Variable focal length lens assembly

Abstract

A variable focal length lens arrangement (310A) comprises: a first variable focal length lens (11); a second variable focal length lens (21) arranged behind the first variable focal length lens (11); a third variable focal length lens (31) arranged behind the second variable focal length lens (21); a fixed focal length lens (41) arranged behind the third variable focal length lens (31); a first conjugate point (1) arranged in front of the first variable focal length lens (11) at a first focal length (f1); a second conjugate point (2) arranged behind the fixed focal length lens (41) at a fourth focal length (f4);and a third conjugate point (3) which is located behind the second variable focal length lens (21) at a second focal length (f2) and in front of the third variable focal length lens (31) at a third focal length (f3), wherein a first optical subsystem (111) is an infinitely conjugate system with respect to the first conjugate point (1), and wherein a second optical subsystem (121) is an infinitely conjugate system with respect to the third conjugate point (3).

Description

FIELD OF TECHNOLOGY

[0001] The present disclosure relates to a variable focal length lens device. STATE OF THE ART

[0002] Optical technology is currently used in various devices such as processing equipment, observation equipment, distance measuring equipment, and lighting equipment. Such devices require the ability to freely adjust the magnification and focal point position of an optical system.

[0003] To change the magnification and focal position of an optical system, it is usually necessary to change the alignment of the optical axis, the arrangement of optical components such as lenses or an image sensor included in the optical system, and the like. A device configuration based on the assumption that optical components move has many problems related to design complexity, device size, manufacturing cost, reliability, and the like. These problems are particularly noticeable in a magnification adjustment mechanism, where it is difficult to accomplish magnification adjustment by simply extending an entire lens group or part of a lens group.The adjustment of the magnification and focal position of an observation device such as a camera or a microscope is still done by a mechanical drive mechanism, which, however, in addition to the problems mentioned above, also has a problem with fast response.

[0004] On the other hand, there are variable focal length lenses that have a variable focal length without a mechanical drive mechanism. For this type of variable focal length lens, for example, liquid lenses using electrowetting technology have been used. These liquid lenses are used as variable focal length lenses. Typically, liquid lenses function as plano-convex lenses or plano-concave lenses. Therefore, it is desirable for the liquid lenses to form an infinitely conjugated system to reduce aberrations.

[0005] Patent Literature 1 describes a shape measuring device using the variable focal length lenses described above. REFERENCE LISTPATENT LITERATURE

[0006] Patent Literature 1: JP 2016-053491 A SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0007] The shape measuring device described in Patent Literature 1 includes three variable focal length lenses. Among them, a variable focal length lens is arranged on the object side to change the focal position. In addition, two variable focal length lenses are arranged on the image side to change the magnification. The principle of variable magnification is that the ratio between the compound focal length of the two image-side variable focal length lenses with a finite size and the focal length of the object-side variable focal length lens is adjusted according to a compound lens formula to achieve a desired magnification. The use of the two variable focal length lenses ensures two degrees of freedom required for adjusting the focal length and adjusting the position of the principal surface.On the other hand, in the disclosure, the two variable focal length lenses on the magnification adjustment side form an infinitely conjugated system as a group. Accordingly, the lens closest to an image is a finite conjugated system when viewed individually. Accordingly, aberrations easily occur.

[0008] The present disclosure has been made to solve the above-mentioned problems, and an object thereof is to provide a variable focal length lens device having a magnification and a focal position that can be changed as needed, which is suitable for variable focal length lenses. SOLUTION TO THE PROBLEM

[0009] A variable focal length lens device according to the present disclosure comprises: a first variable focal length lens having a first focal length; a second variable focal length lens disposed behind the first variable focal length lens and having a second focal length; a third variable focal length lens disposed behind the second variable focal length lens and having a third focal length; a fixed focal length lens disposed behind the third variable focal length lens and having a fourth focal length; a first conjugate point disposed in front of the first variable focal length lens at a distance equal to the first focal length and serving as a focus position; a second conjugate point disposed behind the fixed focal length lens at a distance equal to the fourth focal length and equipped with an image sensor or a light guide means;a third conjugate point located at a distance equal to the second focal length behind the second variable focal length lens and at a distance equal to the third focal length in front of the third variable focal length lens, a first optical subsystem including the first variable focal length lens and the second variable focal length lens is an infinitely conjugate system with respect to the first conjugate point, and a second optical subsystem including the third variable focal length lens and the fixed focal length lens is an infinitely conjugate system with respect to the third conjugate point; ADVANTAGEOUS EFFECTS OF THE INVENTION

[0010] The present disclosure makes it possible to change the magnification and the focal position at will, which is suitable for variable focal length lenses. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A and Fig. 1B are figures showing a configuration of a variable focal length lens device according to a first embodiment. Fig. 2A and Fig. 2B are figures showing another configuration of the variable focal length lens device according to the first embodiment. Fig. 3A and Fig. 3B are figures showing another configuration of the variable focal length lens device according to the first embodiment. Fig. 4A and Fig. 4B are figures showing another configuration of the variable focal length lens device according to the first embodiment. Fig. 5 is a figure for illustrating the operation performed by the variable focal length lens device according to the first embodiment. Fig. 6 is a figure for illustrating further operation performed by the variable focal length lens device according to the first embodiment. Fig. 7 is a figure for illustrating further operation performed by the variable focal length lens device according to the first embodiment. Fig. 8 is a figure for illustrating the operation performed by the variable focal length lens device according to the first embodiment. Fig. 9 is a figure for illustrating another operation performed by the variable focal length lens device according to the first embodiment. Fig. 10A and Fig. 10B are figures showing a configuration of the variable focal length lens device according to the second embodiment. Fig. 11A and Fig. 11B are figures showing another configuration of the variable focal length lens device according to the second embodiment. Fig. 12A and Fig. 12B are figures showing a configuration of a variable focal length lens device according to a third embodiment. Fig. 13A and Fig. 13B are figures showing another configuration of the variable focal length lens device according to the third embodiment. DESCRIPTION OF THE EMBODIMENTS

[0011] In the following, modes for implementing the present disclosure will be explained with reference to the attached figures in order to further explain the present disclosure. First embodiment.

[0012] The variable focal length lens devices 201A to 201D according to a first embodiment are described with reference to Fig. 1A and Fig. 1B to Fig. 9 explained.

[0013] Fig. 1A and Fig. 1B are figures showing a configuration of the variable focal length lens device 201A according to the first embodiment. The Fig. 1A and Fig. The variable focal length lens device 201A shown in FIG. 1B includes an optical system 101 and an image sensor 51. Note that in the variable focal length lens device 201A, a side on which the optical system 101 is arranged is referred to as the front side, and a side on which the image sensor 51 is arranged is referred to as the back side.

[0014] The optical system 101 has a first variable focal length lens 11, a second variable focal length lens 21, a third variable focal length lens 31, and a fixed focal length lens 41.

[0015] The first variable focal length lens 11, the second variable focal length lens 21, the third variable focal length lens 31, and the fixed focal length lens 41 are arranged in this order from the front to the rear. The first variable focal length lens 11, the second variable focal length lens 21, the third variable focal length lens 31, the fixed focal length lens 41, and the image sensor 51 are arranged coaxially, i.e., on the same optical axis.

[0016] The first variable focal length lens 11, the second variable focal length lens 21, and the third variable focal length lens 31 are liquid lenses that use liquids as the lens medium. By electrically controlling the shapes of the liquids, the radii of curvature of the curved surfaces serving as lens surfaces or the like change. Consequently, the focal lengths of the variable focal length lenses 11, 21, and 31 can be changed.

[0017] The variable focal length lenses 11, 21, and 31 are manufactured by sealing the liquids in expandable / contractible resin films. By forcing a portion of the liquids with piezo actuators, the pressure of the liquids changes. This changes the radii of curvature of the curved surfaces that serve as lens surfaces of the variable focal length lenses 11, 21, and 31, and the focal lengths can be changed accordingly. Furthermore, electrowetting can be used for the variable focal length lenses 11, 21, and 31. In this case, by applying a voltage between electrodes with low wettability and few droplets on them, the contact angles of the droplets on the variable focal length lenses 11, 21, and 31 change. Consequently, the focal lengths of the variable focal length lenses 11, 21, and 31 can be changed.

[0018] Since the radius of curvature of a curved surface serving as the lens surface of the fixed focal length lens 41 does not change, the focal length is constant. The fixed focal length lens 41 is formed, for example, from glass or the like.

[0019] The first variable focal length lens 11, the second variable focal length lens 21, the third variable focal length lens 31 and the fixed focal length lens 41 are convex lenses.

[0020] The first variable focal length lens 11 has a first focal length f1. The front surface of the first variable focal length lens 11 is a planar surface, and the rear surface of the first variable focal length lens 11 is a convex curved surface. The second variable focal length lens 21 has a second focal length f2. The front surface of the second variable focal length lens 21 is a convex curved surface, and the rear surface of the second variable focal length lens 21 is a planar surface. The third variable focal length lens 31 has a third focal length f3. The front surface of the third variable focal length lens 31 is a planar surface, and the rear surface of the third variable focal length lens 31 is a convex curved surface. The fixed focal length lens 41 has a fourth focal length f4.The front surface of the third fixed focal length lens 41 is a convex curved surface, and the rear surface of the third fixed focal length lens 41 is a planar surface.

[0021] The interlens distance d between the second variable focal length lens 21 and the third variable focal length lens 31 is defined by the formula (1) described below. d=f2+f3

[0022] A first conjugate point 1 is set in front of the first variable focal length lens 11. The first conjugate point 1 is located at a distance equal to the first focal length f1 in front of the first variable focal length lens 11. The first conjugate point 1 is a point where an image capturing subject is located and is a focal point position. A second conjugate point 2 is set behind the fixed focal length lens 41. The second conjugate point 2 is located behind the fixed focal length lens 41 at a distance equal to the fourth focal length f4. The second conjugate point 2 is a point where the image sensor 51 is located.

[0023] A third conjugate point 3 is set behind the second variable focal length lens 21. The third conjugate point 3 is located behind the second variable focal length lens 21 at a distance equal to the second focal length f2. Furthermore, as can be seen from formula (1), the third conjugate point 3 is also a point in front of the third variable focal length lens 31 at a distance equal to the third focal length f3. In this configuration, the second variable focal length lens 21 and the third variable focal length lens 31 have focal lengths f2 and f3, which are both positive lengths, at this time. Therefore, the third conjugate point 3 is located between the second variable focal length lens 21 and the third variable focal length lens 31.

[0024] In the variable focal length lens device 201A, an image of an object located at the first conjugate point 1 is formed and captured by the optical system 101 on the image sensor 51 located at the second conjugate point 2.

[0025] The first variable focal length lens 11 and the second variable focal length lens 21 are included in a first optical subsystem 111, which forms an infinite conjugate system with respect to the relationship between the first conjugate point 1 and the third conjugate point 3 (see Fig. 1B). Furthermore, the third variable focal length lens 31 and the fixed focal length lens 41 are included in a second optical subsystem 121, which forms an infinite conjugate system with respect to the relationship between the third conjugate point 3 and the second conjugate point 2 (see Fig. 1B).

[0026] This section explains the definition of positivity / negativity in the variable focal length lens device 201A. The interlens distance d always has a positive value. The focal lengths f1 to f4 have positive values ​​in the case of convex lenses and negative values ​​in the case of concave lenses.

[0027] Regarding the measurement of a position with respect to a given position as a reference point, in the case where the position is located in front of the reference point at a distance equal to a positive focal length, this position is defined as being in front of the reference point. Further, in a case where the position is located in front of the reference point at a distance equal to a negative focal length, this position is defined as being behind the reference point. Further, in a case where the position is located behind the reference point at a distance equal to the positive focal length, this position is defined as being behind the reference point. Furthermore, in a case where the position is located behind the reference point at a distance equal to a negative focal length, this position is defined as being in front of the reference point.

[0028] The total magnification of the optical system 101 is defined to have a negative value in the case of an inverted image and a positive value in the case of an erect image. Furthermore, the magnification of an afocal system including the second variable focal length lens 21 and the third variable focal length lens 31 is defined to have a negative magnification when f3 / f2 > 0 and a positive magnification when f3 / f2 < 0.

[0029] Fig. 2A and Fig. 2B are figures showing a configuration of the variable focal length lens device 201B according to the first embodiment. The Fig. 2A and Fig. The variable focal length lens device 201B shown in FIG. 2B differs from the variable focal length lens device 201A with respect to the setting of the second focal length f2 and the third focal length f3. The variable focal length lens device 201B includes an optical system 102 and the image sensor 51.

[0030] The optical system 102 includes the first variable focal length lens 11, a second variable focal length lens 22, a third variable focal length lens 32, and the fixed focal length lens 41. The first variable focal length lens 11, the second variable focal length lens 22, the third variable focal length lens 32, and the fixed focal length lens 41 are arranged in this order from the front to the rear. The first variable focal length lens 11, the second variable focal length lens 22, the third variable focal length lens 32, and the fixed focal length lens 41 are arranged on the same optical axis.

[0031] The second variable focal length lens 22 is a convex lens. The front surface of the second variable focal length lens 22 is a planar curved surface, and the back surface of the second variable focal length lens 22 is a planar surface. The third variable focal length lens 32 is a concave lens. The front surface of the third variable focal length lens 32 is a planar surface, and the back surface of the third variable focal length lens 32 is a concave curved surface.

[0032] The second variable focal length lens 22 has a positive second focal length f2. The third variable focal length lens 32 has a negative third focal length f3. In a case where the focal lengths f2 and f3 satisfy formula (1), the third conjugate point 3 is located behind the third variable focal length lens 32 when the device is viewed as a whole. In other words, relative to the third variable focal length lens 32, the third conjugate point 3 is located in front of the third variable focal length lens 32 at a distance equal to the third focal length f3.

[0033] The first variable focal length lens 11 and the second variable focal length lens 22 are included in a first optical subsystem 112, which forms an infinite conjugate system with respect to the relationship between the first conjugate point 1 and the third conjugate point 3 (see Fig. 2B). The third variable focal length lens 32 and the fixed focal length lens 41 are included in a second optical subsystem 122, which forms an infinite conjugate system with respect to the relationship between the third conjugate point 3 and the second conjugate point 2 (see Fig. 2B).

[0034] Fig. 3A and Fig. 3B are figures showing a configuration of the variable focal length lens device 201C according to the first embodiment. The Fig. 3A and Fig. The variable focal length lens device 201C shown in Figure 3B differs from the variable focal length lens devices 201A and 201B with respect to the setting of the second focal length f2 and the third focal length f3. The variable focal length lens device 201C includes an optical system 103 and the image sensor 51.

[0035] The optical system 103 includes the first variable focal length lens 11, a second variable focal length lens 23, a third variable focal length lens 33, and the fixed focal length lens 41. The first variable focal length lens 11, the second variable focal length lens 23, the third variable focal length lens 33, and the fixed focal length lens 41 are arranged in this order from the front to the rear. The first variable focal length lens 11, the second variable focal length lens 23, the third variable focal length lens 33, and the fixed focal length lens 41 are arranged on the same optical axis.

[0036] The second variable focal length lens 23 is a concave lens. The front surface of the second variable focal length lens 23 is a concave curved surface, and the rear surface of the second variable focal length lens 23 is a planar surface. The third variable focal length lens 33 is a convex lens. The front surface of the third variable focal length lens 33 is a planar surface, and the rear surface of the third variable focal length lens 33 is a convex curved surface.

[0037] The second variable focal length lens 23 has a negative second focal length f2. The third variable focal length lens 33 has a positive third focal length f3. In a case where the focal lengths f2 and f3 satisfy formula (1), the third conjugate point 3 is located behind the second variable focal length lens 23 when the device is viewed as a whole. In other words, relative to the second variable focal length lens 23, the third conjugate point 3 is located behind the second variable focal length lens 23 at a distance equal to the second focal length f2.

[0038] The first variable focal length lens 11 and the second variable focal length lens 23 are included in a first optical subsystem 113, which forms an infinite conjugate system with respect to the relationship between the first conjugate point 1 and the third conjugate point 3 (see Fig. 3B). The third variable focal length lens 33 and the fixed focal length lens 41 are included in a first second subsystem 123, which forms an infinite conjugate system with respect to the relationship between the third conjugate point 3 and the second conjugate point 2 (see Fig. 3B).

[0039] Fig. 4A and Fig. 4B are figures showing a configuration of the variable focal length lens device 201D according to the first embodiment. The Fig. 4A and Fig. The variable focal length lens device 201D shown in Figure 4B differs from the variable focal length lens devices 201A to 201C with respect to the setting of the second focal length f2 and the third focal length f3. The variable focal length lens device 201D includes an optical system 104 and the image sensor 51.

[0040] The optical system 104 includes the first variable focal length lens 11, a second variable focal length lens 24, a third variable focal length lens 34, and the fixed focal length lens 41. The first variable focal length lens 11, the second variable focal length lens 24, the third variable focal length lens 34, and the fixed focal length lens 41 are arranged in this order from the front to the rear. The first variable focal length lens 11, the second variable focal length lens 24, the third variable focal length lens 34, and the fixed focal length lens 41 are arranged on the same optical axis.

[0041] The second variable focal length lens 24 and the third variable focal length lens 34 are tabular planar surface lenses. The front and rear surfaces of the second variable focal length lens 24 are planar surfaces. The front and rear surfaces of the third variable focal length lens 34 are planar surfaces.

[0042] The second variable focal length lens 24 has the second focal length f2 with a negative infinity value. The third variable focal length lens 34 has the third focal length f3 with a positive infinity value. The focal lengths f2 and f3 essentially satisfy formula (1), and the third conjugate point 3 is located at an infinite distance in front of the second variable focal length lens 24 when the device is viewed as a whole. In other words, relative to the second variable focal length lens 24, the third conjugate point 3 is located at a distance equal to the second focal length f2 behind the second variable focal length lens 24. Since the focal lengths f2 and f3 are infinite in the variable focal length lens device 201D, the second variable focal length lens 24 and the third variable focal length lens 34 function as parallel planar plates with parallel front and rear surfaces.

[0043] The first variable focal length lens 11 and the second variable focal length lens 24 are included in a first optical subsystem 114, which forms an infinite conjugate system with respect to the relationship between the first conjugate point 1 and the third conjugate point 3 (see Fig. 4B). The third variable focal length lens 34 and the fixed focal length lens 41 are included in a second optical subsystem 124, which forms an infinite conjugate system with respect to the relationship between the third conjugate point 3 and the second conjugate point 2.

[0044] It should be noted that, although not shown, the optical system 104 can be configured such that the second variable focal length lens 24 has the second focal length f2 with a positive infinity value, and the third variable focal length lens 34 has the third focal length f3 with a negative infinity value. In this case, the third conjugate point 3 is located at an infinite distance behind the third variable focal length lens 34 when the device is viewed as a whole. In other words, relative to the third variable focal length lens 34, the third conjugate point 3 is located in front of the third variable focal length lens 34 at a distance equal to the third focal length f3.

[0045] Furthermore, the variable focal length lens devices 201A to 201D are devices for measuring images of objects and include typical image processing devices and illumination devices. In a case where the variable focal length lens devices 201A to 201D include illumination devices, both a configuration in which the illumination devices share part of the optical systems 101 to 104 and a configuration in which the illumination devices do not share part of the optical systems 101 to 104 are possible.Further, in a case where the illumination devices share part of the optical systems 101 to 104, a configuration in which beam splitters are arranged between the first variable focal length lens 11 and the second variable focal length lenses 21 to 24, and light from the first variable focal length lens 11 and light from the second variable focal length lenses 21 to 24 are coaxially multiplexed, a configuration in which beam splitters are arranged between the first variable focal length lens 11 and the second variable focal length lenses 21 to 24, and light from the first variable focal length lens 11 and light from the second variable focal length lenses 21 to 24 are coaxially multiplexed, and the like is possible.

[0046] Furthermore, in a case where liquid lenses are used as variable focal length lenses, power supplies or control sections not shown, such as driver boards for controlling the liquid lenses, are also included.

[0047] Next, an operation performed by the variable focal length lens device 201A will be described with reference to the Fig. 1A and Fig. 1B. The variable focal length lens assembly 201A has a magnification and focal position that can be changed as needed.

[0048] First, a case will be explained in which the variable focal length lens device 201A adjusts or adjusts the focal position as explained.

[0049] Regarding the first variable focal length lens 11, the variable focal length lens device 201A adjusts the first focal length f1 so that the distance between the first variable focal length lens 11 and an object whose measurement is desired and the first focal length f1 coincide. The adjustment of the focal position of the variable focal length lens device 201A is completed when the distance and the first focal length f1 coincide in this way.

[0050] Next, a case will be explained in which the variable focal length lens device 201A changes the magnification as explained.

[0051] The second focal length f2 and the third focal length f3 are limited by the interlens distance d according to formula (1). In contrast, formula (2) described below is a well-known formula for determining the focal length of compound lenses. In a case where compound lenses satisfy formula (1), the focal length of the compound lenses in formula (2) is infinite and is not defined. f∗=f2×f3 / (f2+f3−d)

[0052] The condition represented by formula (1) is therefore that the system is an afocal system that performs an expansion or reduction of the light flux. At this time, for example, the magnification m of the optical system 101 is determined using formula (3) described below. m=f2 / f1×f4 / f3

[0053] For simplicity, the magnification m* of the afocal system is defined here by the formula (4) described below, separately from the magnification m of the optical system 101. m∗=f3 / f2

[0054] Fig. 5 is a figure showing the performed operation of an afocal system with the second variable focal length lens 21 and the third variable focal length lens 31. Fig. 5 shows three operating modes as examples.

[0055] In each operating state, the second variable focal length lens 21 and the third variable focal length lens 31 are adjusted to have different focal lengths and satisfy formula (1). The variable focal length lens device 201A varies the position of the third conjugate point 3 based on mutually different operating conditions and has, for example, the third conjugate points 3, 3', and 3".

[0056] In a case where the variable focal length lens device 201A has the third conjugate point 3, the magnification m* of the afocal system* is 2. Therefore, the ratio of the light flux behind the third variable focal length lens 31 to the light flux in front of the second variable focal length lens 21 is 2.

[0057] In a case where the variable focal length lens assembly 201A has the third conjugate point 3', the magnification m* of the afocal system* is 1. Therefore, the ratio of the light flux behind the third variable focal length lens 31 to the light flux in front of the second variable focal length lens 21 is 1.

[0058] In a case where the variable focal length lens device 201A has the third conjugate point 3", the magnification m* of the afocal system* is "1 / 2". Therefore, the ratio of the light flux behind the third variable focal length lens 31 to the light flux in front of the second variable focal length lens 21 is 1 / 2.

[0059] Fig. 6 is a figure showing the performed operation of an afocal system with the second variable focal length lens 22 and the third variable focal length lens 32. Fig. 6 shows three operating modes as examples.

[0060] In each operating state, the second variable focal length lens 22 and the third variable focal length lens 32 are adjusted to have different focal lengths, satisfying formula (1). The variable focal length lens device 201B varies the position of the third conjugate point 3 based on mutually different operating conditions and has, for example, the third conjugate points 3, 3', and 3".

[0061] In a case where the variable focal length lens device 201A has the third conjugate point 3, the magnification m* of the afocal system* is "1 / 3." Therefore, the ratio of the light flux behind the third variable focal length lens 32 to the light flux in front of the second variable focal length lens 22 is 1 / 3.

[0062] In a case where the variable focal length lens device 201B has the third conjugate point 3', the magnification m* of the afocal system* is "1 / 2." Therefore, the ratio of the light flux behind the third variable focal length lens 31 to the light flux in front of the second variable focal length lens 21 is 1 / 2.

[0063] In a case where the variable focal length lens device 201B has the third conjugate point 3", the magnification m* of the afocal system* is "3 / 5". Therefore, the ratio of the light flux behind the third variable focal length lens 31 to the light flux in front of the second variable focal length lens 21 is 3 / 5.

[0064] Fig. 7 is a figure showing the performed operation of an afocal system with the second variable focal length lens 23 and the third variable focal length lens 33. Fig. Figure 7 shows three operating modes as examples.

[0065] In each operating state, the second variable focal length lens 22 and the third variable focal length lens 32 are adjusted to have different focal lengths, satisfying formula (1). The variable focal length lens device 201C varies the position of the third conjugate point 3 based on mutually different operating conditions and has, for example, the third conjugate points 3, 3', and 3".

[0066] In a case where the variable focal length lens device 201C has the third conjugate point 3, the magnification m* of the afocal system* is 3. Therefore, the ratio of the light flux behind the third variable focal length lens 33 to the light flux in front of the second variable focal length lens 23 is 3.

[0067] In a case where the variable focal length lens device 201C has the third conjugate point 3', the magnification m* of the afocal system* is 2. Therefore, the ratio of the light flux behind the third variable focal length lens 33 to the light flux in front of the second variable focal length lens 23 is 2.

[0068] In a case where the variable focal length lens device 201C has the third conjugate point 3", the magnification m* of the afocal system* is "5 / 3". Therefore, the ratio of the light flux behind the third variable focal length lens 33 to the light flux in front of the second variable focal length lens 23 is 5 / 3.

[0069] Therefore, it is understandable that in the variable focal length lens devices 201A to 201C, the magnification m* of the afocal system is adjusted to reduce variations in the magnification m, while the focal position is adjusted by changing the first focal length f1.

[0070] By substituting formulas (2) and (3) into formula (4) and organizing formula (4), the magnification m* of the afocal system can be represented by formula (5) described below by substituting the magnification m of the optical system 101, the first focal length f1, and the fourth focal length f4. m∗=f4 / (m×f1)

[0071] In addition, by organizing formula (1) and formula (3), the second focal length f2 can be represented by formula (6) described below, and the third focal length f3 can be represented by formula (7) described below. f2=d×m×f1 / (m×f1+f4) f3=d×f4 / (m×f1+f4)

[0072] Accordingly, an image of an object located at the first conjugate point 1 is formed on the image sensor 51 after being corrected to a specific magnification of the optical system by the second variable focal length lenses 31 to 33 and the third variable focal length lenses 21 to 23. Furthermore, when the first focal length f1 is changed and the position of the first conjugate point 1 is set to a position different from the position where the object is located, in this state, an image of the object is formed on the image sensor 51 after being corrected to a specific magnification of the optical system by the second variable focal length lenses 21 to 23 and the third variable focal length lenses 31 to 33.

[0073] Here, the operation of the variable focal length lens devices 201A to 201C is explained using specific values ​​to facilitate understanding.

[0074] For example, assume that the magnification factor m is "1" and the focal point position (the first conjugate point 1) is varied between 50 mm and 150 mm. Furthermore, assume that the interlens distance d between the second variable focal length lenses 21 to 23 and the third variable focal length lenses 31 to 33 is 200 mm.

[0075] Only the cases where the first focal length f1 is 50 mm and 150 mm are given as representative examples. In a case where the first focal length f1 is 50 mm, the second focal length f2 is 100 mm, the third focal length f3 is 100 mm, and the fourth focal length f4 is 50 mm. In a case where the first focal length f1 is 150 mm, the second focal length f2 is 150 mm, the third focal length f3 is 50 mm, and the fourth focal length f4 is 50 mm. Then, when the first focal length f1 is changed from 50 mm to 150 mm, the second focal length f2 is adjusted from 100 mm to 150 mm according to formula (6). Furthermore, the third focal length f3 is changed from 100 mm to 50 mm according to formula (7).

[0076] Fig. 8 is a figure showing the performed operation of an afocal system with the second variable focal length lenses 21 and 23 and the third variable focal length lenses 31 and 33.

[0077] Since the magnification m of the optical systems 101 to 103 can be either positive or negative, there are two operating modes with identical absolute values ​​of the magnification m in formula (5), formula (6) and formula (7). The two operating modes correspond to the Fig. 5 and Fig. 6 shown operating conditions of magnification reduction or those in the Fig. 5 and Fig. 7. Furthermore, the two operating modes correspond to such a difference whether the magnification m* of the afocal system* has positive or negative values ​​with the same absolute values.

[0078] Fig. 8 shows an example of two modes in a case where the absolute value of the magnification m* of the afocal system* is 2. In a mode where the magnification m* of the afocal system* is 2, the second variable focal length lens 23 and the third variable focal length lens 33 satisfy formulas (1) and (4). On the other hand, in a mode where the magnification m* of the afocal system* is -2, the second variable focal length lens 21 and the third variable focal length lens 31 satisfy formulas (1) and (4). In the two modes described above, the position of the third conjugate point 3 varies, and the positions after the variations are represented as the third conjugate points 3 and 3'.The sign of the magnification of the optical system is reversed when switching from one of the two operating modes to the other, which consequently has the advantageous effect that a captured image to be acquired can be freely inverted.

[0079] Furthermore, it will be explained below that the two operating modes described above are particularly suitable when the lenses with variable focal length, which are liquid lenses, are used.

[0080] It has been reported that liquid lenses exhibit varying degrees of tilt-dependence property deterioration due to gravity or the like. At this time, in a planar optical arrangement where an optical axis is perpendicular to the direction of gravity, the top surface (opposite the bottom surface) of a lens and the bottom surface (bottom surface) of the lens sometimes have different aberration characteristics. It is difficult to correct such asymmetric aberration around the optical axis, but by utilizing the two operation modes described above, it is possible to digitally correct the asymmetric aberration.

[0081] This means that when the magnification m* of the afocal system* is positive, the light beams that have passed through the bottom surfaces of the second variable focal length lenses 21 to 23 will pass through the bottom surfaces of the third variable focal length lenses 31 to 33. At this time, the aberrations corresponding to the inclinations of a pair of variable focal length lenses similarly occur. This means that when the magnification m* of the afocal system* is positive, the light beams that have passed through the bottom surfaces of the second variable focal length lenses 21 to 23 will pass through the bottom surfaces of the third variable focal length lenses 31 to 33. At this time, the aberrations corresponding to the inclinations of a pair of variable focal length lenses are averaged.Due to the difference between the characteristics of an acquired image when the magnification m* of the afocal system* is positive and the characteristics of an acquired image when the magnification m* of the afocal system* is negative, the aberrations corresponding to the tilts appear as the difference between the two. Therefore, the aberrations corresponding to the tilts can be reduced by the digital image correction of the difference described above.

[0082] Fig. 9 is a figure showing the performed operation of an afocal system with the second variable focal length lenses 21 and 24 and the third variable focal length lenses 31 and 34. Fig. 9 shows a concrete example of the two operating modes in which the absolute values ​​of the magnification m are identical values ​​as in Fig. 8, and shows an example showing the two modes of operation in a case where the absolute values ​​of the magnification m are 1.

[0083] In a mode where the magnification m* of the afocal system* is 1, both the second variable focal length lens 24 and the third variable focal length lens 34 are parallel planar plates, and they substantially satisfy formulas (1) and (4). In a mode where the magnification m* of the afocal system* is -1, the second variable focal length lens 21 and the third variable focal length lens 31 satisfy formulas (1) and (4). In the two modes described above, the position of the third conjugate point 3 varies, and the positions after the variations are represented as the third conjugate points 3 and 3'. The sign of the magnification of the optical system is reversed when switching from one of the two modes to the other, thus providing the advantageous effect that a captured image to be acquired can be freely inverted.

[0084] It should be noted that infinity of focal length is strictly speaking not possible from a manufacturing point of view, and therefore it is obvious that in the practical operation of a variable focal length lens, a condition where the refractive power, which is the inverse of the focal length, becomes 0 within the range of variability can be regarded as infinity of focal length.

[0085] As explained so far, the variable focal length lens devices 201A to 201D according to the first embodiment include: the first variable focal length lens 11 having the first focal length f1; the second variable focal length lenses 21 to 24 disposed behind the first variable focal length lens 11 and having the second focal length f2; the third variable focal length lenses 31 to 34 disposed behind the second variable focal length lenses 21 to 24 and having the third focal length f3; the fixed focal length lens 41 disposed behind the third variable focal length lenses 31 to 34 and having the fourth focal length f4; the first conjugate point 1 disposed in front of the first variable focal length lens 11 at a distance equal to the first focal length f1 and serving as a focal position;the second conjugate point 2, which is arranged at a distance equal to the fourth focal length f4 behind the fixed focal length lens 41 and is provided as the image sensor 51;and the third conjugate point 3, which is arranged at a distance equal to the second focal length f2 behind the second variable focal length lenses 21 to 24 and at a distance equal to the third focal length f3 in front of the third variable focal length lenses 31 to 34, wherein the first optical subsystems 111 and 114, which include the first variable focal length lens 11 and the second variable focal length lenses 21 to 24, are infinitely conjugate systems with respect to the first conjugate point 1, and the second optical subsystems 121 to 124, which include the third variable focal length lenses 31 and 34 and the fixed focal length lens 41, are infinitely conjugate systems with respect to the third conjugate point 3. For this reason, the variable focal length lens devices 201A to 201D allow the magnifications and focus positions to be changed as needed, which is suitable for variable focal length lenses.

[0086] It should be noted that although the principles of liquid lenses cited as specific examples of variable focal length lenses—one using a piezo actuator and one using electrowetting—will be explained, it is obvious that the advantageous effects of the invention can be easily achieved even when liquid lenses based on other principles are used. Furthermore, the advantageous effects of the invention can be similarly achieved even when lenses other than liquid lenses with variable focal length functions are used.

[0087] The liquid lenses, which are explained as lenses with variable focal length, can have, in addition to parts with liquid lens functions, also optical functions like solid lenses, e.g. glasses or cover glasses.

[0088] Regarding the mechanisms for adjusting the focus of variable focal length lenses, for example, the liquid lenses are controlled by electrical physical quantities such as a voltage applied to the liquid lenses in a case where liquid lenses are used as variable focal length lenses.

[0089] While it is explained that the shapes of the variable focal length lenses and the fixed focal length lens are plano-convex, plano-concave, or tabular, not all of them need to have a planar portion in the strict sense. It is obvious that the advantageous effects of the invention can be easily achieved even if each of the lenses has a slight curvature on the side of a planar surface, such as a meniscus lens or a so-called best-form lens suitable for an infinitely conjugated system.

[0090] While there are three operating points in the operation of an afocal system in the cases explained in the present first embodiment, it is obvious that the operating points are not limited to these three. For example, if liquid lenses are used as the variable focal length lenses, the range and resolution of the voltage that can be applied to the liquid lenses determine the number of possible operating points. Second embodiment.

[0091] Variable focal length lens devices 202A and 202B according to a second embodiment are described with reference to Fig. 10A and Fig. 10B and Fig. 11A and Fig. 11B. Note that components having similar functions to those explained in the above-mentioned first embodiment are denoted by identical reference numerals, and explanations thereof are omitted.

[0092] Fig. 10A and Fig. 10B are figures showing a configuration of the variable focal length lens device 202A according to the second embodiment. Fig. 10A and Fig. The variable focal length lens device 202A shown in Fig. 10B has a configuration in which, instead of the image sensor 51, an optical fiber 61 is arranged at the position of a third conjugate point 3 at which an image of a first conjugate point 1 is formed.

[0093] Specifically, instead of the image sensor 51 of the variable focal length lens device 201A, the variable focal length lens device 202A includes a light-receiving element 52, the optical fiber 61, an illumination light source 62, and a circulator 63. The optical fiber 61 forms a light guide. The circulator 63 forms an optical path splitter.

[0094] One end of the optical fiber 61 forms the third conjugate point 3. The other end of the optical fiber 61 is connected to the circulator 63. The optical fiber 61 is, for example, a single optical fiber or an optical fiber formed by joining multiple optical fibers into a bundle. The circulator 63 has two terminals. One terminal is optically connected to the illumination light source 62. The other terminal is optically connected to the light receiving element 52. As an optical connection method, for example, a space optical system, an optical fiber system, or the like is used.

[0095] Next, an operation performed by the variable focal length lens device 202A will be explained. The focal position adjustment operation performed by an optical system 101 of the variable focal length lens device 202A is the same as the focal position adjustment operation performed by the optical system 101 of the variable focal length lens device 201A. The magnification m change operation performed by the optical system 101 of the variable focal length lens device 202A is the same as the magnification m change operation performed by the optical system 101 of the variable focal length lens device 201A.

[0096] The illumination light emitted from the illumination light source 62 passes through the optical fiber 61 and the optical system 101 in this order due to the action of the circulator 63. Then, the illumination light that has passed through the optical system 101 is emitted onto an object located at the first conjugate point 1. In contrast, the illumination light reflected and scattered by the object passes through the optical system 101 and the optical fiber 61 in this order. Then, the illumination light that has passed through the optical fiber 61 is incident on the light-receiving element 52 due to the action of the circulator 63. As a result, the variable focal length lens device 202A can obtain a captured image of the object from the light-receiving element 52 that received the illumination light.

[0097] Accordingly, an image of the object located at the first conjugate point 1 is formed on the image sensor 51 after being corrected to a specific magnification of the optical system by the second variable focal length lens 21 and the third variable focal length lens 31. Furthermore, when a first focal length f1 is changed and the position of the first conjugate point 1 is set to a position different from the position where the object is located, in this state, an image of the object is also formed on the image sensor 51 after being corrected to a specific magnification of the optical system by the second variable focal length lens 21 and the third variable focal length lens 31.

[0098] It should be noted that the Fig. 10A and Fig. 10B, the variable focal length lens device 202A includes the optical system 101, but instead of the optical system 101, the Fig. 11A and Fig. 11B may include optical system 103. Fig. 11A and Fig. 11B are figures showing a configuration of the variable focal length lens device 202B according to the second embodiment. The variable focal length lens device 202B includes the optical system 103, the light-receiving element 52, the optical fiber 61, an illumination light source 62, and the circulator 63. In addition, although the variable focal length lens device 202A includes the optical system 101, it may also include the optical system shown in FIGS. Fig. 2A and Fig. 2B or the optical system 102 shown in the Fig. 4A and Fig. 4B shown optical system 104.

[0099] As explained so far, the variable focal length lens devices 202A and 202B according to the second embodiment include: a first variable focal length lens 11 having the first focal length f1; second variable focal length lenses 21 to 23 arranged behind the first variable focal length lens 11 and having a second focal length f2; third variable focal length lenses 31 to 33 arranged behind the second variable focal length lenses 21 to 23 and having a third focal length f3; a fixed focal length lens 41 arranged behind the third variable focal length lenses 31 to 33 and having the fourth focal length f4; the first conjugate point 1 arranged in front of the first variable focal length lens 11 at a distance equal to the first focal length f1 and serving as a focal position;a second conjugate point 2 arranged at a distance equal to the fourth focal length f4 behind the fixed focal length lens 41 and provided with the optical fiber 61;and the third conjugate point 3, which is arranged at a distance equal to the second focal length f2 behind the second variable focal length lenses 21 and 23 and at a distance equal to the third focal length f3 in front of the third variable focal length lenses 31 and 33, wherein the first optical subsystems 111 and 113, which include the first variable focal length lens 11 and the second variable focal length lenses 21 and 23, are infinitely conjugate systems with respect to the first conjugate point 1, and the second optical subsystems 121 and 123, which include the third variable focal length lenses 31 and 33 and the fixed focal length lens 41, are infinitely conjugate systems with respect to the third conjugate point 3. For this reason, the variable focal length lens devices 202A to 202B enable the magnifications and focus positions to be changed as needed, which is suitable for variable focal length lenses. Third embodiment.

[0100] Variable focal length lens devices 203A and 203B according to a third embodiment are described with reference to Fig. 12A and Fig. 12B and Fig. 13A and Fig. 13B. Note that components having similar functions to those explained in the above-mentioned first embodiment are denoted by identical reference numerals, and explanations thereof are omitted.

[0101] Fig. 12A and Fig. 12B are figures showing a configuration of the variable focal length lens device 203A according to the third embodiment. The Fig. 12A and Fig. The variable focal length lens device 203A shown in FIG. 12B has a configuration in which, after the illumination light emitted from an illumination light source 62 is split into a reference optical path 71 and a signal optical path 72a, the illumination light beams obtained after the splitting are multiplexed at a light receiving element 53, thereby making it possible to acquire an interference signal of the light beams. That is, the variable focal length lens device 203A has a configuration in which the reference optical path 71 and the signal optical paths 72a and 72b are added to the above-mentioned variable focal length lens device 202A.

[0102] The reference optical path 71 establishes an optical connection between the illumination light source 62 and the light-receiving element 53. The signal optical path 72a establishes an optical connection between the illumination light source 62 and one terminal of the circulator 63. The signal optical path 72b establishes an optical connection between the other terminal of the circulator 63 and the light-receiving element 53.

[0103] Next, an operation performed by the variable focal length lens device 203A will be explained. The focal position adjustment operation performed by an optical system 101 of the variable focal length lens device 203A is the same as the focal position adjustment operation performed by the optical system 101 of the variable focal length lens device 201A. The magnification m change operation performed by the optical system 101 of the variable focal length lens device 203A is the same as the magnification m change operation performed by the optical system 101 of the variable focal length lens device 201A.

[0104] Illumination light emitted from the illumination light source 62 is split into the reference optical path 71 and the signal optical path 72a. Illumination light split into the reference optical path 71 passes through the reference optical path 71 and is incident on the light-receiving element 53. On the other hand, illumination light split into the signal optical path 72a passes through an optical fiber 61 and the optical system 101 in this order due to an action of the circulator 63. Then, the illumination light that has passed through the optical system 101 is emitted onto an object located at the first conjugate point 1. In contrast, the illumination light reflected and scattered by the object passes through the optical system 101 and the optical fiber 61 in this order.Then, the illumination light that has passed through the optical fiber 61 passes through the optical signal path 72b and is incident on a light-receiving element 52 due to an action of the circulator 63. At this time, the illumination light incident on the light-receiving element 53 from the optical signal path 72b interferes with the illumination light incident on the light-receiving element 53 from the reference optical path 71. As a result, the variable focal length lens device 203A can obtain interference information about the illumination light beams from the light-receiving element 52 that has received two illumination light beams.

[0105] It should be noted that the Fig. 12A and Fig. 12B, the variable focal length lens device 203A includes the optical system 101, but instead of the optical system 101, the Fig. 13A and Fig. 13B may include optical system 103. Fig. 13A and Fig. 13B is a figure showing a configuration of the variable focal length lens device 203B according to the third embodiment. The variable focal length lens device 203B includes the optical system 103, the light-receiving element 53, the optical fiber 61, the illumination light source 62, the circulator 63, the optical reference pad 71, and the optical signal paths 72a and 72b. In addition, although the variable focal length lens device 203A includes the optical system 101, it may also include the optical system shown in FIGS. Fig. 2A and Fig. 2B or the optical system 102 shown in the Fig. 4A and Fig. 4B shown optical system 104.

[0106] In addition, the variable focal length lens devices 203A and 203B include typical interference information processing devices necessary for heterodyne detection systems or the like.

[0107] For example, in a case where the variable focal length lens devices 203A and 203B are interference information processing devices, the variable focal length lens devices 203A and 203B can temporally scan the wavelengths using wavelength-variable light sources instead of the illumination light source 62, thereby enabling FMCW scheme distance measurement based on wavelength differences at the time of multiplexing. In this way, the variable focal length lens devices 203A and 203B, which are interference information processing devices, are capable of performing distance measurement based on wavelength differences and, accordingly, can obtain interference information even from an object located away from the first conjugate point 1.

[0108] It should be noted that, within the scope of the present disclosure, any combination of the embodiments, modifications of any components in the embodiments, or omissions of any components in the embodiments are possible through the disclosure. INDUSTRIAL APPLICABILITY

[0109] A variable focal length lens device according to the present disclosure is suitable for use as a variable focal length lens device or the like having a magnification and a focus position that can be changed as desired and necessary, which is suitable for variable focal length lenses. LIST OF REFERENCE SYMBOLS

[0110] 1: first conjugate point, 2: second conjugate point, 3: third conjugate point, 11: first variable focal length lens, 21 to 24: second variable focal length lens, 31 to 34: third variable focal length lens, 41: fixed focal length lens, 51: image sensor, 52 and 53: light receiving element, 61: optical fiber, 62: illumination light source, 63: circulator, 71: reference optical path, 72a and 72b: optical signal path, 101 to 104: optical system, 111 to 114: first optical subsystem, 121 to 124: second optical subsystem, 201A to 201D, 202A, 202B, 203A and 203B: variable focal length lens device Focal length, f1: first focal length, f2: second focal length, f3: third focal length, f4: fourth focal length, d: lens distance QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2016-053491 A

[0006]

Claims

[1] A variable focal length lens device comprising: a first variable focal length lens having a first focal length; a second variable focal length lens disposed behind the first variable focal length lens and having a second focal length; a third variable focal length lens disposed behind the second variable focal length lens and having a third focal length; a fixed focal length lens located behind the third variable focal length lens and having a fourth focal length; a first conjugate point located in front of the first variable focal length lens at a distance equal to the first focal length and serving as a focus position; a second conjugate point located at a distance equal to the fourth focal length behind the fixed focal length lens and provided with an image sensor or a light guide means; and a third conjugate point located at a distance equal to the second focal length behind the second variable focal length lens and at a distance equal to the third focal length in front of the third variable focal length lens, wherein a first optical subsystem containing the first variable focal length lens and the second variable focal length lens is an infinitely conjugate system with respect to the first conjugate point, and a second optical subsystem containing the third variable focal length lens and the fixed focal length lens is an infinitely conjugate system with respect to the third conjugate point. [2] A variable focal length lens device according to claim 1, further comprising: an optical path splitter arranged behind the light guide means; an illumination light source connected to one end of the optical path splitter; and a light receiving element connected to the other end of the optical path splitter. [3] A variable focal length lens device according to claim 2, further comprising a reference optical path that guides the illumination light split from the illumination light source to the light receiving element. [4] A variable focal length lens device according to claim 3, wherein the illumination light source is a wavelength variable light source.

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