JP2005309059A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens having high optical performance despite its simple configuration by making the entire lens system small. <P>SOLUTION: The zoom lens group has a 1st lens group L1 with positive refracting power, which is fixed on an optical axis in the case of zooming, a 2nd lens group L2 with negative refracting power, which moves on the optical axis in the case of zooming, a 3rd lens group L3 with positive refracting power, whose distance to the 1st lens group L1 is constant in the case of zooming, and a 4th lens group L4 with positive refracting power, which moves on the optical axis in the case of zooming, in order from an object side. The 1st lens group L1 is constituted of one positive lens and one negative lens in order from the object side. When it is assumed that fW is the focal length of the entire system at a wide angle end and f2 is the focal length of the 2nd group, the zoom lens satisfies a condition: 1.52<¾f2¾/fW<2.0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens system and a photographing apparatus having the same, and more particularly to a zoom lens system used in photographing apparatuses such as a video camera, a digital camera, and a film camera, and a photographing apparatus having the same.

  As a lens system used in a camera such as a conventional video camera or digital still camera, a first lens unit having a positive refractive power that is fixed in zooming and focusing in order from the object side, an optical axis having a negative refractive power A second lens group having a zoom action by moving up, a third lens group having a fixed positive refractive power during zooming and focusing, a positive refractive power for moving the optical axis for zooming and focusing There are so-called positive, negative, positive, and positive fourth group rear focus zooms of the fourth lens group having.

  In general, a rear focus type zoom lens has a smaller effective diameter of the first lens unit than a zoom lens that moves the first lens unit to perform focusing, thereby facilitating the miniaturization of the entire lens system. Close-up photography is facilitated, and since the relatively small and light lens group is moved, the driving force of the lens group is small, and quick focusing is possible.

  Japanese Laid-Open Patent Publication No. 2003-107347 proposes a small zoom lens in which a first lens is a convex lens and a second lens is a concave lens in the zoom type four-group zoom lens.

  Japanese Laid-Open Patent Publication No. 6-130297 proposes a small zoom lens in which a first lens is a concave lens, a second lens is a cemented lens, and a convex lens in the zoom type four-group zoom lens.

  In addition, this zoom type four-group zoom lens has been proposed in, for example, JP-A-8-292369, JP-A-8-304700, JP-A-2001-221948, JP-A-2001-305427. Yes.

  In recent years, there has been a demand for a compact and inexpensive zoom lens and a photographing apparatus using the same while having higher performance.

  In general, in a zoom lens, if the refractive power of each group is increased, the amount of movement of each group to obtain a predetermined zoom ratio is reduced, and the overall length of the lens can be shortened.

  However, simply increasing the refracting power of the lenses in each group increases aberration fluctuations associated with zooming, making it very difficult to obtain high optical performance over the entire zoom range.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens having a high optical performance with a small overall lens size and a simple configuration, and a photographing apparatus having the zoom lens.

The zoom lens system according to the first aspect of the present invention includes, in order from the object side, a first lens unit having a positive refractive power that is fixed on the optical axis during zooming, and a second lens having a negative refractive power that moves on the optical axis during zooming. A zoom lens group including a third lens group having a positive refractive power whose distance from the first lens group is unchanged during zooming, and a fourth lens group having a positive refractive power moving on the optical axis during zooming. The first lens group is composed of one positive lens and one negative lens in order from the object side, and fW is the focal length of the entire system at the wide angle end, and f2 is the focal length of the second group. Sometimes, the following conditions are satisfied.
1.52 <| f2 | / fW <2.0
The zoom lens system according to the second aspect of the present invention satisfies the following condition in the first aspect of the invention when d34 is the distance between the third group and the fourth group at the wide-angle end and fW is the focal length of the entire system at the wide-angle end. It is characterized by.
0.27 <d34 / fW <0.7
A zoom lens system according to a third aspect of the invention is characterized in that, in the first and second aspects of the invention, when f1 is a focal length of the first group and f2 is a focal length of the second group, the following conditions are satisfied. Yes.
0.2 <| f2 | / f1 <0.5
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the fourth lens group includes only a positive single lens.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, in the first lens group, the lens surface closest to the object side has a convex surface facing the object side, and the lens surface closest to the image side of the first lens group. Has a concave surface facing the image side.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the third lens group includes a biconcave lens and a biconvex lens adjacent to the object side.

  According to a seventh aspect of the present invention, in the first to sixth aspects of the invention, in the fourth lens group, the lens surface closest to the object side is concave toward the object side, and the lens surface closest to the third lens group is the first lens surface. It is characterized in that the convex surface is directed to the three lens group side.

The invention of claim 8 is characterized in that, in the inventions of claims 1 to 7, the following condition is satisfied when G1n is the refractive index of the positive lens of the first lens group.
1.60 <1Gn <1.85
The invention of claim 9 satisfies the condition when r1 is the radius of curvature of the positive lens in the first lens group on the object side and r2 is the radius of curvature of the positive lens in the first lens group on the image side. It is said.
0.15 <| r1 / r2 | <0.30
According to a tenth aspect of the present invention, in the first to ninth aspects of the invention, the fourth lens group is moved to perform focusing.

  According to an eleventh aspect of the present invention, in any of the first to tenth aspects of the present invention, the surfaces of the lens group are all spherical.

  According to a twelfth aspect of the present invention, in the first to eleventh aspects of the present invention, an image is formed on a solid-state imaging device.

  According to a thirteenth aspect of the present invention, there is provided a photographing apparatus comprising the zoom lens system according to any one of the first to twelfth aspects and a solid-state image sensor that receives an image formed by the variable magnification lens system. .

  According to the present invention, as described above, it is possible to reduce the size of the lens system and achieve a zoom lens having high optical performance despite a simple configuration and a photographing apparatus having the same.

  FIG. 1 is a cross-sectional view of a main part of a zoom lens according to Embodiment 1 of the present invention, and FIGS. 2 to 4 are aberration diagrams of the zoom lens according to Embodiment 1 at a wide angle single lens, an intermediate focal length, and a telephoto end.

  FIG. 5 is a cross-sectional view of an essential part of the zoom lens according to Embodiment 2 of the present invention, and FIGS. 6 to 8 are aberration diagrams of the zoom lens according to Embodiment 2 at a wide angle single lens, an intermediate focal length, and a telephoto end.

  FIG. 9 is a cross-sectional view of a main part of a zoom lens according to Embodiment 3 of the present invention, and FIGS. 10 to 12 are aberration diagrams of the zoom lens according to Embodiment 3 at a wide angle single lens, an intermediate focal length, and a telephoto end.

  13 is a cross-sectional view of a main part of a zoom lens according to Embodiment 4 of the present invention, and FIGS. 15 to 16 are aberration diagrams of the zoom lens according to Embodiment 4 at a wide angle single lens, an intermediate focal length, and a telephoto end.

  FIG. 17 is a cross-sectional view of a main part of a zoom lens according to Embodiment 5 of the present invention, and FIGS. 18 to 20 are aberration diagrams of the zoom lens according to Embodiment 5 at a wide angle single lens, an intermediate focal length, and a telephoto end.

  In each lens sectional view, L1 is a first group (first lens group) having a positive refractive power, L2 is a second group (second lens group) having a negative refractive power, and L3 is a third group having a positive refractive power. (Third lens group), L4 is a fourth group (fourth lens group) having a positive refractive power. SP is a stop, which is disposed in front of the third lens unit L3 and is fixed during zooming. G is a glass block such as a color separation prism, a face plate or a filter.

  In the aberration diagrams, d and g are d and g lines, ΔM is a meridional image plane, ΔS is a sagittal image plane, and lateral chromatic aberration is represented by a g line.

  In the embodiments of the sectional views of the respective lenses, the second lens unit L2 is moved to the image plane side as indicated by an arrow for zooming from the wide-angle end to the telephoto end. Is moved while having a part of a convex locus on the object side.

  Further, a rear focus type is employed in which focusing is performed by moving the fourth lens unit L4 along the optical axis. In this way, by making the fourth lens unit L4 a convex locus on the object side, the space between the third lens unit L3 and the fourth lens unit L4 is effectively used, and the shortening of the total lens length is effectively achieved. .

  In each embodiment, for example, when focusing on an object at infinity and a close object at the telephoto end, the fourth group L4 is extended forward.

  The first group L1 and the third group L3 are fixed at the time of zooming and focusing, simplifying the lens barrel structure and having a lens barrel structure that is resistant to static pressure.

  In each embodiment, the first lens unit L1 that tends to have a large lens diameter is composed of only one positive lens and one negative lens, thereby realizing a reduction in the size of the lens system. In addition, since the positive lens and the negative lens are arranged in order from the object side, the curvatures of the positive lens and the negative lens are loosened to facilitate the manufacture.

  In each embodiment, in the first lens group, the lens surface closest to the object side has a convex surface facing the object side, and the lens surface closest to the object side of the first lens group has a concave surface facing the image side.

  By specifying the shape of the first lens group in this way, it is possible to prevent the distortion from increasing to the plus side at a long focal length.

  In each embodiment, the second lens unit L2 includes a meniscus negative lens having a convex surface facing the object side, and a cemented lens of a negative lens having a concave surface on both lens surfaces and a positive lens. As a result, aberration fluctuations accompanying zooming are corrected satisfactorily.

  In each embodiment, the third lens unit L3 includes a negative lens whose concave surfaces are concave and a positive lens whose convex surfaces are adjacent to the object side, thereby correcting chromatic aberration and spherical aberration. The correction and the coma are corrected well.

  In addition, a positive lens is arranged on the image surface side of the negative lens whose both lens surfaces are concave, and various aberrations are corrected well.

  In each embodiment, in the fourth lens unit L4, a lens surface closest to the image side has a concave surface facing the image side, and a lens surface closest to the object side of the fourth lens unit has a convex surface facing the object side. It consists of a positive lens.

  In each embodiment, the fourth lens unit includes L4 having one positive lens. This shortens the overall lens length.

In each embodiment, fW is the focal length of the entire system at the wide angle end, f1 is the focal length of the first group, f2 is the focal length of the second group, d34 is the distance between the third group and the fourth group at the wide angle end, and 1Gn is the first distance. 1.52 <| f2 | / fW <2. When the refractive index of one group, r1 is the radius of curvature of the positive lens of the first group on the object side, and r2 is the radius of curvature of the positive lens of the first group on the image side. 0 (1)
0.27 <d34 / fW <0.7 (2)
0.2 <| f2 | / f1 <0.5 (3)
1.60 <1Gn <1.85 (4)
0.15 <| r1 / r2 | <0.30 (5)
The conditions are satisfied.

  Conditional expression (1) relates to the refracting power of the second lens group in order to effectively obtain a predetermined zoom ratio while reducing aberration fluctuations associated with zooming. If the refractive power of the second lens becomes too strong beyond the lower limit, it is easy to reduce the size of the lens. However, the Petzval sum increases in the negative direction, the field curvature increases, and aberration fluctuations associated with zooming increase. Come. In addition, if the refractive power of the second lens unit becomes too weak beyond the upper limit, the aberration variation due to zooming becomes small, but the amount of movement of the two units for obtaining a predetermined zoom ratio increases, and the total lens length increases. Because it becomes long, it is not good.

  Conditional expression (2) is for defining the total length with respect to the group interval of the third group and the fourth group. If the distance between the third group and the fourth group is reduced beyond the lower limit, it is advantageous for shortening the total lens length, but the focus movement amount at the time of close-up shooting cannot be accommodated. In addition, if the distance between the third group and the fourth group increases beyond the upper limit, the total lens length increases and a large field curvature occurs.

  Conditional expression (3) relates to the refractive power of the second lens unit and is intended to suppress the front lens diameter to a predetermined size while reducing aberration fluctuations associated with zooming. If the refractive power of the second lens becomes too large beyond the lower limit, the front lens diameter can be reduced, but the amount of aberration generated in the second group becomes large and the performance deteriorates. On the other hand, if the refractive power of the second lens unit becomes small beyond the upper limit, the diameter of the first lens unit becomes large, leading to an increase in size.

  Conditional expression (4) relates to the refractive index of the material of the positive lens closest to the object side in the first lens unit L1. If the refractive index increases beyond the upper limit, the material is not a low dispersion material, and correction of chromatic aberration becomes difficult. If the refractive power is lowered beyond the lower limit, the sagittal image surface becomes under at the intermediate image height, making it difficult to achieve high performance.

  Conditional expression (5) relates to the radius of curvature of the positive lens of the first lens group. If the radius of curvature becomes smaller than the lower limit, it becomes difficult to secure the edge of the first lens and it becomes impossible to manufacture, and the lateral chromatic aberration on the long focal point side increases, making correction difficult. If the radius of curvature increases beyond the upper limit, it is easy to secure the edge, but this is not good because the distortion increases toward the plus side on the long focal point side.

  Next, Numerical Examples 1 to 5 respectively corresponding to Embodiments 1 to 5 of the present invention will be shown. In the numerical examples, I indicates the order of the surfaces from the object side, RI is the radius of curvature of each surface, DI is the I-th and I + 1-th optical member thickness or air spacing, and NI and νI are the I-th optical The refractive index and Abbe number for the member d line. f is a focal length, FNO is an F number, and ω is a half angle of view. The two surfaces closest to the image side are glass materials such as a face plate. Table 1 shows the relationship between some of the above-described conditions and numerical values in the numerical examples.

  Next, an embodiment of a digital still camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 21, 10 is a compact camera body, 11 is an optical system constituted by the zoom lens of the present invention, 12 is a strobe built in the camera body, 13 is an external viewfinder, and 14 is a shutter button. Thus, by applying the zoom lens of the present invention to a photographing apparatus such as a digital still camera, a small photographing apparatus having high optical performance is realized.

Lens sectional view of Numerical Example 1 according to the present invention Aberration diagrams at the wide-angle end in Numerical Example 1 according to the present invention Aberration diagram at intermediate zoom position in Numerical Example 1 according to the present invention Aberration diagram at the telephoto end of Numerical Example 1 according to the present invention. Lens sectional view of Numerical Example 2 according to the present invention Aberration diagrams at the wide-angle end in Numerical Example 2 according to the present invention Aberration diagram in intermediate zoom range of Numerical Example 2 according to the present invention Aberration diagram at telephoto end in Numerical Example 2 according to the present invention Lens sectional view of Numerical Example 3 according to the present invention Aberration diagrams at the wide-angle end in Numerical Example 3 according to the present invention Aberration diagram in intermediate zoom range of Numerical Example 3 according to the present invention Aberration diagram at telephoto end in Numerical Example 3 according to the present invention Lens sectional view of Numerical Example 4 according to the present invention Aberration diagram at wide-angle end in Numerical example 4 according to the present invention Aberration diagram in intermediate zoom range of Numerical Example 4 according to the present invention Aberration diagram at telephoto end in Numerical Example 4 according to the present invention Lens sectional view of Numerical Example 5 according to the present invention Aberration diagrams at the wide-angle end in Numerical Example 5 according to the present invention Aberration diagram in intermediate zoom range of Numerical Example 5 according to the present invention Aberration diagram at telephoto end in Numerical Example 5 according to the present invention Schematic diagram of essential parts of the photographing apparatus of the present invention

Explanation of symbols

L1 First lens group L2 Second lens group L3 Third lens group L4 Fourth lens group SP Aperture d d-line g g-line ΔM meridional image plane ΔS sagittal image plane f focal length ω angle of view fno F-number

Claims (13)

In order from the object side, a first lens unit having a positive refractive power fixed on the optical axis in zooming, a second lens unit having a negative refractive power moving on the optical axis in zooming, and the first lens group in zooming. A zoom lens group having a positive refractive power fourth lens group that moves on the optical axis during zooming, the first lens group being an object A zoom lens comprising one positive lens and one negative lens in order from the side, and satisfying the following conditions.
1.52 <| f2 | / fW <2.0
Here, fW is the focal length of the entire system at the wide-angle end, and f2 is the focal length of the second group. 2. The zoom lens according to claim 1, wherein the following condition is satisfied, where d34 is the distance between the third group and the fourth group at the wide angle end, and fW is the focal length of the entire system at the wide angle end.
0.27 <d34 / fW <0.7 The zoom lens according to claim 1 or 2, wherein f1 is a focal length of the first group and f2 is a focal length of the second group, and the following conditions are satisfied.
0.2 <| f2 | / f1 <0.5   4. The zoom lens according to claim 1, wherein the fourth lens group includes only a positive single lens.   2. The first lens group, wherein the lens surface closest to the object side has a convex surface facing the object side, and the lens surface closest to the image side of the first lens group has a concave surface facing the image side. The zoom lens according to claim 4.   The zoom lens according to any one of claims 1 to 5, wherein the third lens group includes a biconcave lens and a biconvex lens adjacent to the object side thereof.   The fourth lens group has a lens surface closest to the image side facing a concave surface toward the image side, and a lens surface closest to the third lens group facing a convex surface toward the third lens group. The zoom lens according to claim 1. When G1n is the refractive index of the positive lens of the first lens group, 1.60 <1Gn <1.85
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition. When r1 is the radius of curvature of the positive lens in the first lens group on the object side and r2 is the radius of curvature of the positive lens in the first lens group on the image side, 0.15 <| r1 / r2 | <0.30
The zoom lens according to claim 1, wherein the zoom lens satisfies the following condition.   The zoom lens according to claim 1, wherein focusing is performed by moving the fourth lens group.   11. The zoom lens according to claim 1, wherein all surfaces of the lens group are spherical surfaces.   The zoom lens system according to any one of claims 1 to 11, wherein an image is formed on a solid-state imaging device.   An imaging apparatus comprising: the zoom lens system according to any one of claims 1 to 12; and a solid-state imaging device that receives an image formed by the zoom lens system.

Images