Imaging optics and imaging device

Abstract

A periscopic optical system in which the total length of an optical device is shortened is disclosed. The optical system includes a reflecting optical element (P) for bending an optical path by 90 degrees from an object side to an image side; a rear lens group (G_rear) on the optical path after the reflecting optical element (P), the rear lens group (G_rear) as a whole having positive refractive power. The reflecting optical element (P) has a convex curvature on a first surface (S1) on the object side and a concave curvature on a third surface (S3) on the image side.

Description

TECHNICAL FIELD

[0001] The present application relates to an imaging optical device, and more particularly, to an imaging optical device having a reflective optical element and an imaging apparatus.

[0002] The present application relates to an imaging lens focusing an image of an object on a single imaging device, such as a CCD, a CMOS sensor, or the like. The present application particularly relates to a photographic lens mounted on a portable device such as a smartphone, a game console, a PC, an IP camera, a home appliance, a car, a drone, and a photographic apparatus, or the like. BACKGROUND

[0003] With the popularization of smartphones in recent years, the demand for imaging lenses is becoming diversified. Since the size of the imaging lens module is directly related to the size of the product in which the imaging lens is mounted, it is desirable to improve the performance of the imaging lens while maintaining its small module thickness. Specifically, this includes enlargement, extension, enlargement of the diameter, and improvement of optical performance, and the like.

[0004] In recent years, multi-camera systems have become mainstream, and long-focus lenses play an important role in the differentiation of smartphone products.

[0005] Users have many opportunities to use long-focus lenses, such as watching and photographing distant objects at events such as sports, photographing landscapes, and celestial bodies, and the like.

[0006] At present, the periscopic imaging optical device using a right-angle prism is used as an imaging optical device in smartphone products. This imaging optical device is used in an imaging lens module having such a long-focus lens function to achieve the purpose of reducing the height of the lens unit.

[0007] In the prior art, a right-angle prism that does not have refractive power itself is used in the periscopic imaging optical device. Since this structure adds a right-angle prism to a conventional extension optical device, the size of the module in the thickness direction can be reduced by bending the light path. However, since the prism is added, the total length of the optical device increases.

[0008] In addition, in general, a product adopts a vibration prevention mechanism. This mechanism is called an Optical Image Stabilizer (OIS), which can sense vibration during photographing using a sensor and correct the optical axis. Specifically, OIS is implemented by physically tilting or shifting the periscope prism or the imaging lens with respect to the optical axis using a piezoelectric element or the like. SUMMARY

[0009] An imaging lens module having a long-focus lens function can shorten the total length of an optical system. In addition, an imaging lens module can be provided which is capable of providing sufficient vibration-proof performance without employing an additional configuration as a vibration-proof mechanism.

[0010] In a periscopic imaging optical device, a right-angle prism having refractive power is employed. By increasing the refractive power on the prism, the total length of the optical system can be shortened. In this context, the refractive power refers to the degree of refraction caused by an optical system such as a lens, and can also be simply referred to as the refractive index. By utilizing the prism refraction effect, the total length of the optical system can be shortened, thereby reducing the thickness of the imaging lens module while maintaining the vibration-proof configuration.

[0011] According to a first aspect, embodiments of the present application provide a periscopic optical system. The optical system includes a reflective optical element (P) for bending a light path by 90 degrees from an object side to an image side; a rear lens group on the light path after the reflective optical element. Wherein the rear lens group as a whole has positive refractive power, the reflective optical element has convex curvature on a first surface (S1) on the object side, and has concave curvature on a third surface (S3) on the image side.

[0012] With reference to the first aspect, in a possible implementation, the following conditional expressions (1), (2) and (3) are satisfied:

[0013] (1);

[0014] (2);

[0015] (3);

[0016] wherein

[0017] FOV: field angle of the optical system (unit: degree);

[0018] f: focal length of the optical system (unit: mm);

[0019] P_S1: proximal axial curvature radius of the object side of the reflective optical element (mm);

[0020] Pf: focal length of the reflective optical element (unit: mm).

[0021] With reference to the first aspect, in a possible implementation, a first lens (L1) included in the rear lens group and disposed closest to the object side has positive refractive power, wherein the following conditional expression (4) is satisfied:

[0022] 0.18 ≤ L1f / f ≤ 1.0 (4);

[0023] wherein

[0024] L1f: focal length of the first lens (L1) in units of mm.

[0025] With reference to the first aspect, in a possible implementation form, the following condition formulas (1)', (2)' and (3)' are further met:

[0026] FOV < 34° (1)';

[0027] 0.4 < P_S1 / f < 3.5 (2)';

[0028] -0.15 < f / Pf < 0.15 (3)'.

[0029] With reference to the first aspect, in a possible implementation form, the reflective optical element is tilted to provide optical vibration isolation.

[0030] With reference to the first aspect, in a possible implementation form, the reflective optical element is moved in the direction of the optical axis and / or in a direction perpendicular to the optical axis to provide optical vibration isolation.

[0031] With reference to the first aspect, in a possible implementation form, the rear lens group consists of a plurality of lens elements including at least four lens elements;

[0032] wherein a part of the plurality of lens elements is moved in the direction of the optical axis to provide focusing.

[0033] According to a second aspect, embodiments of the present application provide a smartphone comprising the optical system according to any of the possible implementation forms of the first aspect.

[0034] According to a third aspect, embodiments of the present application provide a digital camera comprising the optical system according to any of the possible implementation forms of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly describe the embodiments of the present application, the following will briefly describe the drawings as needed. Obviously, in the following description, the drawings only show some embodiments of the present application, and other drawings in these drawings can also be drawn by those skilled in the art without paying creative labor.

[0036] Figure 1 is a schematic diagram of an imaging lens according to embodiments of the present application.

[0037] Figure 2 is a diagram showing parameters of lenses in an imaging lens according to the present application.

[0038] Figure 3 is a graph showing the spherical aberration, astigmatism and distortion of an imaging lens according to another embodiment of the present application.

[0039] Figure 4 is a schematic view of an imaging lens according to another embodiment of the present application.

[0040] Figure 5 is a graph showing the spherical aberration, astigmatism and distortion of an imaging lens according to another embodiment of the present application. DETAILED DESCRIPTION

[0041] The imaging lens according to the present application is composed of a reflecting optical element (P) for bending the optical path 90 degrees from the object side to the image side, followed by a rear lens group (G_rear). The reflecting optical element (P) is a non-planar prism composed of a first surface (S1) having a convex curvature toward the object side, a second surface (S2) having a reflecting surface, and a third surface (S3) having a concave curvature toward the object side.

[0042] By using such a non-planar reflecting optical element as a periscope optical system, the effect of substantially shortening the total length of the imaging lens optical system can be achieved while maintaining the vibration resistance performance and the high degree of reduction equivalent to a conventional optical system. This can solve the above technical problems.

[0043] Hereinafter, embodiments according to the present application will be described in detail with reference to the accompanying drawings.

[0044] Figure 1 is a schematic view showing the structure of an imaging lens according to a first embodiment of the present application. In the imaging lens according to the present embodiment, there is a reflecting optical element (P) for bending the optical path 90 degrees from the object side, followed by a rear lens group (G_rear). P is a non-planar prism composed of a first surface (S1) having a convex curvature toward the object side, a second surface (S2) having a reflecting surface, and a third surface (S3) having a curvature of the same sign (in the same direction) as the first surface, i.e., a concave curvature. The rear lens group (G_rear) is composed of six lenses including a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6) from the P side toward the imaging surface (IMG). G_rear as a whole has a positive refractive power. In addition, before the image surface (IMG), a filter (IR) such as an infrared cut filter or a cover glass is provided. The filter (IR) can be omitted.

[0045] The case of shortening the entire optical system length will be described below. Now, assume that the reflective optical element (P) is a right-angle prism. The prism generally consists of flat surfaces including a first surface (S1), a second surface (S2), and a third surface (S3), and the prism as a whole does not have refractive power. On the other hand, the first surface (S1) of the prism P for the optical system of the present application is a curved surface having a predetermined curvature in a convex direction toward the object side, and P as a whole has positive refractive power. This makes it possible to shorten the total length of the optical system while continuing to use a conventional rear lens group (G_rear).

[0046] Therefore, if the convex curvature of S1 is increased, the effect of shortening the total length of the optical system also improves. For example, by increasing the curvature, the total length of the optical system can be reduced by about 13%. However, if the curvature is increased too much, the aberration generated in S1 also increases, making it difficult to obtain good imaging performance at IMG. Therefore, in the third surface (S3) of the prism P, it is necessary to adjust the refractive power of the prism P to an appropriate range by providing a concave curvature opposite to S1, that is, a concave curvature toward the object side.

[0047] Furthermore, when the total length of the optical system is shortened by the positive refractive power of P as a whole, the deflection of the image due to camera shake caused by the user becomes relatively large, so it is necessary to improve the efficiency of the Optical Image Stabilizer (OIS). Generally, OIS is implemented by shifting, that is, moving vertically and / or horizontally a part or all of the imaging lens with respect to the optical path (or optical axis).

[0048] Since the prism P of the present application itself has positive refractive power, OIS can be more efficiently implemented by tilting, that is, tilting the entire prism P with respect to the optical path (or optical axis), compared to vertical and / or horizontal movement.

[0049] In the first embodiment as described above, the optical system implements OIS by tilting P on the optical path and / or by shifting L5 and L6 of G_rear in the direction of the optical axis.

[0050] In the above-described first embodiment, it is desirable for the optical system to satisfy the following conditional expressions (1), (2), and (3):

[0051] FOV ≤ 38° (1);

[0052] 0.25 ≤ P_S1 / f ≤ 5.0 (2);

[0053] -0.3 ≤ f / Pf ≤ 0.3 (3).

[0054] As Figure 2As shown, each parameter indicated by the above conditional expression is as follows. FOV is the angle of view of the optical system (unit: degree), f is the focal length of the optical system (unit: mm), P_S1 is the paraxial curvature radius of the object side of the reflective optical element (unit: mm), and Pf is the focal length of the reflective optical element (unit: mm).

[0055] The conditional expression (1) appropriately sets the imaging field angle of the optical system. When this range is exceeded, the field angle becomes too large to maintain the periscope structure, and thus it is difficult to reduce the height of the image lens module. Specifically, a "dark angle" of the circumferential field angle occurs in the reflective optical element P.

[0056] The conditional expression (2) appropriately sets the paraxial curvature radius of the first surface (S1) of the reflective optical element P. When this range is fallen below, the aberration generated in S1 becomes too large, and thus it becomes difficult to obtain good imaging performance. On the other hand, when this range is exceeded, the effect of shortening the total length of the optical system becomes insufficient.

[0057] The conditional expression (3) appropriately sets the refractive power of the reflective optical element P (i.e., 1 / focal length f). When this range is exceeded, the refractive power of the reflective optical element P increases, and thus performance degradation during optical isolation using the reflective optical element P occurs.

[0058] Further, when the range of the above conditional expression is exceeded (particularly for the conditional expression (3)), the performance degradation problem during optical isolation becomes more significant, and in order to avoid this, the effect of the optical isolation generated by shifting or tilting the optical element P in the optical path can become insufficient. In this case, another configuration needs to be employed, which results in the size of the imaging lens module becoming larger.

[0059] On the other hand, in the above first embodiment, the first lens (L1) included in G_rear and disposed closest to the object side has a positive refractive power, and selectively satisfies the following conditional expression (4):

[0060] 0.18 ≤ L1f / f ≤ 1.0 (4).

[0061] As shown, L1f is the focal length of the first lens (L1) (unit: mm). Figure 2

[0062] The conditional expression (4) sets an appropriate range for the focal length of L1. When this range is fallen below, the refractive power of L1 becomes stronger, and thus it is difficult to maintain good resolution performance during isolation. Further, when this range is fallen below, the total length of the optical system of the imaging lens module becomes long, and thus a problem occurs in which the effect of shortening the total length of the optical system achieved using the reflective optical element P cannot be sufficiently utilized. ​

[0063] Further, in the above-described first embodiment, it is desirable that the optical system further satisfy the following conditional expressions (1)', (2)' and (3)' :

[0064] FOV < 34° (1)' ;

[0065] 0.3 < P_S1 / f < 3.5 (2)' ;

[0066] -0.15 < f / Pf < 0.15 (3)'.

[0067] In the optical system of the above-described first embodiment, it is desirable that G_rear include a plurality of lenses having at least four lens elements. Focusing is achieved by shifting, i.e., moving some portions of the lens elements, in the direction of the optical axis.

[0068] Accordingly, G_rear needs to be properly configured. Since the number of lens elements of G_rear is small, it is difficult to maintain good resolution performance. In the present invention, the use of a non-planar prism contributes to the expansion of Fno (F number, or F value) compared to a conventional planar right-angle prism, which has been difficult to do in the past. However, as Fno expands, the demand for aberration correction required for the optical system also increases, making it difficult to achieve sufficient resolution performance in a configuration using a small number of lens elements.

[0069] Further, in a conventional planar right-angle prism, parallel light is incident to G_rear from the object side. Therefore, a method of focusing by shifting the entire G_rear in the direction of the optical axis contributes more to the improvement of macro performance. On the other hand, in the present invention, since converging light is incident to G_rear, it is difficult to ensure macro performance by shifting the entire G_rear. This can be a side effect of achieving a shortened total length of the optical system. However, in order to accommodate this, by adopting an internal focusing type configuration, i.e., using some portions of the lens elements including G_rear for focusing, the required macro performance can be easily ensured.

[0070] Figure 3 The spherical aberration, astigmatism and distortion of the imaging lens according to the above-described first embodiment are shown. Among them, the spherical aberration graph shows the amount of aberration for the wavelengths of F line (486.1 nm), d line (587.6 nm) and C line (656.3 nm) with solid lines, respectively. The astigmatism graph shows the amount of aberration for the d line in the sagittal image plane S with a solid line and in the tangential image plane T with a dashed line. Among them, F denotes F value, and IH denotes image height. The distortion graph shows the aberration for the d line with a solid line. Thus, it is apparent that the imaging lens has sufficient desired optical performance.

[0071] The following Table 1 and Table 2 show lens data of the imaging lens according to the above-described first embodiment. Herein, i is the surface number counted from the object side to the image side, the radius is the curvature radius, the thickness is the thickness of the lens center or the air gap, the refractive index (Nd) is the refractive index to the d line, the Abbe number (vd) is the number of the Abbe number to the d line, and the stop is the aperture. The aspheric surface is represented by adding an (asterisk) symbol after the surface number i. Further, the aspheric shape adopted on the aspheric surface of the lens surface is defined by Equation 1 listed below, where z is the distance (height of a perpendicular) from the vertex of the lens surface in the direction of the optical axis, H is the height in the direction perpendicular to the direction of the optical axis, c is the paraxial curvature at the vertex of the lens (reciprocal of the curvature radius), k is the conic constant (taper constant), A4, A6, A8, A10, A12, A14, A16, A18, and A20 are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, sixteenth, eighteenth, and twentieth orders, respectively. (Equation 1)

[0072] (Equation 1)

[0073]

[0074] Table 1

[0075]

[0076] Table 2

[0077]

[0078] Figure 4 is a schematic view showing the structure of the imaging lens according to the second embodiment of the present application. The overall configuration of the imaging lens of the second embodiment is the same as that of the above-described first embodiment, but the parameters of the prism and each lens element are different.

[0079] Figure 5 The spherical aberration chart, the astigmatism chart, and the distortion chart of the imaging lens according to the above-described second embodiment are shown. Thus, it can be seen that the imaging lens also has sufficiently ideal optical performance.

[0080] The following Table 3 and Table 4 show lens data of the imaging lens according to the above-described second embodiment.

[0081] Table 3

[0082]

[0083] Table 4

[0084]

[0085] Table 5 shows parameters of the imaging lens according to the first and second embodiments described above. Thus, it can be seen that the imaging lens according to the first and second embodiments described above satisfies the conditional expressions (1) to (4) shown in Table 5.

[0086] Table 5

[0087]

[0088] The above description shows the embodiments provided by the present application, but is not intended to limit the present application. Any modification, equivalent replacement or improvement made without departing from the spirit and principle of the present application shall be included in the protection scope of the present application.

[0089] Symbol Explanation

[0090] P: Reflective optical element

[0091] L1: First lens

[0092] S1: First surface of the reflective optical element on the object side

[0093] IR: Filter

[0094] IMG: Imaging surface

Claims

1. A periscope optical system, characterized in that, This includes optical devices with refractive power, wherein the optical devices with refractive power consist only of a reflective optical element (P) and a rear lens group, wherein: The reflective optical element (P) is used to bend the light path 90 degrees from the object side to the image side; The rear lens group is located on the optical path after the reflective optical element, and the rear lens group as a whole has positive refractive power. The reflective optical element (P) has a convex curvature on the first surface (S1) on the object side and a concave curvature on the third surface (S3) on the image side, and the reflective optical element (P) has positive refractive power. The first lens (L1), which is included in the rear lens group and is positioned closest to the object, has positive refractive power, wherein the following condition (4)' is satisfied: （4）’； in f: Focal length of the optical system, in mm; L1f: The focal length of the first lens (L1), in mm.

2. The optical system according to claim 1, characterized in that, The following conditions must be met to express expressions (1), (2), and (3): FOV ≤ 38° (1); （2）； –0.3 ≤ f / Pf ≤ 0.3(3); in FOV: Field angle of the optical system, in degrees; P_S1: The radius of curvature of the proximal axis of the reflective optical element on the object side, in mm; Pf: The focal length of the reflective optical element, in mm.

3. The optical system according to claim 1 or 2, characterized in that, The following conditions are also met in expressions (1)', (2)' and (3)': FOV ≤ 34°(1)'; （2）’； –0.15 ≤ f / Pf ≤ 0.15(3)'.

4. The optical system according to claim 1 or 2, characterized in that, The reflective optical element is tilted to provide optical vibration isolation.

5. The optical system according to claim 1 or 2, characterized in that, The reflective optical element is moved along the optical axis and / or in a direction perpendicular to the optical axis to provide optical vibration isolation.

6. The optical system according to claim 1 or 2, characterized in that, The rear lens group consists of a plurality of lens elements, including at least four lens elements; In this embodiment, a portion of the plurality of lens elements moves along the optical axis to provide focusing.

7. A smartphone, characterized in that, The smartphone includes the optical system according to any one of claims 1 to 6.

8. A digital camera, characterized in that, The digital camera includes the optical system according to any one of claims 1 to 6.

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