JP3994293B2 - Zoom lens and video camera having the same - Google Patents

Description

【００２０】
上記Ｒ１３、Ｒ１８の非球面の形状は光軸方向をｚ軸、これと垂直方向をｙ軸とし、光軸上での曲率半径をｒとしたときに次の式にて非球面形状を定義した。
ｚ＝ｙ² ／｛ｒ＋（ｒ² −ｙ²)^1/2 ｝＋Ａｙ⁴ ＋Ｂｙ⁶ ＋Ｃｙ⁸ ＋Ｄｙ¹⁰
【００２１】
【外２】

【００２２】
本実施例におけるｆ_T ／ｆ_13T の値は０．４１であった。
【００２３】
図３〜図６は、本発明の第１実施例の諸収差図を示す。
図３は、赤外線光カットフィルター装着時の広角端における諸収差図である。
図４は、赤外線光カットフィルター離脱時の広角端における諸収差図である。
図５は、赤外線光カットフィルター装着時の望遠端における諸収差図である。
図６は、赤外線光カットフィルター離脱時の望遠端における諸収差図である。
各収差図において、球面収差図中の実線はｄ線についての球面収差、破線はｇ線についての球面収差である。非点収差図中の実線はサジタル像面、破線はメリディオナル像面を示す。
各収差図から、本実施例は諸収差が良好に補正され、優れた結像性能を有していることは明らかである。また、赤外線光カットフィルターの着脱前後での収差の変動は小さい。
【００２４】
【発明の効果】
以上の説明から明らかなように、本発明によれば、ビデオカメラにおいて、赤外線光カットフィルターを着脱することで赤外線光撮影と可視光撮影が可能となるが、赤外線光カットフィルターをズームレンズ系の中に配置することで、収差変動の少ないレンズを安価に提供できる。また、可視光下における撮影及び赤外線光下における撮影の双方が可能で、比較的安価なビデオカメラを提供できる。
【図面の簡単な説明】
【図１】本発明の１実施例に係るビデオカメラ用ズームレンズの基本的な光学配置を示す断面図である。
【図２】本発明の１実施例に係るビデオカメラの赤外線光カットフィルターの移動機構の一例を示す正面断面図である。
【図３】赤外線光カットフィルター装着時の広角端における諸収差図である。
【図４】赤外線光カットフィルター離脱時の広角端における諸収差図である。
【図５】赤外線光カットフィルター装着時の望遠端における諸収差図である。
【図６】赤外線光カットフィルター離脱時の望遠端における諸収差図である。
【符号の説明】
１１…絞り、１３、１３′…赤外線光カットフィルター、
１５…フィルター駆動モータ、１７…ＣＣＤ、２１…ビデオカメラ、
２３…切替つまみ、２５…本体、２６…エンドストッパー、
２７…ガイドレール、２９…フィルターケース、３１…ガイドレール、
３３…フィルター、３５…フィルターホルダー、３６…エンドストッパー、
３７…レバー、３９…回転軸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zoom lens suitable for a video camera. In particular, the present invention relates to a zoom lens that can perform both photographing under visible light and infrared light, is relatively inexpensive, and has little aberration fluctuation. The present invention also relates to a video camera provided with such a zoom lens.
[0002]
[Prior art]
The prior art will be described by taking a video camera as an example.
An imaging device (CCD) used for a video camera originally has sensitivity in an infrared region (strictly, near infrared region) having a wavelength of 700 nm or more. However, this infrared sensitivity deteriorates the color reproduction and degrades the S / N of the video signal. For this reason, conventionally, an optical system of a video camera for home use and the like is provided with an optical filter that always cuts off the infrared region, that is, an infrared region cut filter.
[0003]
By providing the infrared cut filter in the video camera as described above, an image with a good image quality with a high S / N can be obtained during normal imaging with a certain level of illuminance. However, the subject can no longer be imaged under infrared light such as when low illuminance or an infrared light source is used.
[0004]
In view of this, there has been proposed a video camera that enables photographing under visible light and infrared light by inserting and removing an infrared light cut filter with respect to the optical path. That is, an infrared light cut filter is mounted in the optical path when photographing under visible light, and the filter is detached from the optical path when photographing under infrared light. As such proposals, there are JP-A-2-71677, JP-A-7-107355, and JP-A-336587.
As a position for placing such a detachable infrared light cut filter, in JP-A-2-71677 and JP-A-7-107355, the same filter is arranged between the zoom lens and the CCD. On the other hand, in Japanese Patent Application Laid-Open No. 7-336587, the zoom lens is disposed on the object side.
[0005]
[Problems to be solved by the invention]
The above prior art has the following problems.
(1) When an infrared light cut filter is disposed between the zoom lens and the CCD, the variation in aberration generally increases before and after the filter is attached / detached. Therefore, when the filter is removed, it is necessary to consider that the dummy glass is placed in the optical path to reduce aberration fluctuation.
(2) When an infrared light cut filter is disposed on the object side of the zoom lens, the outer diameter of the filter increases and the cost increases. In addition, the filter attaching / detaching mechanism is also increased in size and easily disturbs, which causes a cost increase.
[0006]
The present invention has been made in view of such problems, and is a zoom lens suitable for a video camera, which can perform both photographing under visible light and infrared light, and is relatively inexpensive. An object of the present invention is to provide a zoom lens with little aberration fluctuation. Moreover, it aims at providing the video camera provided with such a zoom lens.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the zoom lens of the present invention includes, in order from the object side, a first lens group I having a positive refractive power, a second lens group II having a negative refractive power, and a first lens group having a positive refractive power. The third lens group III includes a fourth lens group IV having a positive refractive power, and a position in the optical path or a position outside the optical path is selectively interposed between the third lens group III and the fourth lens group IV. An infrared light cut filter that can be taken is arranged.
[0008]
The video camera of the present invention is a video camera comprising a two-dimensional photoelectric conversion element and an optical system including a zoom lens that forms an image of a subject on the element.
The zoom lens includes, in order from the object side, a first lens group I having a positive refractive power, a second lens group II having a negative refractive power, a third lens group III having a positive refractive power, and a positive refractive power. a fourth lens group IV having,
An infrared light cut filter capable of selectively taking a position in the optical path or a position outside the optical path is disposed between the third lens group III and the fourth lens group IV. .
[0009]
That is, when photographing under visible light, an infrared light cut filter is positioned between the third lens group III and the fourth lens group IV in the optical path so that the infrared light does not reach the CCD, and color reproduction is performed. Prevent deterioration. On the other hand, when photographing under infrared light, the infrared light cut filter is positioned outside the optical path, and the infrared light reaches the CCD to enable so-called night vision photography.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is preferable that the infrared light cut filter is disposed at or near the most afocal position in the lens system. Since the change in the optical path length before and after the filter is attached and detached can be made as small as possible, fluctuations in aberration can be suppressed. From the viewpoint of reducing the filter diameter, it is preferable to dispose the filter as close to the CCD as possible, for example, on the object side of the most image side lens.
[0011]
Furthermore, in the zoom lens according to the present invention, the combined focal length f _{T of the} entire zoom lens at the telephoto end and the combined focal length f _13T from the first lens group to the third lens group at the telephoto end are: 0 It is preferable to satisfy the relationship of 2 <f _T / f _13T <0.6. Within this range, it is possible to suppress the aberration fluctuation accompanying the attachment / detachment of the infrared light cut filter.
[0012]
As the attachment / detachment mechanism of the infrared light cut filter, a swing mechanism using a stepping motor and a rotating arm, or a parallel movement mechanism using a linear motor, a ball screw, or a rack and pinion can be adopted. Manual switching is also possible.
[0013]
Hereinafter, it demonstrates, referring drawings.
FIG. 1 is a sectional view showing a basic optical arrangement of a zoom lens for a video camera according to one embodiment of the present invention.
The zoom lens of this embodiment includes, in order from the object side, a first lens group I having a positive refractive power, a second lens group II having a negative refractive power, a third lens group III having a positive refractive power, A fourth lens group IV having a refractive power of 5. The infrared light cut filter 13 is disposed between the third lens group and the fourth lens group.
[0014]
The first lens group I has three lenses having negative and positive refractive powers arranged in order from the object side. Among these lenses, the first and third lenses have a meniscus shape with the convex surface facing the object side. The second lens is cemented with the first lens. The second lens group II has three lenses having negative and positive refractive powers arranged in order from the object side. Of these, the first lens has a meniscus shape with the convex surface facing the object side. The second lens and the third lens are cemented. The second lens group moves in the optical axis direction at the time of zooming and mainly controls zooming. The third lens group III is composed of a positive single lens that is always fixed and has one or more aspheric surfaces. The fourth lens group IV is composed of two lenses having negative and positive refractive powers. The first lens has a meniscus shape with the convex surface facing the object side. The first lens and the second lens are cemented. The fourth lens group moves in the optical axis direction at the time of zooming and mainly plays a role of a compensator and focusing.
[0015]
The diaphragm 11 is fixedly provided in front of the third lens group.
The infrared light cut filter 13 is a thin disk made of boiling phosphate glass, phosphate glass, or the like. The filter 13 shields infrared light having a wavelength of about 700 nm or more and allows visible light to pass therethrough. In this embodiment, the filter 13 is incorporated in a slide mechanism (not shown) made of a rack and pinion or the like, and a position in the optical path (position indicated by a solid line, reference numeral 13) by the filter drive motor 15. And a position outside the optical path (a position indicated by a broken line, reference numeral 13 '). As described above, in the case of visible light photographing, the filter 13 is in a position in the optical path and shields infrared light so that the infrared light does not reach the CCD 17. On the other hand, in the case of infrared light photography, the filter 13 'moves to a position not on the optical path, and the infrared light reaches the CCD 17 to obtain an infrared light image.
[0016]
FIG. 2 is a front sectional view showing an example of the moving mechanism of the infrared light cut filter of the zoom lens unit in the video camera according to the embodiment of the present invention.
The periphery of the filter 33 is held by a holder 35 made of plastic or light alloy. A substantially L-shaped lever 37 is fixed to the upper end portion of the holder 35. A switching knob 23 is formed at the upper end of the lever 37. A rotating shaft 39 is provided below the knob 23 of the lever 37, and the lever 37, the holder 35, and the filter 33 rotate around the coaxial 39. A position indicated by a solid line in the drawing is a position in the optical path, and a position indicated by a broken line is a position outside the optical path.
[0017]
A part of the main body 25 of the zoom lens unit in the video camera 21 is a filter case 29 that covers the rotating filter 33 and the like. The case 29 slightly protrudes from the side surface of the main body 25. Guide rails 27 and 31 for guiding the rotation of the filter holder 35 are provided in the filter case 29. The rails 27 and 31 are arc-shaped wire-shaped members centering on the rotation shaft 39 and are fitted to a part of the filter holder 35. The rails 27 and 31 serve to maintain the posture of the filter 33. Note that the end of rotation of the filter holder 35 is determined by a part of the holder 35 (a portion protruding in a wing shape) coming into contact with the end stoppers 26 and 36 formed in the filter case 29.
[0018]
【Example】
Next, numerical examples of the present embodiment are shown below.
In the numerical examples, the meaning of each symbol is as follows.
f: Focal length (mm)
F _no : F number 2ω: angle of view Ri: radius of curvature of the i-th surface (mm)
Di: i-th surface interval (mm)
Ni: refractive index of d-line of i-th lens νi: Abbe number of i-th lens
[Outside 1]

[0020]
The aspherical shape of R13 and R18 is defined by the following expression when the optical axis direction is the z axis, the perpendicular direction is the y axis, and the radius of curvature on the optical axis is r. .
z = y ² / {r + (r ² −y ² ) ^1/2 } + Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰
[0021]
[Outside 2]

[0022]
The value of f _T / f _13T in this example was 0.41.
[0023]
3 to 6 are graphs showing various aberrations of the first embodiment of the present invention.
FIG. 3 is a diagram showing various aberrations at the wide-angle end when the infrared light cut filter is attached.
FIG. 4 is a diagram showing various aberrations at the wide-angle end when the infrared light cut filter is detached.
FIG. 5 is a diagram of various aberrations at the telephoto end when the infrared light cut filter is mounted.
FIG. 6 is a diagram of various aberrations at the telephoto end when the infrared light cut filter is detached.
In each aberration diagram, the solid line in the spherical aberration diagram represents the spherical aberration for the d line, and the broken line represents the spherical aberration for the g line. The solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane.
From each aberration diagram, it is clear that the present example has excellent image forming performance with various aberrations corrected well. In addition, the variation in aberration before and after the infrared light cut filter is attached / detached is small.
[0024]
【The invention's effect】
As is apparent from the above description, according to the present invention, it is possible to shoot infrared light and visible light by attaching / detaching the infrared light cut filter in the video camera. By disposing the lens in the lens, a lens with little aberration fluctuation can be provided at low cost. In addition, it is possible to provide a relatively inexpensive video camera that can perform both photographing under visible light and infrared light.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a basic optical arrangement of a zoom lens for a video camera according to an embodiment of the present invention.
FIG. 2 is a front sectional view showing an example of a moving mechanism of an infrared light cut filter of a video camera according to an embodiment of the present invention.
FIG. 3 is a diagram showing various aberrations at the wide-angle end when an infrared light cut filter is attached.
FIG. 4 is a diagram of various aberrations at the wide-angle end when the infrared light cut filter is detached.
FIG. 5 is a diagram of various aberrations at the telephoto end when an infrared light cut filter is attached.
FIG. 6 is a diagram of various aberrations at the telephoto end when the infrared light cut filter is detached.
[Explanation of symbols]
11 ... Aperture, 13, 13 '... Infrared light cut filter,
15 ... filter drive motor, 17 ... CCD, 21 ... video camera,
23 ... Switch knob, 25 ... Main body, 26 ... End stopper,
27 ... guide rail, 29 ... filter case, 31 ... guide rail,
33 ... Filter, 35 ... Filter holder, 36 ... End stopper,
37 ... Lever, 39 ... Rotating shaft

Claims (4)

In order from the object side, a first lens group I having a positive refractive power, a second lens group II having a negative refractive power, a third lens group III having a positive refractive power, and a fourth lens having a positive refractive power With group IV,
Between the third lens group III and the fourth lens group IV, characterized in that the position or the infrared light cut filter which can take outside of the optical path of the position selectively in the optical path is located Zoom lens. The first lens group I has three lenses having negative and positive refractive power arranged in order from the object side,
The second lens group II has three lenses having negative and positive refractive power arranged in order from the object side,
The second lens group moves in the optical axis direction at the time of zooming and mainly controls zooming.
The third lens group III has a positive lens that is always fixed, having one or more aspheric surfaces,
The fourth lens group IV has two lenses having negative and positive refractive powers arranged in order from the object side,
2. The zoom lens according to claim 1, wherein the fourth lens group moves in the optical axis direction at the time of zooming and mainly serves as a compensator and a focus. The combined focal length f _{T of the} entire zoom lens at the telephoto end and the combined focal length f _13T from the first lens group to the third lens group at the telephoto end are:
0.2 <f _T / f _13T <0.6
The zoom lens according to claim 1 , wherein the zoom lens satisfies the following relationship. A video camera comprising a two-dimensional photoelectric conversion element and an optical system including a zoom lens that forms an image of a subject on the element.
The zoom lens includes, in order from the object side, a first lens group I having a positive refractive power, a second lens group II having a negative refractive power, a third lens group III having a positive refractive power, and a positive refractive power. a fourth lens group IV having,
An infrared light cut filter capable of selectively taking a position in the optical path or a position outside the optical path is disposed between the third lens group III and the fourth lens group IV. Video camera.

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