Lens assembly with variable focal length

Abstract

Lens assembly with variable focal length, comprising: a first lens with variable focal length, which has a first focal length; a second lens with variable focal length, which is arranged behind the first lens with variable focal length, and has a second focal length; a third lens with variable focal length, which is arranged behind the second lens with variable focal length, and has a third focal length; a lens with a fixed focal length, which is arranged behind the third lens with a variable focal length, and has a fourth focal length; a first conjugate point, which is located at a distance equal to the first focal length in front of the first lens with variable focal length, and serves 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 equipped with an image sensor or a light guide; and a third conjugate point located at a distance equal to the second focal length behind the second variable-length lens and at a distance equal to the third focal length in front of the third variable-length lens, wherein a first optical subsystem, which contains the first lens with variable focal length and the second lens with variable focal length, is an infinitely conjugate system with respect to the first conjugate point, and a second optical subsystem, which includes the third lens with variable focal length and the lens with fixed focal length, is an infinitely conjugate system with respect to the third conjugate point.

Description

AREA OF TECHNOLOGY

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

[0002] Optical technology is currently used in various devices such as processing equipment, observation equipment, distance measuring devices, and lighting equipment. It is essential that the magnification and focal point position of an optical system can be freely adjusted in such devices.

[0003] To change the magnification and focal point position of an optical system, it is usually necessary to alter the orientation of the optical axis, the arrangement of optical components such as lenses or an image sensor within the optical system, or similar elements. A setup configuration based on the assumption that optical components move presents numerous challenges related to design complexity, setup size, manufacturing costs, reliability, and other factors. These problems are particularly evident in magnification adjustment mechanisms, where simply extending an entire lens group or a portion thereof is difficult.The adjustment of the magnification and focal point position of an observation device such as a camera or microscope is still done via a mechanical drive mechanism, which, however, in addition to the problems mentioned above, also has a problem with regard to fast response time.

[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, liquid lenses using electrowetting technology have been employed, for example. These liquid lenses function as variable focal length lenses. Typically, liquid lenses operate as plano-convex or plano-concave lenses. Therefore, it is desirable for the liquid lenses to form an infinitely conjugate system to reduce aberrations or image defects.

[0005] Patent literature 1 describes a form measuring device using the lenses with variable focal length described above. REFERENCE LIST PATENT LITERATURE Patent Literature 1: JP 2016-053491 A Patent literature 2: US 2015 / 0 055 224 A1 Patent literature 3: US 7,218,429 B2 Patent Literature 4: US 4,407,567 A SUMMARY OF THE INVENTIONAL PROBLEM

[0006] The shape-measuring device described in patent literature 1 comprises three lenses with variable focal lengths. One of these is a variable focal length lens located on the object side to change the focal point position. Additionally, two variable focal length lenses are arranged on the image side to change the magnification. The principle of variable magnification is based on adjusting the ratio between the combined focal length of the two image-side variable focal length lenses (calculated according to a compound lens formula) and the focal length of the object-side variable focal length lens to achieve the desired magnification. The use of the two variable focal length lenses provides two degrees of freedom, necessary for adjusting the focal length and the position of the principal surface.On the other hand, in the revelation, the two lenses with variable focal length on the magnification setting side form an infinitely conjugate system as a group. Accordingly, the lens closest to an image is a finite conjugate system when the lenses are considered individually. Therefore, aberrations occur quite easily.

[0007] Patent literature 2 discloses an optical system using liquid lens cells with variable focal length.

[0008] Patent literature 3 describes a digital focusing lens system that can provide an optical system with a variety of selectable focal lengths.

[0009] Patent literature 4 discloses an optical device with at least two optical elements with variable focal length.

[0010] The present disclosure was made to solve the problems explained above, and one of its objectives is to provide a variable focal length lens arrangement which has a magnification and focal point position which can be changed as required, and which is suitable for variable focal length lenses. SOLUTION TO THE PROBLEM

[0011] A lens arrangement with a variable focal length according to the present disclosure comprises: a first lens with a variable focal length having a first focal length; a second lens with a variable focal length arranged behind the first lens with a variable focal length having a second focal length; a third lens with a variable focal length arranged behind the second lens with a variable focal length having a third focal length; a lens with a fixed focal length arranged behind the third lens with a variable focal length having a fourth focal length; a first conjugate point arranged at a distance equal to the first focal length in front of the first lens with a variable focal length and serving as the focus position; a second conjugate point arranged at a distance equal to the fourth focal length behind the lens with a fixed focal length and equipped with an image sensor or an optical guide;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 containing the first variable-focal-length lens and the second variable-focal-length lens, which 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, which is an infinitely conjugate system with respect to the third conjugate point. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0012] The present disclosure makes it possible to change the magnification and the focal point position at will, which is suitable for lenses with variable focal length. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A and Fig. Figure 1B shows a configuration of a lens device with variable focal length according to a first embodiment. Fig. 2A and Fig. Figures 2B illustrate a further configuration of the lens device with variable focal length according to the first embodiment. Fig. 3A and Fig. Figures 3B illustrate a further configuration of the lens device with variable focal length according to the first embodiment. Fig. 4A and Fig. Figures 4B illustrate a further configuration of the variable focal length lens device according to the first embodiment. Fig. Figure 5 is a figure illustrating the operation carried out by the lens device with variable focal length according to the first embodiment. Fig. Figure 6 is a figure illustrating the further operation carried out by the lens device with variable focal length according to the first embodiment. Fig. Figure 7 is a figure illustrating the further operation carried out by the lens device with variable focal length according to the first embodiment. Fig. Figure 8 is a figure illustrating the operation carried out by the lens device with variable focal length according to the first embodiment. Fig. Figure 9 is a figure illustrating a further operation carried out by the lens device with variable focal length according to the first embodiment. Fig. 10A and Fig. Figures 10B illustrate a configuration of the lens device with variable focal length according to the second embodiment. Fig. 11A and Fig. Figures 11B illustrate a further configuration of the lens device with variable focal length according to the second embodiment. Fig. 12A and Fig. Figures 12B are illustrating a configuration of a lens device with variable focal length according to a third embodiment. Fig. 13A and Fig. Figures 13B illustrate a further configuration of the variable focal length lens device according to the third embodiment. DESCRIPTION OF THE EXECUTION FORMS

[0013] The following sections, with reference to the attached figures, explain ways of implementing the present revelation in order to further clarify the present revelation. First embodiment.

[0014] The variable focal length lens devices 201A to 201D according to a first embodiment are based on Fig. 1A and Fig. 1B to Fig. 9 explained.

[0015] Fig. 1A and Fig. Figures 1B show a configuration of the variable focal length lens assembly 201A according to the first embodiment. The figures shown in the Fig. 1A and Fig. The variable focal length lens assembly 201A shown in Figure 1B comprises an optical system 101 and an image sensor 51. It should be noted that in the variable focal length lens assembly 201A, one side on which the optical system 101 is arranged is referred to as the front side, and one side on which the image sensor 51 is arranged is referred to as the back side.

[0016] The optical system 101 has a first lens with variable focal length 11, a second lens with variable focal length 21, a third lens with variable focal length 31 and a lens with fixed focal length 41.

[0017] 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 front to back. 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, that is, on the same optical axis.

[0018] The first lens with variable focal length 11, the second lens with variable focal length 21, and the third lens with variable focal length 31 are liquid lenses that use liquids as the lens medium. By electrically controlling the shape of the liquids, the radii of curvature of the curved surfaces, which serve as lens surfaces or the like, change. Consequently, the focal lengths of the lenses with variable focal lengths 11, 21, and 31 can be changed.

[0019] The variable focal length lenses 11, 21, and 31 are manufactured by sealing liquids in expandable / contractable resin films. By pressing a portion of the liquids with piezoelectric actuators, the liquid pressure changes. This alters the radii of curvature of the curved surfaces that serve as the lens surfaces of the variable focal length lenses 11, 21, and 31, and consequently, the focal lengths can be changed. Furthermore, electrowetting can be used for the variable focal length lenses 11, 21, and 31. In this case, applying a voltage between electrodes with low wettability and the few droplets on them changes the contact angles of the droplets. As a result, the focal lengths of the variable focal length lenses 11, 21, and 31 can be altered.

[0020] Since the radius of curvature of a curved surface, which serves as the lens surface of the lens with a fixed focal length of 41, does not change, the focal length is constant. The lens with a fixed focal length of 41 is made of glass or a similar material, for example.

[0021] The first lens with variable focal length 11, the second lens with variable focal length 21, the third lens with variable focal length 31 and the lens with fixed focal length 41 are convex lenses.

[0022] The first variable lens 11 has a first focal length f1. The front surface of the first variable lens 11 is planar, and the rear surface of the first variable lens 11 is convex. The second variable lens 21 has a second focal length f2. The front surface of the second variable lens 21 is convex, and the rear surface of the second variable lens 21 is planar. The third variable lens 31 has a third focal length f3. The front surface of the third variable lens 31 is planar, and the rear surface of the third variable lens 31 is convex. The fixed focal length lens 41 has a fourth focal length f4.The front surface of the third lens with fixed focal length 41 is a convex curved surface, and the rear surface of the third lens with fixed focal length 41 is a planar surface.

[0023] The lens spacing d between the second lens with variable focal length 21 and the third lens with variable focal length 31 is defined by the formula (1) described below. d=f2+f3

[0024] A first conjugate point 1 is placed in front of the first lens with variable focal length 11. The first conjugate point 1 is located at a distance equal to the first focal length f1 in front of the first lens with variable focal length 11. The first conjugate point 1 is a point where an image-capturing subject is positioned and is a focal point position. A second conjugate point 2 is placed behind the lens with fixed focal length 41. The second conjugate point 2 is located at a distance equal to the fourth focal length f4 behind the lens with fixed focal length 41. The second conjugate point 2 is a point where the image sensor 51 is positioned.

[0025] A third conjugate point 3 is positioned behind the second lens with variable focal length 21. This third conjugate point 3 is located at a distance equal to the second focal length f2 behind the second lens with variable focal length 21. Furthermore, as can be seen from equation (1), the third conjugate point 3 is also located at a distance equal to the third focal length f3 in front of the third lens with variable focal length 31. In this configuration, the second lens with variable focal length 21 and the third lens with variable focal length 31 have focal lengths f2 and f3, respectively, which are both positive lengths. Therefore, the third conjugate point 3 lies between the second lens with variable focal length 21 and the third lens with variable focal length 31.

[0026] In the variable focal length lens assembly 201A, an image of an object located at the first conjugate point 1 is formed and recorded by the optical system 101 on the image sensor 51 located at the second conjugate point 2.

[0027] The first lens with variable focal length 11 and the second lens with variable focal length 21 are contained 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 contained 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).

[0028] This section explains the definition of positivity / negativity in the variable focal length lens assembly 201A. The lens spacing 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.

[0029] Regarding the measurement of a position relative to a given reference point, if the position is located a distance equal to one positive focal length in front of the reference point, it is defined as being in front of the reference point. Furthermore, if the position is located a distance equal to one negative focal length in front of the reference point, it is defined as being behind the reference point. Similarly, if the position is located a distance equal to one positive focal length behind the reference point, it is defined as being behind the reference point. Finally, if the position is located a distance equal to one negative focal length behind the reference point, it is defined as being in front of the reference point.

[0030] The overall magnification of the optical system 101 is defined such that it has a negative value in the case of an inverted image and a positive value in the case of an upright image. Furthermore, the magnification of an afocal system comprising the second variable focal length lens 21 and the third variable focal length lens 31 is defined such that it has a negative magnification when f3 / f2 > 0 and a positive magnification when f3 / f2 < 0.

[0031] Fig. 2A and Fig. Figures 2B are shown in a configuration of the variable focal length lens assembly 201B according to the first embodiment. The figures in the Fig. 2A and Fig. The variable focal length lens assembly 201B shown in Figure 2B differs from the variable focal length lens assembly 201A with respect to the setting of the second focal length f2 and the third focal length f3. The variable focal length lens assembly 201B comprises an optical system 102 and the image sensor 51.

[0032] Optical system 102 comprises a first variable focal length lens 11, a second variable focal length lens 22, a third variable focal length lens 32, and a 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 that order from front to back. 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 all aligned along the same optical axis.

[0033] The second lens with variable focal length 22 is a convex lens. The front surface of the second lens with variable focal length 22 is a planar curved surface, and the rear surface of the second lens with variable focal length 22 is a planar surface. The third lens with variable focal length 32 is a concave lens. The front surface of the third lens with variable focal length 32 is a planar surface, and the rear surface of the third lens with variable focal length 32 is a concave curved surface.

[0034] The second lens with variable focal length 22 has a positive second focal length f2. The third lens with variable focal length 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 lens with variable focal length 32 when the apparatus is considered as a whole. In other words, relative to the third lens with variable focal length 32, the third conjugate point 3 is located in front of the third lens with variable focal length 32 at a distance equal to the third focal length f3.

[0035] The first lens with variable focal length 11 and the second lens with variable focal length 22 are contained 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 lens with variable focal length 32 and the lens with fixed focal length 41 are contained 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).

[0036] Fig. 3A and Fig. Figures 3B are figures showing a configuration of the variable focal length lens assembly 201C according to the first embodiment. The figures shown in the Fig. 3A and Fig. The variable focal length lens assembly 201C shown in Figure 3B differs from the variable focal length lens assemblies 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 assembly 201C includes an optical system 103 and the image sensor 51.

[0037] Optical system 103 comprises a first variable focal length lens 11, a second variable focal length lens 23, a third variable focal length lens 33, and a 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 that order from front to back. 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 all aligned on the same optical axis.

[0038] The second lens with variable focal length 23 is a concave lens. The front surface of the second lens with variable focal length 23 is a concave curved surface, and the rear surface of the second lens with variable focal length 23 is a planar surface. The third lens with variable focal length 33 is a convex lens. The front surface of the third lens with variable focal length 33 is a planar surface, and the rear surface of the third lens with variable focal length 33 is a convex curved surface.

[0039] 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 in front of the second variable focal length lens 23 when the setup is considered as a whole. In other words, relative to the second variable focal length lens 23, the third conjugate point 3 is located a distance equal to the second focal length f2 behind the second variable focal length lens 23.

[0040] The first lens with variable focal length 11 and the second lens with variable focal length 23 are contained 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 lens with variable focal length 33 and the lens with fixed focal length 41 are contained 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).

[0041] Fig. 4A and Fig. Figures 4B show a configuration of the variable focal length lens assembly 201D according to the first embodiment. The figures shown in the Fig. 4A and Fig. The variable focal length lens assembly 201D shown in Figure 4B differs from the variable focal length lens assembly 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 assembly 201D comprises an optical system 104 and the image sensor 51.

[0042] The optical system 104 comprises 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 that order from front to back. 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.

[0043] The second lens with variable focal length 24 and the third lens with variable focal length 34 are tabular planar lenses. The front and back surfaces of the second lens with variable focal length 24 are planar. The front and back surfaces of the third lens with variable focal length 34 are planar.

[0044] The second variable focal length lens 24 has a second focal length f2 with a negative infinity value. The third variable focal length lens 34 has a third focal length f3 with a positive infinity value. The focal lengths f2 and f3 essentially satisfy equation (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 setup is considered 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 lens setup 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 back surfaces.

[0045] The first lens with variable focal length 11 and the second lens with variable focal length 24 are contained 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 lens with variable focal length 34 and the lens with fixed focal length 41 are contained 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.

[0046] It should be noted that the optical system 104, although not shown, can be configured such that the second variable focal length lens 24 has a second focal length f2 with a positive infinity value, and the third variable focal length lens 34 has a third focal length f3 with a negative infinity value. In this case, the third conjugate point 3 is located at an infinity distance behind the third variable focal length lens 34 when the setup is considered as a whole. In other words, relative to the third variable focal length lens 34, the third conjugate point 3 is located at a distance equal to the third focal length f3 in front of the third variable focal length lens 34.

[0047] Furthermore, the variable focal length lens devices 201A to 201 are devices for measuring images of objects and include typical image processing and illumination devices. In a case where the variable focal length lens devices 201A to 201D include illumination devices, a configuration is possible in which the illumination devices share a portion of the optical systems 101 to 104, as well as a configuration in which the illumination devices do not share any portion of the optical systems 101 to 104.Furthermore, in a case where the lighting devices share part of the optical systems 101 to 104, a configuration is possible 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.

[0048] Furthermore, in a case where liquid lenses are used as lenses with variable focal length, power supplies or control sections not shown, such as driver boards for controlling the liquid lenses, are also included.

[0049] Next, an operation carried out by the variable focal length lens device 201A will be described with reference to the Fig. 1A and Fig. 1B is clearly explained. The variable focal length lens assembly 201A has a magnification and a focal point position, which can be changed as needed.

[0050] First, a case is explained in which the variable focal length lens assembly 201A sets or adjusts the focal point position as explained.

[0051] Regarding the first variable focal length lens 11, the variable focal length lens assembly 201A adjusts the first focal length f1 such that the distance between the first variable focal length lens 11 and an object whose measurement is desired coincides with the first focal length f1. The adjustment of the focal point position of the variable focal length lens assembly 201A is complete when the distance and the first focal length f1 coincide in this way.

[0052] Next, a case will be explained in which the variable focal length lens assembly 201A changes the magnification as explained.

[0053] 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 generally 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 undefined. f*=f2×f3 / (f2+f3−d)

[0054] The condition shown in formula (1) is therefore that the system is an afocal system that performs an expansion or reduction of the luminous flux. At this point, for example, the magnification m of the optical system 101 is determined using formula (3) described below. m=f2 / f1×f4 / f3

[0055] For the sake of 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

[0056] Fig. Figure 5 shows the operation of an afocal system with the second lens with variable focal length 21 and the third lens with variable focal length 31. Fig. Figure 5 shows three operating modes as examples.

[0057] 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 assembly 201A varies the position of the third conjugate point 3 based on mutually different operating conditions and, for example, has the third conjugate points 3, 3' and 3".

[0058] 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 “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 equal to 2.

[0059] 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 equal to 1.

[0060] 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 / 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 equal to 1 / 2.

[0061] Fig. Figure 6 shows the operation of an afocal system with the second lens with variable focal length 22 and the third lens with variable focal length 32. Fig. Figure 6 shows three operating modes as examples.

[0062] 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 assembly 201B varies the position of the third conjugate point 3 based on mutually different operating conditions and, for example, has the third conjugate points 3, 3' and 3".

[0063] 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 / 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 equal to 1 / 3.

[0064] In a case where the variable focal length lens assembly 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 equal to 1 / 2.

[0065] In a case where the variable focal length lens assembly 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 equal to 3 / 5.

[0066] Fig. Figure 7 shows the operation of an afocal system with the second lens with variable focal length 23 and the third lens with variable focal length 33. Fig. Figure 7 shows three operating modes as examples.

[0067] 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 assembly 201C varies the position of the third conjugate point 3 based on mutually different operating conditions and, for example, has the third conjugate points 3, 3' and 3".

[0068] In a case where the variable focal length lens assembly 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 equal to 3.

[0069] In a case where the variable focal length lens assembly 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 equal to 2.

[0070] In a case where the variable focal length lens assembly 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.

[0071] Therefore, it becomes 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 magnification m, while the focal point position is adjusted by changing the first focal length f1.

[0072] 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)

[0073] Furthermore, 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)

[0074] Accordingly, an image of an object located at the first conjugation 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 and the third variable focal length lenses 31 to 33. Furthermore, if the first focal length f1 is changed and the position of the first conjugation point 1 is adjusted to a position different from that of the object, 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 lenses 21 to 23 and the third variable focal length lenses 31 to 33.

[0075] Here, the operation of the variable focal length lens devices 201A to 201C is explained using specific values ​​to facilitate understanding.

[0076] For example, it is assumed 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. It is also assumed that the lens spacing d between the second lenses with variable focal length 21 to 23 and the third lenses with variable focal length 31 to 33 is 200 mm.

[0077] Only the cases where the first focal length f1 is 50 mm and 150 mm are mentioned 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. If the first focal length f1 is then 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).

[0078] Fig. Figure 8 shows the operation of an afocal system with the second lenses with variable focal length 21 and 23 and the third lenses with variable focal length 31 and 33.

[0079] Since the magnification m of optical systems 101 to 103 can be either positive or negative, there are, as is known, two operating modes with identical absolute values ​​of magnification m in formula (5), formula (6) and formula (7). The two operating modes correspond to those in the Fig. 5 and Fig. 6 shown operating conditions of magnification reduction or those in the Fig. 5 and Fig. The 7 operating states of the magnification extension are shown. Furthermore, the two operating modes correspond to a difference depending on whether the magnification m* of the afocal system* has positive or negative values ​​with the same absolute values.

[0080] Fig. Figure 8 shows an example of two operating modes in a case where the absolute values ​​of the magnification m* of the afocal system* are 2. In an operating mode where the magnification m* of the afocal system* is equal to 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 an operating 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 operating 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 that can be acquired can be freely inverted.

[0081] Furthermore, it is explained below that the two operating modes described above are particularly suitable when using variable focal length lenses, which are liquid lenses.

[0082] It has been reported that the degradation of tilt-dependency properties due to gravity or similar forces varies in degree for liquid lenses. In a planar optical arrangement where the optical axis is perpendicular to the direction of gravity, the top (opposite the bottom) and bottom (bottom) surfaces of a lens may, in some cases, exhibit different aberration characteristics. Correcting such asymmetric aberration around the optical axis is challenging, but by utilizing the two operating modes described above, it is possible to digitally correct this asymmetric aberration.

[0083] This means that in a case where the magnification m* of the afocal system* is positive, the light beams that have passed through the bottom surfaces of the second lenses with variable focal length 21 to 23 pass through the bottom surfaces of the third lenses with variable focal length 31 to 33. At this point, the aberrations occur similarly to the inclinations of a pair of lenses with variable focal length. This means that in a case where the magnification m* of the afocal system* is positive, the light beams that have passed through the bottom surfaces of the second lenses with variable focal length 21 to 23 pass through the bottom surfaces of the third lenses with variable focal length 31 to 33. At this point, the aberrations are averaged out according to the inclinations by a pair of lenses with variable focal length.Due to the difference between the features of a captured image when the magnification m* of the afocal system* is positive and those of a captured image when the magnification m* of the afocal system* is negative, the aberrations appear as the difference between these two, corresponding to the slopes. Therefore, these aberrations can be reduced by the digital image correction of the difference described above.

[0084] Fig. Figure 9 shows the operation of an afocal system with the second lenses with variable focal length 21 and 24 and the third lenses with variable focal length 31 and 34. Fig. Figure 9 shows a concrete example of the two operating modes in which the absolute values ​​of the magnification m are identical values ​​to those in Fig. 8 will be shown, and shows an example that demonstrates the two operating modes in a case where the absolute values ​​of the magnification m are 1.

[0085] In an operating mode where the magnification m* of the afocal system* is equal to 1, both the second variable focal length lens 24 and the third variable focal length lens 34 are parallel planar plates, and these essentially satisfy formulas (1) and (4). In an operating mode where the magnification m* of the afocal system* is equal to -1, the second variable focal length lens 21 and the third variable focal length lens 31 satisfy formulas (1) and (4). In the two operating 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.

[0086] It should be noted that, strictly speaking, infinity of focal length is not possible from a manufacturing perspective, and it is therefore obvious that in the practical operation of a variable focal length lens, a condition in which the refractive power, which is the reciprocal of the focal length, becomes 0 within the range of variability can be regarded as infinity of focal length.

[0087] As previously explained, the variable focal length lens arrangements 201A to 201D according to the first embodiment comprise: the first variable focal length lens 11, which has the first focal length f1; the second variable focal length lenses 21 to 24, which are arranged behind the first variable focal length lens 11 and have the second focal length f2; the third variable focal length lenses 31 to 34, which are arranged behind the second variable focal length lenses 21 to 24 and have the third focal length f3; the fixed focal length lens 41, which is arranged behind the third variable focal length lenses 31 to 34 and has the fourth focal length f4; the first conjugate point 1, which is arranged at a distance equal to the first focal length f1 in front of the first variable focal length lens 11 and serves as a focal point position;the second conjugate point 2, which is located 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 lenses with variable focal length 21 to 24 and at a distance equal to the third focal length f3 in front of the third lenses with variable focal length 31 to 34, wherein the first optical subsystems 111 and 114, which contain the first lens with variable focal length 11 and the second lenses with variable focal length 21 to 24, are infinitely conjugate systems with respect to the first conjugate point 1, and the second optical subsystems 121 to 124, which contain the third lenses with variable focal length 31 and 34 and the lens with fixed focal length 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.

[0088] It should be noted that while the principles of the liquid lenses, specifically those cited as examples of variable focal length lenses—one using a piezoelectric actuator and one using electrowetting—are explained, it is obvious that achieving the advantageous effects of the invention is easily accomplished even when using liquid lenses based on other principles. Furthermore, the advantageous effects of the invention can be achieved similarly when using lenses other than liquid lenses with variable focal length capabilities.

[0089] Liquid lenses, which are described as lenses with variable focal length, can have optical functions such as solid lenses, e.g. glasses or coverslips, in addition to parts with liquid lens functions.

[0090] Regarding the mechanisms for adjusting the focal point of variable focal length lenses, liquid lenses are controlled, for example, 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.

[0091] 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, but not every one of them needs to have a planar part in the strict sense. It is obvious that the advantageous effects of the invention can also be easily achieved if each of the lenses has a slight curvature on the side of a planar surface, as in a meniscus lens or a so-called best-form lens suitable for an infinitely conjugated system.

[0092] While in the cases described in the present first embodiment there are three operating points in the operation of an afocal system, 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.

[0093] Variable focal length lens devices 202A and 202B according to a second embodiment are based on Fig. 10A and Fig. 10B as well Fig. 11A and Fig. 11B explained. It should be noted that components having similar functions to those described in the first embodiment mentioned above are designated with identical reference numerals, and further explanations are omitted.

[0094] Fig. 10A and Fig. Figures 10B show a configuration of the variable focal length lens assembly 202A according to the second embodiment. The figures shown in the Fig. 10A and Fig. The variable focal length lens arrangement 202A shown in Figure 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, where an image of a first conjugate point 1 is formed.

[0095] In particular, the variable focal length lens assembly 202A, instead of the image sensor 51 of the variable focal length lens assembly 201A, 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.

[0096] 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 can be, for example, a single optical fiber or an optical fiber formed by joining several optical fibers together to form 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. An optical interconnection method, such as an optical space system, an optical fiber system, or the like, is used.

[0097] Next, an operation performed by the variable focal length lens assembly 202A is explained. The operation performed by an optical system 101 of the variable focal length lens assembly 202A to adjust the focal point position is the same as the operation performed by optical system 101 of the variable focal length lens assembly 201A to adjust the focal point position. The operation performed by optical system 101 of the variable focal length lens assembly 202A to change the magnification m is the same as the operation performed by optical system 101 of the variable focal length lens assembly 201A to change the magnification m.

[0098] The illumination light emitted by the illumination light source 62 passes through the optical fiber 61 and the optical system 101 in that order due to the action of the circulator 63. The illumination light that has passed through the optical system 101 is then emitted onto an object located at the first conjugate point 1. Conversely, the illumination light reflected and scattered by the object passes through the optical system 101 and the optical fiber 61 in that order. The illumination light that has passed through the optical fiber 61 then falls onto the light-receiving element 52 due to the action of the circulator 63. Consequently, the variable focal length lens assembly 202A can receive an image of the object from the light-receiving element 52 that has received the illumination light.

[0099] Accordingly, an image of the object located at the first conjugate point 1 is formed on the light-receiving element 52 after it has been 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, if the first focal length f1 is changed and the position of the first conjugate point 1 is adjusted to a position different from that of the object, an image of the object is also formed on the light-receiving element 52 in this state after it has been 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.

[0100] It should be noted that the in the Fig. 10A and Fig. The lens assembly with variable focal length 202A shown in 10B contains the optical system 101, but instead of the optical system 101, it also contains the one shown in the Fig. 11A and Fig. Optical system 103 shown in 11B may be included. Fig. 11A and Fig. Figures 11B show a configuration of the variable focal length lens assembly 202B according to the second embodiment. The variable focal length lens assembly 202B comprises the optical system 103, the light receiving element 52, the optical fiber 61, an illumination light source 62, and the circulator 63. Furthermore, while the variable focal length lens assembly 202A includes the optical system 101, it can also include, instead of the optical system 101, the element shown in the Fig. 2A and Fig. 2B shown optical system 102 or the one in the Fig. 4A and Fig. Optical system 104 shown in 4B is included.

[0101] As previously explained, the variable focal length lens arrangements 202A and 202B according to the second embodiment comprise: 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, 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, having a third focal length f3; a fixed focal length lens 41 arranged behind the third variable focal length lenses 31 to 33, having the fourth focal length f4; the first conjugate point 1, which is arranged at a distance equal to the first focal length f1 in front of the first variable focal length lens 11 and serves as a focal point position;a second conjugate point 2, which is arranged at a distance equal to the fourth focal length f4 behind the lens with fixed focal length 41 and is equipped 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 lenses with variable focal length 21 and 23 and at a distance equal to the third focal length f3 in front of the third lenses with variable focal length 31 and 33, wherein the first optical subsystems 111 and 113, which contain the first lens with variable focal length 11 and the second lenses with variable focal length 21 and 23, are infinitely conjugate systems with respect to the first conjugate point 1, and the second optical subsystems 121 and 123, which contain the third lenses with variable focal length 31 and 33 and the lens with fixed focal length 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 make it possible to change the magnifications and focus positions as needed, which is suitable for variable focal length lenses. Third embodiment.

[0102] Variable focal length lens devices 203A and 203B according to a third embodiment are based on Fig. 12A and Fig. 12B as well Fig. 13A and Fig. 13B explained. It should be noted that components having similar functions to those described in the first embodiment described above are designated with identical reference numerals, and no further explanations are required.

[0103] Fig. 12A and Fig. Figures 12B show a configuration of the variable focal length lens assembly 203A according to the third embodiment. The figures shown in the Fig. 12A and Fig. The variable focal length lens assembly 203A shown in Figure 12B has a configuration in which, after the illumination light emitted by an illumination light source 62 has been split into an optical reference path 71 and an optical signal path 72a, the illumination light rays obtained after splitting are multiplexed at a light receiving element 53, making it possible to acquire an interference signal of the light rays. That is, the variable focal length lens assembly 203A has a configuration in which the optical reference path 71 and the optical signal paths 72a and 72b are added to the variable focal length lens assembly 202A described above.

[0104] The optical reference path 71 establishes an optical connection between the illumination light source 62 and the light receiving element 53. The optical signal path 72a establishes an optical connection between the illumination light source 62 and one terminal of the circulator 63. The optical signal path 72b establishes an optical connection between the other terminal of the circulator 63 and the light receiving element 53.

[0105] Next, an operation performed by the variable focal length lens assembly 203A is explained. The operation performed by an optical system 101 of the variable focal length lens assembly 203A to adjust the focal point position is the same as the operation performed by optical system 101 of the variable focal length lens assembly 201A to adjust the focal point position. The operation performed by optical system 101 of the variable focal length lens assembly 203A to change the magnification m is the same as the operation performed by optical system 101 of the variable focal length lens assembly 201A to change the magnification m.

[0106] Illumination light emitted from the illumination light source 62 is split between the optical reference path 71 and the optical signal path 72a. Illumination light split into optical reference path 71 passes through the optical reference path 71 and falls upon the light receiving element 53. Illumination light split into optical signal path 72a, on the other hand, passes through an optical fiber 61 and the optical system 101 in that order due to the action of the circulator 63. The illumination light that has passed through the optical system 101 is then 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 that order.The illumination light, having passed through the optical fiber 61, then passes through the optical signal path 72b and, due to the action of the circulator 63, falls upon a light receiving element 52. At this point, 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 optical reference path 71. As a result, the variable focal length lens assembly 203A can receive interference information about the rays of illumination light from the light receiving element 52, which has received two rays of illumination light.

[0107] It should be noted that the in the Fig. 12A and Fig. The lens assembly with variable focal length 203A shown in 12B contains the optical system 101, but instead of the optical system 101, it also contains the one shown in the Fig. 13A and Fig. Optical system 103 shown in 13B may be included. Fig. 13A and Fig. Figure 13B shows a configuration of the variable focal length lens assembly 203B according to the third embodiment. The variable focal length lens assembly 203B comprises 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. Furthermore, while the variable focal length lens assembly 203A includes the optical system 101, it can also include, instead of the optical system 101, the element shown in the Fig. 2A and Fig. 2B shown optical system 102 or the one in the Fig. 4A and Fig. Optical system 104 shown in 4B is included.

[0108] Furthermore, the variable focal length lens devices 203A and 203B contain typical interference information processing devices, which are necessary for heterodyne detection systems or the like.

[0109] In a case where the variable focal length lens devices 203A and 203B are, for example, interference information processing devices, they can temporally sample the wavelengths by using wavelength-variable light sources instead of the illumination light source 62, thus 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 able to perform a distance measurement based on wavelength differences and can accordingly obtain interference information even from an object located at a distance from the first conjugate point 1.

[0110] It should be noted that within the scope of protection of the present disclosure, any combination of embodiments, modifications of any components in the embodiments, or omissions of any components in the embodiments are possible through the disclosure. COMMERCIAL APPLICABILITY

[0111] A lens arrangement with variable focal length according to the present disclosure is suitable for use as a lens arrangement with variable focal length or the like, which has a magnification and a focus position that can be changed as desired and required, which is suitable for lenses with variable focal length. REFERENCE MARK LIST

[0112] 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: optical reference 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 assembly f1: first focal length, f2: second focal length, f3: third focal length, f4: fourth focal length, d: lens spacing

Claims

[1] Variable focal length lens assembly comprising: a first lens with variable focal length, which has a first focal length; a second lens with variable focal length, which is arranged behind the first lens with variable focal length, and has a second focal length; a third lens with variable focal length, which is arranged behind the second lens with variable focal length, and has a third focal length; a lens with a fixed focal length, which is arranged behind the third lens with a variable focal length, and has a fourth focal length; a first conjugate point, which is located at a distance equal to the first focal length in front of the first lens with variable focal length, and serves 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 equipped with an image sensor or a light guide; and a third conjugate point located at a distance equal to the second focal length behind the second variable-length lens and at a distance equal to the third focal length in front of the third variable-length lens, wherein a first optical subsystem, which contains the first lens with variable focal length and the second lens with variable focal length, is an infinitely conjugate system with respect to the first conjugate point, and a second optical subsystem, which includes the third lens with variable focal length and the lens with fixed focal length, is an infinitely conjugate system with respect to the third conjugate point. [2] Lens device with variable focal length according to claim 1, further comprising: an optical path divider located behind the light guide; a light source connected to one end of the optical path splitter; and a light receiving element that is connected to the other end of the optical path splitter. [3] Lens device with variable focal length according to claim 2, further comprising an optical reference path that directs the illumination light split by the illumination light source to the light receiving element. [4] Lens device with variable focal length according to claim 3, wherein the illumination light source is a wavelength-variable light source.

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