Optical imaging system having prism, reflecting member, fixed lens groups, and movable lens groups

There is provided an optical imaging system including a prism, a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The prism is configured to refract light reflected from an object side toward an imaging plane and a reflecting member. The prism is disposed on the first fixed lens group and the first movable lens group is configured to change a position of the imaging plane so that an overall focal length is changed. The second movable lens group is configured to adjust a position of the imaging plane so that a focal length for an object is adjusted. The imaging plane is disposed on the second fixed lens group.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the priority and benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0143647 filed on Oct. 14, 2015, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The following description relates to an optical imaging system of which a focal length may be adjusted.

2. Description of Related Art

In a needle case type optical imaging system, in which a plurality of lenses are disposed linearly or in a row, as a number of lenses is increased, an overall length of the optical imaging system is increased. For example, it is more difficult to miniaturize an optical imaging system including five lenses than to miniaturize an optical imaging system including three lenses. For this reason, there is a limitation in mounting needle case type optical imaging systems in small portable terminals.

Conversely, in a curved optical imaging system, only some lenses are disposed in a row. Therefore, curved optical imaging systems may be mounted in tight spaces. However, because the curved optical imaging system uses a plurality of refracting prisms, manufacturing costs of the optical imaging system are high, and optical performance of the optical imaging system may be deteriorated.

SUMMARY

In accordance with an embodiment, there is provided an optical imaging system, including: a prism configured to refract light reflected from an object side toward an imaging plane and a reflecting member; a first fixed lens group in which the prism is disposed; a first movable lens group configured to change a position of the imaging plane so that an overall focal length is changed; a second movable lens group configured to adjust a position of the imaging plane so that a focal length for an object is adjusted; and a second fixed lens group in which the imaging plane is disposed.

The first fixed lens group may include two or more lenses having different refractive powers.

The first fixed lens group may include: a first lens adjacently disposed to an object-side surface of the prism and having a negative refractive power; and a second lens adjacently disposed to an image-side surface of the prism and having a positive refractive power.

The first movable lens group may include lenses having different refractive powers.

The second movable lens group may include a lens having a negative refractive power.

The second movable lens group may include a lens including a concave object-side surface and a concave image-side surface.

The second fixed lens group may include a lens having a positive refractive power.

The second fixed lens group may include a lens including a convex object-side surface and a convex image-side surface.

The optical imaging system may also include a stop disposed between the first movable lens group and the second movable lens group.

2.0<ft/fw, in which ft may be an overall focal length at a telephoto end, and fw may be an overall focal length at a wide angle end.

np<2.1, in which np may be a refractive index of the prism.

4.5<BFL, in which BFL may be a distance from an image-side surface of a lens closest to the imaging plane in the second fixed lens group to the imaging plane.

Yh/(IMG HT)<0.55, in which Yh may be ½ of a length of a short side of the imaging plane, and IMG HT may be ½ of a diagonal length of the imaging plane.

In accordance with another embodiment, there is provided an optical imaging system, including: a first fixed lens group including lenses; a prism disposed between the lenses of the first fixed lens group; a first movable lens group configured to be movable; a second movable lens group configured to be movable; a stop disposed between the first movable lens group and the second movable lens group; a second fixed lens group including a lens having a positive refractive power; and a reflecting member reflecting light irradiated from the second fixed lens group to an imaging plane.

The prism and the reflecting member may be disposed in a symmetrical form.

The first movable lens group may include a cemented lens.

In accordance with a further embodiment, there is provided an optical imaging system, including: a first fixed lens group including lenses having different refractive powers; a prism disposed between the lenses of the first fixed lens group; a first movable lens group configured to be movable to change an overall focal length; a correction lens group configured to move in an optical axis direction or a direction intersecting with the optical axis; a second movable lens group configured to be movable to finely adjust the overall focal length; and a second fixed lens group, wherein a distance between the first movable lens group and the correction lens group is longest at a wide angle end and is shortest at a telephoto end, and wherein a distance between the correction lens group and the second movable lens group is longest at the wide angle end and shortest at the telephoto end.

A distance between the first fixed lens group and the first movable lens group may be shortest at the wide angle end and may be longest at the telephoto end.

A distance between the second movable lens group and the second fixed lens group are shortest at the wide angle end and longest at the telephoto end.

A distance between the second fixed lens group and the image sensor may be constant or substantially constant.

4.5<BFL, in which BFL may be a distance from an image-side surface of a lens closest to an imaging plane in the second fixed lens group to the imaging plane.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to schematic views illustrating various embodiments. In the drawings, for example, due to manufacturing techniques and/or tolerances, modifications of the shape shown may be estimated. Thus, embodiments should not be construed as being limited to the particular shapes of regions shown herein, for example, to include a change in shape results in manufacturing. The following embodiments may also be constituted by one or a combination thereof.

The various embodiments described below may have a variety of configurations and propose only a required configuration herein, but are not limited thereto.

In addition, a surface of each lens closest to an object is referred to as a first surface or an object-side surface, and a surface of each lens closest to an imaging surface is referred to as a second surface or an image-side surface. A first lens is a lens closest to an object (or a subject), while an eleventh lens or an eighth lens is a lens closest to an imaging plane (or an image sensor). A person skilled in the relevant art will appreciate that other units of measurement may be used. Further, in the present specification, all radii of curvature, thicknesses, OALs (optical axis distances from the first surface of the first lens to the image sensor (OALs), a distance on the optical axis between the stop and the image sensor (SLs), image heights or ½ of a diagonal length of the imaging plane (IMGHs) (image heights), and black focus lengths (BFLs) (back focus lengths) of the lenses, an overall focal length of an optical system, and a focal length of each lens are indicated in millimeters (mm). Further, thicknesses of lenses, gaps between the lenses, OALs, and SLs are distances measured based on an optical axis of the lenses. Further, thicknesses of the lenses, gaps between the lenses, and TTL, a through-the-lens, are distances in optical axes through the lenses. The TTL is a camera feature in which light levels are measured through the lens that captures the pictures, as opposed to a separate metering window.

Further, surface of a lens being convex means that an optical axis portion of a corresponding surface is convex, and a surface of a lens being concave means that an optical axis portion of a corresponding surface is concave. Therefore, even in the case that one surface of a lens is described as being convex, an edge portion of the lens may be concave. Likewise, even in the case that one surface of a lens is described as being concave, an edge portion of the lens may be convex. In other words, a paraxial region of a lens may be convex, while the remaining portion of the lens outside the paraxial region is either convex, concave, or flat. Further, a paraxial region of a lens may be concave, while the remaining portion of the lens outside the paraxial region is either convex, concave, or flat.

In the optical system, according to embodiments, the lenses are formed of materials including glass, plastic or other similar types of polycarbonate materials. In another embodiment, at least one of the lenses is formed of a material different from the materials forming the other lenses.

An optical imaging system includes an optical system including lenses. For example, the optical system of the optical imaging system may include lenses having refractive power. However, the optical imaging system is not limited to including only the lenses having refractive power. For example, the optical imaging system may include a stop to control an amount of light. In addition, the optical imaging system may further include an infrared cut-off filter filtering infrared light. Further, the optical imaging system may further include an image sensor, such as an imaging device, configured to convert an image of a subject incident thereto through the optical system into electrical signals. Further, the optical imaging system may further include a gap maintaining member adjusting a gap between lenses.

The lenses are formed of a material having a refractive index different from that of air. For example, the lenses are formed of plastic or glass. At least one of the lenses has an aspherical shape. An aspherical surface of each of the lenses is represented by the following Equation 1:

In this equation, c is an inverse of a radius of curvature of the 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 the certain point on the aspherical surface of the lens at the distance Y and a tangential plane meeting the apex of the aspherical surface of the lens.

The optical imaging system, in accordance with an embodiment, includes a plurality of lens groups. For example, the optical imaging system includes a first fixed lens group, a first movable lens group, a second movable lens group, and a second fixed lens group. The first fixed lens group, the first movable lens group, the second movable lens group, and the second fixed lens group are sequentially disposed from an object side toward the imaging plane.

The first fixed lens group includes one or more lenses. For example, the first fixed lens group includes a lens having a negative refractive power and a lens having a positive refractive power. The lens having the negative refractive power is adjacently disposed to an object-side surface of a prism, and the lens having the positive refractive power is adjacently disposed to an image-side surface of the prism.

The first movable lens group includes one or more lenses. For example, the first movable lens group includes three lenses. The three lenses are lenses having different refractive powers. For example, the first movable lens group includes two lenses having a negative refractive power and one lens having a positive refractive power. However, a combination of the lenses configuring the first movable lens group is not limited to the described example. In accordance with another example, the first movable lens group includes two lenses having positive refractive power and one lens having negative refractive power.

The second movable lens group includes one or more lenses. For example, the second movable lens group includes one lens having a negative refractive power. However, the second movable lens group is not limited to including only one lens. For example, the second movable lens group may include three lenses. In another configuration, the one lens has a positive refractive power.

The second fixed lens group includes one or more lenses. For example, the second fixed lens group includes one lens having a positive refractive power. In another configuration, the one lens has a negative refractive power.

The optical imaging system includes the prism, a reflecting member, a filter, the stop, and an image sensor.

The prism is disposed in the first fixed lens group. For example, the prism is disposed between or adjacent to the lenses configuring the first fixed lens group. The prism is formed of a material having a substantially low refractive power. For example, the prism has a refractive power of 2.1 or less. In a case in which the prism has the substantially low refractive power, manufacturing costs of the optical imaging system may be reduced.

The reflecting member is disposed between the second fixed lens group and the image sensor. The reflecting member reflects light refracted by the prism to resolve a phenomenon in which the optical imaging system is elongated in one direction.

The filter is disposed between the reflecting member and the image sensor. The filter filters a partial wavelength of incident light to improve resolution of the optical imaging system. For example, the filter filters an infrared wavelength of the incident light.

The stop is disposed in order to adjust an amount of light incident to the lenses. For example, the stop is disposed between the first movable lens group and the second movable lens group.

In accordance with an embodiment, the optical imaging system satisfies the following Conditional Expressions 1 through 4:
2.0<ft/fw[Conditional Expression 1]
np<2.1  [Conditional Expression 2]
4.5<BFL[Conditional Expression 3]
Yh/(IMG HT)<0.55.  [Conditional Expression 4]

In one example, ft is an overall focal length at a telephoto end, where end is an end of a zoom range, fw is an overall focal length at a wide angle end, np is a refractive index of the prism, BFL is a distance from an image-side surface of a lens closest to the imaging plane in the second fixed lens group to the imaging plane, Yh is ½ of a length of a short side of the imaging plane, and IMG HT is ½ of a diagonal length of the imaging plane.

In one embodiment, the optical imaging system meeting the Conditional Expressions 1 through 4 enable miniaturization of the optical imaging system.

Next, optical imaging systems, according to several embodiments, will be described.

An optical imaging system, according to a first embodiment, will be described with reference toFIG. 1.

The optical imaging system1000, according to the first embodiment, includes an optical system including a first lens1010, a second lens1020, a third lens1030, a fourth lens1040, a fifth lens1050, a sixth lens1060, a seventh lens1070, an eighth lens1080, a ninth lens1090, a tenth lens1100, and an eleventh lens1110.

The lenses configuring the optical imaging system1000may be grouped into a plurality of lens groups. For example, the first lens1010and the second lens1020configure a first fixed lens group Gf1, the third to fifth lens1030to1050configure a first movable lens group Gm1, the sixth lens1060and the seventh lens1070configure a correction lens group Go, the eighth to tenth lenses1080to1100configure a second movable lens group Gm2, and the eleventh lens1110configures a second fixed lens group Gf2.

The first movable lens group Gm1changes an overall focal length of the optical imaging system1000. For example, a focal length of the optical imaging system1000changes within a range of 4.80 to 13.56, depending on a position of the first movable lens group Gm1.

The second movable lens group Gm2adjusts the overall focal length of the optical imaging system1000. For example, the focal length of the optical imaging system1000may be finely adjusted depending on a position of the second movable lens group Gm2.

The correction lens group Go corrects shaking of the optical imaging system1000. For example, the correction lens group Go moves in an optical axis direction or a direction intersecting with an optical axis, and corrects noise or vibration generated due to the shaking of the optical imaging system1000.

Next, the lenses configuring each lens group will be described in detail.

The first lens1010has a refractive power. For example, the first lens1010has a negative refractive power. The first lens1010has a meniscus shape. For example, an object-side surface of the first lens1010is convex, and an image-side surface thereof is concave.

The second lens1020has a refractive power. For example, the second lens1020has a positive refractive power. One surface of the second lens1020may be convex. For example, both surfaces of the second lens1020are convex.

The third lens1030has a refractive power. For example, the third lens1030has a negative refractive power. The third lens1030has a meniscus shape. For example, an object-side surface of the third lens1030is convex, and an image-side surface thereof is concave.

The fourth lens1040has a refractive power. For example, the fourth lens1040has a negative refractive power. The fourth lens1040has a meniscus shape. For example, both surfaces of the fourth lens1040are concave.

The fifth lens1050has a refractive power. For example, the fifth lens1050has a positive refractive power. The fifth lens1050has a meniscus shape. For example, an object-side surface of the fifth lens1050is convex, and an image-side surface thereof is concave. The fifth lens1050configured as described above may be cemented to an image-side surface of the fourth lens1040. In other words, the object-side surface of the fifth lens1050is configured with a convex curvature to be able to be enabled to be fit and contact with the image-side surface of the fourth lens1040. In accordance with an alternative embodiment, the object-side surface of the fifth lens1050is configured with a convex curvature with a curvature corresponding to the image-side surface of the fourth lens1040and at a predetermined distance from the image-side surface of the fourth lens1040.

The sixth lens1060has a refractive power. For example, the sixth lens1060has a positive refractive power. The sixth lens1060has a meniscus shape. For example, an object-side surface of the sixth lens1060is convex, and an image-side surface thereof is concave.

The seventh lens1070has a refractive power. For example, the seventh lens1070has a negative refractive power. The seventh lens1070has a meniscus shape. For example, an object-side surface of the seventh lens1070is convex, and an image-side surface thereof is concave. In an alternative example, the object-side surface of the seventh lens1070is concave, and an image-side surface thereof is concave.

The eighth lens1080has a refractive power. For example, the eighth lens1080has a positive refractive power. At least one surface of the eighth lens1080is convex. For example, both surfaces of the eighth lens1080are convex.

The ninth lens1090has a refractive power. For example, the ninth lens1090has a positive refractive power. At least one surface of the ninth lens1090is convex. For example, both surfaces of the ninth lens1090are convex.

The tenth lens1100has a refractive power. For example, the tenth lens1100has a negative refractive power. The tenth lens1100has a meniscus shape. For example, both surfaces of the tenth lens1100are concave. The tenth lens1100configured as described above may be cemented to an image-side surface of the ninth lens1090. In other words, the object-side surface of the tenth lens1100is configured with a concave curvature to be able to be enabled to be fit and contact with the image-side surface of the ninth lens1090. In accordance with an alternative embodiment, the object-side surface of the tenth lens1100is configured with a concave curvature with a curvature corresponding to the image-side surface of the ninth lens1090and at a predetermined distance from the image-side surface of the ninth lens1090.

The eleventh lens1110has a refractive power. For example, the eleventh lens1110has a positive refractive power. At least one surface of the eleventh lens1110is convex. For example, both surfaces of the eleventh lens1110is convex.

In the configurations of the lenses as described above, the first lens1010are divergently disposed or not in parallel with the second to eleventh lenses1020to1110. For example, an optical axis of the first lens1010may intersect with an optical axis of the second to eleventh lenses1020to1110.

The optical imaging system1000includes a prism P, a stop ST, a reflecting member M, a filter1120, and an image sensor1130.

The prism P is disposed between or adjacent to the first lens1010and the second lens1020. The prism P disposed as described above refracts light irradiated from the first lens1010to the second lens1020.

The stop ST is disposed between the first movable lens group Gm1and the second movable lens group Gm2or between the correction lens group Go and the second movable lens group Gm2. In detail, the stop ST is disposed between the seventh lens1070and the eighth lens1080. The stop ST disposed as described above adjusts an amount of light irradiated from the first movable lens group Gm1.

The reflecting member M is disposed between the eleventh lens1110and the filter1120. The reflecting member M reflects light irradiated from the eleventh lens1110to the image sensor1130.

The filter1120is disposed between the reflecting member M and the image sensor1130. The filter1120filters infrared rays, or the like, from the light reflected from the reflecting member M.

The image sensor1130includes a plurality of optical sensors. The image sensor1130converts an optical signal into an electrical signal.

The optical imaging system configured as described above may represent aberration characteristics illustrated inFIGS. 2 through 4.FIG. 2are graphs illustrating aberration curves in a wide angle end position;FIG. 3illustrates graphs aberration curves in an intermediate end position; andFIG. 4illustrates graphs aberration curves in a telephoto end position.

FIG. 5is a table illustrating characteristics of lenses of the optical imaging system according to the first exemplary embodiment.FIG. 6is a table illustrating magnitudes of D1, D2, D3, D4, and D5depending on the wide angle end, the intermediate end, and the telephoto end positions.FIG. 7is a table illustrating aspherical characteristics of the optical imaging system, according to the first embodiment.

As seen inFIG. 6, a distance D1between the first fixed lens group Gf1and the first movable lens group Gm1is shortest at the wide angle end and is longest at the telephoto end. Similarly, a distance D4between the second movable lens group Gm2and the second fixed lens group Gf2are shortest at the wide angle end and be longest at the telephoto end.

In contrast, a distance D2between the first movable lens group Gm1and the correction lens group Go is longest at the wide angle end and is shortest at the telephoto end. Similarly, a distance D3between the correction lens group Go and the second movable lens group Gm2is longest at the wide angle end and shortest at the telephoto end.

A distance D5between the second fixed lens group Gf2and the image sensor1130is constant or substantially constant regardless of the wide angle end, the intermediate end, and the telephoto end.

An optical imaging system, according to a second embodiment, will be described with reference toFIG. 8.

The optical imaging system2000, according to the second embodiment, includes an optical system including a first lens2010, a second lens2020, a third lens2030, a fourth lens2040, a fifth lens2050, a sixth lens2060, a seventh lens2070, and an eighth lens2080.

The lenses configuring the optical imaging system2000are grouped into a plurality of lens groups. For example, the first to third lenses2010to2030configure a first fixed lens group Gf1, the fourth to sixth lenses2040to2060configure a first movable lens group Gm1, the seventh lens2070configures a second movable lens group Gm2, and the eighth lens2080configures a second fixed lens group.

The first movable lens group Gm1changes an overall focal length of the optical imaging system2000. For example, a focal length of the optical imaging system2000is changed in a range of 4.90 to 13.70 depending on a position of the first movable lens group Gm1.

The second movable lens group Gm2adjusts the overall focal length of the optical imaging system2000. For example, the focal length of the optical imaging system2000is finely adjusted depending on a position of the second movable lens group Gm2.

Next, the lenses configuring each lens group will be described in detail.

The first lens2010has a refractive power. For example, the first lens2010has a negative refractive power. The first lens2010has a meniscus shape. For example, an object-side surface of the first lens2010is convex, and an image-side surface thereof is concave.

The second lens2020has a refractive power. For example, the second lens2020has a negative refractive power. The second lens2020has a meniscus shape. For example, both surfaces of the second lens2020are concave.

The third lens2030has a refractive power. For example, the third lens2030has a positive refractive power. The third lens2030has a meniscus shape. For example, an object-side surface of the third lens2030is convex, and an image-side surface thereof is concave. The third lens2030is cemented to an image-side surface of the second lens2020. In other words, the object-side surface of the third lens2030is configured with a convex curvature to be able to be enabled to be fit and contact with the image-side surface of the second lens2020. In accordance with an alternative embodiment, the object-side surface of the third lens2030is configured with a convex curvature with a curvature corresponding to the image-side surface of the second lens2020and at a predetermined distance from the image-side surface of the second lens2020.

The fourth lens2040has a refractive power. For example, the fourth lens2040has a positive refractive power. At least one surface of the fourth lens2040is convex. For example, both surfaces of the fourth lens2040are convex.

The fifth lens2050has a refractive power. For example, the fifth lens2050has a negative refractive power. The fifth lens2050has a meniscus shape. For example, an object-side surface of the fifth lens2050is convex, and an image-side surface of the fifth lens2050is concave.

The sixth lens2060has a refractive power. For example, the sixth lens2060has a positive refractive power. At least one surface of the sixth lens2060is convex. For example, both surfaces of the sixth lens2060are convex. The sixth lens2060formed as described above is cemented to the image-side surface of the fifth lens2050. In other words, the object-side surface of the sixth lens2060is configured with a convex curvature to be able to be enabled to be fit and contact with the image-side surface of the fifth lens2050. In accordance with an alternative embodiment, the object-side surface of the sixth lens2060is configured with a convex curvature with a curvature corresponding to the image-side surface of the fifth lens2050and at a predetermined distance from the image-side surface of the fifth lens2050.

The seventh lens2070has a refractive power. For example, the seventh lens2070has a negative refractive power. The seventh lens2070has a meniscus shape. For example, both surfaces of the seventh lens2070is concave.

The eighth lens2080has a refractive power. For example, the eighth lens2080has a positive refractive power. At least one surface of the eighth lens2080is convex. For example, both surfaces of the eighth lens2080is convex.

In the configurations of the lenses as described above, the first lens2010are divergently disposed or not in parallel with the second to eighth lenses2020to2080. For example, an optical axis of the first lens2010intersect with optical axes of the second to eighth lenses2020to2080.

The optical imaging system2000includes a prism P, a stop ST, a reflecting member M, a filter2120, and an image sensor2130.

The prism P is disposed between or adjacent to the first lens2010and the second lens2020. The prism P disposed as described above refracts light irradiated from the first lens2010to the second lens2020.

The stop ST is disposed between the first movable lens group Gm1and the second movable lens group Gm2. In detail, the stop ST is disposed between the sixth lens2060and the seventh lens2070. The stop ST disposed, as described above, adjusts an amount of light irradiated from the first movable lens group Gm1.

The reflecting member M is disposed between the eighth lens2080and the filter2120. The reflecting member M reflects light irradiated from the eleventh lens2080to the image sensor2130.

The filter2120is disposed between the reflecting member M and the image sensor2130. The filter2120filters an infrared ray, or other light rays, in the light reflected from the reflecting member M.

The image sensor2130includes a plurality of optical sensors. The image sensor2130coverts an optical signal into an electrical signal.

The optical imaging system, configured as described above, may represent aberration characteristics illustrated inFIGS. 9 through 11.FIG. 9illustrates graphs aberration curves in a wide angle end position;FIG. 10illustrates graphs aberration curves in an intermediate end position; andFIG. 11illustrates graphs aberration curves in a telephoto end position.

FIG. 12is a table illustrating characteristics of lenses of the optical imaging system, according to the second embodiment.FIG. 13is a table illustrating magnitudes of D1, D2, and D3depending on a wide angle end, an intermediate end, and telephoto end positions.FIG. 14is a table illustrating aspherical characteristics of the optical imaging system, according to the second embodiment.

As seen inFIG. 13, a distance D1between the first fixed lens group Gf1and the first movable lens group Gm1may be longest at the wide angle end and be shortest at the telephoto end.

In contrast, a distance D2between the first movable lens group Gm1and the second movable lens group Gm2may be shortest at the wide angle end and be longest at the telephoto end. Further, a distance D3between the second movable lens group Gm2and the second fixed lens group Gf2may be shortest at the wide angle end and be longest at the telephoto end.

Table 1 represents calculated values of the optical imaging systems, according to the first and second embodiments, with respect to Conditional Expressions 1 through 4.

As set forth above, according to various embodiments, an optical imaging system of which optical performance may be improved is realized.