Optical imaging system

An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens sequentially disposed from the first lens to the fifth lens from an object-side of the imaging system to an image-side of the imaging system and each having refractive power. The fourth lens has a convex object-side surface and an expression 0.7<TL/f<1.0 is satisfied, where TL is a distance from an object-side surface of the first lens to an imaging plane, and f is an overall focal length of the optical imaging system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2017-0056769 filed on May 4, 2017, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes, and Korean Patent Application No. 10-2017-0085397 filed on Jul. 5, 2017, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

This application relates to a telescopic optical imaging system including five or more lenses.

2. Description of Related Art

Telescopic optical imaging systems capable of capturing images of distant objects may be overly large. For example, the ratio TL/f of the overall length TL of a telescopic optical imaging system to the overall focal length f may be greater than or equal to 1. Thus, it may be difficult to mount such a telescopic optical imaging system in a small electronic device, such as a portable terminal.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art.

SUMMARY

In one general aspect, an optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens, sequentially disposed from the first lens to the fifth lens from an object-side of the imaging system to an image-side of the imaging system and each having refractive power. The fourth lens has a convex object-side surface, and an expression 0.7<TL/f<1.0 is satisfied, where TL is a distance from an object-side surface of the first lens to an imaging plane, and f is an overall focal length of the optical imaging system.

The first lens may have a concave image-side surface. The second lens may have a concave image-side surface. The third lens may have a convex object-side surface. The fourth lens may have a concave image-side surface. The fifth lens may have a convex object-side surface.

The first lens, the third lens, and the fifth lens may have positive refractive power, and the second lens and the fourth lens may have negative refractive power.

A distance from an image-side surface of the third lens to the object-side surface of the fourth lens may be greater than 0.9 mm and less than 1.7 mm.

An expression 0.38<tan θ<0.50 may be satisfied, where θ is a half angle of view of the optical imaging system.

In another general aspect, an optical imaging system, includes a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, and a fifth lens having positive refractive power and a refractive index greater than 1.6 and less than 1.75. The first to fifth lenses are sequentially disposed from an object-side of the optical imaging system to an image-side of the optical imaging system.

The fourth lens may have a convex object-side surface.

An expression 0.7<TL/f<1.0 may be satisfied, where TL is a distance from an object-side surface of the first lens to an imaging plane, and f is an overall focal length of the optical imaging system.

An expression |f2/f1|<1.5 may be satisfied, where f1 is a focal length of the first lens, and f2 is a focal length of the second lens.

An expression 0<f/f3<1.9 may be satisfied, where f is an overall focal length of the optical imaging system, and f3 is a focal length of the third lens.

An expression 2.0<f/EPD<2.7 may be satisfied, where f is an overall focal length of the optical imaging system, and EPD is an entrance pupil diameter.

An expression −1.0<f1G/f2G<−0.1 may be satisfied, where f1G is a composite focal length of the first lens, the second lens, and the third lens, and f2G is a composite focal length of the fourth lens and the fifth lens.

An expression TL/2<f1 may be satisfied, where TL is a distance from an object-side surface of the first lens to the imaging plane, and f1 is a focal length of the first lens.

In another general aspect, an optical imaging system, includes a first lens group and a second lens group. The first lens group includes a first lens, a second lens, and a third lens. A composite focal length of the first lens group is within a range from about 4.5 to about 5.1. The second lens group includes a fourth lens and a fifth lens. A composite focal length of the second lens group is within a range from about −11 to about −6.5. The first to fifth lenses are sequentially disposed from an object-side of the optical imaging system to an image-side of the optical imaging system.

A focal length of the fourth lens may be within a range of about −8.0 to −3.0. A focal length of the fifth lens may be within a range of about 7 to 100.

An overall focal length of the optical imaging system may be within a range of about 5.0 to 6.5. An overall length of the optical imaging system may be within a range of about 5.0 to 5.6. A half angle of view of the optical imaging system may be within a range of about 21 to 31.

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative sizes, proportions, and depictions of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

Subsequently, examples are described in further detail with reference to the accompanying drawings.

Examples described in this application provide an optical imaging system capable of being mounted in a small terminal and capturing an image of a distant object.

In this application, a first lens is a lens closest to an object or a subject of which an image is captured. A fifth lens is a lens closest to an imaging plane or an image sensor. In addition, an entirety of a radius of curvature, a thickness, a distance from an object-side surface of a first lens to the imaging plane (TL), a half diagonal length of the imaging plane (IMG HT), and a focal length of a lens are indicated in millimeters (mm). Further, a thickness of a lens, a gap between lenses, and TL are distances measured based on an optical axis of the lens. In a description of a form of a lens, a surface of a lens being convex means that an optical axis portion of a corresponding surface is convex, while a surface of a lens being concave means that an optical axis portion of a corresponding surface is concave. Therefore, in a configuration in which a surface of a lens is described as being convex, an edge portion of the lens may be concave. In a similar manner, in a configuration in which a surface of a lens is described as being concave, an edge portion of the lens may be convex.

Examples described in this application provide an optical imaging system including a first lens group configured to correct an aberration, a second lens group configured to correct curvature of an imaging plane, and a stop interposed between the first lens group and the second lens group.

An example of an optical imaging system includes two lens groups, a first lens group and a second lens group.

The first lens group includes a plurality of lenses. For example, the first lens group includes a first lens having positive refractive power, a second lens having negative refractive power, and a third lens having positive refractive power. The first lens has a convex object-side surface, the second lens has a concave image-side surface, and the third lens has a convex object-side surface.

The first lens group includes an aspherical lens. For example, at least one surface of one of the lenses forming the first lens group may be aspherical. The first lens group may include a plastic lens. For example, all of the lenses forming the first lens group may be manufactured using plastic.

Next, lenses forming the first lens group will be described.

The first lens has positive refractive power. The first lens has a concave image-side surface. The first lens has a refractive index lower than 1.6 and an Abbe number higher than or equal to 50. Opposing surfaces of the first lens may be aspherical. The first lens may be formed using a plastic material.

The second lens has negative refractive power. The second lens has a concave image-side surface. The second lens has a refractive index higher than or equal to 1.65 and an Abbe number less than 23. Opposing surfaces of the second lens may be aspherical. The second lens may be formed using a plastic material.

The third lens has positive refractive power. The third lens has a convex object-side surface. The third lens has a refractive index higher than or equal to 1.60 and an Abbe number less than 23. Opposing surfaces of the third lens may be aspherical. The third lens may be formed using a plastic material.

The second lens group includes a plurality of lenses. For example, the second lens group may include a fourth lens having negative refractive power and a fifth lens having positive refractive power. In this case, the fourth lens may have a convex object-side surface, while the fifth lens may have a convex object-side surface.

The second lens group includes an aspherical lens. For example, at least one surface of one of the lenses forming the second lens group may be aspherical. The second lens group includes a plastic lens. For example, all of the lenses forming the second lens group may be manufactured using plastic.

Next, lenses forming the second lens group will be described.

The fourth lens has negative refractive power. The fourth lens has a convex object-side surface. The fourth lens has a refractive index lower than 1.6 and an Abbe number higher than or equal to 50. Opposing surfaces of the fourth lens may be aspherical. The fourth lens may be formed using a plastic material.

The fifth lens has positive refractive power. The fifth lens has a convex image-side surface. The fifth lens has a refractive index higher than or equal to 1.60 and an Abbe number less than 23. Opposing surfaces of the fifth lens may be aspherical. The fifth lens may be formed using a plastic material.

The optical imaging system is configured to be easily mounted in a small electronic device. For example, an overall length (a distance from the object-side surface of the first lens to the imaging plane) of the optical imaging system is less than or equal to 6.0 mm.

An aspherical surface of a lens in the optical imaging system may be expressed using Equation 1.

In Equation 1, c is an inverse number of a radius of curvature of a lens, k is a conic constant, r is a distance from a certain point on an aspherical surface of the lens to an optical axis, A to J are aspherical constants, and Z (or SAG) is a distance between a certain point on the aspherical surface of the lens at the distance r and a tangential plane meeting the apex of the aspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor, and a stop.

The filter is interposed between a lens at the end of the second lens group and the image sensor. The filter is configured to block light having an infrared wavelength. The image sensor forms the imaging plane. The stop is disposed to adjust an intensity of light incident on a lens. The stop may be interposed between the second lens and the third lens. However, a position in which the stop is disposed is not limited to a position between the second lens and the third lens.

In the above Conditional Expressions, TL is a distance from the object-side surface of the first lens to the imaging plane, f is an overall focal length of the optical imaging system, d1G2G is a distance from an image-side surface of a lens disposed closest to the imaging plane in the first lens group to an object-side surface of a lens disposed closest to an object-side in the second lens group, f2 is a focal length of the second lens, f3 is a focal length of the third lens, f4 is a focal length of the fourth lens, f5 is a focal length of the fifth lens, Ndi is a refractive index of a lens disposed closest to the imaging plane, θ is a half angle of view of the optical imaging system, EPD is an entrance pupil diameter, f1G is a composite focal length of the first lens group, f2G is a composite focal length of the second lens group, D34 is a distance from an image-side surface of the third lens to an object-side surface of the fourth lens, and D4P is a distance from the object-side surface of the fourth lens to the imaging plane.

Satisfying Conditional Expression 1 is a condition for miniaturization of the optical imaging system.

Satisfying Conditional Expression 2 is a design condition to form a telescopic optical system. For example, in the case of the optical imaging system containing components having a value outside of a lower limit value of Conditional Expression 2, an angle of view is relatively wide, and a relatively long focal length is difficult to implement. In the case of the optical imaging system containing components having a value outside of an upper limit value of Conditional Expression 2, an overall length (TL) of the optical imaging system is relatively long, and miniaturization thereof is difficult to realize.

Satisfying Conditional Expression 3 is a focal length ratio of the first lens to the second lens to reduce a telephoto ratio (TL/f).

Satisfying Conditional Expression 4 is a design condition to prevent an image from being degraded. For example, in a case in which the focal length of the third lens is outside of a numerical range of Conditional Expression 4, an image may be degraded due to an increase in astigmatism.

Satisfying Conditional Expression 5 is a design condition of a lens disposed closest to the imaging plane for a high-resolution optical imaging system. For example, in a case in which a refractive index of a lens disposed closest to the imaging plane satisfies a numerical range of Conditional Expression 5, an effect of correcting astigmatism, a chromatic aberration, and a magnification aberration through the lens may be enhanced.

Satisfying Conditional Expression 6 is a condition of an angle of view for a telescopic optical imaging system, while satisfying Conditional Expression 7 is a range of an f-number for a high-resolution optical imaging system.

Satisfying Conditional Expression 8 suggests an appropriate focus ratio between the first lens group for aberration correction of the optical imaging system and the second lens group for curvature correction of the imaging plane.

Hereinafter, the optical imaging system according to various examples will be described.

With reference toFIG. 1, an optical imaging system according to a first example will be described.

An optical imaging system100includes a first lens group 1G and a second lens group 2G.

The first lens group 1G includes a first lens110, a second lens120, and a third lens130.

The first lens110has positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens120has negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens130has positive refractive power, a convex object-side surface, and a concave image-side surface.

The second lens group 2G includes a fourth lens140and a fifth lens150.

The fourth lens140has negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, the fourth lens140has a shape which includes an inflection point on an image-side surface. For example, the image-side surface of the fourth lens140may be concave in a vicinity of an optical axis and convex on an edge thereof. The fifth lens150has positive refractive power and opposing convex surfaces. In addition, the fifth lens150has a shape which includes an inflection point on an object-side surface.

In an example of the optical imaging system, a composite focal length f1G of the first lens group 1G is 4.920, while a composite focal length f2G of the second lens group 2G is −9.510.

The optical imaging system100includes an image sensor170forming an imaging plane. The optical imaging system100includes a filter160. The filter160is interposed between the fifth lens150and the image sensor170. The optical imaging system100includes a stop ST. The stop ST may be interposed between the second lens120and the third lens130.

The optical imaging system100configured as described above has aberration characteristics as illustrated inFIG. 2. An image height IMG HT of the optical imaging system100according to an example is 2.62 mm as illustrated inFIG. 2.FIG. 3is a table listing examples of aspherical surface characteristics of the optical imaging system100. Table 1 illustrates lens characteristics of the optical imaging system100according to an example.

A second example of an optical imaging system will be described with reference toFIG. 4.

The second example of an optical imaging system200includes a first lens group 1G and a second lens group 2G.

The first lens group 1G includes a first lens210, a second lens220, and a third lens230.

The first lens210has positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens220has negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens230has positive refractive power, a convex object-side surface, and a concave image-side surface.

The second lens group 2G includes a fourth lens240and a fifth lens250.

The fourth lens240has negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, the fourth lens240has a shape including an inflection point on an image-side surface. For example, the image-side surface of the fourth lens240may be concave in a vicinity of an optical axis and convex on an edge thereof. The fifth lens250has positive refractive power and opposing convex surfaces. In addition, the fifth lens250has a shape including an inflection point on an object-side surface.

In the optical imaging system according to an example, a composite focal length f1G of the first lens group 1G is 4.960, while a composite focal length f2G of the second lens group 2G is −10.08.

The optical imaging system200includes an image sensor270forming an imaging plane. The optical imaging system200includes a filter260. The filter260is interposed between the fifth lens250and the image sensor270. The optical imaging system200includes a stop ST. The stop ST is interposed between the second lens220and the third lens230.

The optical imaging system200configured as described above has aberration characteristics as illustrated inFIG. 5. An image height IMG HT of the optical imaging system200according to an example is 2.62 mm as illustrated inFIG. 5.FIG. 6is a table listing examples of aspherical surface characteristics of the optical imaging system200. Table 2 illustrates lens characteristics of the optical imaging system200according to an example.

An optical imaging system according to a third example will be described with reference toFIG. 7.

The third example of an optical imaging system300includes a first lens group 1G and a second lens group 2G.

The first lens group 1G includes a first lens310, a second lens320, and a third lens330.

The first lens310has positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens320has negative refractive power, a convex object-side surface, and a concave image-side surface. The third lens330has positive refractive power, a convex object-side surface, and a concave image-side surface.

The second lens group 2G includes a fourth lens340and a fifth lens350.

The fourth lens340has negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, the fourth lens340has a shape which includes an inflection point on an image-side surface. For example, the image-side surface of the fourth lens340may be concave in a vicinity of an optical axis and convex on an edge thereof. The fifth lens350has positive refractive power and opposing convex surfaces. In addition, the fifth lens350has a shape which includes an inflection point on an object-side surface.

In the optical imaging system according to an example, a composite focal length f1G of the first lens group 1G is 4.960, while a composite focal length f2G of the second lens group 2G is −9.630.

The optical imaging system300includes an image sensor370forming an imaging plane. The optical imaging system300includes a filter360. The filter360is interposed between the fifth lens350and the image sensor370. The optical imaging system300includes a stop ST. The stop ST is interposed between the second lens320and the third lens330.

The optical imaging system300, configured as described above, has aberration characteristics as illustrated inFIG. 8. An image height IMG HT of the optical imaging system300according to an example is 2.62 mm, as illustrated inFIG. 8.FIG. 9is a table listing examples of aspherical surface characteristics of the optical imaging system300. Table 3 illustrates lens characteristics of the optical imaging system100according to an example.

An optical imaging system according to a fourth example will be described with reference toFIG. 10.

The fourth example of an optical imaging system400includes a first lens group 1G and a second lens group 2G.

The first lens group 1G includes a first lens410, a second lens420, and a third lens430.

The first lens410has positive refractive power, a convex object-side surface, and a concave image-side surface. The second lens420has negative refractive power, a concave object-side surface, and opposing concave image-side surfaces. The third lens430has positive refractive power, a convex object-side surface, and a concave image-side surface.

The second lens group 2G includes a fourth lens440and a fifth lens450.

The fourth lens440has negative refractive power, a convex object-side surface, and a concave image-side surface. In addition, the fourth lens440has a shape which includes an inflection point on an image-side surface. For example, the image-side surface of the fourth lens440may be concave in a vicinity of an optical axis and convex on an edge thereof. The fifth lens450has positive refractive power, a convex object-side surface, and a concave image-side surface. In addition, the fifth lens450has a shape which includes an inflection point on an object-side surface.

In the optical imaging system according to an example, a composite focal length f1G of the first lens group 1G is 4.608, while a composite focal length f2G of the second lens group 2G is −7.420.

The optical imaging system400includes an image sensor470forming an imaging plane. The optical imaging system400includes a filter460. The filter460is interposed between the fifth lens450and the image sensor470. The optical imaging system400includes a stop ST. The stop ST is interposed between the second lens420and the third lens430.

The optical imaging system400configured as described above has aberration characteristics as illustrated inFIG. 11. An image height IMG HT of the optical imaging system400according to an example is 3.23 mm as illustrated inFIG. 11.FIG. 12is a table listing examples of aspherical surface characteristics of the optical imaging system400. Table 4 illustrates lens characteristics of the optical imaging system400according to an example.

Table 5 illustrates values satisfying the Conditional Expressions 1-8, 10, and 11, above, for the optical imaging system according to the first example, the second example, the third example, and the fourth example.

In the optical imaging system, a focal length of the first lens is generally set to be within a range of 2.8 to 3.0. In the optical imaging system, a focal length of the second lens is generally set to be within a range of −4.5 to −3.0. In the optical imaging system, a focal length of the third lens is generally set to be within a range of 8 to 200. In the optical imaging system, a focal length of the fourth lens is generally set to be within a range of −8.0 to −3.0. In the optical imaging system, a focal length of the fifth lens is generally set to be within a range of 7 to 100. In the optical imaging system, a composite focal length of the first lens group including the first lens, the second lens, and the third lens is set to be within a range of 4.5 to 5.1. In the optical imaging system, a composite focal length of the second lens group including the fourth lens and the fifth lens is set to be within a range of −11 to −6.5.

Focal lengths of lenses forming the optical imaging system are not limited to the ranges described above. For example, focal lengths of the first lens, the second lens, and the third lens may be changed within a range satisfying the range (4.5 to 5.1) with respect to the composite focal length of the first lens group, described above. Focal lengths of the fourth lens and the fifth lens may be changed within a range satisfying the range (−11 to −6.5) with respect to the composite focal length of the second lens group, described above.

An overall focal length of the optical imaging system is generally set to be within a range of 5.0 to 6.5. An overall length TL of the optical imaging system is generally set to be within a range of 5.0 to 5.6. A half angle of view of the optical imaging system is set to be within a range of 21 to 31.

Hereinafter, with reference toFIGS. 13 and 14, an example optical imaging system mounted in a portable terminal is described.FIG. 13is a rear view of an example of a portable terminal in which an example of an optical imaging system described in this application is mounted.FIG. 14is a cross sectional view taken along I-I ofFIG. 13.

A portable terminal10includes a plurality of camera modules, for example, a first camera module20and a second camera module30. The first camera module20includes a first optical imaging system101configured to image a subject at close range. The second camera module30includes second optical imaging systems100,200,300, and400configured to image a subject at long range.

The first optical imaging system101includes a plurality of lenses. For example, the first optical imaging system101includes four or more lenses. The first optical imaging system101is configured to capture images of objects at close range. For example, the first optical imaging system101has a relatively wide angle of view of 50° or above, while a (TL/f) ratio is equal to or greater than 1.0.

The second optical imaging systems100,200,300, and400each include a plurality of lenses. For example, the second optical imaging systems100,200,300, and400each include five or more lenses. The second optical imaging systems100,200,300, and400may be provided as one of the optical imaging systems from among the example optical imaging systems, according to the first example, the second example, the third example, and the fourth example, described above. The second optical imaging systems100,200,300, and400may be configured to capture an image of a distant object. For example, the second optical imaging systems100,200,300, and400each have an angle of view of 50° or below, while a (TL/f) ratio is less than 1.0.

The first optical imaging system101and the second optical imaging systems100,200,300, and400may be substantially equal in size. For example, an overall length L1 of the first optical imaging system101can be substantially equal to an overall length L2 of the second optical imaging systems100,200,300, and400. Alternatively, a ratio (L1/L2) of the overall length L1 of the first optical imaging system101to the overall length L2 of any of the second optical imaging systems100,200,300, and400may be 0.8 to 1.0. The second optical imaging systems100,200,300, and400are each configured to have an overall length L2 less than a height h of the portable terminal10. For example, a ratio (L2/h) of the overall length L2 of the second optical imaging systems100,200,300, and400to the height h of the portable terminal10is less than or equal to 0.8. In addition, the overall length L2 of each of the second optical imaging systems100,200,300, and400may be less than or equal to 6.5 mm.

As set forth above, according to examples, an optical imaging system capable of capturing a distant image and being mounted in a small terminal may be provided.