JP2020204636A - Zoom lens and image capturing device having the same - Google Patents

Abstract

To provide a zoom lens which can be reduced in size even when consideration is made on focus shift correction associated with temperature variation and offers high optical performance, and to provide an image capturing device having the same.SOLUTION: A zoom lens provided herein comprises a lens group A configured to move when zooming and a lens group B configured to move when zooming, the lens group A and the lens group B being configured to move on different trajectories while zooming from the wide-angle end to the telephoto end. Either the lens group A or the lens group B is used as a focus correction group when correcting for focus shift caused by temperature variation. Either of the lens groups is selected as the focus shift correction group over an entire zoom range from the wide-angle end to the telephoto end, and the focusing group can be switched at any position in the entire zoom range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a zoom lens, and is particularly suitable as a lens used in an imaging device such as a surveillance camera, a digital camera, or a video camera.

For the photographing optical system used in an imaging device such as a surveillance camera, a digital camera, or a video camera using a solid-state image sensor, a lens having high optical performance capable of supporting high definition of the image sensor is required.

In recent years, with the rapid expansion of the surveillance market, various requests for lenses for surveillance cameras have been raised. In addition to the needs for higher specifications (higher magnification, wider angle) and smaller size, there is a demand for lenses that can maintain high optical performance even when large environmental (temperature) changes occur.

In addition, there is a great demand for weight reduction and cost reduction, and for example, a lens using a plastic lens has been proposed. For example, there are zoom lenses using plastic (Patent Documents 1 and 2).

Japanese Patent No. 5767335 Japanese Unexamined Patent Publication No. 2005-266103

Patent Document 1 has a two-group configuration of negative and positive configurations, and is a zoom lens using a plastic lens. This is intended to correct aberrations such as distortion, but there is a problem because the influence of focus shift due to temperature change of the plastic lens is not taken into consideration.

Patent Document 2 is a zoom lens having a 6-group configuration, and uses plastic lenses having positive and negative powers to cancel out-of-focus due to temperature changes. However, in order to cancel the focus of the temperature change in the entire zoom range, there is a problem that the power of the plastic lens is restricted, which makes it difficult to have the power and hinders miniaturization.

Therefore, an object of the present invention is to obtain a zoom lens having high optical performance that can realize miniaturization even when the correction of focus shift due to a temperature change is taken into consideration, and an imaging device having the same. Specifically, when performing focus correction due to a temperature change, it is necessary to secure a space for driving the focus group, which leads to an increase in the total length of the lens, which is a proposal for avoiding this. For this purpose, it is a zoom lens and an imaging device that change the focus driving method by changing the temperature according to the movement of each group due to the scaling.

In order to achieve the above object, the zoom lens according to the present invention is
It has a lens group A that moves when the magnification is changed and a lens group B that moves when the magnification is changed.
Due to the scaling from the wide-angle end to the telephoto end, the lens group A and the lens group B move in different trajectories.
When correcting the out-of-focus caused by a temperature change, either lens group A or lens group B is used as the focus correction group.
It is characterized in that one of the focus correction groups is selected in the entire zoom range from the wide-angle end to the telephoto end, and the focus correction group is changed at any point in the entire zoom range.

According to the present invention, it is possible to obtain a zoom lens having high optical performance that can realize miniaturization even when the correction of focus shift due to a temperature change is taken into consideration, and an image pickup device having the same.

Diagram of lens cross section and movement locus at the wide-angle end of the example The figure for demonstrating the conventional focus correction method The figure for demonstrating the focus correction method of Example 1. The figure for demonstrating the focus correction method of Example 2. Aberration diagram at the wide-angle end of Examples 1 and 2 at room temperature Aberration diagram at the telephoto end of Examples 1 and 2 at room temperature Aberration diagram at the wide-angle end of Example 1 at a low temperature (-15 ° C) Aberration diagram at the telephoto end of Example 1 at a low temperature (-15 ° C) Aberration diagram at the wide-angle end of Example 1 at high temperature (+ 60 ° C) Aberration diagram at the telephoto end of Example 1 at high temperature (+ 60 ° C) Aberration diagram at the wide-angle end of Example 2 at a low temperature (-15 ° C) Aberration diagram at the telephoto end of Example 2 at a low temperature (-15 ° C) Aberration diagram at the wide-angle end of Example 2 at high temperature (+ 60 ° C) Aberration diagram at the telephoto end of Example 2 at high temperature (+ 60 ° C) Example 1 Flow chart of focus correction due to temperature change Example 2 Flow chart of focus correction due to temperature change Diagrams of wide-angle end and telephoto end states of Examples 1 and 2. Numerical values and graphs showing the amount of change in the refractive index due to temperature changes in the glass materials used in Examples 1 and 2. Amount of each out-of-focus when changing from normal temperature (25 ° C) to low temperature (-15 ° C) and high temperature (+ 60 ° C) Examples of the surveillance camera of the present invention

The present invention proposes a zoom lens having high optical performance that can realize miniaturization even when the correction of out-of-focus due to a temperature change is taken into consideration, and an imaging device having the same.

The optical system of the present invention relates to focus correction of out-of-focus caused by a temperature change or the like.

A particularly large cause of out-of-focus due to temperature changes is a change in the refractive index of each lens. In particular, when a plastic lens is incorporated into an optical system, the sensitivity of a change in the refractive index due to a temperature change becomes higher than that of glass. This is a disadvantage of plastic, but its advantages are that it is lighter than glass and its cost is low, and it is often used in lens systems to take advantage of its advantages.

Focus correction is generally performed after the temperature change for the focus shift due to the temperature change, but it is necessary to secure the focus drive amount for the focus shift due to the temperature change. For this reason, there is a big problem that the size of the entire lens becomes large.

The present invention presents means for solving this problem. In particular, we present a method to solve such problems that tend to occur when using a plastic lens.

Hereinafter, the zoom lens and the image pickup apparatus according to the present invention will be described with reference to the drawings.

In the lens cross-sectional view of each embodiment, SP is an aperture diaphragm and is located on the object side of the second lens group L2.

In the cross-sectional view of the lens, the left direction is the object side and the right direction is the image plane side.

F is the focus, and the arrow is the direction of the focus.

G is an optical block corresponding to an optical filter, a face plate, or the like. The IP is an image plane, and when used as a photographing optical system, corresponds to an imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor.

In the aberration diagram, d and g represent the d-line and g-line, and ΔM and ΔS represent the meridional image plane and the sagittal image plane. For astigmatism, ΔM and ΔS on the d line are displayed, for distortion, the d line is displayed, and for chromatic aberration of magnification, the aberration of the g line with respect to the d line is displayed.

First, the problems leading to the present invention will be described.

FIG. 2 shows a conventional focusing method for a zoom lens having a negative / positive configuration, and schematically shows the position and focus shift of each group at the wide-angle end and the telephoto end.

Reference numeral 18 indicates a light ray in a focused state at room temperature, and 16 is a focus position on which a sensor such as a CCD or CMOS is placed. For example, when a temperature change to the low temperature side occurs at the wide-angle end, the focus position moves to the object side like a light ray 19.

In the negative / positive two-group type, the magnification is varied in the second lens group 12, and the image plane correction (compensator) and the focus are performed in the first lens group 11. Therefore, even in the correction of the focus shift due to the temperature change, the first lens group 11 has been driven in the direction of F shown in the figure according to the focus shift direction regardless of the zoom position.

Therefore, when the temperature is high at the wide-angle end, the focus is corrected toward the object side, so it is necessary to take a focus margin for the temperature change. Since the first lens group is configured to be located closest to the image side at the wide-angle end, the total length of the lens barrel becomes large as the focus margin, which hinders miniaturization.

Further, at the telephoto end at low temperature, it is necessary to move the focus lens group 11 to the image side. As a result, it is necessary to secure the lens spacing 14 as the focus margin amount for the temperature change. In the negative / positive zoom lens type, the distance between the first lens group and the second lens group is the smallest at the telephoto end, so it is necessary to increase the lens group distance 14 and this causes an increase in the total length of the lens. ..

Furthermore, although glass is generally used in zoom lenses, plastic is often used because of its advantages such as cost, moldability, and light weight. The problem at this time is that the change in the refractive index due to the temperature change is large.

For example, FIG. 13 shows the change in the refractive index due to the temperature change of the glass type used in Example 1. E48R (manufactured by Nippon Zeon Corporation) is a plastic material, and the others are glass materials (manufactured by HOYA Corporation or OHARA Co., Ltd.). The amount of change in the refractive index is shown with reference to normal temperature (25 ° C.).

Generally, the absolute amount of the change in the refractive index due to the change in temperature of plastic is at least 10 to 20 times or more, and as a characteristic, the higher the temperature, the lower the refractive index tends to be.

Therefore, when the convex lens is made of plastic, the power of the lens is weakened at high temperature, so that the focal length becomes large and the focal position tends to move away from the lens (over). At low temperatures, on the contrary, the power of the lens increases, so it tends to be under.

The present invention proposes means for solving such a problem.

In the present invention, at least two lens groups are moved at the time of magnification change, and a lens group that also serves as a focus group is included in the moving lens group. As a result, the lens group moves at the magnification change, so that the lens spacing from the wide-angle end to the telephoto end changes. Therefore, at least one of the zoom positions has a position with a margin as the lens spacing. An object of the present invention is to make effective use of this margin interval and change the focus group according to the zoom position and the focus correction direction.

The first embodiment will be described in detail.

As shown in FIG. 12, the lens configuration is a negative / positive two-group zoom configuration, and the second lens group is monotonically moved from the image side to the object side for variable magnification, and the focus position is immovable in image plane correction. The first lens group plays a role as a compensator so as to be. The distance between the first lens group and the second lens group is the largest at the wide-angle end and the smallest at the telephoto end.

The first lens group is composed of a negative lens G11, a negative lens G12, and a positive lens G13, and the second lens group is composed of a positive lens G21, a positive lens G22, a negative lens G23, a positive lens G24, and a negative lens G25. Has been done. The positive lens G24 and the negative lens G25 are joined. G21 has an aspherical surface and is adopted on the most object side of the second lens group in which the Fno luminous flux is high, and spherical aberration and the like are satisfactorily corrected.

FIG. 3 schematically shows a state of focus shift when the initial normal temperature state is changed to a low temperature state, or a state of focus movement when the high temperature state is reached. The focus is changed according to the zoom position and temperature change (high temperature or low temperature).

In the embodiment, a plastic having a large change in the refractive index with temperature is used only for the convex lens of G21. Therefore, at high temperatures, the refractive index of the plastic decreases and this effect is large for the entire lens system, so the focal position moves in the over direction. On the contrary, when the temperature is low, it moves to the under side.

Assuming that the focal length of only the plastic lens is fA and the focal length of the entire lens group having the plastic lens is fB, the following relationship is desirable.

0.2 << | fB / fA | <1.0 ... (A)
Further, when plastic is used for the concave lens instead of the convex as in the embodiment, the focus movement direction in FIG. 2 is opposite between the high temperature and the low temperature. Even in this case, the gist of the focus correction method of the present invention does not change.

Regarding the specific correction of the focus correction group, the first lens group 11 focuses on the image side by utilizing the fact that the lens group spacing 13 becomes large at the wide-angle end at a low temperature. The first lens group is selected because the second lens group is located on the image side at the wide-angle end and therefore has the minimum required back focus amount. Further, at the telephoto end at low temperature, the second lens group 12 is used as the focus group. Since the second lens group 12 moves from the image side to the object side in order to change the magnification to the telephoto end, the amount of back focus increases toward the telephoto end, and this interval is used.

At high temperatures, the focus is corrected in the opposite direction of low temperatures, so the focus group is changed from that at low temperatures. That is, since the focus group at high temperature has a margin of lens group spacing 13, the focus correction group is used to move the second lens group toward the object side, and the first lens group is the focus group because there is a margin on the object side at the telephoto end. And.

The low temperature described in this case is represented by -15 ° C (down from 25 ° C to 40 ° C at room temperature), and the high temperature is represented by 60 ° C (rise from 25 ° C to 35 ° C at room temperature).

FIG. 14 shows the calculated amount of out-of-focus.

The amount of change due to the plastic lens of G21 and the amount of change only with other glass are shown. It is in a state of being in focus at room temperature (the amount of deviation is 0). From this, it can be seen that the influence of the plastic lens is increasing. The amount of change in the refractive index is shown in FIG. The specific refractive index is shown in the numerical examples.

The focus shift due to temperature changes is largely affected by changes in the refractive index, but the expansion rate of glass, plastic, and lens barrel members also has a considerable effect. The present invention proposes a focus correction method caused by a temperature change, and does not limit the factor of focus shift to a change in refractive index.

FIG. 10 shows the focus flow of the first embodiment.

As described above, in order to avoid an increase in the size of the lens, the drive group for focus correction due to defocus at the wide-angle end and the telephoto end is changed according to the temperature change and the zoom position. It is preferable to select a focusing method not only at the wide-angle end and the telephoto end, which easily affect the total length of the lens, but also near the zoom range according to the gist of the present invention.

The flow has a means for detecting a temperature change in the main body of the image pickup apparatus, calculates the amount of the temperature change by the measurement thereof, and selects the focus correction means previously stored in the image pickup apparatus according to the calculation.

Since the focus correction amount differs depending on the temperature change amount, a means such as storing the temperature and the correction amount in the image pickup apparatus in advance may be selected.

In the intermediate zoom position where the securing of the focus margin is not affected, the correction is performed only by the first lens group in the first embodiment. The zoom position for changing the focus correction group may be appropriately selected.

Next, Example 2 will be described.

The lens type is the same negative / positive two-group zoom lens as in the first embodiment.

The same applies to lens data at room temperature.

A different method for correcting the out-of-focus is presented, and this will be described in detail.

FIG. 4 shows focus correction of focus movement due to temperature change at the wide-angle end and the telephoto end at low temperature.

At the wide-angle end at low temperature, focus correction is performed using two first lens groups and two second lens groups. The drive ratio is changed between the wide-angle end and the telephoto end. In the embodiment, the focus amount is determined by a drive ratio of about 4.5: 1 at the wide-angle end and about 1:10 at the telephoto end.

The purpose of using the two drive groups is to reduce the amount of drive in one lens group and share the drive amount between the two lens groups for rapid focus correction. Further, there is also an object of suppressing the amount of change in the focal length of the entire lens system that occurs when one lens group is focused.

In the focus correction method at high temperature, as shown in FIG. 4, at the wide-angle end, the drive ratio for focus correction of the first lens group and the second lens group is as high as 6: 1. At the telephoto end, only the first lens group is driven, and the drive ratio is 1: 0. The amount of focus margin obtained from the zoom locus may be taken into consideration, and it may be appropriately determined whether the two lens groups are moved or executed with only one lens group.

It is an image pickup apparatus having a solid-state image pickup element that receives an image formed by the zoom lens of the present invention.

This relates to an image pickup apparatus having an element that receives an image taken by a zoom lens. In recent years, CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) sensors have been mainly used for digitally processing images, and the present invention also includes an image pickup device having a solid-state image sensor equivalent thereto. To do.

Further, the image pickup apparatus may have a configuration in which a dome cover is attached when used as a surveillance camera, for example, and the method of the present proposal may be adopted for correction of out-of-focus caused by the dome cover.

Next, the lens configuration of the embodiment will be described.

Hereinafter, unless otherwise specified, the lens configurations will be described in the order in which they are arranged in order from the object side to the image side.

The zoom lens of each embodiment is a photographing lens system used in an imaging device such as a surveillance camera, a digital camera, and a video camera. In the cross-sectional view of the lens, the left side is the subject side (object side) and the right side is the image side.

The wide-angle end and the telephoto end are the zoom positions when the variable magnification lens group is located at both ends of the movable range on the optical axis of the mechanism. The movement of each lens group from the wide-angle end to the telephoto end follows a locus like the arrow (solid line) shown in the lens cross-sectional view.
When focusing, it is moved as shown by arrow F.

Next, an example of an imaging device (surveillance camera) using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.

In FIG. 15, 31 is a surveillance camera body, and 32 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built in the camera body and receives a subject image formed by the lens unit 35. Reference numeral 33 denotes a memory unit that records information corresponding to the subject image photoelectrically converted by the solid-state image sensor 12. Reference numeral 34 denotes a network cable for transferring the subject image photoelectrically converted by the solid-state image sensor 12.

The image pickup device is not limited to a surveillance camera, but can also be used in a video camera, a digital camera, or the like.

As described above, according to each embodiment, it is possible to obtain a zoom lens having high optical performance that can realize miniaturization even when the correction of focus shift due to a temperature change is taken into consideration, and an imaging device having the same.

In each embodiment, the following means configuration may be adopted.
-The shape and number of glasses shown in the examples are not limited, and should be changed as appropriate.
-Apply to zoom lenses with more than 2 lens groups.
-Change the lens drive ratio for focusing and the lens group to drive as appropriate.
-It is not limited to when using a plastic lens, but it also supports correction of out-of-focus when a zoom lens is constructed using only glass material.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, the number of movable lens groups, and the like, and various modifications can be made within the scope of the gist thereof.

Next, numerical examples corresponding to each embodiment are shown. In each numerical example, the surface numbers are shown in order from the object side, r is the radius of curvature, d is the interval, and nd and vd are the refractive index and Abbe number with respect to the d line, respectively. * Means an aspherical surface. Further, in each numerical example, the two surfaces on the image side are planes corresponding to the optical block G.

For the aspherical shape, when the displacement in the optical axis direction at the height h from the optical axis is x with respect to the surface apex, x = (h ² / r) / [1 + {1- (1 + K) ( h / r) ² } ^1/2 ]
＋ A4 ・ h ⁴ ＋ A6 ・ h ⁶ ＋ A8 ・ h ⁸ ＋ A10 ・ h ¹⁰ ＋ A12 ・ h ¹²
It is represented by.

However, r is the radius of curvature of the paraxial axis. K is a conical constant, and A4, A6, A8, A10, and A12 are 4th, 6th, 8th, 10th, and 12th aspherical coefficients, respectively. Further, for example, the display of "e-Z" means "10- ^Z ". Regarding the angle of view, it is a numerical value of a half angle of view (ω) regarding a shootable angle of view in consideration of the amount of distortion.

Further, in the numerical example, the position sensitivity es (ratio of the movement amount of the focus to the movement amount of the focus group) is shown. When the focus movement amount is Δ and the sensitivity of the lens group is es, the lens group drive amount for focus correction is estimated by Δ / es.

The lateral magnification and position sensitivity of the focus lens group are related as follows.
es = (1-βf ² ) × βr ²
However, es: focus sensitivity βf: lateral magnification of the focus lens group βr: composite magnification of all lens groups arranged on the image side of the focus lens group. When there is no lens group after the second lens group L2 as in the embodiment, the lateral magnification βr is 1.

L1 1st lens group, L2 2nd lens group,
d d line (587.56 nm), gg line (435.84 nm),
ΔM meridional image plane, ΔS sagittal image plane, SP aperture, IP image plane,
Face plates such as G CCD and glass blocks such as low-pass filters,
ω Half angle of view, Fno F number, F focus

Claims (8)

It has a lens group A that moves when the magnification is changed and a lens group B that moves when the magnification is changed.
Due to the scaling from the wide-angle end to the telephoto end, the lens group A and the lens group B move in different trajectories.
When correcting the out-of-focus caused by a temperature change, either lens group A or lens group B is used as the focus correction group.
A zoom lens characterized in that one of the focus correction groups is selected in the entire zoom range from the wide-angle end to the telephoto end, and the focus correction group is changed at any position in the entire zoom range. The zoom lens according to claim 1, wherein in the focus correction, different lens groups are selected when the temperature changes and when the temperature changes. It has a lens group A that moves when the magnification is changed and a lens group B that moves when the magnification is changed.
Due to the scaling from the wide-angle end to the telephoto end, the lens group A and the lens group B move in different trajectories.
When correcting the out-of-focus caused by a temperature change, two lens groups A and B are used as the focus correction group.
A zoom lens characterized in that the focus drive ratio of lens group A and lens group B is changed according to the zoom position from the wide-angle end to the telephoto end. The zoom lens according to claim 3, wherein in the focus correction group, different focus drive ratios are used when the temperature changes at a high temperature and when the temperature changes at a low temperature. It has a temperature sensor inside the camera body
The amount of change to the high temperature side or the low temperature side is calculated by the measurement of the temperature sensor.
The zoom lens according to any one of claims 1 to 4, wherein the driving method and the driving amount of the focus correction group are determined accordingly. The zoom lens according to any one of claims 1 to 5, wherein the entire lens system has at least one or more plastic lenses. The method according to any one of claims 1 to 6, wherein the lens group A that moves at the time of magnification change and the lens group B that moves at the time of change of magnification have different powers as the lens groups. Described zoom lens. An image pickup apparatus according to any one of claims 1 to 7, further comprising a zoom lens and a solid-state image pickup device that receives an image formed by the zoom lens.