Optical imaging system

Abstract

An optical imaging system is disclosed, comprising: a first lens having a negative refractive power; a second lens having a refractive power; a third lens having a positive refractive power; a fourth lens having a negative refractive power; a fifth lens having a refractive power; a sixth lens having a positive refractive power; and a seventh lens having a negative refractive power, wherein the first lens to the seventh lens are arranged in sequence from the object side to the image side, wherein, -0.5 < f / f4 < -0.1 is satisfied, where f4 is the focal length of the fourth lens and f is the total focal length of the optical imaging system.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2017-0167715 filed on December 7, 2017, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety for all purposes by reference. Technical Field

[0002] The present application relates to an optical imaging system. Background Art

[0003] Generally, a camera module is installed in a mobile communication terminal, a computer, a vehicle, etc., making it possible to capture an image.

[0004] According to the trend of slimmer mobile communication terminals, such camera modules have been required to have a small size and high image quality.

[0005] Meanwhile, camera modules for vehicles have also been required to have a small size and high image quality so as not to obstruct the driver's field of view and not to spoil the appearance of the vehicle.

[0006] In particular, a camera used in a rearview mirror of a vehicle should be able to capture a clear image to ensure rear visibility during driving of the vehicle, and thus is required to have high image quality.

[0007] In addition, cameras used in vehicles should be able to clearly capture images of objects even when illumination is low at night, and therefore require a lens system that has a small size and can capture images in both the visible light wavelength region and the near-infrared region.

[0008] The above information is presented as background information only to assist with understanding the present disclosure. No determination has been made, and no statement is made, as to whether any of the above information may be applicable as prior art with respect to the present disclosure. Summary of the invention

[0009] This summary is provided to introduce selected concepts in a simplified form and further describe the concepts in the following detailed description. This summary is neither intended to identify key features or essential features of the claimed subject matter nor to be used as an aid in determining the scope of the claimed subject matter.

[0010] In a general aspect, an optical imaging system includes: a first lens having negative refractive power; a second lens having negative refractive power; a third lens; a fourth lens; a fifth lens; a sixth lens; and a seventh lens. The first to seventh lenses are sequentially arranged from the object side toward the image side, the third lens, the fourth lens, the sixth lens, and the seventh lens are formed of plastic, and the first lens, the second lens, and the fifth lens are formed of glass.

[0011] The object-side surface and the image-side surface of each of the first lens and the second lens may be spherical surfaces, and the object-side surface and the image-side surface of each of the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens may be aspherical surfaces.

[0012] The third lens, the fourth lens, and the seventh lens may be formed using plastic having the same optical characteristics.

[0013] The sixth lens and the seventh lens may be disposed closer to each other than any other adjacent lenses.

[0014] The sixth lens and the seventh lens may be formed using plastics having different optical characteristics from each other.

[0015] The optical imaging system may further include a stop disposed between the fourth lens and the fifth lens.

[0016] In the optical imaging system, TTL is the distance from the object surface of the first lens to the imaging surface of the image sensor along the optical axis, IMGH is half of the diagonal length of the imaging surface of the image sensor, and TTL / (2×IMGH) may be less than 3.0.

[0017] In the optical imaging system, f3 is the focal length of the third lens, f is the total focal length of the optical imaging system including the first lens to the seventh lens, and f / f3 may be greater than 0.25 and less than 0.65.

[0018] In the optical imaging system, f4 is the focal length of the fourth lens, and f / f4 may be greater than -0.5 and less than -0.1.

[0019] In the optical imaging system, f6 is the focal length of the sixth lens, and f / f6 may be greater than 0.25 and less than 0.65.

[0020] In the optical imaging system, f7 is the focal length of the seventh lens, and f / f7 may be greater than -0.5 and less than -0.1.

[0021] The refractive index of the third lens may be less than 1.64. The refractive index of the fourth lens may be less than 1.64. The refractive index of the sixth lens may be less than 1.535, and the refractive index of the seventh lens may be less than 1.64.

[0022] In another general aspect, an optical imaging system includes: a first lens having negative refractive power and having a meniscus shape, an object-side surface of the first lens being convex; a second lens having negative refractive power and including two concave surfaces; a third lens; a fourth lens; a fifth lens; a sixth lens; and a seventh lens. The first to seventh lenses are sequentially arranged from the object side toward the image side, the third lens, the fourth lens, the sixth lens, and the seventh lens are formed of plastic, the first lens, the second lens, and the fifth lens are formed of glass, a distance between the sixth lens and the seventh lens along the optical axis is shorter than a distance between any other adjacent lenses along the optical axis, and the sixth lens and the seventh lens are formed of plastic having different optical properties from each other.

[0023] The third lens, the fourth lens, and the seventh lens may be formed using plastic having the same optical characteristics, the third lens may have positive refractive power, the fourth lens may have negative refractive power, and the seventh lens may have negative refractive power.

[0024] Both surfaces of the third lens may be convex, and both surfaces of the fourth lens may be concave.

[0025] The object-side surface and the image-side surface of the first lens may be spherical surfaces.

[0026] An object-side surface and an image-side surface of the second lens may be spherical surfaces, and an object-side surface and an image-side surface of each of the third lens and the fifth lens may be aspherical surfaces.

[0027] Other features and aspects will be apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a diagram illustrating a first example of an optical imaging system.

[0029] Figure 2 Shown Figure 1 An example of a curve of aberration characteristics of an optical imaging system is shown in FIG.

[0030] Figure 3 is a diagram illustrating a second example of the optical imaging system.

[0031] Figure 4 Shown Figure 3 An example of a curve of aberration characteristics of an optical imaging system is shown in FIG.

[0032] In all drawings and detailed description, the same reference numerals refer to the same elements. The drawings may not be drawn to scale, and the relative sizes, proportions, and depictions of the elements in the drawings may be exaggerated for clarity, illustration, and convenience. DETAILED DESCRIPTION

[0033] The following specific embodiments are provided to help the reader gain a comprehensive understanding of the methods, devices and / or systems described herein. However, after understanding the disclosure of the present application, various permutations, modifications and equivalents of the methods, devices and / or systems described herein will be apparent. For example, the order of operations described herein is merely an example, and is not limited to the examples set forth herein, but in addition to the operations that must occur in a particular order, changes that will be apparent may be made after understanding the disclosure of the present application. In addition, in order to improve clarity and brevity, descriptions of features known in the art may be omitted.

[0034] The features described herein may be implemented in different forms and will not be interpreted as being limited to the examples described herein. Rather, the examples described herein are provided only to illustrate some of the many possible ways of implementing the methods, devices and / or systems described herein that will be apparent after understanding the disclosure of the present application.

[0035] In the drawings, the thickness, size and shape of the lens have been slightly exaggerated for ease of explanation. In particular, the shape of the spherical surface or aspherical surface shown in the drawings is shown by way of example. That is, the shape of the spherical surface or aspherical surface is not limited to the shape shown in the drawings.

[0036] In this application, the first lens refers to a lens closest to an object, and the seventh lens refers to a lens closest to an image sensor.

[0037] In addition, the first surface of each lens refers to its surface closest to the object side (or object side surface), and the second surface of each lens refers to its surface closest to the image side (or image side surface). In addition, all values ​​of the radius of curvature and thickness of the lens, image height (IMGH, half the diagonal length of the imaging surface of the image sensor), etc. are expressed in millimeters (mm), and the field of view (FOV) of the optical imaging system is expressed in degrees.

[0038] In addition, in the description of the shape of each of the lenses, "one surface of the lens is convex" means that the paraxial region portion of the corresponding surface is convex, and "one surface of the lens is concave" means that the paraxial region portion of the corresponding surface is concave. Therefore, although one surface of the lens is described as convex, the edge portion of the one surface of the lens may be concave. Similarly, although one surface of the lens is described as concave, the edge portion of the one surface of the lens may be convex.

[0039] The paraxial region refers to a very narrow region near the optical axis.

[0040] One aspect of the present disclosure provides an optical imaging system in which the aberration improvement effect can be enhanced, a high level of resolution can be achieved, imaging can be performed even in a low-illuminance environment, and deviation in resolution can be suppressed even if there is a large change in temperature.

[0041] The optical imaging system in the examples described herein may include seven lenses.

[0042] For example, the optical imaging system may include a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens which are sequentially arranged from an object side.

[0043] However, the optical imaging system is not limited to including only seven lenses, but may also include other components if necessary.

[0044] For example, the optical imaging system may further include an image sensor configured to convert an image of an object incident on the image sensor into an electrical signal. The image sensor may be configured to capture an image of the object in a near infrared region as well as a visible light region.

[0045] In addition, the optical imaging system may further include an aperture configured to control the amount of light. For example, the aperture may be disposed between the fourth lens and the fifth lens.

[0046] In the optical imaging system of the example described here, some of the first to seventh lenses may be formed using plastic, and other lenses of the first to seventh lenses may be formed using glass. In addition, the lens formed using glass may have optical properties different from those of the lens formed using plastic.

[0047] For example, the first lens, the second lens, and the fifth lens may be formed using glass, and the third lens, the fourth lens, the sixth lens, and the seventh lens may be formed using plastic.

[0048] In addition, in the optical imaging system in the examples described herein, some of the first to seventh lenses may be aspherical lenses, and other lenses of the first to seventh lenses may be spherical lenses.

[0049] As an example, the first surface and the second surface of at least one of the first lens and the second lens may be spherical surfaces. The first surface and the second surface of at least one of the third lens to the seventh lens may be aspherical surfaces. For example, the first surface and the second surface of each of the third lens to the seventh lens may be aspherical surfaces. Alternatively, the first surface and the second surface of each of the third lens and the fifth lens may be aspherical surfaces.

[0050] That is, the first lens and the second lens may be formed using glass and have first and second surfaces that are spherical surfaces, and the fifth lens may be formed using glass and may have first and second surfaces that are aspherical surfaces.

[0051] In addition, the third lens, the fourth lens, the sixth lens, and the seventh lens may be formed using plastic, and may respectively have first and second surfaces that are aspherical surfaces.

[0052] The aspherical surface of each of the lenses may be expressed by the following Equation 1:

[0053]

[0054] In Formula 1, c is the curvature of the lens (the inverse of the radius of curvature), K is a conic constant, and Y is the distance from a point on the aspheric surface of the lens to the optical axis in a direction perpendicular to the optical axis. In addition, constants A to D are aspheric coefficients. In addition, Z is the distance between a point on the aspheric surface of the lens at a distance Y from the optical axis and a tangent plane that intersects the vertex of the aspheric surface of the lens.

[0055] The first to seventh lenses sequentially included in the optical imaging system from the object side may have negative refractive power, negative refractive power, positive refractive power, negative refractive power, positive refractive power, positive refractive power, and negative refractive power, respectively.

[0056] The optical imaging system in the example described herein may satisfy the following Conditional Expression 2 to Conditional Expression 10:

[0057] TTL / (2×IMGH)<3.0 (Conditional expression 2)

[0058] 0.25<f / f3<0.65 (Conditional Expression 3)

[0059] -0.5<f / f4<-0.1 (Conditional Expression 4)

[0060] 0.25<f / f6<0.65 (Conditional Expression 5)

[0061] -0.5<f / f7<-0.1 (Conditional Expression 6)

[0062] n3<1.64 (Conditional Expression 7)

[0063] n4<1.64 (Conditional Expression 8)

[0064] n6<1.535 (Conditional Expression 9)

[0065] n7<1.64 (Conditional Expression 10)

[0066] In the above Conditional Expression 2 to Conditional Expression 10, TTL is the distance from the object-side surface of the first lens to the imaging plane of the image sensor along the optical axis, IMGH is half the diagonal length of the imaging plane of the image sensor, f is the total focal length of the optical imaging system, f3 is the focal length of the third lens, f4 is the focal length of the fourth lens, f6 is the focal length of the sixth lens, f7 is the focal length of the seventh lens, n3 is the refractive index of the third lens, n4 is the refractive index of the fourth lens, n6 is the refractive index of the sixth lens, and n7 is the refractive index of the seventh lens.

[0067] In the optical imaging systems of some examples described herein, multiple lenses can perform an aberration correction function, thereby enhancing aberration improvement performance.

[0068] In addition, the optical imaging system may have an f-number (Fno) (a constant indicating brightness of the optical imaging system) of 2.1 or less, thereby being able to clearly capture an image of an object even in a low-illuminance environment.

[0069] Additionally, the optical imaging system can clearly capture images of objects in both the visible light region and the near-infrared region.

[0070] Furthermore, in the optical imaging system of some examples described herein, at least one of the first lens and the second lens may be configured as a spherical lens, thereby reducing the cost of manufacturing the optical imaging system.

[0071] In addition, in the optical imaging system of some examples described herein, since the first lens, the second lens, and the fifth lens are formed using glass having a relatively small thermal expansion coefficient, and the third lens, the fourth lens, the sixth lens, and the seventh lens are formed using plastic, a constant resolution can be maintained even in a temperature range of about -40° C. to about 80° C. Therefore, the optical imaging system of some examples described herein can achieve a high level of resolution even in an environment where the temperature varies over a wide range.

[0072] The housing provided with the first to seventh lenses may be formed of plastic, and the housing may shrink or expand according to the temperature change of the surrounding environment. Therefore, the distance between the seventh lens and the image sensor may be changed by deformation of the housing according to the temperature change, which may cause the problem that the focus cannot be properly converged.

[0073] However, in the optical imaging system in some examples described herein, since the third lens, the fourth lens, the sixth lens, and the seventh lens are formed using plastic, the third lens, the fourth lens, the sixth lens, and the seventh lens may shrink or expand according to temperature changes in the surrounding environment.

[0074] Therefore, by designing the deformation amounts of the third lens, the fourth lens, the sixth lens, and the seventh lens in consideration of the shape deformation amounts of the housing according to changes in temperature, the focal position does not change even when the temperature changes.

[0075] That is, the optical imaging system in some examples described herein may be configured such that a change in the distance between the seventh lens and the image sensor according to a temperature change corresponds to a change in the focal position according to the temperature change.

[0076] Will refer to Figure 1 and Figure 2 An optical imaging system according to a first example disclosed herein is described.

[0077] The optical imaging system according to the first exemplary embodiment may include an optical system including a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160 and a seventh lens 170, and may further include a stop ST, a filter 180 and an image sensor 190.

[0078] Table 1 shows the lens characteristics of each lens (radius of curvature of the lens, thickness, distance between lenses, refractive index, and Abbe number).

[0079] The image height may be about 3.3 mm to about 3.4 mm.

[0080] Table 1

[0081]

[0082] In the surface numbers in Table 1, the symbol * indicates an aspherical surface.

[0083] In a first example, the first lens 110 may have negative refractive power and a meniscus shape, and its object-side surface is convex. For example, the first surface of the first lens 110 may be convex in the paraxial region, and the second surface thereof may be concave in the paraxial region.

[0084] The second lens 120 may have negative refractive power, and both surfaces thereof may be concave. For example, the first surface and the second surface of the second lens 120 may be concave in the paraxial region.

[0085] The third lens 130 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the third lens 130 may be convex in the paraxial region.

[0086] The fourth lens 140 may have negative refractive power, and both surfaces thereof may be concave. For example, the first surface and the second surface of the fourth lens 140 may be concave in the paraxial region.

[0087] The fifth lens 150 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the fifth lens 150 may be convex in the paraxial region.

[0088] The sixth lens 160 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the sixth lens 160 may be convex in the paraxial region.

[0089] The seventh lens 170 may have negative refractive power and have a meniscus shape whose image-side surface is convex. For example, a first surface of the seventh lens 170 may be concave in a paraxial region, and a second surface thereof may be convex in the paraxial region.

[0090] The first surface and the second surface of each of the third to seventh lenses 130 to 170 may have the aspheric coefficients shown in Table 2.

[0091] Table 2

[0092] 5 6 7 8 10 11 12 13 14 15 K 0.440136 6.848888 6.135658 1.33456 15 -2.49737 -4.74098 0.30031 0.763848 18.52056 A 0.005715 0.02412 0.010521 0.002348 0.006184 -0.00795 0.003907 -0.02091 -0.00098 0.017304 B -3.23E-05 -0.00466 -0.00776 -0.00388 -0.00117 0.000652 -0.00026 0.004831 0.000503 -0.00311 C 0.000163 0.000627 0.000145 0.001091 0 0 -5.16E-06 -0.00049 1.71E-06 0.000286 D -2.86E-05 -0.00046 -0.00032 -0.00022 0 0 1.85E-07 2.37E-05 5.83E-06 -1.10E-05

[0093] In addition, the first lens 110 and the second lens 120 may be spherical lenses and may be formed using glass. The fifth lens 150 may be an aspherical lens and may be formed using glass. The third lens 130, the fourth lens 140, the sixth lens 160, and the seventh lens 170 may be aspherical lenses and may be formed using plastic.

[0094] In addition, the third lens 130 , the fourth lens 140 , and the seventh lens 170 may be formed using plastic having the same optical characteristics.

[0095] The sixth lens 160 and the seventh lens 170 may be disposed close to each other. For example, among the distances along the optical axis between the adjacent lenses, the distance between the sixth lens 160 and the seventh lens 170 along the optical axis may be the shortest. In addition, the sixth lens 160 and the seventh lens 170 may be formed using plastics having different optical properties.

[0096] The sixth lens 160 and the seventh lens 170 formed using plastics having different optical characteristics may be disposed closer to each other than any other adjacent lenses to improve aberration correction performance.

[0097] In addition, the stop ST may be disposed between the fourth lens 140 and the fifth lens 150 .

[0098] In addition, the optical imaging system constructed as described above may have Figure 2 Aberration characteristics shown in .

[0099] Will refer to Figure 3 and Figure 4 An optical imaging system according to a second example disclosed herein is described.

[0100] The optical imaging system according to the second example may include an optical system including a first lens 210 , a second lens 220 , a third lens 230 , a fourth lens 240 , a fifth lens 250 , a sixth lens 260 , and a seventh lens 270 , and may also include a stop ST, a filter 280 , and an image sensor 290 .

[0101] Table 3 shows the lens characteristics of each lens (radius of curvature of the lens, thickness, distance between lenses, refractive index, and Abbe number).

[0102] The image height may be about 3.3 mm to about 3.4 mm.

[0103] In the surface numbers of Table 3, the symbol * indicates an aspherical surface.

[0104] In a second example, the first lens 210 may have negative refractive power and a meniscus shape, and its object-side surface is convex. For example, the first surface of the first lens 210 may be convex in the paraxial region, and the second surface thereof may be concave in the paraxial region.

[0105] The second lens 220 may have negative refractive power, and both surfaces thereof may be concave. For example, the first surface and the second surface of the second lens 220 may be concave in the paraxial region.

[0106] The third lens 230 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the third lens 230 may be convex in the paraxial region.

[0107] The fourth lens 240 may have negative refractive power, and both surfaces thereof may be concave. For example, the first surface and the second surface of the fourth lens 240 may be concave in the paraxial region.

[0108] Table 3

[0109]

[0110] The fifth lens 250 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the fifth lens 250 may be convex in the paraxial region.

[0111] The sixth lens 260 may have positive refractive power, and both surfaces thereof may be convex. For example, the first surface and the second surface of the sixth lens 260 may be convex in the paraxial region.

[0112] The seventh lens 270 may have negative refractive power and have a meniscus shape whose image-side surface is convex. For example, a first surface of the seventh lens 270 may be concave in a paraxial region, and a second surface thereof may be convex in the paraxial region.

[0113] The first surface and the second surface of each of the third to seventh lenses 230 to 270 may have aspheric coefficients as shown in Table 4.

[0114] Table 4

[0115] 5 6 7 8 10 11 12 13 14 15 K 0.157622 0 0 0 15 -1.44397 -4.84012 0.225957 0.905192 61.64189 A 0.006202 0.0127 -0.00517 0.000124 0.009688 -0.00285 0.003132 -0.01954 0.00075 0.018517 B -0.00026 0.000346 0 0 -0.00138 0.000269 -0.00027 0.004597 0.00019 -0.00326 C 0.000211 0 0 0 0 0 -2.13E-05 -0.00049 3.60E-05 0.000293 D -3.78E-05 0 0 0 0 0 -9.81E-07 2.33E-05 5.70E-06 -1.15E-05 .

[0116] In addition, the first lens 210 and the second lens 220 may be spherical lenses and may be formed using glass. The fifth lens 250 may be an aspherical lens and may be formed using glass. The third lens 230, the fourth lens 240, the sixth lens 260, and the seventh lens 270 may be aspherical lenses and may be formed using plastic.

[0117] In addition, the third lens 230 , the fourth lens 240 , and the seventh lens 270 may be formed using plastic having the same optical characteristics.

[0118] The sixth lens 260 and the seventh lens 270 may be disposed close to each other. For example, among the distances along the optical axis between the adjacent lenses, the distance along the optical axis between the sixth lens 260 and the seventh lens 270 may be the shortest. In addition, the sixth lens 260 and the seventh lens 270 may be formed using plastics having different optical properties.

[0119] The sixth lens 260 and the seventh lens 270 formed using plastics having different optical characteristics may be disposed closer to each other than any other adjacent lenses, thereby improving aberration correction performance.

[0120] In addition, the stop ST may be disposed between the fourth lens 240 and the fifth lens 250 .

[0121] In addition, the optical imaging system constructed as described above may have Figure 4 Aberration characteristics shown in .

[0122] As explained above, in the optical imaging system in the example disclosed here, the aberration improvement effect can be enhanced, a high level of resolution can be achieved, imaging can be performed even in a low illumination environment, and resolution deviation can be suppressed even if there is a large change in temperature.

[0123] Although the present disclosure includes specific examples, it will be apparent after understanding the disclosure of the present application that various changes in form and detail may be made to these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein will be considered to be descriptive only and not for limiting purposes. The description of the features or aspects in each example will be understood to be applicable to similar features or aspects in other examples. If the described techniques are performed in a different order, and / or if the components in the described system, architecture, device or circuit are replaced or added in a different form combination and / or by other components or their equivalents, suitable results can be achieved. Therefore, the scope of the present disclosure is not limited by specific embodiments but by claims and their equivalents, and all variations within the scope of the claims and their equivalents will be understood to be included in the present disclosure.

Claims

1. An optical imaging system, comprising: A first lens element having negative refractive power; The second lens has negative refractive power and a concave object-side surface; A third lens element having positive refractive power; A fourth lens element having negative refractive power; a fifth lens element having positive refractive power; a sixth lens element having positive refractive power; and The seventh lens has negative refractive power. The optical imaging system includes a total of seven lenses with refractive power, and the first lens to the seventh lens are arranged in sequence from the object side to the image side. Among them, -0.5 < f / f4 < -0.1, TTL / (2 IMGH) < 3.0, n3 < 1.64 and n4 < 1.64, wherein f4 is the focal length of the fourth lens, f is the total focal length of the optical imaging system, TTL is the distance from the object surface of the first lens to the imaging plane, IMGH is half of the diagonal length of the imaging plane, n3 is the refractive index of the third lens, n4 is the refractive index of the fourth lens, The sixth lens and the seventh lens are formed of plastics having different optical characteristics from each other, and the sixth lens and the seventh lens are disposed closer to each other than any other adjacent lenses.

2. The optical imaging system according to claim 1, wherein: n7 is the refractive index of the seventh lens, and n7<1.

64.

3. The optical imaging system according to claim 1, wherein: The second lens has a concave image-side surface.

4. The optical imaging system according to claim 3, wherein: The third lens has a convex object-side surface and a convex image-side surface.

5. The optical imaging system according to claim 4, wherein: The fourth lens has a concave object-side surface.

6. The optical imaging system according to claim 5, wherein: The fifth lens has a convex image-side surface.

7. The optical imaging system according to claim 6, wherein: The sixth lens has a convex object-side surface and a convex image-side surface.

Images