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Zoom optical systemZoom optical system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070024987, Zoom optical system. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a zoom optical system used in an image pickup device such as a portable telephone, a portable computer, or a similar device. BACKGROUND OF THE INVENTION [0002] Recently, in devices such as portable telephones and portable computers, picture image information is incorporated in an image pickup device. In an image recording or photographic optical system used in such an image pickup device, it is necessary to make the optical system light-weight and compact in order to obtain the desired portability. When the optical axis of an objective lens extends in the thickness direction of an image pickup device, a technique for reducing the thickness of the casing of the device has been developed that uses a prism to bend the optical axis of the optical system. [0003] On the other hand, additional functionality is also desirable in image recording and photographic optical systems used in such image pickup devices, and image recording and photographic optical systems that include a zoom function have been proposed, for example, in Japanese Laid-Open Patent Application 2004-264585 and Japanese Laid-Open Patent Application 2000-131610. [0004] However, in Japanese Laid-Open Patent Application 2004-264585, in the case of forming the zoom lens of three lens groups With the third lens group from the object side being movable both for zooming and for focusing, the third lens group is moved continuously toward the object side during zooming toward the telephoto end so that the distance between the second lens group and the third lens group becomes small. Thus, little distance is left for assuring sufficient movement of the third lens group for focusing. Particularly, in short-distance photography, focusing movement becomes greater at the telephoto end than at the wide-angle end so that the focusing lens, which in this case is the third lens group, requires increased movement. That is, large movements are required at the telephoto end. Japanese Laid-Open Patent Application 2000-131610 operates differently with a zoom lens that includes four lens groups, but the use of the four lens groups limits miniaturization and reduction of the costs of the zoom lens. BRIEF SUMMARY OF THE INVENTION [0005] The present invention relates to a zoom optical system that is small, that has an inexpensive construction, that assures sufficient movement of the third lens group from the object side for focusing as desired, and that is capable of short-distance photography at the telephoto end. BRIEF DESCRIPTION OF THE DRAWINGS [0006] The present invention will become more fully understood from the detailed description given below and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, wherein: [0007] FIGS. 1A-1B show the cross-sectional views of the zoom optical system of Embodiment 1 at the wide-angle end and at the telephoto end, respectively; [0008] FIGS. 2A-2D show the spherical aberration, astigmatism, distortion, and lateral color, respectively, of the zoom optical system of Embodiment 1 at the wide-angle end; [0009] FIGS. 2E-2H show the spherical aberration, astigmatism, distortion, and lateral color, respectively, of the zoom optical system of Embodiment 1 at the telephoto end; [0010] FIG. 3A-3B show cross-sectional views of the zoom optical system of Embodiment 2 at the wide-angle end and at the telephoto end, respectively; [0011] FIGS. 4A-4D show the spherical aberration, astigmatism, distortion, and lateral color, respectively, of the zoom optical system of Embodiment 2 at the wide-angle end; and [0012] FIGS. 4E-4H show the spherical aberration, astigmatism, distortion, and lateral color, respectively, of the zoom optical system of Embodiments 2 at the telephoto end. DETAILED DESCRIPTION OF THE INVENTION [0013] A general description of the zoom optical system of the present invention that pertains to disclosed embodiments of the invention will now be described with reference to FIGS. 1A-1B that show Embodiment 1. In FIG. 1A, the object side of the zoom optical system is at the left where the reference symbol X indicates the optical axis of the zoom optical system. The image pickup plane, indicated by reference symbol 1 in FIG. 1A, is on the image side of the zoom optical system. In FIG. 1A, lens elements are referenced by the letter L with a subscript number denoting their order from the object side of the zoom optical system along the optical axis X, from L.sub.1 to L.sub.7. Similarly, the radii of curvature of the optical surfaces are referenced by the letter R with a subscript number denoting their order from the object side of the zoom optical system, from R.sub.1 to R.sub.18. The on-axis surface spacings along the optical axis X of the various optical surfaces are referenced by the letter D with a subscript number denoting their order from the object side of the zoom optical system, from D.sub.1 to D.sub.17. In the same manner, three lens groups are labeled G.sub.1, G.sub.2, and G.sub.3 in order from the object side of the zoom optical system, and the optical components belonging to each lens group are indicated by brackets adjacent the labels G.sub.1, G.sub.2, and G.sub.3. [0014] The term "lens group" is defined in terms of "lens elements" and "lens components" as explained herein. The term "lens element" is herein defined as a single transparent mass of refractive material having two opposed refracting surfaces, which surfaces are positioned at least generally transversely of the optical axis of the zoom optical system. The term "lens component" is herein defined as (a) a single lens element spaced so far from any adjacent lens element that the spacing cannot be neglected in computing the optical image forming properties of the lens elements or (b) two or more lens elements that have their adjacent lens surfaces either in full overall contact or overall so close together that the spacings between adjacent lens surfaces of the different lens elements are so small that the spacings can be neglected in computing the optical image forming properties of the two or more lens elements. Thus, some lens elements may also be lens components. Therefore, the terms "lens element" and "lens component" should not be taken as mutually exclusive terms. In fact, the terms may frequently be used to describe a single lens element in accordance with part (a) above of the definition of a "lens component." The term "lens group" is herein defined as an assembly of one or more lens components in optical series and with no intervening lens components along an optical axis that during zooming is movable as a single unit relative to another lens component or other lens components. [0015] The zoom optical system of the present invention includes, arranged in order from the object side, a first lens group G.sub.1 having positive refractive power, a second lens group G.sub.2 having negative refractive power, and a third lens group G.sub.3 having positive refractive power. [0016] A light beam incident along the optical axis X from the object side passes through lens groups G.sub.1, G.sub.2, and G.sub.3 and is imaged on the image pickup plane 1 where an image pickup element, such as a CCD, is located. Moreover, a cover glass 4, which may also include a filter element, is arranged between the third lens group G.sub.3 and the image pickup plane 1. [0017] While FIG. 1A shows the positions of lens groups G.sub.1, G.sub.2, and G.sub.3 at the wide-angle end, lines adjacent reference symbols G.sub.2 and G.sub.3 indicate the locus of points of movement of lens groups G.sub.2 and G.sub.3 along the optical axis X during zooming from the wide-angle end to the telephoto end, with FIG. 1B showing the positions of the lens groups at the telephoto end. The straight line adjacent reference symbol G.sub.2 indicates that lens group G.sub.2 moves continuously toward the image side during zooming from the wide-angle end to the telephoto end. The line adjacent reference symbol G.sub.3 is convex upward, that is, convex toward the object side, and indicates that the third lens group G.sub.3 moves first toward the object side and then back toward the image side during zooming from the wide-angle end to the telephoto end. The second lens group G.sub.2 and the third lens group G.sub.3 generally become closer together during zooming from the wide-angle end to the telephoto end, and the movements enable the third lens group G.sub.3 having positive refractive power to move properly also for focusing adjustment, simplifying the construction and movements required so that costs can be reduced and particularly enabling short-distance photography at the telephoto end. [0018] As shown in FIG. 1A, the first lens group G.sub.1 includes, arranged in order from the object side, a first lens element L.sub.1 having negative refractive power, a prism 2 for bending the optical axis, and a second lens element L.sub.2 having positive refractive power. Miniaturization and cost reduction can be achieved by arranging at least one lens element having negative refractive power on the object side of the prism 2 so as to decrease the diameter of the light beam to the prism 2 and thus reduce the required size of the prism 2. It is preferable that a lens element having positive refractive power of the first lens group G.sub.1 include an aspheric surface, and when an aspheric lens element is used as the second lens element L.sub.2, field curvature and distortion can be well corrected. [0019] The second lens group G.sub.2 includes, arranged in order from the object side, a biconcave third lens element L.sub.3 and a fourth lens element L.sub.4 having positive refractive power. Continue reading about Zoom optical system... Full patent description for Zoom optical system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Zoom optical system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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