aberration curve diagrams of the object point at infinity of Example 2, and FIG. FIG. 12 is an aberration curve diagram of an object point at infinity of Example 3, FIGS. 13 to 15 are aberration curve diagrams of an object point of close range of Example 1, and FIGS. 16 to 18 are diagrams of Example 2. FIGS. 19 to 21 are aberration curve diagrams of a short-distance object point, and FIGS.

Claims (2)

[Claims] 1. A zoom lens system comprising, in order from the object side, a first lens unit having a positive focal length, a variable power system including a variator having a negative focal length and a compensator having a negative focal length, and a relay system. The relay system includes a front lens group and a rear lens group, and the front lens group has, in order from the object side, a positive lens, a positive lens having a strong convex surface facing the object side, and a negative lens having a strong concave surface facing the object side. The rear group includes a negative lens and at least two positive lenses, and the first group is fixed, and the rear group of the relay system is extended toward the object side along the optical axis. A large-aperture zoom lens that focuses on a distance object and satisfies the following conditions. (1) -0.3 <f _W / f _A <0.2 (2) 0.14f _IV <D <0.5f _IV (3) 1.5f _IV <l <2.2f _IV where f _W is The shortest focal length of the entire system, f _A is the composite focal length from the first group to the front group of the relay system, f _IV is the composite focal length of the relay system, and D is the front group of the relay system when focusing on an object point at infinity. The distance between the rear lens group and the rear lens group, l is the distance from the object side surface of the negative lens in the front lens group of the relay system to the rear focal point of the zoom lens. 2. A positive lens closest to the object in the rear group is a convex surface having a stronger curvature on the image side, and a positive lens closer to the image is a convex surface having a stronger curvature on the object side. A large aperture zoom lens according to claim (1).