WO2020230915A1

WO2020230915A1 - Internal focus wide-angle lens system and electronic apparatus including the same

Info

Publication number: WO2020230915A1
Application number: PCT/KR2019/005710
Authority: WO
Inventors: Moon Kyung Kim
Original assignee: Samyang Optics Co., Ltd.
Priority date: 2019-05-13
Filing date: 2019-05-13
Publication date: 2020-11-19

Abstract

Provided are a wide-angle lens system and an electronic apparatus including the same. The wide-angle lens system includes a first lens group located closest to an object side, a second lens group located at a side of the first lens group to be close to an image side and configured to perform focusing, and a third lens located at a side of the second lens group to be close to the image side, wherein the first lens group and the third lens group are fixed during focusing.

Description

INTERNAL FOCUS WIDE-ANGLE LENS SYSTEM AND ELECTRONIC APPARATUS INCLUDING THE SAME

One or more embodiments relate to an internal focus wide-angle lens system and an electronic apparatus including the same.

A wide angle of a single focus lens system is a viewing angle mainly used for landscape photography and nearby portrait photography. Since a focal length in the single focus lens system is fixed, focusing is required to correct an image point position that varies according to a position of an object, and in this case, optical performance for both a far object and a near object has to be stably maintained.

A compact system camera (CSC), that is, a mirrorless camera, has a structure in which a penta prism or a reflecting mirror is removed from a digital single lens reflex camera (DSLR) and is small in volume and light in weight, and thus has high mobility and high portability. However, since the CSC requires interchangeable lenses using a full-frame imaging device in order to obtain a high quality image, volumes and weights of the interchangeable lenses increase as a size of the full-frame imaging device increases. In this case, since the interchangeable lenses coupled to the CSC are heavy and thus portability and mobility deteriorate, although the full-frame imaging device is used, it is necessary to reduce a total length of the CSC to some extent.

Examples of a focusing method include a front lens group focusing method, a rear lens group focusing method, an internal focusing method of moving an inner lens group only, and a floating method of simultaneously moving two or more lens groups during focusing. The internal focusing method may be advantageous in having a dust-resistant and moisture-resistant construction because a front lens group and a rear lens group are fixed. The floating method may be advantageous in correcting aberrations because aberrations are corrected by moving two or more lens groups, but may be disadvantageous in that an internal structure of a camera becomes complicated and a weight increases.

Accordingly, the internal focusing method is used so that a product size is kept small by fixing a total length during focusing.

One or more embodiments include a wide-angle lens system using an internal focusing method.

One or more embodiments include an electronic apparatus including a wide-angle lens system using an internal focusing method.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.

According to one or more embodiments, a wide-angle lens system includes: a first lens group located closest to an object side; a second lens group located at a side of the first lens group to be close to an image side and configured to perform focusing; and a third lens group located at a side of the second lens group to be close to the image side, wherein the first lens group and the third lens group are fixed during focusing, and the wide-angle lens system satisfies

, and

where BF is a back focal length of the wide-angle lens system, FL is an effective focal length of the wide-angle lens system, and ω is a half field of view.

The first lens group may have a positive refractive power, the second lens group may have a positive refractive power, and the third lens group may have a negative refractive power.

The first lens group may include a meniscus lens having a negative refractive power.

The second lens group may include one or two lenses.

The second lens group may include two meniscus lenses convex toward the image side.

The third lens group may include one lens having a negative refractive power.

The third lens group may include a plano-concave lens or a bi-concave lens.

The second lens group may include one aspherical lens.

The first lens group may include one aspherical lens.

The wide-angle lens system may satisfy

where fm is a composite focal length of the first lens group and the second lens group of the wide-angle lens system, and f_L3 is a focal length of the third lens group.

The wide-angle lens system may satisfy

where L1 is a distance along an optical axis from an object-side surface of a lens closest to the object side to an image-side surface of a lens closest to the image side from among lenses included in the first lens group, L3 is a thickness of one lens included in the third lens group, and LF is a movement distance of the second lens group during focusing from infinity to a closest distance.

The wide-angle lens system may satisfy

where G1V is an Abbe number of a lens closest to the object side from among lenses included in the first lens group, and G2V is an Abbe number of a second lens from the object side from among the lenses included in the first lens group.

The wide-angle lens system may further include an image sensor located at a side of the third lens group to be close to the image side, wherein the wide-angle lens system satisfies

where Y is a half diagonal image height of the image sensor, and BFL is a back focal length.

The wide-angle lens system may further include a stop located between lenses included in the first lens group or located at a closest image side of the first lens group.

The first lens group may include a meniscus lens convex toward the object side, a meniscus lens concave toward the object side, a bi-convex lens, and a meniscus lens convex toward the object side, which are sequentially arranged from the object side to the image side.

These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a view of a wide-angle lens system according to a first embodiment;

FIG. 2 is an aberration diagram of the wide-angle lens system of FIG. 1;

FIG. 3 is a view of a wide-angle lens system according to a second embodiment;

FIG. 4 is an aberration diagram of the wide-angle lens system of FIG. 3;

FIG. 5 is a view of a wide-angle lens system according to a third embodiment;

FIG. 6 is an aberration diagram of the wide-angle lens system of FIG. 5;

FIG. 7 is a view of a wide-angle lens system according to a fourth embodiment;

FIG. 8 is an aberration diagram of the wide-angle lens system of FIG. 7; and

FIG. 9 is a view of an electronic apparatus according to an embodiment.

Hereinafter, various embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to these particular embodiments but also includes various modifications, equivalents, and/or alternatives thereof. Throughout the specification and drawings, like reference numerals may be used to denote like elements or components.

When used herein, terms such as "comprise," "may comprise", "include," and "may include" specify the presence of stated features (e.g., values, functions, operations, parts, elements, and components) but do not preclude the presence or addition of one or more other features.

As used herein, expressions such as "A or B," "at least one of A and/or B," and "one or more of A and/or B" may include any and all combinations of one or more of the associated listed items. For example, "A or B," "at least one of A and B," or "at least one of A or B" may denote all of the cases of (1) including at least one A, (2) including at least one B, and (3) including at least one A and at least one B.

Terms such as "first" and "second" used herein may use various elements or components regardless of their order and/or importance. These terms may be used only to distinguish one element or component from another element, and these elements should not be limited by these terms. For example, a first user device and a second user device may refer to different user devices regardless of their order or importance. For example, without departing from the scope of the present disclosure, a first component may be referred to as a second component, and vice versa.

It will be understood that when a component (e.g., a first component) is referred to as being "(operatively or communicatively) coupled to/with" or "connected to/with" another component (e.g., a second component), it may be coupled to/with or connected to/with the other component directly or indirectly through one or more other components (e.g., third components). On the other hand, when a component (e.g., a first component) is referred to as being "directly coupled to/with" or "directly connected to/with" another component (e.g., a second component), no other components (e.g., third components) exist therebetween.

The expression "configured to (or set to)" used herein may be replaced with, for example, "suitable for," "having the capacity to," "designed to," "adapted to," "made to," or "capable of" according to cases. The expression "configured to (or set to)" may not necessarily mean "specifically designed to" in a hardware level. Instead, in some case, the expression "apparatus configured to ..." may mean that the apparatus is "capable of ..." along with other devices or parts.

An apparatus according to various embodiments of the present disclosure may include at least one of, for example, a smartphone, a tablet personal computer (PC), a mobile phone, a video phone, an e-book reader, a desktop PC, a laptop PC, a netbook computer, a workstation, a server, a personal digital assistant (PDA), a portable multimedia player (PMP), a motion picture experts group (MPEG) audio layer 3 (MP3) player, a mobile medical device, a camera, and a wearable device. According to various embodiments, the wearable device may include at least one of accessory-type devices (e.g., watches, rings, wristlets, anklets, necklaces, spectacles, contact lenses, or head-mounted devices (HMDs)), textile or clothing-integrated devices (e.g., electronic clothing), body-attachable devices (e.g., skin pads or tattoos), and bio-implantable devices (e.g., implantable circuits).

In other embodiments, the electronic apparatus may include at least one of any type of medical device (e.g., any type of portable medical meter (e.g., a blood sugar meter, a heart rate meter, a blood pressure meter, or a body temperature meter), a magnetic resonance angiography (MRA) device, a magnetic resonance imaging (MRI) device, a computerized tomography (CT) device, a tomograph, or an ultrasound machine), a navigation device, a global navigation satellite system (GNSS), an event data recorder (EDR), a flight data recorder (FDR), an automotive infotainment device, electronic ship equipment (e.g., a ship navigation device or a gyrocompass), an avionic device, a security device, a vehicle head unit, an industrial or home robot, an automatic teller machine (ATM) of a financial institution, a point-of-sale (POS) device of a store, and an Internet-of-Things (IoT) device (e.g., an electric bulb, any type of sensor, an electricity or gas meter, a sprinkler, a fire alarm, a thermostat, a street lamp, a toaster, exercise equipment, a hot-water tank, a heater, or a boiler).

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one of", when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

FIG. 1 is a view of a wide-angle lens system 100 according to a first embodiment.

The wide-angle lens system 100 includes a first lens group G11, a second lens group G21, and a third lens group G31 which are sequentially arranged from an object side O to an image side I. The second lens group G21 may be a focusing lens group that performs focusing to correct an image distance change according to an object distance change. The first lens group G11 and the third lens group G31 may be fixed during focusing. The first lens group G11 may be provided at a side of the second lens group G21, which performs focusing, to be close to the object side O, and the third lens group G31 may be provided at the other side of the second lens group G21 to be close to the image side I.

Hereinafter, the image side I may refer to a side adjacent to an image plane IMG on which an image is formed, and the object side O may refer to a side adjacent to an object. Also, an "object-side surface" may refer to a surface of a lens facing the object, for example, a left surface of the lens in FIG. 1, and an "image-side surface" may refer to a surface of a lens facing the image plane IMG, for example, a right surface of the lens in FIG. 1. The image plane IMG may be, for example, a surface of an imaging device or an image sensor. Examples of the image sensor may include a complementary metal oxide semiconductor (CMOS) image sensor and a charge-coupled device (CCD). The image sensor is not limited thereto, and may be, for example, a device that converts an image of the object into an electrical image signal.

For example, the first lens group G11 may have a positive refractive power, the second lens group G21 may have a positive refractive power, and the third lens group G31 may have a negative refractive power.

The first lens group G11 may include, for example, a first lens L11 having a negative refractive power. The first lens L11 may be a meniscus lens. The first lens L11 may include an object-side surface 1 convex toward the object side O. Since the first lens L11 has a negative refractive power, the first lens L11 may converge light of a wide angle area.

A second lens L21, a third lens L31, and a fourth lens L41 may be arranged closer to the image side I than the first lens L11. The second lens L21 may have, for example, a positive or negative refractive power. The second lens L21 may be, for example, a meniscus lens concave toward the object side O. The third lens L31 may have, for example, a positive refractive power. The third lens L31 may be, for example, a bi-convex lens. The fourth lens L41 may have a positive or negative refractive power. The fourth lens L41 may be, for example, a meniscus lens convex toward the object side O.

A stop ST may be provided at a closest image side of the first lens group G11.

The first lens group G11 may include at least one aspherical lens. For example, the third lens L31 and the fourth lens L41 may be aspherical lenses.

The second lens group G21 may include, for example, one lens or two lenses. The second lens group G21 may include a small number of lenses, and thus may easily perform focusing, may be rapidly driven, and may easily correct aberrations. The second lens group G21 may include a fifth lens L51 and a sixth lens L61. The fifth lens L51 may have, for example, a negative refractive power. The fifth lens L51 may include, for example, an image-side surface 11 convex toward the image side I. The fifth lens L51 may be, for example, a meniscus lens convex toward the image side I. The sixth lens L61 may have, for example, a positive refractive power. The sixth lens L61 may include, for example, an image-side surface 13 convex toward the image side I. The sixth lens L61 may be, for example, a meniscus lens convex toward the image side I.

The first lens group G11 may include at least one aspherical lens. When the first lens group G11 includes at least one aspherical lens, a total length of the wide-angle lens system 100 may be reduced, power balancing with the remaining lens groups may be maintained, and a change in performance according to an object distance may be effectively corrected.

The second lens group G21 may include one aspherical lens. For example, the fifth lens L51 may be an aspherical lens.

The third lens group G31 may include one lens. For example, the third lens group G31 may include a seventh lens L71. The seventh lens L71 may have a negative refractive power. The seventh lens L71 may be, for example, a plano-concave lens. For example, an object-side surface 14 of the seventh lens L71 may be flat. The seventh lens L71 may be a spherical lens.

In order for the wide-angle lens system 100 to converge light of a wide viewing angle, the first lens L11 of the first lens group G11 that is located closest to the object side O may have a negative refractive power. The second lens group G21 that is a focusing lens group for correcting an image distance change according to an object distance change may have a positive refractive power and may include two or fewer lenses. When the focusing lens group includes two or fewer lenses, aberration correction and rapid autofocusing may be achieved.

When the first lens group G11 and the second lens group G21 converge light of a wide viewing angle by each having a positive refractive power, a field curvature in which the image plane IMG is curved toward the object side O may occur. In this case, the third lens group G31 having a negative refractive power may easily correct the field curvature. The seventh lens L71 of the third lens group G31 may function as a field flattener that corrects the field curvature.

It is preferable to reduce a focal length in order to make the wide-angle lens system 100 compact according to various embodiments. When the focal length is reduced, a degree of freedom in selecting a focusing driving source may increase. Also, when a focusing lens group includes spherical lenses only, the number of lenses may increase and a total weight of the focusing lens group may increase. Accordingly, in order to reduce the number of lenses and facilitate aberration correction, the focusing lens group may include at least one aspherical lens. When the focusing lens group includes an aspherical lens, the number of lenses may be reduced, aberration correction may be facilitated, and focusing sensitivity may be reduced.

According to various embodiments, at least one optical device OD may be provided between the seventh lens L71 and the image plane IMG. The optical device OD may include at least one of, for example, a broadband-pass filter and a cover glass. For example, when the broadband-pass filter is provided as the optical device OD, the optical device OD may include a broadband coating through which light having a wavelength ranging from 400 nm to 1000 nm passes. The broadband-pass filter may pass, for example, both visible and infrared rays. Alternatively, the optical device OD may include a visible pass filter. However, the wide-angle lens system 100 may not include the optical device OD.

The wide-angle lens system 100 according to various embodiments may have a viewing angle of, for example, 80° or more, and may have high resolving power.

In general, the wide-angle lens system 100 may be designed as a reverse-telephoto lens system in which a back focal length is greater than an effective focal length. However, the wide-angle lens system 100 according to various embodiments may be applied to a lens system for a CSC in which a mirror is removed from an existing DSLR lens system. In this case, a flange back distance that is a distance from a mount surface of a camera to the image plane IMG is less than a flange back distance in the existing DSLR lens system. Accordingly, the wide-angle lens system 100 according to various embodiments may be designed as a telephoto lens system in which an effective focal length is greater than a back focal length to satisfy the condition of a relatively short flange back distance and a wide angle. The term 'back focal length' may refer to a distance along an optical axis OA from an image-side surface of a lens closest to the image side I of the wide-angle lens system 100 to the image plane IMG.

Since the wide-angle lens system 100 according to various embodiments includes 9 or fewer lenses, a total length may be reduced.

FIG. 3 is a view of a wide-angle lens system 200 according to a second embodiment. The wide-angle lens system 200 may include a first lens group G12 having a positive refractive power, a second lens group G22 having a positive refractive power, and a third lens group G32 having a negative refractive power.

The first lens group G12 may include, for example, a first lens L12 having a negative refractive power. The first lens L12 may be a meniscus lens. The first lens L12 may include an object-side surface 1 convex toward the object side O.

A second lens L22, a third lens L32, and a fourth lens L42 may be arranged closer to the image side I than the first lens L12. The second lens L22 may have, for example, a positive or negative refractive power. The second lens L22 may be, for example, a meniscus lens concave toward the object side O. The third lens L23 may have, for example, a positive refractive power. The third lens L32 may be, for example, a bi-convex lens. The fourth lens L42 may have a positive or negative refractive power. The fourth lens L42 may be, for example, a meniscus lens convex toward the object side O. The stop ST may be provided at any position between lenses included in the first lens group G21. For example, the stop ST may be provided between the third lens L32 and the fourth lens L42.

The first lens group G12 may include at least one aspherical lens. For example, the third lens L32 and the fourth lens L42 may be aspherical lenses. The third lens L32 and the fourth lens L42 may be double-sided aspherical lenses.

The second lens group G22 may include, for example, a fifth lens L52 and a sixth lens L62. The fifth lens L52 may have, for example, a negative refractive power. The fifth lens L52 may include, for example, an image-side surface 11 convex toward the image side I. The fifth lens L52 may be, for example, a meniscus lens convex toward the image side I. The sixth lens L62 may have, for example, a positive refractive power. The sixth lens L62 may be, for example, a meniscus lens convex toward the image side I.

The second lens group G22 may include one aspherical lens. For example, the fifth lens L52 may be an aspherical lens. The fifth lens L52 may be a double-sided aspherical lens.

The third lens group G32 may include one lens. For example, the third lens group G32 may include a seventh lens L72. The seventh lens L72 may have a negative refractive power. The seventh lens L72 may be, for example, a bi-concave lens. At least one optical device OD may be provided between the seventh lens L72 and the image plane IMG.

FIG. 5 is a view of a wide-angle lens system 300 according to a third embodiment. The wide-angle lens system 300 may include a first lens group G13 having a positive refractive power, a second lens group G23 having a positive refractive power, and a third lens group G33 having a negative refractive power.

The first lens group G13 may include, for example, a first lens L13 having a negative refractive power. The first lens L13 may be a meniscus lens. The first lens L13 may include an object-side surface 1 convex toward the object side O.

A second lens L23, a third lens L33, and a fourth lens L43 may be arranged closer to the image side I than the first lens L13. The second lens L23 may have, for example, a positive or negative refractive power. The second lens L23 may be, for example, a meniscus lens concave toward the object side O. The third lens L33 may have, for example, a positive refractive power. The third lens L33 may be, for example, a bi-convex lens. The fourth lens L43 may have a positive or negative refractive power. The fourth lens L43 may be, for example, a meniscus lens convex toward the object side O. The stop ST may be provided at a side of the fourth lens L43 to be close to the image side I.

The first lens group G13 may include at least one aspherical lens. For example, the third lens L33 and the fourth lens L43 may be aspherical lenses. The third lens L33 and the fourth lens L43 may be double-sided aspherical lenses.

The second lens group G23 may include, for example, a fifth lens L53 and a sixth lens L63. The fifth lens L53 may have, for example, a negative refractive power. The fifth lens L53 may include, for example, an image-side surface 11 convex toward the image side I. The fifth lens L53 may be, for example, a meniscus lens convex toward the image side I. The sixth lens L63 may have, for example, a positive refractive power. The sixth lens L63 may be, for example, a meniscus lens convex toward the image side I.

The second lens group G23 may include one aspherical lens. For example, the fifth lens L53 may be an aspherical lens. The fifth lens L53 may be a double-sided aspherical lens.

The third lens group G33 may include one lens. For example, the third lens group G33 may include a seventh lens L73. The seventh lens L73 may have a negative refractive power. The seventh lens L73 may be, for example, a bi-concave lens. At least one optical device OD may be provided between the seventh lens L73 and the image plane IMG.

FIG. 7 is a view of a wide-angle lens system 400 according to a fourth embodiment. The wide-angle lens system 400 may include a first lens group G14 having a positive refractive power, a second lens group G24 having a positive refractive power, and a third lens group G34 having a negative refractive power.

The first lens group G14 may include, for example, a first lens L14 having a negative refractive power. The first lens L14 may be a meniscus lens. The first lens L14 may include an object-side surface 1 convex toward the object side O.

A second lens L24, a third lens L34, and a fourth lens L44 may be arranged closer to the image side I than the first lens L14. The second lens L24 may have, for example, a positive or negative refractive power. The second lens L24 may be, for example, a meniscus lens convex toward the object side O. The third lens L34 may have, for example, a positive refractive power. The third lens L34 may be, for example, a bi-convex lens. The fourth lens L44 may have a positive or negative refractive power. The fourth lens L44 may be, for example, a meniscus lens concave toward the object side O. The stop ST may be provided between the third lens L34 and the fourth lens L44.

The first lens group G14 may include at least one aspherical lens. For example, the third lens L34 and the fourth lens L44 may be aspherical lenses. The third lens L34 and the fourth lens L44 may be double-sided aspherical lenses.

The second lens group G24 may include, for example, a fifth lens L54 and a sixth lens L64. The fifth lens L54 may have, for example, a negative refractive power. The fifth lens L54 may include, for example, an image-side surface 11 convex toward the image side I. The fifth lens L54 may be, for example, a meniscus lens convex toward the image side I. The sixth lens L64 may have, for example, a positive refractive power. The sixth lens L64 may be, for example, a meniscus lens convex toward the image side I.

The second lens group G24 may include one aspherical lens. For example, the fifth lens L54 may be an aspherical lens. The fifth lens L54 may be a double-sided aspherical lens.

The third lens group G34 may include one lens. For example, the third lens group G34 may include a seventh lens L74. The seventh lens L74 may have a negative refractive power. The seventh lens L74 may be, for example, a bi-concave lens. At least one optical device OD may be provided between the seventh lens L74 and the image plane IMG.

A wide-angle lens system according to various embodiments may satisfy the following formulae. Although the following formulae are described with reference to FIG. 1, the following formulae may be applied to wide-angle lens systems according to other embodiments.

(Formula 1)

(Formula 2)

When (BF/FL) exceeds an upper limit of Formula 1, as a viewing angle increases, high order aberrations may increase, the number of lenses may increase to suppress the high order aberrations, and a total length may increase. When (BF/FL) exceeds a lower limit of Formula 1, the back focal length BF may be reduced and it may be difficult to mechanically combine the wide-angle lens system with a camera. Formula 2 is a ratio between a half diagonal image height of an image sensor and a focal length of the wide-angle lens system. When Formula 2 is satisfied, a wide-angle lens according to an embodiment may be used for interior photography or landscape photography. When a viewing angle exceeds an upper limit of Formula 2, high order aberrations increase and it is difficult to realize a compact optical system.

The wide-angle lens system according to an embodiment may satisfy the following formula.

(Formula 3)

where fm is a composite focal length of the first lens group G11 and the second lens group G21 of the wide-angle lens system, and f_L3 is a focal length of the third lens group G31.

Formula 3 defines a field curvature correction amount with respect to the composite focal length of the first lens group G11 and the second lens group G21. When (fm/f_L3) exceeds a lower limit of Formula 3, a refractive power of the third lens group G31 may be reduced and it may be difficult to correct a field curvature. When (fm/f_L3) exceeds an upper limit of Formula 3, a field curvature may be overcorrected.

(Formula 4)

where L1 is a distance from an object-side surface of a lens closest to the object side O to an image-side surface of a lens closest to the image side I from among lenses included in the first lens group G11, L3 is a thickness of one lens included in the third lens group G31, and LF is a movement distance of the second lens group G21 during focusing from infinity to a closest distance. L1 may be a distance along the optical axis OA from an object-side surface of the first lens L11 to an image-side surface of the fourth lens L41.

Formula 4 defines a movement amount for focusing and a total length. When an upper limit of Formula 4 is exceeded, the total length of the wide-angle lens system increases and it is difficult to make the wide-angle lens system compact. When a lower limit of Formula 4 is exceeded, the movement amount for focusing may be limited. When the movement amount is small, a change in performance according to focusing may increase sensitively.

(Formula 5)

where G1V is an Abbe number of a lens closest to the object side O from among lenses included in the first lens group G11, and G2V is an Abbe number of a second lens from the object side O from among the lenses included in the first lens group G11. For example, G1V is an Abbe number of the first lens L11, and G2V is an Abbe number of the second lens L21 of the first lens group G11.

When Formula 5 is satisfied, chromatic aberration of the wide-angle lens system may be effectively reduced. When an upper limit of Formula 5 is exceeded, as a dispersion difference increases, chromatic aberration may be effectively reduced. However, since lenses having low dispersion have small refractive indices, it may be difficult to correct a field curvature of the wide-angle lens system. When a lower limit of Formula 5 is exceeded, a dispersion difference between two lenses may not be large and thus chromatic aberration may not be effectively corrected.

(Formula 6)

The wide-angle lens system is located in front of the image sensor to improve light receiving efficiency. Since a CSC has no mirror box and has a small flange back distance, an angle at which light is incident on the image sensor increases. When (Y/BFL) is greater than an upper limit of Formula 6, an angle of incident light may be greater than a light acceptance angle of the image sensor, thereby resulting in image quality degradation due to light loss according to a wavelength. When (Y/BFL) is less than a lower limit of Formula 6, a back focal length may increase, thereby making it difficult to make the wide-angle lens system compact.

The wide-angle lens system according to an embodiment may stably correct a change in performance according to a position of an object and may reduce a total length of the wide-angle lens system. The wide-angle lens system may include 9 or fewer lenses in order to reduce a total length and may include 3 or fewer aspherical lenses in order to suppress aberrations. As an aspherical lens is closer to a first lens surface or a last lens surface of the wide-angle lens system, a size of an aspherical surface may increase and manufacturing costs may increase. Accordingly, when aspherical lenses are continuously arranged in the middle of the wide-angle lens system, a size of a lens may be reduced and an astigmatism and a distortion may be corrected. Also, the aspherical lenses may be located as close to a stop of the wide-angle lens system as possible to correct spherical aberration and coma.

Next, an aspherical surface used in the wide-angle lens system according to an embodiment will be defined as follows.

An aspherical shape may be represented as the following formula with a traveling direction of rays as a positive direction when an optical axis direction is a z-axis and a direction perpendicular to the optical axis direction is a y-axis. Z is a distance in the optical axis direction from a vertex of a lens, Y is a distance in the direction perpendicular to the optical axis OA, K is a conic constant, A, B, C, D, E, F .. are aspherical coefficients, and c is a reciprocal number (1/R) of a radius of curvature at the vertex of the lens.

(Formula 7)

According to the present disclosure, the wide-angle lens system may be implemented by embodiments according to various designs as follows. Hereinafter, the effective focal length FL is expressed in millimeters (mm), the half field of view HFOV is expressed in degrees, and Fno is an F number. obj is an object, R is a radius of curvature, Dn is a thickness of the lens or an air gap between lenses and is expressed in millimeters, nd is a refractive index, and vd is an Abbe number. In each embodiment,

lens surface numbers

1, 2, 3, .., and n (n is a natural number) are sequentially added from the object side O to the image side I.

FIG. 1 is a view of the wide-angle lens system 100 according to the first embodiment, and Table 1 shows design data of the first embodiment.

Lens Data		FL=25mm Fno= 2.89 HFOV=41.1°
Lens surface	R	Dn	nd	vd	Note
obj	infinity	D0
1	47.29	0.7	1.437	95.1	First lens group
2	12.058	4.558
3	-20.539	1.1	1.98613	16.48
4	-37.723	0.3
5	20.001	3.638	1.80755	40.89
6*	-20.326	0.1
7	18.751	1.1	1.51815	64.03
8*	9.599	2.037
9(ST)	infinity	D1
10	-10.324	2.724	1.69815	31.19	Second lens group
11*	-14.074	0.1
12	-187.408	5.142	1.7725	49.62
13	-12.176	D2
14	infinity	0.7	1.92286	20.88	Third lens group
15	30.89	21.523			Third lens group
16	infinity	2.5	1.5168	64.2	Optical device
17	infinity	0.5			Optical device
IMG	infinity	0

Table 2 shows aspherical coefficients in the first embodiment.

	6	8	11
K	-52.01448	-10.05487	0.60401
A	-1.21E-04	3.41E-04	2.06E-04
B	2.21E-06	1.27E-06	4.04E-07
C	-2.60E-08	-1.94E-07	3.52E-08
D	1.42E-10	3.56E-09	-3.62E-10

Table 3 shows, in the first embodiment, variable distances D0, D1, and D2, a focal length FL, a magnification MAG, an F number Fno, and a half field of view HFOV for an infinite object distance, an object distance having a magnification MAG of -1/40, and TL=0.2m. TL is a distance from an object to the image plane IMG and thus is an object-to-image distance. TL may be used to indicate a minimum focusing distance in a lens optical system. OAL is a total length along the optical axis OA from an object-side surface of a lens closest to the object side O to the image plane IMG, and MAG is a magnification. "in air" is a distance from an image-side surface of a lens closest to the image side I of the wide-angle lens system 100 to the image plane IMG (imaging device) when there is no optical device. That is, "in air" may denote a back focal length when there is no optical device.

Config	infinity	MAG=-1/40	TL=0.2m
D0	infinity	993.49977	200.04902
D1	4.33946	4.11302	3.25312
D2	2.13342	2.35986	3.21976
in Air	23.467	23.467	23.467
FL	25
MAG		0.025	0.12144
HFOV	41.131	41.178	41.212
Fno	2.892	2.9	2.905
OAL	53.196	53.196	53.196

FIG. 2 is a lateral aberration diagram (a ray fan diagram) of the first embodiment at an infinite object distance. A dashed line shows lateral aberration for a wavelength of 656.2800 NM, a solid line shows lateral aberration for a wavelength of 587.5600 NM, and a dash-dotted line shows lateral aberration for a wavelength of 486.1300 NM. The lateral aberrations are aberrations in tangential and sagittal image planes.

FIG. 3 is a view of the wide-angle lens system 200 according to the second embodiment, and Table 4 shows design data of the second embodiment.

Lens Data		FL=25mm Fno=2.86 HFOV=41°
Lens surface	R	Dn	nd	vd	Note
obj	infinity	D0
1	109.458	0.7	1.48749	70.44	First lens group
2	11.93	2.918
3	-17.409	2.578	1.94595	17.98
4	-27.894	0.1
5*	17.195	2.478	1.77196	49.7
6*	-30.062	2.392
7(ST)	infinity	1
8*	55.949	2.492	1.51815	64.03
9*	88.049	D1
10*	-7.43	1.497	1.68915	31.19	Second lens group
11*	-10.404	0.707
12	-175.664	6.157	1.7725	49.62
13	-11.656	D2
14	-26.745	0.7	1.69895	30.05	Third lens group
15	68.774	18.844			Third lens group
16	infinity	2.5	1.5168	64.2	Optical device
17	infinity	0.5			Optical device
IMG	infinity	0

Table 5 shows aspherical coefficients in the second embodiment.

Lens Surface	5	6	8	9	10	11
K	-7.0818	3.19105	56.49835	0	-1.20736	0.8041
A	1.25E-04	3.99E-05	1.81E-04	1.42E-04	5.88E-04	9.68E-04
B	-2.15E-06	-5.01E-07	3.29E-06	6.78E-06	1.76E-05	1.68E-05
C	3.61E-08	1.66E-08	-5.79E-08	-1.57E-07	-9.58E-07	-5.91E-07
D	-6.88E-10	-5.08E-10	1.57E-09	3.42E-09	1.00E-08	6.12E-09

Table 6 shows, in the second embodiment, variable distances, a focal length FL, a magnification MAG, an F number Fno, and a half field of view HFOV for an infinite object distance, an object distance having a magnification MAG of -1/40, and TL=0.2m. In Table 6, "in air" is a distance from an image-side surface of a lens closest to the image side I of the wide-angle lens system 200 to the imaging device (the image plane IMG) when there is no optical device, and denotes a back focal length when there is no optical device.

Config	infinity	MAG=-1/40	TL=0.2m
D0	infinity	993.49977	200.04902
D1	3.71697	3.45971	2.54755
D2	0.60647	0.86373	1.77589
in Air	20.953	20.961	21.051
FL	24.7817
MAG		0.0247	0.11873
HFOV	41.041	41.379	42.527
Fno	2.862	2.86	2.868
OAL	49.887	49.887	49.887

FIG. 4 is a lateral aberration diagram (a ray fan diagram) of the second embodiment at an infinite object distance. A dashed line shows lateral aberration for a wavelength of 656.2800 NM, a solid line shows lateral aberration for a wavelength of 587.5600 NM, and a dash-dotted line shows lateral aberration for a wavelength of 479.9100 NM.

FIG. 5 is a view of the wide-angle lens system 300 according to the third embodiment, and Table 7 shows design data of the third embodiment.

Lens Data		FL=25mm Fno=2.86 HFOV=40.8°
Lens surface	R	Dn	nd	vd	Note
obj	infinity	D0
1	40.299	0.7	1.48749	70.44	First lens group
2	12.737	3.827
3	-25.924	1.1	1.94595	17.98
4	-55.884	0.1
5*	33.01	2.681	1.87795	37.3
6*	-23.853	0.1
7*	6.629	1.1	1.51815	64.03
8*	5.545	2.771
9(ST)	infinity	D1
10*	-6.174	1.1	1.69815	31.19	Second lens group
11*	-8.119	0.1
12	-124.61	5.473	1.6968	55.46
13	-9.943	D2
14	-118.344	0.7	1.84666	23.78	Third lens group
15	49.684	22.021			Third lens group
16	infinity	2.5	1.5168	64.2	Optical device
17	infinity	0.5			Optical device
IMG	infinity	0

Table 8 shows aspherical coefficients in the third embodiment.

Lens Surface	5	6	7	8	10	11
K	2.80089	-84.11654	-1.35019	-4.48155	-0.52134	-0.89928
A	1.74E-04	1.73E-05	6.39E-05	1.10E-03	5.38E-04	5.82E-04
B	-2.54E-06	-3.15E-07	1.97E-05	1.12E-06	2.79E-05	2.16E-05
C	4.09E-08	9.23E-09	-4.44E-07	-2.68E-07	-1.12E-06	-6.65E-07
D	-3.45E-10	-1.45E-10	7.93E-09	1.25E-08	1.22E-08	6.15E-09

Table 9 shows, in the third embodiment, variable distances, a focal length FL, a magnification MAG, an F number Fno, and a half field of view HFOV for an infinite object distance, an object distance having a magnification MAG of -1/40, and TL=0.2m.

Config	infinity	MAG-1/40	TL=0.2m
D0	infinity	949.99284	149.99281
D1	4.23505	3.96995	2.6137
D2	1	1.26511	2.62135
in Air	24.117	24.141	24.234
FL	25
MAG		0.02618	0.16241
HFOV	40.828	40.876	40.819
Fno	2.9	2.918	3.089
OAL	50.008	50.008	50.008

FIG. 6 is a lateral aberration diagram (a ray fan diagram) of the third embodiment at an infinite object distance. A dashed line shows lateral aberration for a wavelength of 656.2700 NM, a solid line shows lateral aberration for a wavelength of 587.5600 NM, and a dash-dotted line shows lateral aberration for a wavelength of 479.9100 NM.

FIG. 7 is a view of the wide-angle lens system 400 according to the fourth embodiment, and Table 10 shows design data of the fourth embodiment.

▶ Lens Data		FL=16mm Fno=2.88 HFOV=54.8°
Lens Surface	R	Dn	nd	vd	Note
obj	infinity	D0
1	14.442	1.4	1.7725	49.62	First lens group
2	6.862	4.068
3	19.266	1.4	1.497	81.61
4	7.611	1.015
5*	11.941	3.491	1.56622	54.79
6*	-34.854	2.318
7(ST)	infinity	2.23
8*	-128.474	2.584	1.78235	37.43
9*	-16.332	D1
10*	-6.732	1.503	1.97922	29.29	Second lens group
11*	-9.583	0.484
12	-86.806	3.124	1.7725	49.62
13	-9.335	D2
14	-48.744	1.4	1.94595	17.98	Third lens group
15	68.774	22		8.41	Third lens group
16	infinity	2.5	1.5168	64.2	Optical device
17	infinity	0.5	25		Optical device
IMG	infinity	0

Table 11 shows aspherical coefficients in the fourth embodiment.

Lens Surface	5	6	8	9	10	11
K	-2.53078	0	0	0	-1.00223	0.697
A	4.04E-04	2.95E-05	-8.43E-05	-1.68E-04	5.13E-04	9.07E-04
B	3.45E-06	-5.10E-06	-2.20E-05	-6.98E-06	2.06E-05	1.85E-05
C	-1.30E-08	5.91E-08	6.50E-07	-3.45E-07	-1.24E-06	-5.54E-07
D	1.30E-09	-1.24E-09	-4.18E-08	9.32E-10	2.01E-08	6.50E-09

Table 12 shows, in the fourth embodiment, variable distances, a focal length FL, a magnification MAG, an F number Fno, and a half field of view HFOV for an infinite object distance, an object distance having a magnification MAG of -1/40, and TL=0.2m.

Config	infinity	MAG=-1/40	TL=0.2m
D0	infinity	993.49977	200.04902
D1	1.88351	1.80216	1.49975
D2	0.1	0.18135	0.48376
in Air	24.217	24.243	24.356
FL	16
MAG		0.01598	0.07704
HFOV	54.801	54.96	55.546
Fno	2.88	2.88	2.88
OAL	52	52	52

Table 13 shows that the first through fourth embodiments satisfy Formulae 1 through 6.

	First Embodiment	Second Embodiment	Third Embodiment	Fourth Embodiment
BF	23.669	20.991	24.167	24.146
FL	25	24.782	25	16
fm	14.63	13.93	15.69	8.73
f_L3	-33.10	-26.95	-40.85	-29.60
L1	11.50	14.66	9.61	-20.09
L3	0.7	0.7	0.7	1.4
LF	1.086	1.169	1.621	0.384
G1V	95.1004	70.4412	70.4412	49.6243
G2V	16.4839	17.9843	17.9843	81.6084
Y	21.63	21.63	21.63	21.63
BFL	24.52	21.84	25.02	24.146
	0.947	0.847	0.967	1.509
	0.865	0.872	0.865	1.35
	-0.44	-0.52	-0.38	-0.30
	11.23	13.14	6.36	51.84
	78.6165	52.4569	52.4569	31.9841
	0.91	1.03	0.89	0.90

An embodiment may be a wide-angle lens system having high resolving power in a wide angle area having a half field of view HFOV of 40° or more. A wide angle single focus lens system may be mainly used for landscape photography and nearby portrait photography. Since a focal length is fixed, focusing is required to correct an image point position that varies according to a position of an object and, in an embodiment, optical performance for both a far object and a near object may be stably maintained.

A wide-angle lens system according to an embodiment may be applied to various electronic apparatuses. FIG. 9 is a view of an imaging apparatus including a wide-angle lens system 500 according to an embodiment. The wide-angle lens system 500 is substantially the same as any of the wide-

angle lens systems

100, 200, 300, and 400 of FIGS. 1, 3, 5, and 7. The imaging apparatus may include an image sensor 512 that receives light formed by the wide-angle lens system 500. The imaging apparatus may include a display 515 on which an object image is displayed. The imaging apparatus may be applied to, for example, a mirrorless camera.

The wide-angle lens system according to an embodiment may be miniaturized by using an internal focusing method that performs focusing by moving some inner lenses. Also, the imaging apparatus may be conveniently carried by using the internal focusing method.

The internal focusing method may be advantageous in having a dust-resistant and moisture-resistant construction because a front lens group and a rear lens group are fixed. The wide-angle lens system according to various embodiments may reduce a total length. As the total length is reduced, various aberrations may occur. However, such aberrations may be effectively controlled by using aspherical lenses.

A wide-angle lens system according to an embodiment may be miniaturized by using an internal focusing method. Also, an embodiment may provide a telephoto lens system having a wide angle. A wide-angle lens system according to various embodiments may be applied to a mirrorless camera.

While the present disclosure has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims. The embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the present disclosure is defined not by the detailed description of the present disclosure but by the appended claims, and all differences within the scope will be construed as being included in the present disclosure.

Claims

A wide-angle lens system comprising:

a first lens group located closest to an object side;

a second lens group located at a side of the first lens group to be close to an image side and configured to perform focusing; and

a third lens group located at a side of the second lens group to be close to the image side,

wherein the first lens group and the third lens group are fixed during focusing, and the wide-angle lens system satisfies

, and

where BF is a back focal length of the wide-angle lens system, FL is an effective focal length of the wide-angle lens system, and ω is a half field of view.
The wide-angle lens system of claim 1, wherein the first lens group has a positive refractive power, the second lens group has a positive refractive power, and the third lens group has a negative refractive power.
The wide-angle lens system of claim 1, wherein the first lens group comprises a meniscus lens having a negative refractive power.
The wide-angle lens system of claim 1, wherein the second lens group comprises one or two lenses.
The wide-angle lens system of claim 1, wherein the second lens group comprises two meniscus lenses convex toward the image side.
The wide-angle lens system of claim 1, wherein the third lens group comprises one lens having a negative refractive power.
The wide-angle lens system of claim 1, wherein the third lens group comprises a plano-concave lens or a bi-concave lens.
The wide-angle lens system of claim 1, wherein the second lens group comprises one aspherical lens.
The wide-angle lens system of claim 1, wherein the first lens group comprises one aspherical lens.
The wide-angle lens system of claim 1, wherein the wide-angle lens system satisfies

where fm is a composite focal length of the first lens group and the second lens group of the wide-angle lens system, and f_L3 is a focal length of the third lens group.
The wide-angle lens system of claim 1, wherein the wide-angle lens system satisfies

where L1 is a distance along an optical axis from an object-side surface of a lens closest to the object side to an image-side surface of a lens closest to the image side from among lenses included in the first lens group, L3 is a thickness of one lens included in the third lens group, and LF is a movement distance of the second lens group during focusing from infinity to a closest distance.
The wide-angle lens system of claim 1, wherein the wide-angle lens system satisfies

where G1V is an Abbe number of a lens closest to the object side from among lenses included in the first lens group, and G2V is an Abbe number of a second lens from the object side from among the lenses included in the first lens group.
The wide-angle lens system of claim 1, further comprising an image sensor located at a side of the third lens group to be close to the image side,

wherein the wide-angle lens system satisfies

where Y is a half diagonal image height of the image sensor, and BFL is a back focal length.
The wide-angle lens system of claim 1, further comprising a stop located between lenses included in the first lens group or located at a closest image side of the first lens group.
The wide-angle lens system of claim 1, wherein the first lens group comprises a meniscus lens convex toward the object side, a meniscus lens concave toward the object side, a bi-convex lens, and a meniscus lens convex toward the object side, which are sequentially arranged from the object side to the image side.
An electronic apparatus comprising the wide-angle lens system of claim 1.