JP2015084032A - Zoom lens and imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which is compact and light weight and in which aberrations are well corrected.SOLUTION: The zoom lens includes, in order from the object side to the image plane side: a first lens group 2 having positive refractive power; a second lens group 3 having negative refractive power; a third lens group 4 having negative refractive power; a fourth lens group 5 having positive refractive power; and an extender lens group 6 provided attachably/detachably on the image plane side of the forth lens group 5. When varying power, the second lens group 3 and the third lens group 4 are moved so that the second lens group 3 is located closest to the object side at the wide angle end and the third lens group 4 is located closest to the image plane side at the telephoto end. The zoom lens satisfies the following conditional expressions, where m2W is the magnification of the second lens group at the wide angle end, m2T is the magnification of the second lens group at the telephoto end, m3W is the magnification of the third lens group at the wide angle end, and m3T is the magnification of the third lens group at the telephoto end.

Description

  The present invention relates to a television camera, a video camera, a digital camera, a zoom lens used for surveillance purposes, and an imaging apparatus using the zoom lens.

  A first lens group having a positive refractive power from the object side toward the image plane side, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a positive refractive power A lens group is provided, and at the time of zooming, the second lens group, the third lens group are positioned closest to the object side at the wide-angle end, and the third lens group is positioned closest to the image plane side at the telephoto end. A zoom lens that moves a lens group is known (see Patent Document 1).

Further, as this type of zoom lens, a lens in which an extender lens group can be inserted into and removed from a fourth lens group is known (see Patent Document 2).
Further, as this type of zoom lens, a zoom lens including a diffractive optical element in the first lens group is also known (see Patent Document 3).

  Further, in this type of zoom lens, a diffractive optical element is not provided, but a lens that corrects chromatic aberration up to the near infrared region is also known (see Patent Document 4).

  Various types of zoom lenses for TV cameras are considered. For example, as suitable for high zooming, a first lens group having a positive focal length from the object side to the image side, a second lens group having a negative focal length, and a third lens group having a negative focal length It is known that a fourth lens group having a positive focal length is disposed and the second lens group and the third lens group are moved during zooming.

  In this type of zoom lens, the second lens group often serves as a variator for zooming, and the third lens group serves as a compensator for correcting fluctuations in image plane position due to zooming. However, in order to achieve both a reduction in size and a high zoom ratio, some third lens groups also bear a part of the zooming action.

  In Patent Document 1, the third lens group also bears a part of the zooming action, but the zoom ratio is less than 20 times. In Patent Document 2, an extender lens is incorporated, but the zoom ratio is still 20 times or less.

  In a television camera for surveillance use, imaging with sensitivity up to the near-infrared region having a wavelength of about 900 nm or less may be performed. For example, in the daytime when there is enough light, the near-infrared light is cut to obtain an accurate color image using only visible light, and all light from the visible to the near-infrared region is transmitted during bad weather, twilight, and dawn. Operations such as increasing the amount of light, cutting visible light at night, and projecting and illuminating infrared rays with a wavelength of about 850 nm are performed.

  Therefore, a zoom lens used as a photographing lens is required to correct chromatic aberration not only in the visible range but also in the near infrared range. When chromatic aberration correction is not performed up to the near infrared range, it is necessary to refocus when switching between visible light and near infrared light, or when all light from the visible range to the near infrared range is transmitted. This is because sufficient resolution cannot be obtained.

  In this type of zoom lens, in order to satisfactorily correct chromatic aberration, the first lens group in which the axial marginal ray height is increased on the telephoto side, and the fourth lens group in which the axial marginal ray height is increased on the wide angle side. In general, special low dispersion glass represented by FPL51 (trade name made by OHARA INC.) And FPL53 (trade name made by OHARA INC.) Is generally used. There has also been proposed a technique in which a diffractive optical element is provided in the first lens group and chromatic aberration is corrected using negative dispersion of the diffractive optical element.

  In Patent Document 3, chromatic aberration is corrected using a diffractive optical element in the first lens group, but when the zoom ratio exceeds 25, the telephoto ratio at the telephoto end (ratio of the total lens length to the focal length) is It is as large as around 1.0 and is not sufficiently downsized.

  In Patent Document 4, aberration correction to the near infrared region is performed using special low dispersion glass for the first lens group and the fourth lens group, but the zoom ratio is about 22 times and smaller than 25 times. .

  By the way, television cameras and video cameras have various requests from users. In particular, high image quality and miniaturization are always requested by users, and the weight is large. Therefore, the zoom lens is also required to achieve both high performance and downsizing. Furthermore, it is desired that the zoom ratio is as large as possible.

  An object of the present invention is to provide a small zoom lens with good aberration correction.

The zoom lens according to claim 1 of the present invention has a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a negative refractive power from the object side to the image plane side. A third lens group having a positive refractive power and a fourth lens group having a positive refractive power. The fourth lens group is detachably provided on the image plane side of the fourth lens group, and includes a first lens group to a fourth lens group. An extender lens group that shifts the focal length of the entire system to the long side without changing the distance between the lens group and the image plane. During zooming, the second lens group is located closest to the object side at the wide-angle end. The three lens groups are zoom lenses that move the second lens group and the third lens group so that they are located closest to the image plane at the telephoto end.
When m _2W is the magnification of the second lens group at the wide angle end, m _2T is the magnification of the second lens group at the telephoto end, m _3W is the magnification of the third lens group at the wide angle end, and m _3T is the magnification of the third lens group at the telephoto end. The following conditional expressions are satisfied.

  According to the present invention, it is possible to provide a small zoom lens with good aberration correction.

FIG. 1 is a cross-sectional view showing the configuration of a zoom lens of Numerical Example 1 (without an extender lens group). FIG. 1A shows a state in which the second lens group is closest to the object side at the wide-angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 2 is a cross-sectional view showing a configuration of a zoom lens (with an extender lens group inserted) in Numerical Example 1. FIG. 2A shows a state in which the second lens group is closest to the object side at the wide-angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 3 is a cross-sectional view showing a configuration of a zoom lens of Numerical Example 2 (without an extender lens group). FIG. 3A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 4 is a cross-sectional view showing a configuration of a zoom lens of Numerical Example 2 (with an extender lens group inserted). FIG. 4A shows a state in which the second lens group is closest to the object side at the wide-angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 5 is a cross-sectional view showing a configuration of a zoom lens of Numerical Example 3 (without an extender lens group inserted). FIG. 5A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 6 is a cross-sectional view showing a configuration of a zoom lens of Example 3 (with an extender lens group inserted), and FIG. 6A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 7 is a cross-sectional view showing a configuration of a zoom lens of Numerical Example 4 (without an extender lens group). FIG. 7A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 8 is a cross-sectional view showing a configuration of a zoom lens (with an extender lens group inserted) in Numerical Example 4, and FIG. 8A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 9 is a cross-sectional view showing a configuration of a zoom lens of Numerical Example 5 (with no extender lens group inserted). FIG. 9A shows a state in which the second lens group is closest to the object side at the wide-angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 10 is a cross-sectional view showing a configuration of a zoom lens of Example 5 (with an extender lens group inserted). FIG. 10A shows a state in which the second lens group is closest to the object side at the wide angle end. (C) shows a state where the third lens group is closest to the image plane side at the telephoto end, and (b) shows a state where the zoom lens is at an intermediate focal length. FIG. 11 is an aberration curve diagram at the wide-angle end of the zoom lens according to Numerical Example 1 (without the extender lens group inserted). FIG. 12 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 1 (without the extender lens group inserted). FIG. 13 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 1 (without the extender lens group inserted). FIG. 14 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 1 (with the extender lens group inserted). FIG. 15 is an aberration curve diagram at the intermediate focal length of the zoom lens of Numerical Example 1 (with the extender lens group inserted). FIG. 16 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 1 (with the extender lens group inserted). FIG. 17 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 2 (without the extender lens group inserted). FIG. 18 is an aberration curve diagram at the intermediate focal length of the zoom lens of Numerical Example 2 (without the extender lens group inserted). FIG. 19 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 2 (without the extender lens group inserted). FIG. 20 is an aberration curve diagram at the wide-angle end of the zoom lens according to Numerical Example 2 (with the extender lens group inserted). FIG. 21 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 2 (with the extender lens group inserted). FIG. 22 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 2 (with the extender lens group inserted). FIG. 23 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 3 (without the extender lens group inserted). FIG. 24 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 3 (without the extender lens group inserted). FIG. 25 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 3 (without the extender lens group inserted). FIG. 26 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 3 (with the extender lens group inserted). FIG. 27 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 3 (with the extender lens group inserted). FIG. 28 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 3 (with the extender lens group inserted). FIG. 29 is an aberration curve diagram at the wide-angle end of the zoom lens according to Numerical Example 4 (without the extender lens group inserted). FIG. 30 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 4 (without the extender lens group inserted). FIG. 31 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 4 (without the extender lens group inserted). FIG. 32 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 4 (with the extender lens group inserted). FIG. 33 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 4 (with the extender lens group inserted). FIG. 34 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 4 (with the extender lens group inserted). FIG. 35 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 5 (without the extender lens group inserted). FIG. 36 is an aberration curve diagram at the intermediate focal length of the zoom lens of Numerical Example 5 (without the extender lens group inserted). FIG. 37 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 5 (without the extender lens group inserted). FIG. 38 is an aberration curve diagram at the wide-angle end of the zoom lens of Numerical Example 5 (with the extender lens group inserted). FIG. 39 is an aberration curve diagram at an intermediate focal length of the zoom lens of Numerical Example 5 (with the extender lens group inserted). FIG. 40 is an aberration curve diagram at the telephoto end of the zoom lens of Numerical Example 5 (with the extender lens group inserted). FIG. 41 is an explanatory diagram schematically showing an embodiment of the imaging apparatus.

Embodiments of a zoom lens according to the present invention will be described below with reference to the drawings.
As shown in FIGS. 1 to 10, the zoom lens 1 of the present invention includes a first lens group 2 having a positive refractive power and a second lens group having a negative refractive power from the object side to the image plane side. 3. A third lens group 4 having negative refractive power and a fourth lens group 5 having positive refractive power.

  2, 4, 6, 8, and 10, the zoom lens 1 includes a lens group between the first lens group 2 to the fourth lens group 5 and an image plane S. An extender lens group 6 that changes the focal length of the entire system to the longer side without changing the distance is provided to be detachable from the image plane S side of the fourth lens group 5.

  For example, as shown in FIGS. 1 to 8 corresponding to Numerical Example 1 to Numerical Example 4, the first lens group 2 includes three lenses of a lens L1, a lens L2, and a lens L3. The second lens group 3 includes, for example, three lenses of a lens L6, a lens L7, and a lens L8.

  The third lens group 4 includes, for example, two lenses, a lens L9 and a lens L10. The fourth lens group 5 includes, for example, six lenses including a lens L11, a lens L12, a lens L13, a lens L14, a lens L15, and a lens L16.

The extender lens group 6 includes, for example, five lenses including a lens L17, a lens L18, a lens L19, a lens L20, and a lens L21.
Between the third lens group 4 and the fourth lens group 5, a parallel plate FP2 is disposed immediately before the lens L11 of the fourth lens group 5. This parallel plate FP2 is assumed to be an ND filter for light amount adjustment. A diaphragm SB is provided between the parallel plate FP2 and the lens L11. On the image plane S side of the fourth lens group 5, a parallel plate FP1 is disposed. This parallel plate FP1 assumes various filters such as an optical low-pass filter and an infrared cut filter, and a cover glass (seal glass) of an image sensor such as a CCD sensor.

  The zoom lens 1 composed of four lens groups of positive, negative, negative, and positive is generally configured as a so-called variator in which the second lens group 3 bears a main zooming action. It can share the doubling action and is suitable for high zooming.

  In this embodiment, as shown in FIGS. 1 (a) to 10 (a), the second lens group 3 is located closest to the object side at the wide-angle end, and is shown in FIGS. 1 (c) to 10 (c). As described above, by moving the second lens group 3 and the third lens group 4 so that the third lens group 4 is located closest to the image plane at the telephoto end, the third lens group 4 can achieve a sufficient zooming effect. To have.

  When zooming from the wide-angle end to the telephoto end, as shown in FIGS. 1A to 10A to 1B to 10B, the second lens group 3 and the third lens group 4 are used. The interval between and becomes once smaller, and takes an extreme value in the intermediate range of zooming. Thereafter, as shown in FIGS. 1C to 10C, the distance between the second lens group 3 and the third lens group 4 is increased again. The second lens group 3 and the third lens group 4 are integrated as a variator that bears the zooming action, and fulfill the function of compensation of the image plane position, that is, a so-called compensator by changing the distance between them.

  In the zoom lens 1 according to this embodiment, each lens from the first lens group 2 to the fourth lens group 5 is provided by an extender lens group 6 that is detachably provided on the image plane side of the fourth lens group 5. The focal length of the entire system is shifted to the longer side without changing the distance between the group and the image plane S.

  The reason for adopting such a configuration is that the extender lens group 6 can be built in the zoom lens 1. In a configuration in which the distance between each lens group from the first lens group 2 to the fourth lens group 5 and the image plane S is changed by the insertion / removal of the extender lens group 6, the focus state is increased as the extender lens group 6 is inserted / removed. In order to maintain this, the first lens group 2 to the fourth lens group 5 must be moved.

  For this reason, in order to drive the zoom lens 1, a very complicated mechanism is required. In addition, by providing the extender lens group 6 on the image plane side of the fourth lens group 5 instead of in the middle of the fourth lens group 5, the assembly accuracy of the fourth lens group 5 can be easily maintained.

Further, the zoom lens 1 of this embodiment is configured to satisfy the following conditional expression.

Where m _2W is the magnification of the second lens group 3 at the wide angle end, m _2T is the magnification of the second lens group 3 at the telephoto end, m _3W is the magnification of the third lens group 4 at the wide angle end, and m _3T is at the telephoto end. The magnification of the third lens group 4 is shown.

In other words, the meaning that m _2T / m _2W and m _3T / m _3W are both negative means that the magnification of the third lens group 4 becomes “0” during zooming from the wide-angle end to the telephoto end. It means to include.

  The state in which the magnification of the third lens group 4 is “0” is a state in which the combined refractive power of the first lens group 2 and the second lens group 3 is “0”. The signs of the magnifications of the second lens group 3 and the third lens group 4 are reversed (when the magnification of the third lens group 4 is “0”, the magnification of the second lens group 3 is infinite). By configuring the zoom lens 1 so as to include this state, it is possible to balance the contribution of the second lens group 3 and the third lens group 4 to the zooming and realize a good aberration correction.

Furthermore, by controlling the contribution of the second lens group 3 and the third lens group 4 to zooming so that (m _3T / m _3W ) / (m _2T / m _2W ) falls within a predetermined range, While achieving a sufficiently high zoom ratio, a significant reduction in size can be realized.

If (m _3T / m _3W ) / (m _2T / m _2W ) is 0.8 or less, the contribution of the third lens group 4 to zooming becomes too small, and (m _3T / m _3W ) / (m _{If 2T} / m _2W ) is 3.0 or more, the contribution of the second lens group 3 to zooming becomes too small, and in either case, it becomes difficult to correct various monochromatic aberrations, and high zooming is achieved. And miniaturization are difficult to achieve.

In the zoom lens 1 according to the first embodiment, since the focal length is shifted to the longer side by the extender lens group 6, the aberration when the extender lens group 6 is not inserted needs to be corrected better.
Therefore, it is more desirable that the following conditional expression is satisfied.

In order to make the zoom lens 1 more suitable for high zoom ratio, it is desirable to further satisfy the following conditional expression.
However, D _{34 W} is the wide-angle end of the third lens group 4 and the distance between the fourth lens group 5, D _34T is the distance between the third lens group 4 at the telephoto end and the fourth lens group 5, f _w at the wide-angle end The focal length of the entire system at.

(D _34W - D _34T) / If f _w is 2.5 or less, likely contributed to the third zoom lens group 4 is _{reduced, (D 34W - D 34T)} / f w is 6.0 or higher If this is the case, the contribution of the second lens group 3 to zooming tends to be small, and in any case, it may be impossible to correct aberrations.

In the zoom lens 1 of this embodiment, the wide open F number in the telephoto range is regulated not by the aperture stop SB provided in the vicinity of the object side of the fourth lens group 5 but by the effective diameter of the first lens group 2. can be configured, in which _{case, (D 34W - D 34T)} / f w is greater than 2.5, it has the effect of reducing the effective diameter of the third lens group 4, which also aberration correction It works in an advantageous manner.

In the zoom lens 1 of this embodiment, it is desirable that the following conditional expression is satisfied with respect to the arrangement of the fourth lens group 5 that bears the main imaging action.
However, L ₄ is the distance along the optical axis from the most object side surface (surface number 19) of the fourth lens group 5 to the most image side surface (surface number 28), and T _4F-I is the fourth lens group. 5 is a distance along the optical axis from the most object side surface (surface number 28) to the image plane S, and includes an optical element having no refractive power on the image plane side from the fourth lens group 5. The air equivalent length assumed that it does not exist is shown.

If L ₄ / T _4F-I is 0.2 or less, the degree of freedom regarding the configuration of the fourth lens group 5 is hindered, and various aberration corrections (correction of spherical aberration, astigmatism, distortion aberration, coma aberration) May be difficult. On the other hand, if L ₄ / T _4F-I is 0.5 or more, a sufficient space cannot be secured between the fourth lens group 5 and the image plane S, and the degree of freedom regarding the configuration of the extender lens group 6 is hindered. Is done.

Further, it is not preferable because various aberration corrections are insufficient, and a switching mechanism such as an infrared light cut filter and a visible light cut filter is hindered in the zoom lens 1.
Furthermore, it is not preferable because ghosts are easily generated due to reflection of each surface and filter in the fourth lens group 5 and the extender lens group 6.
It is more desirable to satisfy the following conditional expression.

In the zoom lens 1 of the embodiment, it is desirable that the positive lens included in the first lens group 2 satisfies the following conditional expression.
Here, ν _1GP indicates the average value of the Abbe number of the material of the positive lens included in the first lens group 2. If the zooming ratio is increased, in particular, if the focal length at the telephoto end is increased, it is difficult to correct the secondary spectrum of longitudinal chromatic aberration on the telephoto side. In the zoom lens 1 of this embodiment, since the focal length is shifted to the longer side by the extender lens group 6, the axial chromatic aberration needs to be corrected even better.

 For example, when the magnification (lateral magnification) of the extender lens group 6 is “2”, the F number is doubled, so the focal depth is doubled, but the axial chromatic aberration is a longitudinal aberration, so it contributes by the square. This is because the amount of aberration becomes four times.

Therefore, it is desirable to use a positive lens with small dispersion for the first lens group 2 whose axial marginal ray height is large on the telephoto side.
When ν _1GP is 75 or less, chromatic aberration correction in the telephoto range tends to be insufficient. On the other hand, there is no material with ν _1GP of 96 or more, or even if it exists, it is very special and expensive and cannot be used in practice.

Even when other chromatic aberration correction means such as a diffractive optical element is provided in the first lens group 2, it is preferable to satisfy this conditional expression when chromatic aberration correction up to the near infrared region is required.
More preferably, the following conditional expression should be satisfied.

 In the embodiment shown in FIGS. 1 to 8 corresponding to Numerical Example 1 to Numerical Example 4 of this embodiment, each lens L1 to L3 of the first lens group 2 has a concave surface directed toward the image surface side in order from the object side. A negative meniscus lens, a positive lens having a convex surface with a smaller radius of curvature than the image side facing the object side, and a positive lens L3 having a convex surface having a smaller radius of curvature than the image side facing the object side. And a diffractive optical element RF.

  By adopting a configuration in which the first lens group 2 includes the diffractive optical element RF, even when the chromatic aberration correction in the telephoto range including the near infrared region is sufficiently performed, the number of components of the first lens group 2 having a large lens diameter is 3 It can be suppressed to a sheet, and the weight can be reduced.

When the diffractive optical element RF is provided in the first lens group 2, it is desirable to satisfy the following conditional expression.
Here, f _TC is the focal length of the entire system at the telephoto end with the extender lens group 6 inserted, and f _DOE is the focal length of the diffractive portion of the diffractive optical element RF.

If the refractive power of the diffractive optical element RF is so weak that f _TC / f _DOE is 0.02 or less, it becomes difficult to sufficiently perform chromatic aberration correction in the telephoto range. On the other hand, if the refractive power of the diffractive optical element RF is so strong that f _TC / f _DOE is 0.10 or more, correction of chromatic aberration on the telephoto side becomes excessive, which is also not preferable.

 As shown in FIGS. 9 and 10 corresponding to Numerical Example 5, the first lens group 2 includes, in order from the object side, a negative meniscus lens L1 ′ having a concave surface on the image surface side, and a curvature on the object side that is larger than that on the image side. A positive lens L2 ′ having a convex surface having a small radius and a negative meniscus lens L3 ′ having a concave surface on the image side, and a positive lens L4 having a convex surface having a smaller radius of curvature than the image side on the object side It is also possible to adopt a five-lens configuration of a positive lens L5 ′ having a convex surface with a smaller radius of curvature than the image side on the object side.

 In this case, the diffractive optical element RF is not necessary for the first lens group 2. In this case, there is an advantage that unnecessary high-order diffracted light due to the wavelength dependency of the diffractive optical element RF, flare due to the structure of the diffractive optical element RF, etc. need not be taken into consideration.

In the zoom lens 1, the fourth lens group 5 is composed of six lenses L11 to L16 arranged in order from the object side, but it is sufficient that the fourth lens group 5 has at least three positive lenses. It is desirable to satisfy the following conditional expression.
Here, ν _4GP represents the average value of the Abbe number of at least three positive lenses.
By configuring the fourth lens group 5 in this way, chromatic aberration from the visible range to the near infrared range can be corrected more satisfactorily, particularly in the wide-angle range of the zooming range.

Although the second lens group 3 is three in this embodiment, it is desirable that the second lens group 3 is composed of three or less lenses.
In the zoom lens 1 of this embodiment, the second lens group 3 and the third lens group 4 are divided into three second lens groups 3 in order to perform zooming and aberration correction comprehensively without distinction as a variator / compensator. Even with a configuration including the following lenses and a configuration in which the aberration correction capability of the second lens group 3 alone is relatively low, sufficient imaging performance can be ensured.

The lenses L6, L7, and L8 of the second lens group 3 shown in FIG. 1 to FIG. 10 corresponding to the numerical examples have a three-lens configuration of a negative lens, a positive lens, and a negative lens in order from the object side.
In zooming, it is desirable that the first lens group 2 and the fourth lens group 5 are fixed with respect to the image plane S.

As a zoom lens 1 for a television camera / video camera, it is desired that the total length is constant and the weight balance does not change upon zooming. For this reason, it can be realized by adopting a configuration in which the first lens group 2 and the fourth lens group 5 are not moved.
In addition, the small number of moving lens groups is advantageous in terms of mechanism, leading to a reduction in the number of parts, weight reduction, and improvement in reliability.

It is desirable that the refractive power of each lens group satisfies the following conditional expressions.
However, f ₁ is the focal length of the first lens group 2, f ₂ is the focal length of the second lens group 3, f ₃ is the focal length of the third lens group 4, f ₄ is the focal length of the fourth lens group 5, f _w represents the focal length of the entire system at the wide-angle end.

  A lens that is more suitable for the zoom lens 1 having a zoom ratio of more than 25 times and a half angle of view at the telephoto end of about 0.5 degrees by keeping the refractive power of each lens group within the range of the conditional expression. It becomes.

It is desirable that at least one of the positive lenses included in the first lens group 2 and at least one of the positive lenses included in the fourth lens group 5 satisfy the following conditional expression.
Where ν _d is the Abbe number of the material constituting the positive lens, and θ _{C, A ′} is the partial dispersion ratio of the material constituting the positive lens.

Here, θ _{C, A ′} = (n _C −n _{A ′} ) / (n _F −n _C ), where n _F , n _C and n _{A ′} are F of the material constituting the negative lens, respectively. Refractive index for line, C line, and A 'line.
By providing a positive lens that satisfies the above conditional expression in each of the first lens group 2 and the fourth lens group 5, chromatic aberration including the near-infrared region can be satisfactorily corrected over the entire zoom range from the wide-angle end to the telephoto end. It becomes possible.

  The extender lens group 6 includes, in order from the object side, an extender lens front group including a positive lens L17, a positive lens L18, and a negative lens L19, and an extender lens rear group including a positive lens L20 and a negative lens L21. It is desirable to have a configuration having

  The front lens group of the extender lens has a positive refractive power as a whole, and the rear lens group of the extender lens as a whole has a negative refractive power, so that each lens group from the first lens group 2 to the fourth lens group 5 and the image surface The focal length of the entire system can be shifted to the longer side without changing the distance to S.

  Furthermore, if the extender lens front group and the extender lens rear group are each composed of a plurality of lenses, the aberration correction of the extender lens group 6 can be performed more satisfactorily.

It is desirable that the refractive power of the extender lens group 6 satisfies the following conditional expression.
Where f _E is the focal length of the extender lens group, and f _w is the focal length of the entire system at the wide angle end.

By keeping the refractive power of the extender lens group 6 within the range of the conditional expression, it becomes more suitable for the built-in extender lens having about twice the focal length.
In the zoom lens 1 of this embodiment, various methods can be considered for focusing to a finite distance. The simplest configuration is performed by moving the first lens group 2.

  Hereinafter, specific numerical examples of the zoom lens 1 will be shown. The maximum image height y ′ is 4.0 mm in Numerical Example 1, Numerical Example 2, Numerical Example 4, and Numerical Example 5, and 4.5 mm in Numerical Example 3.

  The material of each lens is optical glass except for the case where the resin is used for the diffractive portion of the first lens group 2 in Numerical Example 1 to Numerical Example 4. The product made by OHARA INC. Is used for this optical glass, and the glass material name is described in the numerical example.

  The aberrations of Numerical Example 1 to Numerical Example 5 are sufficiently corrected, and it is possible to deal with an image sensor with 2 million pixels or more. As in this embodiment, by configuring the zoom lens 1, it is clear from the embodiment that a very good imaging performance can be ensured while achieving a zoom ratio exceeding 25 times and a sufficiently small size. It is.

The meanings of symbols in Numerical Example 1 to Numerical Example 5 are as follows.
f: Focal length of the entire system
F: F number ω: Half angle of view
r: radius of curvature
d: Surface spacing
n _d : Refractive index ν _d : Abbe number θ _{C, A ′} : Partial dispersion ratio: (n _C −n _{A ′} ) / (n _F −n _C )
C ₂ : Second order coefficient of phase function
C ₄ : Fourth-order coefficient of phase function
K: Aspheric conical constant
A ₄ : Aspherical fourth-order coefficient
A ₆ : 6th order coefficient of aspherical expression
A ₈ : 8th order coefficient of aspherical formula

However, the diffraction surface used here is represented by the following phase function, where λ is the reference wavelength and h is the height from the optical axis. Note that the imaging beam using first-order diffracted light, the refractive power of the diffractive portion is -2 · C _2.
The aspherical surface used here is represented by the following aspherical expression, where R is the paraxial radius of curvature and H is the height from the optical axis.
The broken line in the spherical aberration diagram indicates the sine condition.
In the figure of astigmatism, the solid line indicates sagittal aberration, and the broken line indicates meridional aberration.

(Numerical example 1)
When extender lens group 6 is not provided
The third surface means surface number 3.

(Numerical example 1)
When the extender lens group 6 is provided

(Numerical example 2)
If no extender is provided

(Numerical example 2)
When an extender is provided

(Numerical example 3)
If no extender is provided

(Numerical example 3)
When an extender is provided

(Numerical example 4)
If no extender is provided
The nineteenth surface means surface number 19.

(Numerical example 4)
When an extender is provided

(Numerical example 5)
If no extender is provided

(Numerical example 5)
When an extender is provided

Next, an imaging apparatus 10 to which the zoom lens 1 is applied will be described with reference to FIG.
The imaging device 10 includes a photographing lens 11 and an imaging element 16 (for example, an area sensor). As the photographic lens 11, the zoom lens 1 described above can be used. The photographing lens 11 is focus-controlled by a focus control unit 12. That is, the focus control unit 12 performs a focusing operation.

  Further, zoom control is performed by the zoom lens control unit 13. That is, the zoom control unit 13 performs a scaling operation. The aperture member SB is controlled by the aperture controller 14 ', filters such as the plane parallel plate FP2 are inserted into and removed from the imaging optical path by the filter controller 14, and the extender lens group 6 is inserted into and removed from the imaging optical path by the extender controller 15. . The aperture controller 14 'plays a role of controlling the F number by changing the diameter of the aperture stop SB. The filter control unit 14 has a role of switching between an infrared light cut filter, a visible light cut filter, and the like, for example.

  A subject image is formed on the image plane S of the image sensor 16 by the photographing lens 11. The image sensor 16 photoelectrically converts the subject image formed on the image plane S and outputs it as an image signal to the signal processing unit 17.

The signal processing unit 17 processes the image signal and converts it into digital information. The image information digitized by the signal processing unit 17 is subjected to predetermined image processing in an image processing unit (not shown) and recorded in a semiconductor memory (not shown) or transmitted to the outside by a communication unit (not shown). .
In addition, an image being photographed may be displayed on a monitor (not shown), or an image recorded in a semiconductor memory or the like may be displayed on the monitor.

  According to the imaging apparatus 10 described above, since the zoom lens 1 of Numerical Example 1 to Numerical Example 5 can be used as the photographing lens 11, it corresponds to seamless imaging from the visible range to the near infrared range, and has 2 million pixels or more. Thus, a small and high-quality image pickup apparatus 10 using the image pickup element 16 can be realized.

  Summarizing the effects of this embodiment, the zoom ratio has a zoom ratio exceeding 25 times and a built-in extender of about 2 times, the number of components is small, the telephoto ratio at the telephoto end (ratio of the total lens length to the focal length) is small. Therefore, it is possible to provide a zoom lens 1 having a resolving power corresponding to an image sensor with 2 million pixels or more. For this reason, it is possible to realize an image pickup apparatus with high zoom ratio, sufficiently small size and light weight, and high image quality.

  Further, according to this embodiment, it is possible to provide a high-performance zoom lens 1 in which chromatic aberrations in the telephoto range are corrected more favorably. For this reason, it is possible to provide a high-quality image pickup apparatus that is less susceptible to image quality degradation and excellent in usability in a telephoto area that is particularly important for monitoring purposes.

  Further, according to this embodiment, it is possible to provide a high-performance zoom lens 1 in which chromatic aberration in the entire zooming range is corrected with a better balance. Therefore, it is possible to realize an image pickup apparatus that has higher image quality and is free from stress during use.

  Furthermore, according to this embodiment, the contribution of the third lens group 4 to aberration correction can be controlled, and the zoom lens 1 suitable for higher performance and smaller size can be provided. For this reason, it is possible to provide a small imaging device having high resolution over the entire screen.

  In addition, the zoom lens 1 can be provided which is suitable for miniaturization and high zooming by making the roles of the second lens group 3 and the third lens group 4 suitable for zooming. For this reason, it is possible to provide a small imaging device with sufficiently high zoom ratio.

  In addition, it is possible to provide the zoom lens 1 capable of higher performance while appropriately arranging the fourth lens group 5 with respect to the image plane S and ensuring sufficient back focus. For this reason, it is possible to provide a high-quality image pickup apparatus that does not have an unreasonable arrangement of a filter switching mechanism or the like.

  In addition, an appropriate configuration example of each lens group is shown, and the zoom lens 1 can be realized more. Therefore, the zoom lens 1 is highly variable, small and light, and the focus fluctuation and the image quality decrease from the visible range to the near infrared range. It is possible to more reliably realize a high-quality image pickup apparatus that suppresses the above.

 It is possible to provide a high-performance zoom lens 1 that is excellent in operability by limiting the movable lens group at the time of zooming and having no change in the overall length and is not easily lost in weight balance. Therefore, it is possible to realize an imaging apparatus that is easy to use and highly reliable.

  In addition, the extender lens group 6 having a zoom ratio exceeding 25 times and about 2 times is built in, the number of components is small, and the telephoto ratio at the telephoto end (ratio of the total lens length to the focal length) is 0.60. Therefore, it is possible to provide a small-sized and high-quality image pickup apparatus using a zoom lens having a resolving power corresponding to an image pickup device having 2 million pixels or more as a photographing optical system. For this reason, the user can perform imaging from the visible region to the near infrared region without stress.

DESCRIPTION OF SYMBOLS 1 ... Zoom lens 2 ... 1st lens group 3 ... 2nd lens group 4 ... 3rd lens group 5 ... 4th lens group 6 ... Extender lens group

Japanese Patent Laid-Open No. 10-054937 JP 2012-185272 A JP 2008-197534 JP 2008-241884

Claims (11)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a first lens group having a positive refractive power from the object side to the image plane side. 4 lens groups are provided so that they can be inserted into and removed from the image side of the fourth lens group, and all the lens groups from the first lens group to the fourth lens group can be changed without changing the distance between them and the image plane. And an extender lens group that shifts the focal length of the system to the long side. During zooming, the second lens group is positioned closest to the object side at the wide-angle end, and the third lens group is positioned closest to the image plane at the telephoto end In the zoom lens for moving the second lens group and the third lens group so as to be located at the position, the following conditional expression is satisfied:
Where m _2W is the magnification of the second group at the wide angle end, m _2T is the magnification of the second group at the telephoto end, m _3W is the magnification of the third group at the wide angle end, and m _3T is the magnification of the third group at the telephoto end. Represent. 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
However, D _{34 W} is the focal point of the entire system at the third lens group and the distance between the fourth lens group, D _34T is the distance between the third lens group and the fourth lens group at the telephoto end, f _w is a wide-angle end at the wide-angle end Represents distance. The zoom lens according to claim 1 or 2, wherein the following conditional expression is satisfied.
Where L ₄ is the distance along the optical axis from the most object side surface of the fourth lens group to the most image side surface, and T _4F-I is the distance from the most object side surface of the fourth lens group to the image surface. This is the distance along the optical axis, and when an optical element having no refractive power is included on the image plane side from the fourth lens group, it represents the air-converted length that is assumed to be absent. 4. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expression. 5.

Here, ν _1GP represents the average value of the Abbe number of the material of the positive lens included in the first lens group.   5. The zoom lens according to claim 4, wherein the first lens unit has a negative meniscus lens having a concave surface directed toward the image surface side in order from the object side, and a convex surface having a smaller radius of curvature than the image side toward the object side. A zoom lens comprising a positive lens and a positive lens having a convex surface having a smaller radius of curvature than the image side on the object side and including a diffractive optical element in the first lens group. 6. The zoom lens according to claim 5, wherein the following conditional expression is satisfied.
Here, f _TC represents the focal length of the entire system at the telephoto end with the extender lens group inserted, and f _DOE represents the focal length of the diffractive portion of the diffractive optical element.   5. The zoom lens according to claim 4, wherein the first lens unit has a negative meniscus lens having a concave surface directed toward the image surface side in order from the object side, and a convex surface having a smaller radius of curvature than the image side toward the object side. Positive lens, negative meniscus lens with concave surface facing the image surface, positive lens with convex surface having a smaller radius of curvature than the image side on the object side, absolute value of radius of curvature smaller than the image side on the object side A zoom lens comprising five positive lenses with convex surfaces. The zoom lens according to any one of claims 1 to 7, wherein the fourth lens group includes at least three positive lenses in order from the object side, and satisfies the following conditional expression: Zoom lens to be used.
However, ν _4GP represents the average value of the Abbe number of the at least three positive lenses.   9. The zoom lens according to claim 1, wherein the second lens group is composed of three or less lenses. 10.   10. The zoom lens according to claim 1, wherein the first lens unit and the fourth lens unit are fixed with respect to the image plane during zooming. 10.   An image pickup apparatus comprising the zoom lens according to claim 1 as a photographing optical system.