A large depth of field medical dental mirror optical lens

Abstract

This invention discloses a large depth-of-field medical dental endoscope optical lens, comprising, from the object side to the image side, a first lens, a second lens, an aperture stop, a third lens, and a fourth lens; one of the first and second lenses is an aspherical lens, and the other lens has a dispersion coefficient Vd≥65; one of the third and fourth lenses is an aspherical lens, and the other lens has a dispersion coefficient Vd≥65; the first and second lenses in front of the aperture stop and the third and fourth lenses behind the aperture stop form a symmetrical optical path architecture; the combination of two sets of aspherical and spherical lenses in the symmetrical optical path structure of this technical solution can improve the field of view and balance and correct off-axis aberrations and optical distortion. A high dispersion coefficient is present in front of and behind the aperture stop to balance and correct chromatic aberration, and the optical power and focal length of each lens are rationally allocated, achieving effects such as ultra-large depth of field, low distortion, and high resolution. The entire optical system has a compact structure and significantly reduced cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical lens, in particular to a large depth of field medical oral mirror optical lens. BACKGROUND

[0002] In the medical field, endoscopes are usually used for minimally invasive surgery, but with the development of periodontology, the demand for periodontal oral endoscopes is increasing. The oral endoscope greatly facilitates clinicians to observe periodontal diseases through good illumination and magnification, but the mainstream products on the market have problems such as low resolution, large chromatic aberration, and small depth of field. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a large depth of field medical oral mirror optical lens, which effectively solves the problems of low resolution, large chromatic aberration, and small depth of field.

[0004] According to the large depth of field medical oral mirror optical lens of the embodiment of the present application, from the object side to the image side, there are sequentially arranged: a first lens with negative focal power, a second lens with positive focal power, a diaphragm, a third lens with positive focal power, and a fourth lens with negative focal power.

[0005] One of the first lens and the second lens is a non-spherical lens, and the other has a dispersion coefficient Vd≥65; one of the third lens and the fourth lens is a non-spherical lens, and the other has a dispersion coefficient Vd≥65; the first lens and the second lens on the front side of the diaphragm and the third lens and the fourth lens on the rear side of the diaphragm are in a symmetrical optical path architecture.

[0006] The focal lengths of the above lenses satisfy the following relationship:

[0007] -1.5≤f1 / f≤-1.0;

[0008] 2.0≤f2 / f≤6.0;

[0009] 0.8≤f3 / f≤2.0;

[0010] -4.0≤f4 / f≤-1.5;

[0011] Wherein, f is the effective focal length of the large depth of field medical oral mirror optical lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, and f4 is the focal length of the fourth lens.

[0012] According to the large depth of field medical oral mirror optical lens of the embodiment of the present application, at least the following beneficial effects are achieved:

[0013] The two groups of aspheric surfaces and spherical lenses in the symmetrical optical path structure can improve the field of view, balance the correction of off-axis aberration and optical distortion, balance the correction of chromatic aberration by the high chromatic dispersion coefficients before and after the diaphragm, and reasonably distribute the optical power and focal length of each lens, so that the effects of super large depth of field, low distortion and high resolution are achieved, the number of lenses is small, the optical system structure is compact, and the cost is greatly reduced.

[0014] According to some embodiments of the present application, the first lens is an aspheric lens, the second lens is a spherical lens with a chromatic dispersion coefficient Vd≥65, the third lens is a spherical lens with a chromatic dispersion coefficient Vd≥65, and the fourth lens is an aspheric lens.

[0015] According to some embodiments of the present application, the first surface of the first lens from the object side to the image side along the optical axis is convex, and the second surface is concave; the first surface of the second lens from the object side to the image side along the optical axis is concave, and the second surface is convex.

[0016] According to some embodiments of the present application, the first surface of the third lens from the object side to the image side along the optical axis is convex, and the second surface is convex; the first surface of the fourth lens from the object side to the image side along the optical axis is concave and M-shaped, and the second surface is convex and M-shaped.

[0017] According to some embodiments of the present application, the first lens is a spherical lens with a chromatic dispersion coefficient Vd≥65, the second lens is an aspheric lens, the third lens is an aspheric lens, and the fourth lens is a spherical lens with a chromatic dispersion coefficient Vd≥65.

[0018] According to some embodiments of the present application, the aspheric lens is an organic optical glass or an inorganic optical glass.

[0019] According to some embodiments of the present application, an image sensor is further arranged on the image side.

[0020] According to some embodiments of the present application, a filter group is arranged between the fourth lens and the image sensor.

[0021] According to some embodiments of the present application, a protective glass is arranged between the filter group and the image sensor.

[0022] According to some embodiments of the present application, the focal length of the large-depth-of-field medical oral mirror optical lens is EFL=1.59mm, and the aperture value is Fno=6.5.

[0023] Additional aspects and advantages of the present application will be given in part in the following description, part will become apparent from the following description, or will be understood by those skilled in the art through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described below in conjunction with the accompanying drawings and embodiments, in which:

[0025] Figure 1 A schematic view of a large depth of field medical dental mirror optical lens structure according to an embodiment of the present application;

[0026] Figure 2 A chromatic aberration, astigmatic field curvature, distortion map of a large depth of field medical dental mirror optical lens according to an embodiment of the present application;

[0027] Figure 3 A ray aberration map of a large depth of field medical dental mirror optical lens according to an embodiment of the present application;

[0028] Figure 4 An MTF map of a large depth of field medical dental mirror optical lens according to an embodiment of the present application;

[0029] Figure 5 A relative illuminance map of a large depth of field medical dental mirror optical lens according to an embodiment of the present application.

[0030] Reference Signs:

[0031] A first lens L1, a second lens L2, a stop STO, a third lens L3, a fourth lens L4, an image sensor IMG, an optical filter set IR, a protective glass CG. DETAILED DESCRIPTION

[0032] Embodiments of the present application will be described in detail below, examples of which are shown in the accompanying drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are for the purpose of explaining the present application only, and should not be understood as limiting the present application.

[0033] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, etc. is based on the orientation or position relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0034] In the description of the present application, the plural refers to two or more. If there is a description of first, second, etc., it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the order of indicated technical features.

[0035] In the description of the present application, unless otherwise explicitly defined, the words such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0036] Referring to Figure 1 As shown in the figure, it is a large depth of field medical oral mirror optical lens of an embodiment of the present application, comprising, from the object side to the image side, in sequence: a first lens L1 with negative focal power, a second lens L2 with positive focal power, a stop STO, a third lens L3 with positive focal power, and a fourth lens L4 with negative focal power; the first lens L1 controls the incidence angle of the optical system and reduces the height of the light first, then the second lens L2 corrects the on-axis chromatic aberration of the system, the stop STO is used to limit the beam aperture, the third lens L3 corrects the on-axis chromatic aberration and distortion of the system, and finally the fourth lens L4 with negative focal power corrects the off-axis aberration of the system.

[0037] One of the first lens L1 and the second lens L2 is a non-spherical lens, and the other has a dispersion coefficient Vd≥65; one of the third lens L3 and the fourth lens L4 is a non-spherical lens, and the other has a dispersion coefficient Vd≥65; the first lens L1 and the second lens L2 in front of the stop STO and the third lens L3 and the fourth lens L4 behind the stop STO are symmetrical optical path structures;

[0038] The focal lengths of the above lenses satisfy the following relationship:

[0039] -1.5≤f1 / f≤-1.0;

[0040] 2.0≤f2 / f≤6.0;

[0041] 0.8≤f3 / f≤2.0;

[0042] -4.0≤f4 / f≤-1.5;

[0043] Wherein, f is the effective focal length of the large depth of field medical oral mirror optical lens, f1 is the focal length of the first lens L1, f2 is the focal length of the second lens L2, f3 is the focal length of the third lens L3, and f4 is the focal length of the fourth lens L4.

[0044] As described above, the two groups of non-spherical and spherical lenses of the symmetrical optical path structure in the technical solution can improve the field of view and balance the correction of off-axis aberration and optical distortion, and the high dispersion coefficient before and after the stop balances the correction of chromatic aberration, and reasonably allocates the focal length and focal length relationship of each lens, realizes the effects of super large depth of field, low distortion, high resolution and the like, and has only four lenses, the whole optical system structure is compact and the cost is greatly reduced.

[0045] In some embodiments of the present application, the first lens L1 is an aspherical lens, the second lens L2 is a spherical lens with a dispersion coefficient Vd≥65, the third lens L3 is a spherical lens with a dispersion coefficient Vd≥65, and the fourth lens L4 is an aspherical lens, thereby forming a symmetric optical path structure of the first embodiment.

[0046] In some embodiments of the present application, the first surface of the first lens L1 along the optical axis from the object side to the image side is convex, and the second surface is concave; the first surface of the second lens L2 along the optical axis from the object side to the image side is concave, and the second surface is convex, thereby balancing the astigmatism field curvature of the lens.

[0047] In some embodiments of the present application, the first surface of the third lens L3 along the optical axis from the object side to the image side is convex, and the second surface is convex; the first surface of the fourth lens L4 along the optical axis from the object side to the image side is concave and M-shaped, and the second surface is convex and M-shaped.

[0048] In some embodiments of the present application, the first lens L1 is a spherical lens with a dispersion coefficient Vd≥65, the second lens L2 is an aspherical lens, the third lens L3 is an aspherical lens, and the fourth lens L4 is a spherical lens with a dispersion coefficient Vd≥65, thereby forming a symmetric optical path structure of the second embodiment.

[0049] In some embodiments of the present application, the aspherical lens is an organic optical glass or an inorganic optical glass.

[0050] The following table shows the specific parameters of the embodiments of the present application:

[0051] Surface Radius Thickness Nd Vd Object INF 15 - - ASP S1 34.94 1.45 1.54 55.7 ASP S2 0.984 0.665 - - S3 -6.96 0.87 1.50 81.6 S4 -2.4 0.1 - - S5 INF 0.1 - - S6 1.813 1.525 1.50 81.6 S7 -1.095 0.1 - - ASP S8 6 0.4 1.63 23.3 ASP S9 1.74 1.375 - - S10 INF 0.6 1.52 64.2 S11 INF 0.3 - - Image INF - - -

[0052] Table 1

[0053] The aspherical curve driving equation of the above embodiments is as follows:

[0054]

[0055] In the formula, c is the aspherical curvature, r is the radial coordinate, k is the conic coefficient of the quadratic surface, and AR1..30 is the aspherical coefficient of each order. The specific aspherical parameters are as shown in Table 2 below:

[0056] Surface S1 S2 S8 S9 Radius 34.94 0.984 6 1.74 c 0.028620492 1.016260163 0.166666667 0.574712644 K 0 0 0 0 A 0.07605507822 0.365626199 -0.63105423 -0.6121182474 B -0.028938017 0.1824337352 0.07392834709 0.514701121 C 0.0073494415 -0.9637710135 0.4098612 -0.30213704695 D -0.000889565 2.1396747688 -0.8031902083 0.07224364658 E 3.734862922e-005 - - -

[0057] Table 2

[0058] The present embodiment adopts a symmetric structure, which is compact and simple, and is very suitable for application in the narrow space of the oral cavity. The aperture of Fno 6.5 does not require too strong additional light irradiation, and ensures high physical resolution and large light aperture while ensuring large depth of field.

[0059] In some embodiments of the present application, an image sensor IMG is arranged on the image side for capturing imaging signals, the image sensor IMG has a size of 1 / 4 inch and has a high resolution, and is most suitable for an imaging target surface of 4.2 mm. It should be noted that the sensor (image sensor, such as COMS, CCD, etc.) is not limited to a specific type.

[0060] In some embodiments of the present application, an optical filter set IR is arranged between the third lens group G3 and the image sensor IMG, the optical filter set IR is a parallel flat plate with a certain thickness, and the optical surface thereof is coated with different bandwidth film layers according to day and night. The optical filter set IR can adopt an infrared cutoff or absorption filter, or a full-spectrum filter, which can filter out interfering light to enable the image sensor IMG to obtain the best imaging effect.

[0061] Further, in some embodiments of the present application, a protective glass CG is arranged between the optical filter set IR and the image sensor IMG, which can protect the image sensor IMG from direct damage by external forces.

[0062] In some embodiments of the present application, the focal length EFL of the large-depth-of-field medical oral mirror optical lens is 1.59 mm, the ultra-short light path is suitable for specific medical oral scenes, the aperture value Fno is 6.5, the larger aperture requires less light compensation, in the commonly used object distance 10 mm-30 mm of the oral endoscope, a clear picture can be presented without additional focusing, and a lens with an optical distortion of less than 5% can be realized.

[0063] Figures 2 to 5 The figure is an optical evaluation diagram of an embodiment of the present application. Figure 2 The figure is a spherical aberration field curvature diagram of an embodiment of the present application, and it can be seen that the red-green axial chromatic aberration is corrected; under the premise of ultra-wide angle, the optical distortion is less than 5%, and the picture distortion degree is small. Figure 3 The figure is a ray aberration diagram of an embodiment of the present application, the balance correction of each aberration is good, the magnification chromatic aberration is about 2 um, the actual shooting picture chromatic aberration effect is good, and the best image surface difference of each field of view is small (the field curvature balance is good). Figure 4 The figure is an MTF diagram of an embodiment of the present application, the average MTF is greater than 0.35 under 100 lp / mm, the MTF in the normalized 0.7 field of view is greater than 0.4, and the imaging effect is excellent. Figure 5 The figure is a relative luminance curve of an embodiment of the present application, the brightness ratio of the picture peripheral region to the central region is greater than 45%, and the naked eye will not have a large light and dark difference.

[0064] The embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the purpose of the present application.

Claims

1. A large depth-of-field medical dental endoscope optical lens, characterized in that, It includes the following components arranged sequentially from the object side to the image side: a first lens with negative optical power (L1), a second lens with positive optical power (L2), an aperture stop (STO), a third lens with positive optical power (L3), and a fourth lens with negative optical power (L4). One of the first lens (L1) and the second lens (L2) is an aspherical lens, and the dispersion coefficient Vd of the other lens is ≥65; one of the third lens (L3) and the fourth lens (L4) is an aspherical lens, and the dispersion coefficient Vd of the other lens is ≥65; the first lens (L1) and the second lens (L2) on the front side of the aperture stop (STO) and the third lens (L3) and the fourth lens (L4) on the rear side of the aperture stop (STO) form a symmetrical optical path architecture; The focal lengths of the above lenses satisfy the following relationship: -1.5≤f1 / f≤-1.0; 2.0 ≤ f² / f ≤ 6.0; 0.8 ≤ f³ / f ≤ 2.0; -4.0≤f4 / f≤-1.5; Where f is the effective focal length of the large depth-of-field medical dental mirror optical lens, f1 is the focal length of the first lens (L1), f2 is the focal length of the second lens (L2), f3 is the focal length of the third lens (L3), and f4 is the focal length of the fourth lens (L4).

2. The large depth-of-field medical dental endoscope optical lens according to claim 1, characterized in that: The first lens (L1) is an aspherical lens, the second lens (L2) is a spherical lens with a dispersion coefficient Vd≥65, the third lens (L3) is a spherical lens with a dispersion coefficient Vd≥65, and the fourth lens (L4) is an aspherical lens.

3. The optical lens for a large depth-of-field medical dental endoscope according to claim 1 or 2, characterized in that: The first lens (L1) has a convex surface on the first side and a concave surface on the second side along the optical axis from the object side to the image side; the second lens (L2) has a concave surface on the first side and a convex surface on the second side along the optical axis from the object side to the image side.

4. The optical lens for a large depth-of-field medical dental endoscope according to claim 1 or 2, characterized in that: The third lens (L3) has a convex surface on the first surface and a convex surface on the second surface along the optical axis from the object side to the image side; the fourth lens (L4) has a concave surface and an M-shape on the first surface and a convex surface and an M-shape on the second surface along the optical axis from the object side to the image side.

5. The optical lens for a large depth-of-field medical dental endoscope according to claim 1, characterized in that: The first lens (L1) is a spherical lens with a dispersion coefficient Vd≥65, the second lens (L2) is an aspherical lens, the third lens (L3) is an aspherical lens, and the fourth lens (L4) is a spherical lens with a dispersion coefficient Vd≥65.

6. A large depth-of-field medical dental endoscope optical lens according to claim 2 or 5, characterized in that: The aspherical lens is made of organic optical glass or inorganic optical glass.

7. The optical lens for a large depth-of-field medical dental endoscope according to claim 1, characterized in that: It also includes an image sensor (IMG) located on the image side.

8. The optical lens for a large depth-of-field medical dental endoscope according to claim 7, characterized in that: A filter group (IR) is disposed between the fourth lens (L4) and the image sensor (IMG).

9. The optical lens for a large depth-of-field medical dental endoscope according to claim 8, characterized in that: A protective glass (CG) is disposed between the filter group (IR) and the image sensor (IMG).

10. The optical lens for a large depth-of-field medical dental endoscope according to claim 1, characterized in that: The large depth-of-field medical dental endoscope optical lens has a focal length EFL = 1.59mm and an aperture value Fno = 6.5.

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