Focusing optical system and endoscope

Abstract

The utility model discloses a focusable optical system and endoscope, focusable optical system includes first lens group, second lens group and third lens group, have negative focal power, positive focal power and positive focal power in proper order, by moving the second lens group along the optical axis, realize the switching between wide angle observation state and close shot observation state. The second lens group comprises a positive meniscus lens, the focal power of the positive meniscus lens can be small, and large variation of aberration and large variation of a main optical angle can be avoided. The third lens group comprises at least two lenses, two continuous lenses arranged close to the image surface are negative lenses, light can be gradually deflected in the direction away from the optical axis, the main light angle theta of the optical system can be increased, and the main light angle theta of the optical system can meet the requirement that theta is larger than or equal to 18 degrees and smaller than or equal to 34 degrees. Therefore, the focusable optical system provided by the utility model can obtain a larger main light angle, and can better correct aberration.

Description

Technical Field

[0001] The utility model relates to the field of optical systems, in particular to a focus-adjustable optical system and an endoscope. Background Art

[0002] Endoscopes are increasingly used in the medical field. By inserting an endoscope into a body cavity, images of the interior can be obtained, helping doctors effectively diagnose lesions. Some existing optical systems used in endoscopes feature focusing capabilities, enabling the endoscope to obtain clear images from near to far perspectives. This allows for observation over a wide range of distances, facilitating the search and observation of lesions through the endoscope.

[0003] The chief ray angle (CRA) of an optical system must match the principal ray angle of incidence of the image sensor used. A mismatch, such as a small CRA, can result in dark edges or color casts in the image. In recent years, with the advancement of CMOS image sensor technology, they have gradually replaced CCD image sensors due to their low cost, low power consumption, and high frame rate. Optical systems using CMOS image sensors typically require a large chief ray angle to ensure compactness.

[0004] However, for an optical system with adjustable focus, the movement of the lens will cause significant changes in the principal ray angle and aberrations. Increasing the principal ray angle of the optical system will be very detrimental to the correction of aberrations. Utility Model Content

[0005] The purpose of the utility model is to provide a focus-adjustable optical system and an endoscope, which can obtain a larger main light angle and can better correct aberrations.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] A focus-adjustable optical system, including a wide-angle observation state and a close-up observation state, is applied to an endoscope. The focus-adjustable optical system includes a first lens group, a second lens group, and a third lens group, which are arranged in sequence from the object side to the image side. The first lens group has negative optical power, the second lens group has positive optical power, and the third lens group has positive optical power. Switching between the wide-angle observation state and the close-up observation state is achieved by moving the second lens group along the optical axis.

[0008] The second lens group includes a positive meniscus lens, wherein both the object-side surface and the image-side surface of the positive meniscus lens are curved toward the image side;

[0009] The third lens group includes at least two lenses, and two consecutive lenses disposed close to the image plane among the at least two lenses are negative lenses;

[0010] The focus-adjustable optical system satisfies the following condition (1):

[0011] 18°≤θ≤34°…(1);

[0012] Wherein, θ represents the principal light angle of the focus-adjustable optical system.

[0013] Exemplarily, the focus-adjustable optical system further satisfies the following conditions (2) and (3):

[0014] f G3 / f w >1.3…(2);

[0015] -2 <f8 / f G3 <-0.6 ... (3);

[0016] Among them, f G3 represents the focal length of the third lens group, f w represents the focal length of the adjustable-focus optical system in the wide-angle observation state, and f8 represents the focal length of the lens disposed closest to the image plane.

[0017] Exemplarily, the focus-adjustable optical system further satisfies the following conditional formula (4):

[0018] f G3 / f w <3…(4).

[0019] Exemplarily, the focus-adjustable optical system further satisfies the following conditional formula (5):

[0020] 9 <f G2 / d<30…(5);

[0021] Among them, f G2 represents the focal length of the second lens group, and d represents the movement distance of the second lens group during the focusing process of the adjustable-focus optical system.

[0022] Exemplarily, the focus-adjustable optical system further includes a fixed aperture arranged between the second lens group and the third lens group.

[0023] Exemplarily, the first lens group includes a first lens, a second lens and a third lens, the first lens has negative optical power, the second lens has negative optical power, the third lens has positive optical power, and the lens group formed by the combination of the second lens and the third lens has positive optical power.

[0024] Exemplarily, the second lens and the third lens are cemented together.

[0025] Exemplarily, the third lens group includes a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged in sequence from the object side to the image side, wherein the seventh lens and the eighth lens are two consecutive lenses arranged close to the image plane, and the fifth lens and the sixth lens are both positive lenses.

[0026] Exemplarily, the sixth lens is cemented to the seventh lens.

[0027] An endoscope comprises an optical system and an image sensor arranged on an image plane of the optical system, wherein the optical system adopts the focus-adjustable optical system described in any of the above examples.

[0028] It can be seen from the above technical solution that the utility model provides a focus-adjustable optical system, including a wide-angle observation state and a close-up observation state, which is applied to endoscopes. The focus-adjustable optical system includes a first lens group, a second lens group and a third lens group, which are arranged in sequence from the object side to the image side. The first lens group has negative optical focal length, the second lens group has positive optical focal length, and the third lens group has positive optical focal length. The switching between the wide-angle observation state and the close-up observation state is achieved by moving the second lens group along the optical axis. Among them, the second lens group includes a positive meniscus lens, the object side surface and the image side surface of the positive meniscus lens are both bent toward the image side. The optical focal length of the positive meniscus lens can be relatively small, which helps to avoid large changes in aberrations and large changes in the main light angle caused by the movement of the second lens group. The third lens group cooperates with the first lens group to correct the aberrations of the optical system, and controls the incident angle of the light of the optical system incident on the image plane through the third lens group. The third lens group includes at least two lenses, and two consecutive lenses located near the image plane of the at least two lenses are negative lenses. This can gradually deflect the passing light away from the optical axis, which helps to increase the principal angle of the optical system. The principal angle θ of this optical system can meet the requirement of 18°≤θ≤34°. Therefore, the adjustable focus optical system of the present invention can achieve a larger principal angle and effectively correct aberrations.

[0029] The endoscope provided by the utility model can achieve the above beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 A schematic diagram of a focus-adjustable optical system in a wide-angle observation state provided by one embodiment of the present utility model;

[0032] Figure 2 for Figure 1 A schematic diagram of a focus-adjustable optical system in a close-up observation state is shown;

[0033] Figure 3-1 The MTF curve of a focus-adjustable optical system in a wide-angle observation state provided in Example 1 of the present utility model;

[0034] Figure 3-2 This is an MTF curve of a focus-adjustable optical system in a close-range observation state provided in Example 1 of the present utility model;

[0035] Figure 4-1 The MTF curve of a focus-adjustable optical system in a wide-angle observation state provided in the second embodiment of the present utility model;

[0036] Figure 4-2 The MTF curve of a focus-adjustable optical system in close-range observation state provided in the second embodiment of the present invention;

[0037] Figure 5-1 This is an MTF curve of a focus-adjustable optical system in a wide-angle observation state provided by Example 3 of the present utility model;

[0038] Figure 5-2 This is the MTF curve of a focus-adjustable optical system in close-range observation state provided by Example 3 of the present utility model.

[0039] The reference numerals in the drawings of the specification include:

[0040] G1-first lens group, G2-second lens group, G3-third lens group, L1-first lens, L2-second lens, L3-third lens, L4-fourth lens, L5-fifth lens, L6-sixth lens, L7-seventh lens, L8-eighth lens, ST-aperture, IMG-image plane. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will be combined with the drawings of the embodiments of the present invention to clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0042] When using an endoscope to observe within a body cavity, clear images can be obtained from a wide range of perspectives, from near to far, facilitating the doctor's search and observation of lesions. An endoscope with a focus function can meet this requirement, providing good imaging quality across the entire depth of field.

[0043] In recent years, with the development of complementary metal oxide semiconductor (CMOS) image sensor technology, it has gradually replaced CCD image sensors due to its advantages of low cost, low power consumption, and high frame rate. Optical systems using CMOS image sensors typically have specific CRA requirements to ensure compactness. If the CRA of the optical system does not match the CRA of the image sensor used, for example, a small CRA can result in dark edges or color casts in the image. Furthermore, for adjustable focus optical systems, since these systems involve lens movement, increasing the principal angle is very detrimental to aberration correction.

[0044] To address this issue, this embodiment provides a focus-adjustable optical system and an endoscope, which can obtain a larger principal light angle and better correct aberrations.

[0045] Specifically, this embodiment provides a focus-adjustable optical system, including a wide-angle observation state and a close-up observation state, for use in an endoscope. The focus-adjustable optical system includes a first lens group, a second lens group, and a third lens group, which are arranged in sequence from the object side to the image side. The first lens group has negative optical power, the second lens group has positive optical power, and the third lens group has positive optical power. Switching between the wide-angle observation state and the close-up observation state is achieved by moving the second lens group along the optical axis.

[0046] The second lens group includes a positive meniscus lens, wherein both the object-side surface and the image-side surface of the positive meniscus lens are curved toward the image side;

[0047] The third lens group includes at least two lenses, and two consecutive lenses disposed close to the image plane among the at least two lenses are negative lenses;

[0048] The focus-adjustable optical system satisfies the following condition (1):

[0049] 18°≤θ≤34°…(1);

[0050] Wherein, θ represents the principal light angle of the focus-adjustable optical system.

[0051] The second lens group is movable, and focusing is adjusted by moving the second lens group along the optical axis, enabling the optical system to switch between wide-angle and close-up viewing modes. The field of view of the optical system in the wide-angle viewing mode is greater than that in the close-up viewing mode. The second lens group has positive optical power and includes a positive meniscus lens. This positive meniscus lens can have a relatively low optical power, helping to avoid significant changes in aberrations and principal angle when the second lens group is moved.

[0052] The first lens group and the third lens group are both fixed lens groups. The first lens group has negative optical power, and the third lens group has positive optical power. The two lens groups cooperate to correct aberrations of the optical system. The third lens group includes at least two lenses, and two consecutive lenses of the at least two lenses disposed near the image plane are both negative lenses. That is, the lens disposed closest to the image plane in the third lens group is a negative lens, and the lens adjacent to the negative lens is also a negative lens. This arrangement allows the two consecutive negative lenses to gradually deflect the passing light away from the optical axis, which is conducive to continuously increasing the incident angle of the principal ray, thereby ensuring that the principal ray angle θ of the adjustable-focus optical system in the wide-angle observation state and the principal ray angle θ in the close-range observation state both meet the requirement of 18°≤θ≤34°.

[0053] Therefore, the focus-adjustable optical system of this embodiment can obtain a larger principal light angle and can better correct aberrations.

[0054] In some embodiments, the focus-adjustable optical system further satisfies the following conditions (2) and (3):

[0055] f G3 / f w >1.3…(2);

[0056] -2 <f8 / f G3 <-0.6 ... (3);

[0057] Among them, f G3 represents the focal length of the third lens group, f w represents the focal length of the adjustable-focus optical system in a wide-angle observation state, and f8 represents the focal length of the lens closest to the image plane.

[0058] In this embodiment, the third lens group converges the divergent light beams passing through the first lens group and the second lens group and forms an image on the image plane. On the one hand, it is used to improve the chief ray angle (CRA) of the adjustable focus optical system, and on the other hand, it is used to correct the residual aberration of the optical system. After multiple simulation tests, it was found that when f G3 / f w When it is lower than 1.3, the focal length of the third lens group is too large, which will cause serious light deflection and is not conducive to the correction of aberrations.G3 If the value is lower than the lower limit of the above conditional formula (3), the focal length of the lens closest to the image plane is too small, and the light deflection is insufficient, which may cause the main light angle of the optical system to fail to meet the requirements; if f8 / f G3 If the value is higher than the upper limit of the above conditional expression (3), the focal length of the lens closest to the image plane will be too large, and the light will be deflected too sharply, which is not conducive to aberration correction.

[0059] Therefore, when the focus-adjustable optical system satisfies the above-mentioned conditional expressions (2) and (3), it is possible to improve the principal angle of the optical system while better correcting aberrations.

[0060] In some embodiments, the focus-adjustable optical system further satisfies the following conditional formula (4):

[0061] f G3 / f w <3…(4).

[0062] As mentioned above, in order to improve the principal angle of the optical system and better correct the aberration, the focusable optical system can satisfy the above condition (2), that is, f G3 / f w >1.3; however, if f G3 / f w If the value is higher than the upper limit of the above conditional expression (4), the optical power of the third lens group is too small, and the convergence and deflection of light are insufficient, which will increase the distance between the image plane and the third lens group, making the optical system too long.

[0063] Therefore, when the focusing optical system satisfies the above-mentioned conditional expressions (2) to (4), it is possible to improve the principal ray angle of the optical system while better correcting the aberration and avoiding the optical system from being too long.

[0064] In some embodiments, the focus-adjustable optical system further satisfies the following conditional equation (5):

[0065] 9 <f G2 / d<30…(5);

[0066] Among them, f G2 represents the focal length of the second lens group, and d represents the movement distance of the second lens group during the focusing process of the adjustable focus optical system (i.e., during the process of the adjustable focus optical system switching from a wide-angle observation state to a close-up observation state or from a close-up observation state to a wide-angle observation state). G2 If / d is lower than the lower limit of the above conditional expression (5), the optical power of the second lens group is too large relative to its moving stroke, which will cause large changes in aberrations and is not conducive to aberration correction; if f G2If / d is higher than the upper limit of the above conditional expression (5), the optical power of the second lens group is too small relative to its moving stroke, which will lead to an increase in the moving stroke and make the size of the optical system too large.

[0067] Therefore, when the focal length of the second lens group is f G2 When the movement stroke d of the second lens group satisfies the above-mentioned conditional expression (5), it is beneficial to reduce the aberration variation caused by the movement of the second lens group, facilitate the correction of aberrations, and shorten the length of the optical system.

[0068] In some embodiments, the adjustable-focus optical system further includes a fixed aperture stop disposed between the second lens group and the third lens group. The position of the aperture does not change when the second lens group is moved along the optical axis. The aperture is disposed behind the movable lens group, i.e., the second lens group. This ensures that the angle between the aperture stop and the image plane remains substantially constant or changes minimally during focusing, facilitating aberration correction.

[0069] In some embodiments, the first lens group may include a first lens, a second lens, and a third lens. The first lens has negative optical power, the second lens has negative optical power, and the third lens has positive optical power. The lens group formed by the combination of the second and third lenses has positive optical power. The first lens may have a relatively large negative optical power, i.e., the absolute value of the optical power of the first lens is relatively large, which facilitates wide-angle viewing. The positive lens group formed by the combination of the second and third lenses has a relatively small optical power to correct for aberrations. In some embodiments, the second and third lenses may be cemented together to help correct chromatic aberration of the optical system.

[0070] In some embodiments, the second lens group includes a fourth lens having positive optical power. The fourth lens can specifically be a positive meniscus lens, whose object side surface and image side surface are both curved toward the image side. Its optical power is generally small, which helps to avoid causing large changes in aberrations and large changes in the main light angle.

[0071] In some embodiments, the third lens group includes a fifth lens, a sixth lens, a seventh lens, and an eighth lens, arranged in order from the object side to the image side. The seventh lens and the eighth lens are two consecutive lenses arranged close to the image plane, and the fifth lens and the sixth lens are both positive lenses. The fifth and sixth lenses are both positive lenses, resulting in a positive optical power for the third lens group as a whole. The seventh and eighth lenses can be negative lenses. In some embodiments, the sixth lens and the seventh lens are cemented together to help correct chromatic aberration of the optical system.

[0072] For example, reference may be made to Figure 1 and Figure 2 , Figure 1A schematic diagram of a focus-adjustable optical system in a wide-angle observation state provided by an embodiment is shown. Figure 2 for Figure 1 The schematic diagram of a focusable optical system in a close-up observation state is shown in FIG. As shown in the figure, the optical system includes a first lens group G1, a second lens group G2, a stop ST and a third lens group G3.

[0073] The first lens group G1 includes a first lens L1, a second lens L2, and a third lens L3. First lens L1 has negative power, second lens L2 has negative power, and third lens L3 has positive power. The lens group formed by the combination of second lens L2 and third lens L3 has positive power. First lens L1 can be a plano-concave lens with a relatively large negative power, with its image-side surface being concave.

[0074] The second lens group G2 includes a fourth lens L4, which can be a positive meniscus lens with both the object side and the image side curved toward the image side. Figure 1 and Figure 2 As shown, by moving the second lens group G2 along the optical axis toward the third lens group G3, the focusable optical system can be switched from a wide-angle observation state to a close-up observation state. During this period, the first lens group G1 and the third lens group G3 remain stationary, and the aperture ST remains stationary.

[0075] The third lens group G3 includes a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8, each of which has a power of positive, positive, negative, and negative, respectively. The sixth lens L6 and the seventh lens L7 are cemented together.

[0076] The focus-adjustable optical system is described in detail below with reference to specific embodiments.

[0077] It is understood that the optical structures of the following embodiments are similar to Figure 1 and Figure 2 The optical structures shown are the same and therefore will not be described in detail later.

[0078] Example 1

[0079] Detailed optical data of the adjustable focus optical system of this embodiment are shown in Table 1-1. Serial numbers 1 and 2 represent the object-side and image-side surfaces of the first lens element L1, respectively; 3 represents the object-side surface of the second lens element L2; 4 represents the image-side surface of the second lens element L2 and the object-side surface of the third lens element L3; 5 represents the image-side surface of the third lens element L3; 6 and 7 represent the object-side and image-side surfaces of the fourth lens element L4, respectively; ST represents an aperture stop; 9 and 10 represent the object-side and image-side surfaces of the fifth lens element L5, respectively; 11 represents the object-side surface of the sixth lens element L6; 12 represents the image-side surface of the sixth lens element L6 and the object-side surface of the seventh lens element L7; 13 represents the image-side surface of the seventh lens element L7; and 14 and 15 represent the object-side and image-side surfaces of the eighth lens element L8, respectively. The object-side and image-side surfaces of each lens element are spherical. The units of curvature radius and thickness are both in millimeters.

[0080] Table 1-1

[0081]

[0082] The specification data of the focus-adjustable optical system of this embodiment in the wide-angle observation state and the close-range observation state are shown in Table 1-2, wherein ordinary observation corresponds to the wide-angle observation state, and close-range observation corresponds to the close-range observation state. The F number is the effective F value, the units of the field angle and CRA (i.e., the main light angle) are both in degrees, and the unit of the effective focal length is millimeters. D0 represents the object distance, D5 represents the distance between the first lens group G1 and the second lens group G2, and D7 represents the distance between the second lens group G2 and the aperture ST. The units of D0, D5, and D7 are all in millimeters, and D0, D5, and D7 change corresponding to the two observation states. The MTF curve of the focus-adjustable optical system of this embodiment in the wide-angle observation state is shown in Figure 1-2. Figure 3-1 As shown, the MTF curve in the close-range observation state is as follows Figure 3-2 As shown, Figure 3-1 and Figure 3-2 The horizontal axis of the MTF curve shown represents the spatial frequency in lp / mm, and the vertical axis represents the MTF value. Figure 3-1 and Figure 3-2 It can be seen from the MTF curve shown that the focus-adjustable optical system provided by this embodiment can achieve better imaging effects no matter in a near-view observation state or a long-view observation state.

[0083] Table 1-2

[0084]

[0085] Example 2

[0086] Detailed optical data of the adjustable focus optical system of this embodiment are shown in Table 1-1. Serial numbers 1 and 2 represent the object-side and image-side surfaces of the first lens element L1, respectively; 3 represents the object-side surface of the second lens element L2; 4 represents the image-side surface of the second lens element L2 and the object-side surface of the third lens element L3; 5 represents the image-side surface of the third lens element L3; 6 and 7 represent the object-side and image-side surfaces of the fourth lens element L4, respectively; ST represents an aperture stop; 9 and 10 represent the object-side and image-side surfaces of the fifth lens element L5, respectively; 11 represents the object-side surface of the sixth lens element L6; 12 represents the image-side surface of the sixth lens element L6 and the object-side surface of the seventh lens element L7; 13 represents the image-side surface of the seventh lens element L7; and 14 and 15 represent the object-side and image-side surfaces of the eighth lens element L8, respectively. The object-side and image-side surfaces of each lens element are spherical. The units of curvature radius and thickness are both in millimeters.

[0087] Table 2-1

[0088]

[0089] The specification data of the focus-adjustable optical system of this embodiment in the wide-angle observation state and the close-range observation state are shown in Table 2-2, wherein ordinary observation corresponds to the wide-angle observation state, and close-range observation corresponds to the close-range observation state. The F number is the effective F value, the units of the field angle and CRA (i.e., the principal light angle) are both in degrees, and the unit of the effective focal length is millimeters. D0 represents the object distance, D5 represents the distance between the first lens group G1 and the second lens group G2, and D7 represents the distance between the second lens group G2 and the stop ST. The units of D0, D5, and D7 are all in millimeters, and D0, D5, and D7 change corresponding to the two observation states. The MTF curve of the focus-adjustable optical system of this embodiment in the wide-angle observation state is shown in FIG. Figure 4-1 As shown, the MTF curve in the close-range observation state is as follows Figure 4-2 As shown, Figure 4-1 and Figure 4-2 The horizontal axis of the MTF curve shown represents the spatial frequency in lp / mm, and the vertical axis represents the MTF value. Figure 4-1 and Figure 4-2 It can be seen from the MTF curve shown that the focus-adjustable optical system provided by this embodiment can achieve better imaging effects no matter in a near-view observation state or a long-view observation state.

[0090] Table 2-2

[0091]

[0092] Example 3

[0093] Detailed optical data of the adjustable focus optical system of this embodiment are shown in Table 1-1. Serial numbers 1 and 2 represent the object-side and image-side surfaces of the first lens element L1, respectively; 3 represents the object-side surface of the second lens element L2; 4 represents the image-side surface of the second lens element L2 and the object-side surface of the third lens element L3; 5 represents the image-side surface of the third lens element L3; 6 and 7 represent the object-side and image-side surfaces of the fourth lens element L4, respectively; ST represents an aperture stop; 9 and 10 represent the object-side and image-side surfaces of the fifth lens element L5, respectively; 11 represents the object-side surface of the sixth lens element L6; 12 represents the image-side surface of the sixth lens element L6 and the object-side surface of the seventh lens element L7; 13 represents the image-side surface of the seventh lens element L7; and 14 and 15 represent the object-side and image-side surfaces of the eighth lens element L8, respectively. The object-side and image-side surfaces of each lens element are spherical. The units of curvature radius and thickness are both in millimeters.

[0094] Table 3-1

[0095]

[0096] The specification data of the focus-adjustable optical system of this embodiment in the wide-angle observation state and the close-range observation state are shown in Table 3-2, where ordinary observation corresponds to the wide-angle observation state, and close-range observation corresponds to the close-range observation state. The F number is the effective F value, the units of the field angle and CRA (i.e., the main light angle) are both in degrees, and the unit of the effective focal length is millimeters. D0 represents the object distance, D5 represents the distance between the first lens group G1 and the second lens group G2, and D7 represents the distance between the second lens group G2 and the aperture ST. The units of D0, D5, and D7 are all in millimeters, and D0, D5, and D7 change corresponding to the two observation states. The MTF curve of the focus-adjustable optical system of this embodiment in the wide-angle observation state is shown in Figure 3-2. Figure 5-1 As shown, the MTF curve in the close-range observation state is as follows Figure 5-2 As shown, Figure 5-1 and Figure 5-2 The horizontal axis of the MTF curve shown represents the spatial frequency in lp / mm, and the vertical axis represents the MTF value. Figure 5-1 and Figure 5-2 It can be seen from the MTF curve shown that the focus-adjustable optical system provided by this embodiment can achieve better imaging effects no matter in a near-view observation state or a long-view observation state.

[0097] Table 3-2

[0098]

[0099] Table 4 below shows the numerical values ​​of the conditional expressions in Examples 1 to 3.

[0100] Table 4

[0101]

[0102] As can be seen from the above, the optical system with a focusing function provided by the present invention has a principal ray angle θ in a wide-angle observation state and a principal ray angle θ in a close-range observation state that both satisfy 18°≤θ≤34°. Therefore, it can be adapted to most high-pixel CMOS image sensors on the market. In addition, the adjustable-focus optical systems provided in the above embodiments all have a high MTF and high imaging quality, indicating that the optical system with a focusing function provided by the present invention has a good aberration correction effect.

[0103] In summary, the present invention improves the adaptability of the endoscope optical system to the CMOS image sensor by improving the CRA of the endoscope optical system, and at the same time has a focusing function, so that the endoscope optical system has a higher MTF and a wider field of view within the entire depth of field range, and the change in the field of view during the focusing process is small.

[0104] This embodiment further provides an endoscope, comprising an optical system and an image sensor arranged on an image plane of the optical system, wherein the optical system adopts the focus-adjustable optical system described in any one of the above embodiments.

[0105] The endoscope of this embodiment adopts an optical system that can have a larger principal light angle and can better correct aberrations.

[0106] The above describes in detail the adjustable focus optical system and endoscope provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above examples is only intended to help understand the method and core concept of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, various improvements and modifications can be made to the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A focusable optical system, including a wide-angle observation state and a close-up observation state, applied to an endoscope, characterized in that: The focus-adjustable optical system comprises a first lens group, a second lens group, and a third lens group arranged in sequence from the object side to the image side, wherein the first lens group has negative optical power, the second lens group has positive optical power, and the third lens group has positive optical power; Switching between the wide-angle observation state and the close-range observation state is achieved by moving the second lens group along the optical axis; The second lens group includes a positive meniscus lens, wherein both the object-side surface and the image-side surface of the positive meniscus lens are curved toward the image side; The third lens group includes at least two lenses, and two consecutive lenses disposed close to the image plane among the at least two lenses are negative lenses; The focus-adjustable optical system satisfies the following condition (1): 18°≤θ≤34°…(1); Wherein, θ represents the principal light angle of the focus-adjustable optical system.

2. The focus-adjustable optical system according to claim 1, wherein: The following conditions (2) and (3) are also satisfied: f G3 / f w >1.3…(2); -2<f8 / f G3 <-0.6 …(3); Among them, f G3 represents the focal length of the third lens group, f w represents the focal length of the adjustable-focus optical system in the wide-angle observation state, and f8 represents the focal length of the lens disposed closest to the image plane.

3. The focus-adjustable optical system according to claim 2, wherein: The following condition (4) is also satisfied: f G3 / f w <3…(4)。 4. The focus-adjustable optical system according to claim 1, wherein: The following condition (5) is also satisfied: 9<f G2 / d<30…(5); Among them, f G2 represents the focal length of the second lens group, and d represents the movement distance of the second lens group during the focusing process of the adjustable-focus optical system.

5. The focus-adjustable optical system according to claim 1, wherein: The lens system further includes a fixed aperture disposed between the second lens group and the third lens group.

6. The focus-adjustable optical system according to any one of claims 1 to 5, wherein: The first lens group includes a first lens, a second lens and a third lens. The first lens has negative optical power, the second lens has negative optical power, the third lens has positive optical power, and the lens group formed by the second lens and the third lens has positive optical power.

7. The focus-adjustable optical system according to claim 6, wherein: The second lens and the third lens are cemented together.

8. The focus-adjustable optical system according to any one of claims 1 to 5, wherein: The third lens group includes a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged in sequence from the object side to the image side, wherein the seventh lens and the eighth lens are two consecutive lenses arranged close to the image plane, and the fifth lens and the sixth lens are both positive lenses.

9. The focus-adjustable optical system according to claim 8, wherein: The sixth lens is cemented to the seventh lens.

10. An endoscope, characterized in that: The invention comprises an optical system and an image sensor arranged on an image plane of the optical system, wherein the optical system adopts the focus-adjustable optical system according to any one of claims 1 to 9.

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