A negative first group optical system, a positive second group optical system, and a positive third group optical system are sequentially arranged from the object side. A stop moving integrally with the second group optical system is provided on the object side of the second group optical system. The focal length is changed by changing distances between the group optical systems, and the third group optical system is moved on an optical axis. The first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens. The second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens. The third group optical system includes one positive lens not including an aspherical surface.
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1. A variable focal length lens comprising:
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, at least one surface of the two negative meniscus lenses being an aspherical surface,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, a surface on the object side of the positive lens on the most object side being an aspherical surface, and
the third group optical system includes one positive lens not including an aspherical surface.
5. A variable focal length lens comprising:
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing relative distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side,
the third group optical system includes one positive lens,
at least one surface of the negative meniscus lens in the first group optical system and a surface on the most object side in the second group optical system being aspherical surfaces, and
the third group optical system includes only a spherical lens.
11. A camera comprising a variable focal length lens as a photographing optical system, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, at least one surface of the two negative meniscus lenses being an aspherical surface,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, a surface on the object side of the positive lens on the most object side being an aspherical surface, and
the third group optical system includes one positive lens not including an aspherical surface.
9. A photographing lens unit comprising a variable focal length lens as an optical system, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, at least one surface of the two negative meniscus lenses being an aspherical surface,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, a surface on the object side of the positive lens on the most object side being an aspherical surface, and
the third group optical system includes one positive lens not including an aspherical surface.
12. A camera comprising a variable focal length lens as a photographing optical system, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing relative distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side,
the third group optical system includes one positive lens,
at least one surface of the negative meniscus lens in the first group optical system and a surface on the most object side in the second group optical system being aspherical surfaces, and
the third group optical system includes only a spherical lens.
10. A photographing lens unit comprising a variable focal length lens as an optical system, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing relative distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side,
the third group optical system includes one positive lens,
at least one surface of the negative meniscus lens in the first group optical system and a surface on the most object side in the second group optical system being aspherical surfaces, and
the third group optical system includes only a spherical lens.
13. A portable information terminal device comprising a variable focal length lens as a photographing optical system of a camera function unit, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, at least one surface of the two negative meniscus lenses being an aspherical surface,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, a surface on the object side of the positive lens on the most object side being an aspherical surface, and
the third group optical system includes one positive lens not including an aspherical surface.
14. A portable information terminal device comprising a variable focal length lens as a photographing optical system of a camera function unit, the variable focal length lens including
a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and
a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system, wherein
a focal length is changed by changing relative distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis,
the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side,
the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side,
the third group optical system includes one positive lens,
at least one surface of the negative meniscus lens in the first group optical system and a surface on the most object side in the second group optical system being aspherical surfaces, and
the third group optical system includes only a spherical lens.
2. The variable focal length lens according to
wherein the positive lens of the third group optical system is a positive meniscus lens.
3. The variable focal length lens according to
wherein when R1 is a radius of curvature a surface on an object side of the positive lens of the third group optical system, and R2 is a radius of curvature of a surface on an image side of the positive lens of the third group optical system, then the relation
−0.75<{(R1−R2)/(R1+R2)}<−0.65 holds true.
4. The variable focal length lens according to
wherein when D23w is a distance between the second group optical system and the third group optical system at the wide-angle end, fw is a focal length of all the systems at the wide-angle end, and f3 is a focal length of the third group optical system, then the relation
1.5<{(D23w×f3)/fw2}<2.5 holds true.
6. The variable focal length lens according to
7. The variable focal length lens according to
when R1 is a radius of curvature a surface on an object side of the positive lens of the third group optical system, and R2 is a radius of curvature of a surface on an image side of the positive lens of the third group optical system, then the relation
−0.75<{(R1−R2)/(R1+R2)}<−0.65 holds true.
8. The variable focal length lens according to
when D23w is a distance between the second group optical system and the third group optical system at the wide-angle end, fw is a focal length of all the systems at the wide-angle end, and f3 is a focal length of the third group optical system, then the relation
1.5<{(D23w×f3)/fw2}<2.5 holds true.
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The present document incorporates by reference the entire contents of Japanese priority document, 2003-191519 filed in Japan on Jul. 3, 2003.
1. Field of the Invention
The present invention relates to an improvement of a variable focal length lens such as a zoom lens that is used as a photographing optical system in various cameras including a so-called silver-salt camera. In particular, the present invention relates to a variable focal length lens that can be preferably used in cameras such as digital cameras and video cameras, and to a photographing lens unit, a camera, and a portable information terminal device that includes such a variable focal length lens.
2. Description of the Related Art
Recently, cameras such as digital cameras and electronic cameras have become common. Such a camera acquires a photograph of a subject image with a solid-state image pickup element such as a charge-coupled device (CCD) image pickup element to obtain image data of a still image or a moving image (movie image) and digitally records the image data in a nonvolatile semiconductor memory or the like. A flash memory is an example of the nonvolatile semiconductor memory. A traditional camera in which a conventional silver-salt film is used, that is, a silver-salt camera is gradually becoming outdated.
A market for such a digital camera has grown to be extremely large, and demands of users for the digital camera have been diversified. Above all, the users often demand for an improvement in image quality and miniaturization of the digital cameras.
To achieve the characteristics such as small size, light weight, and high performance, variable focal length lenses such as zoom lenses are often used in the digital cameras. Such a zoom lens generally has a two-lens group or three-lens group structure, i.e., a structure that includes only a few lenses. If the zoom lens includes lens groups having several lenses, when the lenses are moved in focusing, the advantage of miniaturization cannot be fully achieved, moreover, the operability become poor, because movement of a center of gravity of the lenses is large. Therefore, sometimes the focusing is performed by moving only some of the lens groups.
For example, zoom lenses have been disclosed in Japanese Patent Application Laid-Open Publication Nos. 2003-131134, 2003-107352, and 2003-35868 as zoom lenses that can be preferably used in digital cameras and are suitable for miniaturization. A typical zoom lens includes a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power. The first to the third group optical systems are sequentially arranged from an object side. A stop is provided on the object side of the second group optical system that moves integrally with the second group optical system. The focal length of the zoom lens can be changed by changing the distance between the respective group optical systems.
The first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens that are sequentially arranged from the object side. The second group optical system includes a positive lens, a negative lens, a positive lens, and a positive lens that are sequentially arranged from the object side. The third group optical system includes one positive lens.
In the zoom lens disclosed in Japanese Patent Application Laid-Open Publication No. 2003-131134, an image side surface of the negative meniscus lens second from the object side of the first group optical system, a surface on the most object side of the second group optical system, a surface on the most image side of the second group optical system, and a surface on the object side of the third group optical system are formed as aspherical surfaces, respectively.
In another exemplary structure, the positive lens on the most object side and the negative lens adjacent to the positive lens of the second group optical system are formed as a cemented lens, and an image side surface of the negative meniscus lens second from the object side of the first group optical system, a surface on the most object side of the second group optical system, a surface on the most image side of the second group optical system, and a surface on the object side of the third group optical system are formed as aspherical surfaces, respectively.
In still another exemplary structure, the positive lens on the most object side and the negative lens adjacent to the positive lens of the second group optical system are formed as a cemented lens, and an image side surface of the negative meniscus lens second from the object side of the first group optical system, a surface on the most object side of the second group optical system, and a surface on the object side of the third group optical system are formed as aspherical surfaces, respectively.
In still another exemplary structure, the negative lens and the negative lens second from the mage side adjacent to the negative lens of the second group optical system are formed as a cemented lens, and an image side surface of the negative meniscus lens second from the object side of the first group optical system, a surface on the most object side of the second group optical system, a surface on the most image side of the second group optical system, and a surface on the object side of the third group optical system are formed as aspherical surfaces, respectively.
In this way, in the technology disclosed in Japanese Patent Application Laid-Open Publication No. 2003-131134, the image surface is corrected by using the aspherical surface for the positive lens of the third group optical system. Japanese Patent Application Laid-Open Publication Nos. 2003-107352 and 2003-35868 disclose similar structures.
Thus, in the conventional technology, the image surface is corrected by using the aspherical surface for the positive lens of the third group optical system.
Although it is effective to use the aspherical surface for the third group optical system for correction of the image surface, deterioration of image performance due to the focusing occurs when the third group optical system is moved along an optical axis for focusing.
This point is explained in more detail below. When the third group optical system is used for focusing, it is necessary to secure an amount of movement of the third group optical system. For securing the amount of movement of the third group optical system, one approach is to increase the distance between the second and the third group optical systems or to increase a refracting power of the third group optical system to reduce the amount of movement of the third group optical system. However, the total length of the zoom lens increases and it becomes bulky if the distance between the second and the third group optical systems is increased. On the other hand, the aberration correction becomes difficult if the refracting power of the third group optical system is increased.
It is an object of the present invention to solve at least the problems in the conventional technology.
A variable focal length lens according to one aspect of the present invention includes a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system. A focal length is changed by changing distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis, the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, at least one surface of the two negative meniscus lenses being an aspherical surface, the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, a surface on the object side of the positive lens on the most object side being an aspherical surface, and the third group optical system includes one positive lens not including an aspherical surface.
A variable focal length lens according to another aspect of the present invention includes a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power, wherein the first through the third group optical systems are sequentially arranged from an object side; and a stop provided on the object side of the second group optical system and that moves integrally with the second group optical system. A focal length is changed by changing relative distances between the first through the third group optical systems and when performing focusing the third group optical system is moved along an optical axis, the first group optical system includes a negative meniscus lens, a negative meniscus lens, and a positive lens those are sequentially arranged from the object side, the second group optical system includes a cemented lens of a positive lens and a negative lens, a positive lens, and a positive lens those are sequentially arranged from the object side, the third group optical system includes one positive lens, at least one surface of the negative meniscus lens in the first group optical system and a surface on the most object side in the second group optical system being aspherical surfaces, and the third group optical system includes only a spherical lens.
A photographing lens unit, a camera, a portable information terminal device according to still another aspect of the present invention include the above variable focal length lens according to the present invention.
The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.
Exemplary embodiments of a variable focal length lens, a photographing lens unit, a camera, and a portable information terminal device of the present invention will be hereinafter explained in detail with reference to the accompanying drawings. The principle of the present invention will be explained first.
The variable focal length lens according to the present invention is, in general, a zoom lens. This variable focal length lens includes a first group optical system having a negative refracting power, a second group optical system having a positive refracting power, and a third group optical system having a positive refracting power that are sequentially arranged from an object side, and a stop provided on the object side of the second group optical system that moves integrally
According to the variable-focal-length lens of a sixth aspect of this invention, by a variable-focal-length lens of any of the first to fifth aspect of this invention, in particular aberrations can be corrected, the minimum picture-taking distance can be made short and the picture-taking range can be made wide, and a contact configuration can be made at low cost. According to the camera of a seventh aspect of this invention, by including as its picture-taking optical system a variable-focal-length lens of any of the first to fifth aspect of this invention, it is possible to satisfactorily correct aberrations, have a short minimum picture-taking distance and a wide picture-taking range, and have a compact configuration at low cost. According to the portable information terminal of an eighth aspect of this invention, by including as the picture-taking optical system of its camera function unit a variable-focal-length lens of any of the first to fifth aspect of this invention, in particular it is possible to satisfactorily correct aberrations, have a short minimum picture-taking distance and a wide picture-taking range, and have a compact configuration at low cost.
where R1 is the radius of curvature of the object-side surface of the positive lens of the third group optical system, and R2 is the radius of curvature of the image-side surface of the positive lens of the third group optical system (corresponding to claim 4). If the lower limit of this condition formula (1) is not satisfied, the surrounding image surface will fall on the plus side, that is, in the direction away from the object, and if it exceeds the upper limit, the surrounding image surface will fall on the minus side.
where D23w is the distance between the second group optical system and the third group optical system at the wide-angle end, fw is the focal length of the entire system at the wide-angle end, and f3 is the focal length of the third group optical system. If the upper limit of this condition formula (2) is exceeded, it becomes difficult to obtain a good image, due to an increase in the Petzval sum and an increase in the negative distortion aberration, and if the lower limit is not satisfied, distortion correction becomes difficult because the refractive power of the third group optical system becomes too strong to ensure the spacing between the second group optical system and the third group optical system (corresponding to claim 5).
where R1 is the radius of curvature of the object-side surface of the positive lens of the third group optical system, and R2 is the radius of curvature of the image-side surface of the positive lens of the third group optical system, in particular better correction is possible.
where D23w is the distance between the second group optical system and the third group optical system at the wide-angle end, fw is the focal length of the entire system at the wide-angle end, and f3 is the focal length of the third group optical system, in particular the minimum picture-taking distance can be shortened while minimizing the increase in overall length, and distortion aberration and other aberrations can be satisfactorily corrected.
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Executed on Assignor Assignee Conveyance Frame Reel Doc
Jun 18 2008 Ricoh Company, Ltd. (assignment on the face of the patent) /
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