Lens system and photographing apparatus having the same

A lens system and a photographing apparatus including the lens system are provided, the lens system including a first sub lens system that includes a plurality of lens groups, and a second sub lens system that includes a replacement lens group that replaces or is replaced by some of the plurality of lens groups.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2010-0022434, filed on Mar. 12, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Various embodiments of the invention relate to a lens-replaceable lens system and a photographing apparatus including the lens-replaceable lens system.

Photographing apparatuses, such as digital cameras or cellular phone cameras that use imaging devices, such as charge-coupled devices (CCDs) or complementary metal-oxide semiconductors (CMOSs), are required to be compact, lightweight, and inexpensive. Together with these demands, various optical performances are also required. For example, zoom lens systems are different in terms of optical characteristics according to the types of lens groups used. Users should select zoom lenses for a photographing apparatus according to intended uses of the photographing apparatus. For example, if a user wants to photograph a landscape, the user should select a wide-angle zoom lens system having an excellent wide angle performance and a wide viewing angle. In order to photograph a remote subject, a user should select a telephoto zoom lens system having a narrow viewing angle and a long focal length. As such, users should purchase different zoom lenses for different photographing purposes, and thus zoom lens systems may need to be replaced between photographing.

SUMMARY

According to an embodiment of the invention, there is provided a lens system having various types of focal lengths as a single lens system.

According to another embodiment of the invention, there is provided a photographing apparatus that achieves various types of focal lengths by using a single lens system.

According to an embodiment of the invention, there is provided a lens system including a first sub lens system that includes at least one lens group and a first replacement lens group and performs zooming between a wide angle position and a telephoto position; and a second sub lens system that shares the at least one lens group with the first sub lens system, includes a second replacement lens group that replaces or is replaced by the first replacement lens group, and has a focal length shorter than a focal length of the first sub lens system at the wide angle position.

The at least one lens group may include a lens group having a negative refractive power, and the first replacement lens group may be disposed between the lens group having the negative refractive power and an image plane.

The first sub lens system may include a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The second replacement lens group may replace or is replaced by the second lens group or the third lens group.

When the first sub lens system performs zooming from the wide angle position to the telephoto position, an interval between the first lens group and the second lens group may decrease and an interval between the second lens group and the third lens group may increase.

The third lens group may perform focusing.

The first sub lens system may include a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. The second replacement lens group may replace or may be replaced by the third lens group or the fourth lens group.

The second replacement lens group may include one lens.

The second sub lens system may have a viewing angle of 90 degrees or greater.

The second sub lens system may have a distortion of 15% or greater.

The first replacement lens group and the second replacement lens group may include at least one aspherical surface.

The lens system may satisfy the following equation:
0.6<EFL2/EFL1<1.1
where EFL1represents a focal length of the first replacement lens group and EFL2represents a focal length of the second replacement lens group.

According to another embodiment of the invention, there is provided a lens system including a first sub lens system that includes at least one lens group and a first replacement lens group and performs zooming between a wide angle position and a telephoto position; and a second sub lens system that shares the at least one lens group with the first sub lens system and includes a second replacement lens group that replaces or is replaced by the first replacement lens group, wherein the first replacement lens group includes a first stop, the second replacement lens group includes a second stop. When the first replacement lens group is replaced by the second replacement lens group, the second sub lens system may have an F number smaller than an F number of the first sub lens system at the wide angle position.

According to another embodiment of the invention, there is provided a photographing apparatus including a lens system; and an imaging device for converting an image formed by the lens system into an electrical signal, wherein the lens system includes a first sub lens system that includes at least one lens group and a first replacement lens group and is for performing zooming between a wide angle position and a telephoto position; and a second sub lens system that shares the at least one lens group with the first sub lens system, includes a second replacement lens group that replaces or is replaced by the first replacement lens group, and has a focal length shorter than a focal length of the first sub lens system at the wide angle position.

DETAILED DESCRIPTION

A lens system according to various embodiments of the invention and a photographing apparatus including the lens system will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

A lens system according to an embodiment of the invention includes a plurality of lens groups, among which some lens groups are replaceable and may be replaced by other replacement lens groups to achieve different types of focal lengths. Referring toFIG. 1, a lens system110according to an embodiment of the invention includes a first sub lens system110aincluding at least one lens group and a first replacement lens group GE1, and a second sub lens system110bincluding the at least one lens groups and a second replacement lens group GE2that may replace or may be replaced by the first replacement lens group GE1. The first sub lens system110aand the second sub lens system110bmay share lens groups other than lens groups that may be replaced between the first and second sub lens system110aand110b. The first sub lens system110amay include, for example, a zoom lens system, and the second sub lens system110bmay include a single-focus lens system. The second sub lens system110bmay have a focal length shorter than a focal length of the first sub lens system110aat a wide angle position.

Alternatively, the first sub lens system110aand the second sub lens system110bmay include zoom lens systems having different zoom magnifications, respectively. For example, the first sub lens group110amay include a lens group having a negative refractive power, and the first replacement lens group GE1may be disposed between the lens group having the negative refractive power and an image plane and may be replaced by the second replacement lens group GE2. When the first replacement lens group GE1is replaced by the second replacement lens group GE2, the first replacement lens group GE1is moved off an optical axis and the second replacement lens group GE2is moved to be aligned with the optical axis.

As described above, the lens system110according to the embodiment of the invention is constructed to include a zoom lens system and a single-focus lens system in a single lens system, whereby the single lens system may obtain various magnifications. In other words, the single lens system replaces some lens groups without needing to include a zoom lens and a wide-angle lens separately, thereby achieving various focal lengths. Since the first sub lens system110aand the second sub lens system110bshare some lens groups and an imaging device, the number of components used to form the lens system110is reduced compared to a lens system including two types of lens systems separately, and the lens system110may be manufactured compactly and thinly at a low material cost.

FIG. 2Aillustrates a lens system120according to an embodiment of the invention at a wide angle position, a middle position, and a telephoto position.FIG. 2Billustrates the lens system120at an ultra-wide angle position. The lens system120includes a first sub lens system120ahaving a first replacement lens group and a second sub lens system120bhaving a second replacement lens group. The first sub lens system120aand the second sub lens system120bshare lens groups other than the replacement lens groups. The first sub lens system120amay include a first lens group G1, a second lens group G2, and a third lens group G3, for example, in a sequence from an object side O to an image side I, and the second sub lens system120bmay include the first lens group G1, a fourth lens group G4that may replace or be replaced by the second lens group G2, and the third lens group G3. The first lens group G1may have a negative refractive power, the second lens group G2may have a positive refractive power, and the third lens group G3may have a positive refractive power. In this embodiment, the second lens group G2is used as the first replacement lens group, and the fourth lens group G4is used as the second replacement lens group. When the first sub lens system120ais changed to the second sub lens system120b, the second lens group G2may be moved off an optical axis and the fourth lens group G4may be moved to be aligned with the optical axis.

When the first sub lens system120aperforms zooming from the wide angle position to the telephoto position, an interval between the first and second lens groups G1and G2may decrease, and an interval between the second and third lens groups G2and G3may increase. In this case, the second lens group G2may be moved toward the object side O. The third lens group G3may perform focusing.

FIG. 3Aillustrates longitudinal spherical aberration, astigmatic field curvature, and distortion of the first lens system120aillustrated inFIG. 2Aat a wide angle position. A tangential field curvature T and a sagittal field curvature S are illustrated to indicate the astigmatic field curvature. In the distortion, a vertical axis represents an image height IMG HT.FIGS. 3B and 3Cillustrate longitudinal spherical aberration, astigmatic field curvature, and distortion of the first lens system120aillustrated inFIG. 2Aat a middle position and the telephoto position.FIG. 3Dillustrates longitudinal spherical aberration, astigmatic field curvature, and distortion of the second lens system120billustrated inFIG. 2Bat an ultra-wide angle position.

FIGS. 4A and 4Billustrate a lens system210according to another embodiment of the invention. The lens system210may include a first sub lens system210aand a second sub lens system210b. The first sub lens system210amay include a first lens group G1a, a second lens group G2a, a third lens group G3a, and a fourth lens group G4a, for example, in a sequence from an object side O to an image side I, and the second sub lens system210bmay include the first lens group G1a, the second lens group G2a, a fifth lens group G5athat may replace or be replaced by the third lens group G3a, and the fourth lens group G4a. The third lens group G3ais used as a first replacement lens group and the fifth lens group G5ais used as a second replacement lens group. When the first sub lens system210ais changed to the second sub lens system210b, the third lens group G3amay be moved off an optical axis and the fifth lens group G5amay be moved to be aligned with the optical axis.

The first sub lens system210amay be a zoom lens system capable of continuously changing a focal length, and the second sub lens system210bmay be an ultra-wide angle lens system. The fifth lens group G5amay include one lens. Thereby, when a camera having the firth lens group G5aperforms retracting, the size of the camera may be reduced and thus the camera may be made compact.

The second sub lens system210bmay have a viewing angle of 90 degrees or greater. Alternatively, the second sub lens system210bmay have a distortion of 15% or greater. As described above, an effect of a fisheye lens may be obtained by replacement of the second replacement lens group G5aof the second sub lens system210b. The second sub lens system210bhaving a fisheye lens effect does not have a strict limit to distortion aberration and thus may have fewer lenses or a smaller size than the first replacement lens group G3aof the first sub lens system210b.

FIGS. 5A,5B, and5C illustrate longitudinal spherical aberration, astigmatic field curvature, and distortion of the first lens system210aillustrated inFIG. 4Aat a wide angle position, a middle position, and a telephoto position.FIG. 5Dillustrates longitudinal spherical aberration, astigmatic field curvature, and distortion of the second lens system210billustrated inFIG. 4Bat an ultra-wide angle position.

FIG. 6Aillustrates a first lens system310aof a lens system310according to another embodiment of the invention.FIG. 6Billustrates a second lens system310bof the lens system310ofFIG. 6A. The first sub lens system310amay include a first lens group G1b, a second lens group G2b, a third lens group G3b, and a fourth lens group G4b, for example, in a sequence from an object side O to an image side I, and the second sub lens system310bmay include the first lens group G1b, the second lens group G2b, a fifth lens group G5bthat may replace or be replaced by the third lens group G3b, and the fourth lens group G4b. The third lens group G3bis used as a first replacement lens group, and the fifth lens group G5bis used as a second replacement lens group. The fifth lens group G5bmay include, for example, three lenses. The first lens group G1b, may have, for example, a positive refractive power, the second lens group G2bmay have a negative refractive power, the third lens group G3bmay have a positive refractive power, and the fourth lens group G4bmay have a positive refractive power. The fifth lens group G5bmay have a positive refractive power. However, the invention is not limited thereto.

The third lens group G3bmay include a first stop ST1, and the fifth lens group G5bmay include a second stop ST2. Due to the inclusion of stops in the replacement lens groups, the second sub lens system310bmay have an F number smaller than the F number of the first sub lens system310aat the wide angle position. For example, the focal lengths of the first sub lens system310aand the second sub lens system310bmay not be changed but only the F numbers thereof may be changed. Alternatively, not only the focal lengths but also the F numbers of the first sub lens system310aand the second sub lens system310bmay be changed.

When the first sub lens system310aperforms zooming from the wide angle position to the telephoto position, all of intervals between the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4may be changed. The second sub lens system310bmay have a shorter focal length than the focal length of the first sub lens system310aat the wide angle position.

FIGS. 7A,7B, and7C illustrate longitudinal spherical aberration, astigmatic field curvature, and distortion of the first lens system310aillustrated inFIG. 6Aat a wide angle position, a middle position, and a telephoto position.FIG. 7Dillustrates longitudinal spherical aberration, astigmatic field curvature, and distortion of the second lens system310billustrated inFIG. 6Bat an ultra-wide angle position.

A lens system according to an embodiment of the invention may satisfy the following Equation 1:
0.6<EFL2/EFL1<1.1  (1)
where EFL1represents the focal length of a first replacement lens group and EFL2represents the focal length of a second replacement lens group.

The first replacement lens group and the second replacement lens group of the lens system according to an embodiment of the invention may include at least one aspherical surface. The aspherical surface used in the lens system according to the invention is defined as follows.

When the direction of the optical axis is set to be an x axis direction, a direction perpendicular to the optical axis direction is set to be a y axis direction, and a proceeding direction of a light beam is set to be the positive x axis direction, the aspherical surface may be expressed as Equation 2:

x=cy21+1-(K+1)⁢c2⁢y2+Ay4+By6+Cy8+Dy10(2)
where x denotes a distance from an apex of the lens along the x axis, y denotes a distance from the apex of the lens along the y axis, K denotes a conic constant, A, B, C, and D denote aspherical coefficients, and c denotes a reciprocal (1/R) of the radius of curvature of the apex of the lens.

Design data about the lens systems according to previous embodiments will now be described.

Hereinafter, EFL is referred to as the overall focal length of the lens system, FOV is referred to as a viewing angle, Fno is referred to as the F number, D1, D2, D3, and D4are variable distances, and ST is referred to as a stop.

As described above, a lens system according to an embodiment of the invention may achieve different types of focal lengths by using only a single lens system and may still be manufactured to be compact and thin.

FIG. 8schematically illustrates a photographing apparatus1100including a lens system1111, according to an embodiment of the invention. The photographing apparatus1100includes the lens system1111, and an imaging device1112for converting an image formed by the lens system1111into an electrical signal. Examples of the lens system1111includes the lens systems described above with reference toFIGS. 1,2A,2B,4A,4B,6A, and6B. The photographing apparatus1100may include a recording unit1113in which information corresponding to a subject image photoelectrically converted by the imaging device1112is recorded, a viewfinder1114for observing the subject image, and a display unit1115on which the subject image is displayed. Although the viewfinder1114and the display unit1115are separately provided inFIG. 8, the present embodiment is not limited thereto and only the display unit1115may be provided without the viewfinder1114. The lens system1111can be retracted so as to be received within the main body of the photographing apparatus1100. Although the photographing apparatus1100ofFIG. 8is exemplarily shown, the present embodiment is not limited thereto and any of various other optical equipments may be used. If a zoom lens according to the invention is applied to photographing apparatuses, such as a digital camera, an optical equipment that is compact and inexpensive, has a bright lens system, and achieves wide angle photographing is provided.

A photographing apparatus according to an embodiment of the invention achieves various focal lengths by simply replacing some lens groups without needing to replace the entire lens system, thereby satisfying various user's demands at low costs. In addition, since a user does not need to carry two separate lens systems having two types of focal lengths, the user can very conveniently use a photographing apparatus according to the invention.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated as incorporated by reference and were set forth in its entirety herein.

The present invention may be described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of components that perform the specified functions.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) should be construed to cover both the singular and the plural. Furthermore, recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Finally, the steps of all methods described herein are performable in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

The words “mechanism” and “element” are used herein generally and are not limited solely to mechanical embodiments. Numerous modifications and adaptations will be readily apparent to those skilled in this art without departing from the spirit and scope of the present invention.