Optical Department

Abstract

The optical system disclosed in the embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens that are sequentially arranged along the optical axis from the object side to the image side. The second lens has a positive refractive power, the third lens has a negative refractive power, the seventh lens has a positive refractive power, the eighth lens has a negative refractive power. The refractive indices of the first, third, and fifth lenses are greater than those of the second, fourth, sixth, and eighth lenses, and have a relationship of 1.2 < F / D1 < 2.4, where F is the overall effective focal length of the optical system and D1 is the effective aperture of the first lens.

Description

Technical Field

[0001] The embodiments relate to an optical system for high resolution.

Background Art

[0002] A camera module functions to photograph an object and store it as an image or video, and is mounted in various applications. In particular, the camera module is manufactured in a super-small size and is applied not only to portable devices such as smartphones, tablet PCs, and notebook computers, but also to drones, vehicles, etc., providing various functions.

[0003] For example, the optical system of a camera module may include an imaging lens that forms an image and an image sensor that converts the formed image into an electrical signal. At this time, the camera module can perform an autofocus (AF) function to automatically adjust the distance between the image sensor and the imaging lens to align the focal length of the lens, and can perform a zooming function of zooming in (zoom up) or zooming out (zoom out) by increasing or decreasing the magnification of a distant object through a zoom lens. Also, the camera module adopts an image stabilization (IS) technology to correct or prevent blurring of the video caused by the movement of the camera due to an unstable fixing device or the movement of the user.

[0004] The most important element for such a camera module to obtain an image is the imaging lens that forms the image. Recently, there has been an increasing interest in high resolution, and research using five or six lenses has been conducted to realize this. In addition, research has been conducted using a plurality of imaging lenses having positive (+) refractive power or negative (-) refractive power to realize high resolution. However, when arranging a plurality of lenses, there is a problem that it is difficult to derive excellent optical characteristics and aberration characteristics. Therefore, a new optical system that can solve the above problems is required.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An embodiment of the invention aims to provide an optical system with improved optical characteristics.

[0006] An embodiment of the invention aims to provide an optical system having at least eight lenses.

Means for Solving the Problems

[0007] The optical system according to an embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens that are sequentially arranged along the optical axis from the object side to the image side. The second lens has a positive refractive power, the third lens has a negative refractive power, the seventh lens has a positive refractive power, the eighth lens has a negative refractive power, the refractive indices of the first, third, and fifth lenses are greater than those of the second, fourth, sixth, and eighth lenses, and they have a relationship of 1.2 < F / D1 < 2.4, where F is the overall effective focal length of the optical system and D1 is the effective aperture of the first lens.

[0008] According to an embodiment of the invention, the central thickness of the second lens may be thicker than those of the first, third to eighth lenses respectively. The Abbe numbers of the second, fourth, sixth, and eighth lenses are 50 or more, and the Abbe numbers of the third and fifth lenses may be less than 30.

[0009] According to an embodiment of the invention, an image sensor is provided on the image side of the eighth lens, and an optical filter is included between the image sensor and the eighth lens. The optical system satisfies Equations 1 and 2: [Equation 1] 0 < BFL / TTL < 0.5 [Equation 2] 0 < BFL / Img < 0.5. Here, BFL is the distance from the vertex of the image-side surface of the eighth lens to the image sensor, TTL is the distance from the vertex of the object-side first surface of the first lens to the image sensor, and Img is the vertical distance from the optical axis to the end of the diagonal line (1.0F) on the image sensor.

[0010] According to an embodiment of the invention, an image sensor is provided on the image side of the eighth lens, and an optical filter is included between the image sensor and the eighth lens. The optical system satisfies Equation 5: [Equation 5] 0.5 < TTL / D8 < 1.5. Here, TTL is the distance from the vertex of the object-side first surface of the first lens to the image sensor, and D8 is the effective aperture of the eighth lens.

[0011] According to an embodiment of the invention, the optical system satisfies the following equations: [Equation] 0.5 < F2 / F < 1.5, [Equation] -5 < F2 / F3 < 0. Here, F is the overall effective focal length of the optical system, F2 is the focal length of the second lens, and F3 is the focal length of the third lens.

[0012] The optical system according to an embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, which are sequentially arranged along the optical axis from the object side to the image side. The central thickness of the second lens is greater than the central thicknesses of the first, third to eighth lenses respectively. The Abbe number of the second lens is greater than the Abbe numbers of the third and fifth lenses, and satisfies the following equation: 0.5 < TTL / D8 < 1.5 and 0 < |f2 / F3| < 5 Here, TTL is the distance from the vertex of the object-side first surface of the first lens to the image sensor, D8 is the effective aperture of the eighth lens, F2 is the focal length of the second lens, and F3 is the focal length of the third lens.

[0013] According to an embodiment of the invention, when the radius of curvature of the object side surface of the second lens is L2R1 and the absolute value of the radius of curvature of the image side surface of the second lens is defined as |L2R2|, 0 < L2R1 / |L2R2| < 1 can be satisfied.

[0014] According to an embodiment of the invention, when the radius of curvature of the object side surface of the third lens is L3R1 and the absolute value of the radius of curvature of the image side surface of the second lens is |L3R2|, the relationship of 0 < L3R2 / |L3R1| < 1 can be satisfied.

[0015] According to an embodiment of the invention, when the refractive index of the second lens at 587 nm is G2 and the refractive index of the third lens at 587 nm is G3, the relationship of 0.7 < G2 / G3 < 1.2 can be satisfied. When the central thickness of the second lens is T2 and the central thickness of the third lens is T3, the relationship of 1 < T2 / T3 < 5 can be satisfied.

[0016] The optical system according to an embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens sequentially arranged along the optical axis from the object side to the image side, and can satisfy the following mathematical formulas: [Equation 4] 1.2 < F / D1 < 2.4 [Equation 5] 0.5 < TTL / D8 < 1.5 [Equation 7] 0 < |f2 / F3| < 5 Here, F is the overall effective focal length of the optical system, D1 is the effective aperture of the first lens, TTL is the distance from the vertex of the first surface on the object side of the first lens to the image sensor, D8 is the effective aperture of the eighth lens, F2 is the focal length of the second lens, and F3 is the focal length of the third lens.

[0017] According to an embodiment of the invention, the distance between the seventh lens and the eighth lens along the optical axis may be greater than the second distance between the first lens and the second lens. The first interval and the second interval may have a value of 0.4 mm or more. The center thickness of the second lens may be in the range of 2 to 4 times compared to the center thickness of the third lens.

Effects of the Invention

[0018] The optical system according to the embodiment can correct aberration characteristics and can embody a slim optical system. Thereby, the optical system can be miniaturized, and high image quality and high resolution can be achieved.

[0019] Also, the optical system according to the embodiment can block unnecessary light entering the optical system. Thereby, aberration can be reduced and the performance of the optical system can be improved.

Brief Description of the Drawings

[0020] [Figure 1] It is a configuration diagram of an optical system according to a first embodiment of the invention.

[0021] [Figure 2] It is a configuration diagram of an optical system according to a second embodiment of the invention.

[0022] [Figure 3] It is a configuration diagram of an optical system according to a third embodiment of the invention.

[0023] [Figure 4] It is a perspective view of a mobile terminal having an optical system according to an embodiment of the invention.

Modes for Carrying Out the Invention

[0024] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. It should be noted that the technical concept of the present invention is not limited to the embodiments described, but can be embodied in a variety of forms, and within the scope of the technical concept of the present invention, components between embodiments can be selectively combined or substituted. Furthermore, terms used in the embodiments of the present invention (including technical and scientific terms) shall be interpreted as generally understood by a person with ordinary skill in the art to which the present invention belongs, unless explicitly specified. Commonly used terms, such as those defined in dictionaries, may be interpreted considering their meaning in the context of the technology in question. Also, the terms used in the embodiments of the present invention are for illustrative purposes only and are not intended to limit the present invention. In this specification, singular forms may also include plural forms unless specifically limited in the description, and when it is written as "at least one (or more) of A and B, C," it may include one or more of all possible combinations of A, B, and C. Furthermore, terms such as 1st, 2nd, A, B, (a), (b), etc., may be used in the description of the components of the embodiments of the present invention. Such terminology is used to distinguish one component from another, and does not limit the nature or order of the component in question. When it is stated that a component is “connected,” “joined,” or “connected” to another component, this includes both cases where the component is directly connected to or connected to the other component, and cases where other components are further “connected,” “joined,” or “connected” between each component. Furthermore, when it is stated that a component is formed or positioned “above or below” each component, “above or below” includes not only cases where two components are in direct contact, but also cases where one or more other components are formed or positioned between the two components. Also, when expressed as “above or below,” it can include not only the upward direction but also the downward direction, with respect to one component as the reference point.

[0025] In the description of the invention, the first lens refers to the lens closest to the object, and the last lens refers to the lens closest to the image side (or sensor surface). In the description of the invention, unless otherwise specified, the units for lens radius, effective aperture, thickness, distance, BFL (Back Focal Length), TTL (Total track length or Total Top Length), etc., are all in mm. In this specification, the shape of the lens is shown with respect to the optical axis of the lens. For example, when it is stated that the object side of the lens is convex, it means that the area near the optical axis on the object side of the lens is convex, not that the area around the optical axis is convex. Therefore, even when it is stated that the object side of the lens is convex, the area around the optical axis on the object side of the lens may be concave. In this specification, it should be explicitly stated that the thickness and radius of curvature of the lens are measured with respect to the optical axis of the lens. Furthermore, "object side" can refer to the surface of the lens that faces the object side with respect to the optical axis, while "image side" can refer to the surface of the lens that faces the imaging plane with respect to the optical axis.

[0026] The optical system according to the embodiment of the invention may include multiple lenses. More specifically, the optical systems according to the first to third embodiments may include at least eight lenses. As resolution increases, the size of the image sensor also increases, and the number of lenses gradually increases with the resolution of the image sensor. The embodiment of the invention aims to provide a high-resolution optical system using at least eight lenses.

[0027] Referring to Figure 1, the optical system of the first embodiment may include, for example, a first lens 111, a second lens 112, a third lens 113, a fourth lens 114, a fifth lens 115, a sixth lens 116, a seventh lens 117, and an eighth lens 118 arranged sequentially from the object side to the image side. The optical system may also include an optical filter 192 and an image sensor 190. An optical system having the plurality of lenses 111 to 118 can be defined as a lens optical system, and an optical system further including the lenses 111 to 118, an optical filter 192, and an image sensor 192 can be defined as a camera module.

[0028] The first to eighth lenses 111, 112, 113, 114, 115, 116, 117, and 118 are arranged sequentially along the optical axis Lx of the optical system. Light corresponding to the image information of an object enters through the first lens 111, second lens 112, third lens 113, fourth lens 114, fifth lens 115, sixth lens 116, seventh lens 117, and eighth lens 118, passes through the optical filter 192, and is acquired as an electrical signal by the image sensor 190.

[0029] Each of the first to eighth lenses 111, 112, 113, 114, 115, 116, 117, and 118 may include an effective region and an ineffective region. The effective region may be the region through which light incident on each lens passes. That is, the effective region may be the region where incident light is refracted and exhibits optical properties. The ineffective region is arranged around the effective region. The ineffective region may be a region through which no light is incident. That is, the ineffective region may be a region unrelated to the optical properties. Furthermore, the ineffective region may be a region fixed to a barrel (not shown) that houses the lens, or a region where light is blocked by a light-shielding portion or spacer.

[0030] The optical system according to the embodiment may include an aperture ST for adjusting the amount of incident light. The aperture ST is positioned between two lenses selected from the first to eighth lenses 111, 112, 113, 114, 115, 116, 117, and 118. For example, the aperture ST may be positioned around the outside between the first lens 111 and the second lens 112, or around the outside between the second lens 112 and the third lens 113. The aperture ST may be positioned so as to be adjacent to the exit side of the first lens 111 rather than the fourth lens 114. As another example, at least one of the first to eighth lenses 111, 112, 113, 114, 115, 116, 117, and 118 may act as an aperture. For example, one surface selected from the lens surfaces of the first to eighth lenses 111, 112, 113, 114, 115, 116, 117, and 118 may act as an aperture for adjusting the amount of light. For example, the area around the image side of the first lens 111 or the area around the object side of the second lens 112 can act as an aperture.

[0031] The first lens 111 may have a positive (+) or negative (-) refractive power. The first lens 111 may be made of a plastic material. The first lens 111 may include a first surface S1 defined as the object side and a second surface S2 defined as the image side. The first surface S1 may be convex in the optical axis Lx, and the second surface S2 may be concave in the optical axis Lx. That is, the first lens 111 may have a meniscus shape that bulges towards the object side.

[0032] In the first lens 111, at least one of the first surface S1 and the second surface S2 may be aspherical. For example, both the first surface S1 and the second surface S2 may be aspherical. At least one of the first surface S1 and the second surface S2 may have an inflection point. Specifically, the first surface S1 may include a first inflection point defined by an inflection point. The first inflection point is located at approximately 80% to approximately 99% when the optical axis Lx is the starting point and the frame of the first lens 111 is the ending point. Here, the position of the first inflection point is set with respect to the vertical direction of the optical axis Lx. The second surface S2 may include a second inflection point defined by an inflection point. The second inflection point is located at approximately 60% to approximately 80% when the optical axis Lx is the starting point and the frame of the first lens 111 is the ending point. Here, the position of the second inflection point is a position set with reference to the vertical direction of the optical axis Lx.

[0033] The second lens 112 may have a positive (+) refractive power. The second lens 112 may be made of plastic or glass material. The second lens 112 may have a third surface S3 defined as an object side surface and a fourth surface S4 defined as an image side surface. The third surface S3 may be convex in the optical axis Lx, and the fourth surface S4 may be convex in the optical axis Lx. That is, both surfaces of the second lens 112 may be convex. As another example, the third surface S3 may be convex, and the fourth surface S4 may be planar (infinity) or concave. At least one of the third surface S3 and the fourth surface S4 may be spherical or aspherical. For example, both the third surface S3 and the fourth surface S4 may be aspherical. The size of the effective aperture of the first lens 111 and / or the second lens 112 may be larger than the larger of the effective aperture of the third lens 113. Here, the effective aperture is the diameter of the region into which light is incident.

[0034] The third lens 113 may have a negative refractive power. The third lens 113 may be made of plastic or glass. The third lens 113 may have a fifth surface S5 defined as the object side and a sixth surface S6 defined as the image side. The fifth surface S5 may be convex in the optical axis Lx, and the sixth surface S6 may be concave in the optical axis Lx. That is, the third lens 113 may have a meniscus shape that bulges towards the object side. As another example, the fifth surface S5 may be planar or concave, and both surfaces of the second lens 112 may be concave. At least one of the fifth surface S5 and the sixth surface S6 may be spherical or aspherical. For example, both the fifth surface S5 and the sixth surface S6 may be aspherical.

[0035] The fourth lens 114 may have a positive (+) or negative (-) refractive power. The fourth lens 114 may be made of a plastic material. The fourth lens 114 may include a seventh surface S7 defined as the object side and an eighth surface S8 defined as the image side. The seventh surface S7 may be concave in the optical axis Lx, and the eighth surface S8 may be convex in the optical axis Lx. That is, the fourth lens 114 may have a meniscus shape that bulges towards the image side. Conversely, the seventh surface S7 may be flat. At least one of the seventh surface S7 and the eighth surface S8 may be aspherical. For example, both the seventh surface S7 and the eighth surface S8 may be aspherical.

[0036] The fifth lens 115 may have a positive (+) or negative (-) refractive power. The fifth lens 115 may be made of a plastic material. The fifth lens 115 may include a ninth surface S9 defined as an object side surface and a tenth surface S10 defined as an image side surface. The ninth surface S9 may be concave in the optical axis Lx, and the tenth surface S10 may be convex in the optical axis Lx. That is, the fifth lens 115 may have a meniscus shape that bulges towards the image side. Alternatively, the ninth surface S9 may be flat. At least one of the ninth surface S9 and the tenth surface S10 may be aspherical. For example, the ninth surface S9 and the tenth surface S10 may be aspherical.

[0037] The sixth lens 116 may have a positive (+) or negative (-) refractive power. The sixth lens 116 may be made of plastic or glass material. The sixth lens 116 may include an eleventh surface S11 defined as an object side surface and a twelfth surface S12 defined as an image side surface. The eleventh surface S11 may be concave in the optical axis Lx, and the twelfth surface S12 may be convex in the optical axis Lx. That is, the sixth lens 116 may have a meniscus shape that bulges towards the image side. At least one of the eleventh surface S11 and the twelfth surface S12 may be aspherical. For example, both the eleventh surface S11 and the twelfth surface may be aspherical.

[0038] At least one of the 11th surface S11 and the 12th surface S12 may have an inflection point. The radius of curvature at the center of the 11th surface S11 of the 6th lens 116 may be smaller than the radius of curvature at the center of the 7th surface S7 and 9th surface S9 of the 4th and 5th lenses 114 and 116. Here, the effective aperture of the 3rd, 4th, 5th, and 6th lenses 113, 114, 115, and 116 may be larger than the effective aperture of the lens adjacent to the image side on the object side.

[0039] The seventh lens 117 may have a positive (+) refractive power. The seventh lens 117 may be made of a plastic material. The seventh lens 117 may include a thirteenth surface S13 defined as an object side surface and a fourteenth surface S14 defined as an image side surface. The thirteenth surface S13 may be convex in the optical axis Lx, and the fourteenth surface S14 may be concave in the optical axis Lx. The thirteenth surface S13 and the fourteenth surface S14 may be aspherical. At least one or both of the thirteenth surface S13 and the fourteenth surface S14 may have at least one inflection point. Specifically, the thirteenth surface S13 may have an inflection point around its center, and the inflection point is located at approximately 40% to approximately 60% when the optical axis Lx is the starting point and the edge of the seventh lens 117 is the ending point. Here, the position of the inflection point on the 13th surface S13 is a position set with reference to the vertical direction of the optical axis Lx. The inflection point on the 14th surface S14 is located closer to the edge than the inflection point on the 13th surface S13.

[0040] The eighth lens 118 may have a negative refractive power. The eighth lens 118 may include a plastic material. The eighth lens 118 may include a 15th surface S15 defined as an object side surface and a 16th surface S16 defined as an image side surface. The 15th surface S15 may be convex in the optical axis Lx, and the 16th surface S16 may be concave in the optical axis Lx. The 15th surface S15 and the 16th surface S16 may be aspherical. Each of the 15th surface S15 and the 16th surface S16 may have at least one inflection point. At least one of the surfaces of the 15th surface S15 and the 16th surface S16 may have an inflection point. More specifically, the 15th surface S15 may have an inflection point around its center, and this inflection point is located at approximately 15% to 50% of the distance between the optical axis Lx (start point) and the edge of the 8th lens 118 (end point). Here, the position of the inflection point on the 15th surface S15 is set with reference to the vertical direction of the optical axis Lx. The inflection point on the 16th surface S16 is located closer to the edge than the inflection point on the 15th surface S15.

[0041] The optical filter 192 may include at least one of the following optical filters: an infrared filter, a cover glass, etc. The optical filter 192 can allow light in a set wavelength band to pass through and filter out light in a different wavelength band. If the optical filter 192 includes an infrared filter, it can block radiant heat emitted from external light from being transmitted to the image sensor. The optical filter 192 can also transmit visible light and reflect infrared light. The image sensor 190 can sense light. The image sensor 190 may include a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), etc.

[0042] In the optical system of the first embodiment, the first to 16th surfaces S1 to S16 of the first to 8th lenses 111 to 118 may all be aspherical. Of the radii of curvature (converted to absolute values) of the first to 16th surfaces S1 to S16, the radius of curvature of the 7th surface S7 is the largest. When converted to absolute values, the 3rd surface S3 and the 13th surface S13 can have radii of curvature of 2.5 mm or less, which are smaller than the radii of curvature of the other surfaces. The Abbe numbers of the first to 8th lenses 111 to 118 are 50 or more for the 2nd lens 112, the 4th lens 114, the 6th lens 116, and the 8th lens 118, while the Abbe numbers of the 1st lens 111, the 3rd lens 113, the 5th lens 115, and the 7th lens 117 may be 30 or less. Looking at the refractive indices of the first to eighth lenses 111 to 118, the first lens 111, the third lens 113, the fifth lens 115, and the seventh lens 117 have refractive indices of 1.6 or higher, while the second lens 112, the fourth lens 114, the sixth lens 116, and the eighth lens 118 may have refractive indices of less than 1.6. The refractive indices of the third lens 113 and the fifth lens 115 have the highest refractive indices and may be 1.65 or higher.

[0043] Table 1 shows the data for the radius of curvature, thickness, spacing, refractive index, and Abbe number of each lens surface in the first embodiment. [Table 1]

[0044] In Table 1, thickness refers to the thickness at the center of each lens (mm), and spacing refers to the spacing between two adjacent lenses (mm). S17 indicates the incident side of the optical filter, and S18 is the exit surface of the optical filter. Comparing the radii of curvature in absolute value, the radius of curvature of the 7th surface S7 of the 4th lens 114 is the largest among the lenses, and may be more than twice as large as the radii of curvature of the 9th surface S9 and the 10th surface S10 of the 5th lens 115. The radius of curvature of the 10th surface S10 may be larger than the radius of curvature of the 9th surface S9. Among the 1st to 5th lenses 111 to 115, the lens with the thickest center is the 2nd lens, and the spacing between the 3rd and 4th lenses 113 and 114 may be larger than the spacing between the 1st and 2nd lenses 111 and 112, and smaller than the center thickness of the 7th and 8th lenses 117 and 118. The center thickness of the 2nd lens 112 may be the thickest among the lenses.

[0045] Table 2 shows the aspheric coefficients for each lens surface in Figure 1. [Table 2]

[0046] Referring to Figure 2, the optical system of the second embodiment may include, for example, a first lens 121, a second lens 122, a third lens 123, a fourth lens 124, a fifth lens 125, a sixth lens 126, a seventh lens 127, and an eighth lens 128 arranged sequentially from the object side to the image side. The optical system may include an optical filter 192 and an image sensor 190. The first to eighth lenses 121, 122, 123, 124, 125, 126, 127, and 128 are arranged sequentially along the optical axis Lx of the optical system. Light corresponding to the image information of the object enters through the first lens 121, the second lens 122, the third lens 123, the fourth lens 124, the fifth lens 125, the sixth lens 126, the seventh lens 127, and the eighth lens 128, passes through the optical filter 192, and is acquired as an electrical signal by the image sensor 190. Each of the first to eighth lenses 121, 122, 123, 124, 125, 126, 127, and 128 may include an effective region and an ineffective region. The effective region is the region through which light incident on each lens passes. That is, the effective region is the region where incident light is refracted and exhibits optical properties. The ineffective region is arranged around the effective region. The ineffective region is the region through which light does not enter. That is, the ineffective region is a region unrelated to the optical properties. Furthermore, the ineffective region may be a region fixed to a barrel (not shown) that houses the lens, or a region where light is blocked by a light-shielding part or spacer.

[0047] The aperture ST is positioned between two lenses selected from the first to eighth lenses 121 to 128. For example, the aperture ST is positioned around the outside of the first lens 121 and the second lens 122, or around the outside of the second lens 122 and the third lens 123. The aperture ST is positioned so as to be more adjacent to the output side of the first lens 121 than to the fourth lens 124. As another example, at least one of the first to eighth lenses 121 to 128 can act as an aperture. For example, one surface selected from the lens surfaces of the first to eighth lenses 121 to 128 can act as an aperture to adjust the amount of light. For example, the area around the image side of the first lens 121 or the area around the object side of the second lens 122 can act as an aperture. In such an optical system of the second embodiment, each lens may have differences in the curvature of the object side and image side of each lens, the difference in thickness or refractive index of the center of each lens, and the spacing between the other lenses, as described below.

[0048] Referring to Figure 2, in the optical system of the second embodiment, the first to sixteenth surfaces S1 to S16 of the first to eighth lenses 121 to 128 may all be aspherical. Of the radii of curvature (including absolute values) of the first to sixteenth surfaces S1 to S16, the radius of curvature of the seventh surface S7 is the largest, and the third surface S3 and the thirteenth surface S13 may have radii of curvature of 2.5 mm or less, which are smaller than the radii of curvature of the other surfaces. The Abbe numbers of the first to eighth lenses 121 to 128 are 50 or more for the first lens 121, the second lens 122, the fourth lens 124, the sixth lens 126, and the eighth lens 128, while the Abbe numbers of the third lens 123, the fifth lens 125, and the seventh lens 127 may be 30 or less. Looking at the refractive indices of the first to eighth lenses 121 to 128, the first lens 121, the third lens 123, the fifth lens 125, and the seventh lens 127 have refractive indices of 1.6 or higher, while the second lens 122, the fourth lens 124, the sixth lens 126, and the eighth lens 128 may have refractive indices of less than 1.6. The refractive indices of the third lens 123 and the fifth lens 125 have the highest refractive indices and may be 1.65 or higher.

[0049] Table 3 shows the data for the radius of curvature, thickness, spacing, refractive index, and Abbe number of each lens surface in the second embodiment. [Table 3]

[0050] In Table 2, thickness refers to the thickness at the center of each lens (mm), and spacing refers to the distance between two adjacent lenses (mm). S17 indicates the incident side of the optical filter, and S18 is the outgoing side of the optical filter. Comparing the radii of curvature in absolute value, the radius of curvature of the 7th surface S7 of the 4th lens 124 is the largest among the lenses, and may be 40 times or more larger than the radius of curvature of the 9th surface S9 of the 5th lens 125. The radius of curvature of the 10th surface S10 may be larger than the radius of curvature of the 9th surface S9. Among the 1st to 5th lenses 121 to 125, the lens with the thickest center is the 2nd lens, and the distance between the 3rd and 4th lenses 123 and 124 may be larger than the distance between the 1st and 2nd lenses 121 and 122, and may be smaller than the center thickness of the 7th and 8th lenses 127 and 128. The center thickness of the 2nd lens 122 may be the thickest among the lenses.

[0051] Table 4 shows the aspheric coefficients for each lens surface in Figure 2. [Table 4]

[0052] Referring to Figure 3, the optical system of the third embodiment may include, for example, a first lens 131, a second lens 132, a third lens 133, a fourth lens 134, a fifth lens 135, a sixth lens 136, a seventh lens 137, and an eighth lens 138 arranged sequentially from the object side to the image side. The optical system may include an optical filter 192 and an image sensor 190. The first to eighth lenses 131, 132, 133, 134, 135, 136, 137, and 138 are arranged sequentially along the optical axis Lx of the optical system. Light corresponding to the image information of the object is incident through the first lens 131, the second lens 132, the third lens 133, the fourth lens 134, the fifth lens 135, the sixth lens 136, the seventh lens 137, and the eighth lens 138, passes through the optical filter 192, and is acquired as an electrical signal by the image sensor 190. Each of the first to eighth lenses 131 to 138 may include an effective region and an ineffective region. The effective region is the region through which light incident on each lens passes. That is, the effective region is the region where incident light is refracted and exhibits optical properties. The ineffective region is arranged around the effective region. The ineffective region is the region through which light does not enter. That is, the ineffective region is a region unrelated to the optical properties. Furthermore, the ineffective region may be a region fixed to a barrel (not shown) housing the lens, or a region where light is blocked by a light-shielding portion or spacer.

[0053] The aperture ST is positioned between two lenses selected from the first to eighth lenses 131 to 138. For example, the aperture ST is positioned around the outside of the first lens 131 and the second lens 132, or around the outside of the second lens 132 and the third lens 133. The aperture ST is positioned so as to be more adjacent to the exit side of the first lens 131 than to the fourth lens 134. As another example, at least one of the first to eighth lenses 131 to 138 can act as an aperture. For example, one surface selected from the lens surfaces of the first to eighth lenses 131 to 138 can act as an aperture to adjust the amount of light. For example, the area around the image side of the first lens 131 or the area around the object side of the second lens 132 can act as an aperture. In the optical system of the third embodiment, each lens may have differences in the curvature of the object side and image side of each lens disclosed in the optical system of the first embodiment, differences in the thickness or refractive index of the center of each lens, and differences in the spacing between the other lenses, which will be described below.

[0054] In the optical system of Figure 3, the first to sixteenth surfaces S1 to S16 of the first to eighth lenses 131 to 138 may all be aspherical. Of the radii of curvature (converted to absolute values) of the first to sixteenth surfaces S1 to S16, the radius of curvature of the seventh surface S7 is the largest, and if converted to absolute values, the radius of curvature of the third surface may be the smallest. The Abbe numbers of the first to eighth lenses 131 to 138 are 50 or greater for the second lens 132, the fourth lens 134, the sixth lens 136, the seventh lens 137, and the eighth lens 138, while the Abbe numbers of the first lens 131, the third lens 133, and the fifth lens 135 may be 30 or less. Looking at the refractive indices of the first to eighth lenses 131 to 138, the first lens 131, the third lens 133, and the fifth lens 135 have refractive indices of 1.6 or higher, while the second lens 132, the fourth lens 134, the sixth lens 136, the seventh lens 137, and the eighth lens 138 may have refractive indices of less than 1.6. The refractive indices of the third lens 133 and the fifth lens 135 have the highest refractive indices and may be 1.65 or higher.

[0055] Table 5 shows the data for the radius of curvature, thickness, spacing, refractive index, and Abbe number of each lens surface in the third embodiment. [Table 5]

[0056] In Table 5, thickness refers to the thickness at the center of each lens (mm), and spacing refers to the spacing between two adjacent lenses (mm). S17 indicates the incident side of the optical filter, and S18 is the exit surface of the optical filter. Comparing the radii of curvature in absolute value, the radius of curvature of the 7th surface S7 of the 4th lens 134 is the largest within the lens, and may be 7 times or more larger than the radii of curvature of the 9th and 10th surfaces S9 and S10 of the 5th lens 135. The radius of curvature of the 10th surface S10 may be larger than the radius of curvature of the 9th surface S9. Among the 1st to 5th lenses 131 to 135, the lens with the thickest thickness at its center is the 2nd lens 132, and the spacing between the 3rd and 4th lenses 133 and 134 may be larger than the spacing between the 1st and 2nd lenses 131 and 132, and smaller than the thickness at the center of the 7th and 8th lenses 137 and 138. The thickness of the central part of the second lens 132 may be the thickest of all the lenses.

[0057] Table 6 shows the aspheric coefficients for each lens surface in Figure 3. [Table 6]

[0058] As shown in the above embodiments, each lens can be made entirely of plastic, and each lens surface can have an aspherical coefficient. In the first to third embodiments of the invention, the center thickness of the second lenses 112, 122, and 132 is the thickest, and can be, for example, 0.7 mm or more. The spacing between the third lenses 113, 123, and 133 and the fourth lenses 114, 124, and 134 along the optical axis, and the spacing between the seventh lenses 117, 127, and 137 and the eighth lenses 118, 128, and 138 may be greater than the spacing between the first lenses 111, 121, and 131 and the second lenses 112, 122, and 132, or between the second lenses 112, 122, and 132 and the third lenses 113, 123, and 133, or greater than the spacing between the fourth to sixth lenses, and can be, for example, 0.4 mm or more.

[0059] The optical systems according to the first to third embodiments of the invention can satisfy at least one or more of the following mathematical formulas. As a result, the optical systems according to the first to third embodiments can have improved optical effects. Formula 1

[0060] 0 <BFL / TTL<0.5 In Equation 1, BFL is the distance from the vertex of the image-side 16th surface S16 of the 8th lens 118, 128, 138 to the image sensor 190, and TTL is the distance from the vertex of the object-side 1st surface S1 of the 1st lens 111, 121, 131 to the image sensor 190. Such an Equation 1 can provide a high-resolution optical system by providing TTL with a longer length than BFL. Equation 2

[0061] 0 <BFL / Img<0.5 In Equation 2, Img is the vertical distance from the optical axis Lx to the end of the diagonal, 1.0F, on the image sensor 190. Equation 2 shows the relationship between the distance from the vertex of the image-side 16th surface S16 of the 8th lens 118, 128, and 138 to the image sensor 190 and the distance from the optical axis Lx to 1.0F. Equation 3

[0062] 0.5 <F / TTL<1.2 In Equation 3, F represents the total effective focal length of the optical system. Equation 4

[0063] 1.2 <F / D1<2.4 In Equation 4, D1 represents the effective aperture of the first lenses 111, 121, and 131. The effective aperture of the first lenses 111, 121, and 131 can be provided to be smaller than the overall effective focal length F. Equation 5

[0064] 0.5 <TTL / D8<1.5 In Equation 5, D8 represents the effective aperture of the eighth lens 118, 128, and 138. The effective aperture of the eighth lens 118, 128, and 138 may be greater than or less than the overall effective focal length F. Equation 6

[0065] 0.5 <F2 / F<1.5 In equation 6, f2 is the focal length of the second lens at 112, 122, and 132. Equation 7

[0066] -5 <F2 / F3<0 In Equation 7, f3 is the focal length of the third lens at 113, 123, and 133. Equation 8

[0067] 0.5 <F2 / F28<1.5 In Equation 8, f28 is the combined focal length of the second to eighth lenses in the optical systems of the first to third embodiments. Equation 9

[0068] 0.5 <F2 / F12<1.5 In Equation 9, f12 is the combined focal length of the first lens (111, 121, 131) and the second lens (112, 122, 132). Equation 10

[0069] 0.5 <F28 / F<1.5 As shown in Equation 10, the combined focal length of the second to eighth lenses in the optical system may be smaller or larger than the overall focal length F. Equation 11

[0070] 0.5 <F12 / F<1.5 As shown in Equation 11, in the optical system, the combined focal length of the first and second lenses may be smaller or larger than the overall focal length F. Equation 12

[0071] 0 <L2R1 / |L2R2|<1 In equation 12, L2R1 is the radius of curvature of the object-side third surface S3 of the second lens 112, 122, 132, and |L2R2| is the absolute value of the radius of curvature of the image-side fourth surface S4. The radius of curvature of the third surface S3 may be smaller than the absolute value of the radius of curvature of the fourth surface S4. Equation 13

[0072] 0 <L3R2 / |L3R1|<1 In Equation 12, L3R1 is the radius of curvature of the object-side fifth surface S5 of the third lens 113, 123, 133, and |L3R2| is the absolute value of the radius of curvature of the image-side sixth surface S6. The radius of curvature of the fifth surface S5 may be greater than the absolute value of the radius of curvature of the sixth surface S6. Equation 14

[0073] 0.7 <G2 / G3<1.2 In Equation 14, G2 is the refractive index of the second lens 112, 122, 132 at 587 nm, and G3 is the refractive index of the third lens 113, 123, 133 at 587 nm. Equation 15

[0074] 1 <T2 / T3<5 In equation 15, T2 is the thickness of the center of the second lens 112, 122, 132 (thickness along the optical axis), and T3 is the thickness of the center of the third lens 113, 123, 133 (thickness along the optical axis). The center thickness T2 of the second lens 112, 122, 132 may be more than 1 and less than or equal to 5 times the center thickness T3 of the third lens 113, 123, 133, for example, it can be in the range of 2 to 4 times, and the optical performance can be improved by the difference between the thicknesses T2 and T3 of the second and third lenses.

[0075] The optical systems according to the first to third embodiments of the invention can satisfy at least one, two or more, or all of the equations 1 to 15. In this case, the optical system is This enables the realization of high-quality and high-resolution imaging lens systems. Furthermore, at least one of equations 1 to 15 can block unnecessary light entering the optical system, correct aberrations, and improve the performance of the optical system.

[0076] Table 7 shows examples of preferred values ​​for the items disclosed in formulas 1 to 15 of the first to third embodiments.

[0077] [Table 7]

[0078] Table 8 shows the preferred values ​​obtained using formulas 1 to 15, which utilize the values ​​in Table 1. [Table 8]

[0079] As shown in Tables 1 to 8 above, it can be confirmed that the first to third embodiments of the invention satisfy formulas 1 to 15.

[0080] Figure 4 is a perspective view showing an example of a mobile device to which an optical system according to an embodiment of the invention is applied. As shown in Figure 4, the mobile terminal 1500 may include a camera module 1520, a flash module 1530, and an autofocus device 1510 provided on one or the rear side. Here, the autofocus device 1510 may include a surface-emitting laser element and a light-receiving unit as an emitting layer. The flash module 1530 may include an emitter that emits light inside. The flash module 1530 can be operated by the camera operation of the mobile terminal or by user control. The camera module 1520 may include an image capture function and an autofocus function. For example, the camera module 1520 may include an image-based autofocus function. The autofocus device 1510 may include a laser-based autofocus function. The autofocus device 1510 is mainly used in conditions where the image-based autofocus function of the camera module 1520 is reduced, such as close proximity of 10m or less or in dark environments.

[0081] The features, structures, and effects described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to a single embodiment. Furthermore, the features, structures, and effects exemplified in each embodiment can be combined or modified and implemented in other embodiments by a person with ordinary skill in the art to which the embodiment belongs. Therefore, such combinations and modifications should be interpreted as being within the scope of the present invention. In addition, although the above has focused on embodiments, these are merely examples and do not limit the present invention. A person with ordinary skill in the art to which the present invention belongs can make various modifications and applications not exemplified above, as long as they do not deviate from the essential characteristics of these embodiments. For example, each component specifically presented in the embodiments can be modified and implemented. And the differences related to such modifications and applications should be interpreted as being within the scope of the present invention as defined in the appended claims.

Claims

1. It consists of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, which are sequentially arranged along the optical axis from the object side to the image side. The second lens has a positive refractive power, The third lens has a negative refractive power, The seventh lens has a positive refractive power, The eighth lens has a negative refractive power, The refractive indices of the first, third, and fifth lenses are greater than those of the second, fourth, sixth, and eighth lenses, and satisfy the following formula: 1.2<F / D1<2.4 F is the overall effective focal length of the optical system, D1 is the effective aperture of the first lens, the effective aperture includes only the effective region within the effective region and non-effective region of the first lens, the effective region is the region through which light incident on the first lens passes and is refracted to realize its optical properties, and the non-effective region is the region arranged around the effective region and where light is blocked. The central thickness of the second lens is greater than the central thicknesses of the first, third to eighth lenses, The Abbe number of the second lens is greater than the Abbe numbers of the third and fifth lenses. The following formula is satisfied, 0.5<TTL / D8<1.5 0<|f2 / F3|<5 The TTL is the distance from the vertex of the first object-side surface of the first lens to the image sensor, D8 is the effective aperture of the eighth lens, F2 is the focal length of the second lens, and F3 is the focal length of the third lens. The second lens includes a convex object side and a convex image side on the optical axis, The radius of curvature of the object side of the second lens is L2R1. When the absolute value of the radius of curvature of the image surface of the second lens is defined as |L2R2|, the condition 0 < L2R1 / |L2R2| < 1 is satisfied. optical system.

2. The optical system according to claim 1, wherein the central thickness of the second lens is greater than the central thicknesses of the first, third to eighth lenses, respectively.

3. The optical system according to claim 1 or 2, wherein the Abbe numbers of the second, fourth, sixth, and eighth lenses are 50 or more, and the Abbe numbers of the third and fifth lenses are less than 30.

4. The image sensor is located on the image side of the eighth lens, and an optical filter is included between the image sensor and the eighth lens. The aforementioned optical system satisfies the following equation: 0<BFL / TTL<0.5 0<BFL / Img<0.5 The optical system according to any one of claims 1 to 3, wherein BFL is the distance from the vertex of the image side of the eighth lens to the image sensor, TTL is the distance from the vertex of the first object-side surface of the first lens to the image sensor, and Img is the vertical distance from the optical axis to 1.0F, which is the end of the diagonal, in the image sensor.

5. The image side of the eighth lens includes an image sensor and an optical filter between the image sensor and the eighth lens. The aforementioned optical system satisfies the following equation: 0.5<TTL / D8<1.5 The optical system according to any one of claims 1 to 4, wherein TTL is the distance from the vertex of the first object-side surface of the first lens to the image sensor, and D8 is the effective aperture of the eighth lens.

6. The aforementioned optical system satisfies the following equation: 0.5<F2 / F<1.5 -5<F2 / F3<0 The aforementioned F is the total effective focal length of the optical system, The F2 mentioned above is the focal length of the second lens, The optical system according to any one of claims 1 to 5, wherein F3 is the focal length of the third lens.

7. The optical system according to claim 1, wherein when the radius of curvature of the object side surface of the third lens is L3R1 and the absolute value of the radius of curvature of the image side surface of the third lens is |L3R2|, the relationship 0 < L3R2 / |L3R1| < 1 is satisfied.

8. The optical system according to any one of claims 7, wherein when the refractive index of the second lens at 587 nm is G2 and the refractive index of the third lens at 587 nm is G3, the relationship 0.7 < G2 / G3 < 1.2 is satisfied.

9. The optical system according to any one of claims 7 to 8, wherein the central thickness of the second lens is T2 and the central thickness of the third lens is T3, satisfying the relationship 1 < T2 / T3 < 5.

10. The following formula is satisfied, 1.2<F / D1<2.4 0.5<TTL / D8<1.5 0<|f2 / F3|<5 F is the overall effective focal length of the optical system, D1 is the effective aperture of the first lens, TTL is the distance from the vertex of the first object-side surface of the first lens to the image sensor, D8 is the effective aperture of the eighth lens, F2 is the focal length of the second lens, and F3 is the focal length of the third lens. The optical system according to claim 1, wherein the seventh lens includes a convex object side surface and a concave image side surface on the optical axis.

11. The optical system according to claim 10, wherein the first distance between the seventh lens and the eighth lens along the optical axis is greater than the second distance between the first lens and the second lens.

12. The optical system according to claim 11, wherein the first and second intervals are 0.4 mm or more.

13. The central thickness of the second lens is in the range of 2 to 4 times the central thickness of the third lens. The optical system according to any one of claims 10 to 12, wherein the central thickness of the second lens is the thickest of the central thicknesses of the first to eighth lenses.

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