JP2000305018A - Zoom lens - Google Patents

Abstract

(57) [Problem] To dispose an aperture device including an ND filter immediately after a third lens group for miniaturization, and harmful ghost generated by the ND filter and the image sensor is practically harmful. At the same time,
The imbalance between the upper and lower peripheral light amounts at the time of a small aperture is also improved. SOLUTION: In order from an object side, a first lens group L1 having a fixed position and a positive refractive power, a second lens group L2 having a movable position and a negative refractive power, and a positive refraction having a fixed position. The zoom lens includes a third lens unit L3 having a power, a fourth lens unit L4 having a movable position and a positive refractive power, and an image pickup device IMG. The first to third lens units constitute a substantially afocal system. In the lens 1, a diaphragm device 2 including an ND filter is arranged between the third lens group and the fourth lens group, and the diaphragm device including the ND filter is arranged such that one end is closer to the object and the other end is closer to the image plane. As a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens structure of a zoom lens for a video camera and a still picture video camera and an arrangement of an aperture device including an ND filter, and more particularly to an arrangement of an aperture device suitable for downsizing the zoom lens. The purpose of the present invention is to provide means for solving the problem of image quality degradation caused by the side effect.

[0002]

2. Description of the Related Art A conventional zoom lens for a consumer video camera has a fixed refractive power and a positive refractive power in order from the object side, as schematically shown in FIG. A first lens group L1, a second lens group L2 having a movable position and a negative refractive power, a third lens group L3 having a fixed position and a positive refractive power, and a fourth lens group having a movable position and a positive refractive power. Generally, the lens group includes a lens group L4 and an image sensor IMG.

When the second lens unit L2 moves on the optical axis to the image plane side and zooms from the wide-angle side to the telephoto side,
As shown by the solid and broken arrows in FIG. 3, when the object point is at infinity, the fourth lens unit L4 interlocks with the second lens unit L2 to keep the image position constant as shown by the solid line. When the object point approaches, the fourth lens unit L4 serves to keep the image position constant by the interlocking positional relationship with the second lens unit different from the solid line as shown by the broken line.

There are embodiments in which the diaphragm blades of the diaphragm device are disposed immediately before, immediately after, or in the configuration of the third lens unit L3. The aperture blades have a two-piece configuration and form a substantially rhombic opening shape. One of the aperture blades has a wide variable range of light amount, and the aperture becomes small when the subject is bright, and the image quality is deteriorated due to a diffraction phenomenon. In many cases, an ND filter is adhered to alleviate the problem.

[0005] As described above, the zoom lens a has a fixed first lens unit L1 having a positive refractive power, a movable second lens unit L2 having a negative refractive power, a diaphragm device IR, and a fixed positive lens unit. Is a zoom lens composed of a third lens unit L3 having a refractive power of 4, a movable fourth lens unit L4 having a positive refractive power, and an image sensor IMG. The distance from the first lens unit L1 to the third lens unit L3 is The thickness of the second lens unit L2 and the second lens unit L
2 and the total thickness of the diaphragm device. The aperture device IR includes aperture blades b1, b2 and an ND filter N.
D.

FIG. 3 shows the arrangement of lens groups at the wide-angle end of the zoom lens a. That is, in the zoom lens a, the divergent light beam emitted from the second lens unit L2 continues to spread until it enters the third lens unit L3. If the third lens unit L3 is made substantially afocal, the fourth lens unit L
The focal length of the first lens unit L1 is the focal length at the wide-angle end.
Is determined by dividing by the angular magnification from to the third lens unit L3. When the angular magnification is reduced, the focal length of the fourth lens unit L4 is increased, and it is difficult to reduce the size.

FIG. 4 shows a zoom lens c having an optical system having the same refractive index arrangement as that of the above-mentioned zoom lens a, and having a diaphragm device arranged similarly to that used for a zoom lens of the present invention described later. It is.

In the zoom lens c, the distance from the first lens unit L1 to the third lens unit L3 can be shortened by disposing the diaphragm device IR immediately after the third lens unit L3. the first lens unit L
The angular magnification of the substantially afocal optical system from the first lens unit L3 to the third lens unit L3 can be increased, and the focal length of the fourth lens unit L4 can be reduced inevitably, which is extremely advantageous for miniaturization. Has become.

However, in the configuration of the zoom lens c, as shown in FIG. 5, the light which is imaged and reflected on the image pickup device IMG goes backward, enters the ND filter ND as a parallel light beam, and again as a parallel light beam. Since the light returns to the four-lens group L4, there is a problem that a ghost image of the light source is formed near the image sensor IMG.

In order to prevent the ghost image from being formed, there is an example in which a method of attaching an ND filter ND to the aperture blades b1 and b2 at an angle is performed. However, when the pixel pitch of the image pickup device IMG becomes finer due to higher resolution, a diffraction phenomenon caused by the influence of the aperture of the aperture blade and the ND filter ND becomes a problem. Further, when the density of the ND filter ND is set to two levels, three levels, or the like, and a means for gradually inserting the density from the low density to the high density in the opening is implemented, the number of the ND filters becomes two. In some cases, it becomes difficult to simply tilt and attach the diaphragm blades b1 and b2 to the diaphragm blades b1 and b2 as described above due to repeated use and an increase in area.

Next, a description will be given, with reference to FIG. 6, of insufficient peripheral light quantity in the state of a small aperture.

That is, the two diaphragm blades b1 and b2 are configured to be able to move in contact with each other or with a slight gap in a space formed by the base plate of the diaphragm device (not shown). I have. Since the aperture blades b1 and b2 need an appropriate thickness in order to maintain rigidity, when the aperture area is reduced, the aperture blades are divided into a beam toward the center of the screen, a beam toward the top of the screen, and a beam toward the bottom of the screen. There is a difference in the cross-sectional area of the light beam that can pass through, and this may cause an imbalance in the light amount between the upper and lower parts of the screen.

[0013]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and has been described in view of the above.
At the same time, a diaphragm device including a filter is arranged, and a strong ghost generated by the ND filter and the image sensor is prevented from becoming practically harmful. The task is to improve imbalance.

[0014]

In order from the object side, a first lens group having a fixed position and a positive refractive power, a second lens group having a movable position and a negative refractive power, and a fixed lens position having a negative refractive power. A third lens group having a positive refractive power, a fourth lens group having a movable position and a positive refractive power, and an image sensor;
In a zoom lens that forms a substantially afocal system from a lens group to a third lens group, a diaphragm device including an ND filter is disposed between the third lens group and the fourth lens group, and the diaphragm device including the ND filter is The whole is inclined so that one end is closer to the object and the other end is closer to the image plane.

Accordingly, it is possible to simultaneously realize the refractive power arrangement of the optical system suitable for miniaturization and to make the harmful ghost caused by the arrangement of the ND filter accompanying the refractive power arrangement practically no problem. At the same time, it is possible to improve the vertical imbalance of the peripheral light amount at the time of the small aperture.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, the outline of the present invention will be described.

In order from the object side, a first lens unit L1 having a fixed position and a positive refractive power, a second lens unit L2 having a movable position and a negative refractive power, and a positive lens having a fixed position and a positive refractive power. , A fourth lens group L4 having a movable position and a positive refracting power, and an image sensor IMG. The second lens group L2 moves on the optical axis to the image plane side and has a wide angle. When zooming from the side to the telephoto side, as shown by the solid and broken arrows in FIG. 1, when the object point is at infinity, the fourth lens unit L4 becomes the second lens unit L4 as shown by the solid line.
The fourth lens unit L4 acts to keep the image position constant in conjunction with the second lens unit L4 when the object point approaches, as shown by the broken line, due to the interlocking positional relationship with the second lens unit different from the solid line. The first lens unit L1 to the third lens unit L3 form a substantially afocal system in the zoom lens 1, and the third lens unit L3 and the fourth lens unit L3 serve to keep the image position constant.
A diaphragm device 2 including an ND filter ND is arranged between the lens unit L4 and the diaphragm device 2 including the ND filter ND is entirely inclined such that one end is closer to the object and the other end is closer to the image plane. It is characterized by having.

In the zoom lens 1, the inclination angle of the diaphragm device 2 is represented by θ, the inclination angle of the ND filter ND with respect to a plane perpendicular to the optical axis, Y is の of the length of the screen diagonal, and f4 is the fourth. When the focal length of the lens unit L4, (tan ^-1 0.
6Y / f4) / 2 <θ.

Further, in the zoom lens 1, the aperture opening shape of the aperture device 2 is such that two aperture blades 3a moving opposite to each other,
3b, the blade 3a forming one notch of the rhombic opening shape is closer to the image plane in the optical axis direction than the blade 3b forming the other notch opposed thereto. (On the side of the imaging element IMG).

Further, the zoom lens 1 has a first driving device (not shown) for driving the two diaphragm blades 3a and 3b and a second driving device for driving the ND filter ND. The blades 3a and 3b are characterized in that the apertures can be rapidly closed by the first driving device so that they can also function as a shutter.

Next, details of the above configuration will be described.

In the zoom lens 1, a stop device 2 including an ND filter (hereinafter simply abbreviated as "filter") ND is disposed immediately after the third lens unit L3 as a means for reducing the size of the four-group optical system. By doing so, the first lens unit L1
When the distance to the lens unit L3 is shortened and the focal length of the fourth lens unit L4 is shortened, ghost due to mutual reflection between the filter ND and the image pickup device IMG, which occurs as a side effect, is not practically harmful. The main purpose is to use the sun as a light source for generating a harmful ghost in practical use.

That is, when the first lens unit L1 to the third lens unit L3 are afocal, the image of the sun formed on the screen is reflected and goes backward, and enters the filter ND as a parallel light beam. Return to the image sensor I
Since the image is formed on the MG, an extremely bright ghost is formed.
Note that the positional relationship between the ghost and the sun is substantially point-symmetric with respect to the optical axis.

As an extremely general photographing posture under backlight conditions,
When taking a picture with the video camera held horizontally, the sun is predominantly located outside the upper screen or above the center of the screen even if it is reflected on the screen.

Therefore, when the sun image is located above the center of the screen, if the ghost position deviates outside the lower screen, it can be said that it is not harmful in practical use.

When the image of the sun is lower than the center of the screen, the above-mentioned ghost image appears in the screen and is harmful for practical use. When the area of the filter ND as the reflection surface is large, the intensity of the ghost is reduced. Becomes brighter than

The filter ND is generally fixed to the diaphragm blade 3b or an ND filter holding member separate from the diaphragm blade with an adhesive so as to cover the diaphragm opening. The area including the bonding allowance is larger. Further, the image pickup device IMG is more than the aperture blades 3a and 3b.
When the filter ND is arranged at a position close to the aperture, the area related to the ghost becomes the area including the bonding allowance.
If the ghost is disposed closer to the object side than a and 3b, the ghost only affects the range seen through the opening when viewed from the image sensor IMG, and it is possible to reduce the intensity of the ghost that is harmful in practical use.

The position of a ghost due to reflection on the filter ND when an image of the sun is formed on the optical axis at the center of the screen will be described.

That is, as shown in FIG. 1, assuming that the inclination angle of the filter ND with respect to the plane 4 orthogonal to the optical axis is θ, the light beam reflected by the image pickup device IMG and reflected on the optical axis is:
The light is reflected by the filter ND having an inclination of θ with respect to the plane 4 orthogonal to the optical axis, and enters the fourth lens unit L4 with an inclination of 2θ with the optical axis. Since the light beam enters the fourth lens unit L4 in a substantially afocal state, the image height of the ghost is substantially ft
At an2θ, an image is formed near the image sensor.

At this time, in order to avoid a ghost outside the lower screen, assuming that 1/2 of the screen diagonal length is Y, the image height on the short side of the screen is 0.6Y. f ・ t
It is a necessary condition that it becomes an2θ. Therefore, the inclination angle θ of the filter ND needs to satisfy the above conditional expression.

As shown in FIG. 6, the opening shape of the rhombus formed by the two diaphragm blades becomes extremely small when the diaphragm is stopped down to a small aperture or at the moment when the diaphragm blades are closed as a shutter at a high speed. When the light beam goes to the upper part of the screen and the light beam goes to the lower part of the screen, the cross-sectional area of the light beam that can pass through the aperture is different because the inclination angle with the optical axis is different, and the exposure amount is different between the upper and lower parts of the screen. Become like

As shown in FIG. 2, when the upper side of the aperture device 2, that is, the aperture blades 3a and 3b is tilted toward the object and the lower side is tilted toward the image plane, as shown in FIG. When the blade b1 forming the notch portion is disposed closer to the image surface side than the blade b2 forming the notch portion on the lower side, a difference in the exposure amount may occur up and down when the blade is not tilted. Also, by giving the above inclination, the imbalance of the exposure amount can be alleviated.

As described above, according to the present invention, in the four-unit zoom lens, a refractive power arrangement suitable for miniaturization can be implemented, and a harmful ghost caused by the arrangement of the ND filter accompanying the refractive power arrangement has a practical problem. In addition, it is possible to obtain the effect of reducing the difference in the amount of light between the upper and lower parts of the screen caused by the step between the two diaphragm blades by applying the ghost solution.

Further, the apparatus has a first driving device for driving the two aperture blades and a second driving device for driving the ND filter. The two aperture blades are used to open the aperture by the first driving device. By providing a structure in which the shutter can be quickly closed and can also serve as a shutter, it is not necessary to provide a shutter as a separate member, and the structure of the entire zoom lens can be simplified.

It should be noted that the specific shapes and structures of the respective parts shown in the above-described embodiment are merely examples for embodying the present invention, and the technical features of the present invention are not limited thereto. The scope should not be construed as limiting.

[0037]

The zoom lens according to the present invention comprises, in order from the object side, a first lens group having a fixed position and a positive refractive power;
A second lens group having a movable position and a negative refractive power, a third lens group having a fixed position and a positive refractive power, and a fourth lens group having a movable position and a positive refractive power and an image sensor. In a zoom lens having a substantially afocal system composed of the first lens group to the third lens group, a diaphragm device including an ND filter is disposed between the third lens group and the fourth lens group, and the ND filter is included. Since the diaphragm device is entirely tilted so that one end is closer to the object and the other end is closer to the image plane, realization of the refractive power arrangement of the optical system suitable for miniaturization and ND associated with the refractive power arrangement Harmful ghosts caused by the arrangement of the filters can be made virtually harmless at the same time, and the imbalance of the peripheral light amount at the time of small aperture can be improved.

According to the second aspect of the present invention, the inclination angle of the diaphragm device is defined as: θ is the inclination angle of the ND filter with respect to a plane perpendicular to the optical axis, and Y is 1 of the screen diagonal length.
/ 2, f4 as the focal length of the fourth lens group, (t
An ^-1 0.6Y / f4) / 2 <θ is satisfied, so that a harmful ghost image is displayed on the screen especially when a sun image is formed on the optical axis at the center of the screen. It can be avoided outside to make it virtually harmless.

Further, according to the third aspect of the present invention, the aperture opening of the aperture device is formed in a substantially rhombic shape by two diaphragm blades moving in opposition to each other, and one of the rhombic aperture shapes is formed. The blades forming the notch portion are arranged closer to the image plane in the optical axis direction than the blades forming the other notch portion facing the same, so that the upper and lower portions of the screen that occur when the aperture is stopped down to the small aperture are reduced. The imbalance of the exposure amount can be reduced.

Further, according to the invention described in claim 4, a first driving device for driving two diaphragm blades,
Since a second driving device for driving the D filter is provided, and the two diaphragm blades are configured so that the aperture of the diaphragm can be rapidly closed by the first driving device so that they can also function as a shutter, the zooming is performed. The structure of the entire lens can be simplified.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a zoom lens according to the present invention together with FIG. 2, and is a view schematically showing a refractive power arrangement and an aperture arrangement of an optical system.

FIG. 2 is a diagram for explaining the principle of reducing the difference in light amount between the top and bottom of a screen by tilting a diaphragm device.

3 shows an example of a conventional zoom lens having an optical system of a four-group configuration together with FIG. 4 and FIG. 5, and FIG. 3 schematically shows the arrangement of the refractive power of the optical system and the arrangement of the diaphragm. It is.

FIG. 4 is a diagram showing a state in which the zoom lens shown in FIG. 3 is arranged with a diaphragm suitable for further miniaturization.

FIG. 5 is a diagram for explaining a cause of a ghost caused by the configuration of FIG. 4;

FIG. 6 is a diagram for explaining a cause of a difference in light amount between the upper and lower portions of a screen.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Zoom lens, 2 ... Aperture device, 3a ... Aperture blade, 3
b: aperture blade, 4: plane orthogonal to the optical axis, L1: first lens group, L2: second lens group, L3: third lens group, L
4: Fourth lens group, IMG: Image sensor, ND: ND filter

Claims (4)

[Claims] 1. A first lens group having a fixed position and a positive refractive power, a second lens group having a movable position and a negative refractive power, and a positive position having a fixed position. And a fourth lens group having a movable refractive position and a positive refracting power, and an image sensor, and the first lens group to the third lens group constitute a substantially afocal system. An aperture device including an ND filter is disposed between the third lens group and the fourth lens group. The overall aperture device including the ND filter is arranged such that one end is closer to the object and the other end is closer to the image plane. A zoom lens characterized in that it is tilted at an angle. 2. The zoom lens according to claim 1, wherein the inclination angle of the aperture device satisfies the following condition. (Tan ⁻¹ 0.6Y / f4) / 2 <θ, where θ: the inclination angle of the ND filter with respect to a plane orthogonal to the optical axis, Y: の of the length of the screen diagonal, f4: the fourth lens group The focal length, 3. The diaphragm opening of the diaphragm device is formed in a substantially rhombic shape by two diaphragm blades moving in opposition to each other, and the blade forming one notch of the rhombic opening shape is 2. The zoom lens according to claim 1, wherein the zoom lens is arranged on the image plane side in the optical axis direction with respect to the blade forming the other cutout portion facing the zoom lens. 4. A first driving device for driving two aperture blades, and a second driving device for driving an ND filter, wherein the two aperture blades have an aperture opening by the first driving device. 2. The zoom lens according to claim 1, wherein the zoom lens is configured to be quickly closed so as to be able to double as a shutter.