JP2008242392A - Zoom lens and imaging apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which obtains excellent optical performance while having a wider viewing angle, and is compact as a whole system, and to provide an imaging apparatus with the zoom lens. <P>SOLUTION: The zoom lens is composed of a first lens group having negative refractive power and a second lens group having positive refractive power in this order from an object side to an image side, and the respective lens groups independently move in zooming from a wide angle end to a telephoto end. The second lens group comprises a twenty-first lens having positive refractive power, a twenty-second lens having positive refractive power, a twenty-third lens having negative refractive power, and a twenty-fourth lens having positive refractive power in order from the object side to the image side. When the focal distances of the first and the second lens groups are defined as f1 and f2 respectively, and the focal distance of the entire system at the wide angle end is defined as fw, the zoom lens satisfies conditional expressions; 1.4<f2/fw<2.3 and 1.2<¾f1¾/fw<1.6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zoom lens, and is suitable for an imaging apparatus such as a digital still camera, a video camera, a silver salt film camera, or a surveillance camera.

  In recent years, a photographing lens used in an imaging apparatus such as a digital still camera or a video camera has been required to have a wide angle of view, high optical performance over the entire screen, and a small zoom lens for the entire optical system.

  As a zoom lens that satisfies these requirements, in order from the object side to the image side, the zoom lens includes a first lens group having a negative refractive power and a second lens group having a positive refractive power, and performs zooming by moving each lens group. A two-group zoom lens is known (Patent Documents 1 to 3).

In the negative lead type two-group zoom lens preceded by the lens unit having the negative refractive power, a zoom lens is known in which the second lens unit is composed of four to five lenses and the entire optical system is reduced in size. (Patent Documents 4 and 5).
Japanese Patent Laid-Open No. 11-052235 JP 2003-131128 A JP 2004-102111 A JP 2004-226850 A Japanese Patent Laid-Open No. 10-161024

  Since the negative lead type two-group zoom lens can be configured with a relatively small number of lenses, the entire lens system can be easily downsized and a wide angle of view can be easily obtained.

  However, in a negative lead type two-group zoom lens, if an attempt is made to secure a wide angle of view and a predetermined zoom ratio (for example, a zoom ratio of 3 or more) while further miniaturizing the entire optical system, aberration fluctuations due to zooming may occur. It will increase.

  Therefore, in order to obtain high optical performance (high-quality images) over the entire zoom range while achieving a wide field angle and downsizing in a negative lead type two-group zoom lens, the lens configuration of each lens group is set appropriately. It has become important to do.

  In general, in a zoom lens, if the refractive power of each lens group is increased, the amount of movement of each lens group to obtain a predetermined zoom ratio is shortened, so that widening of the angle can be facilitated while shortening the total lens length. .

  However, if the refractive power of each lens group is simply increased, aberration fluctuations associated with zooming will increase, and it will be difficult to obtain good optical performance over the entire zoom range, especially when widening the angle of view. .

  In particular, in a negative lead type two-group zoom lens, unless the refractive power and lens configuration of each lens group are set appropriately, high optical performance can be obtained while widening the angle of view and reducing the size of the entire lens system. It becomes difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens having an excellent optical performance while having a wide angle of view and having a small overall system, and an imaging apparatus having the same.

The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and each lens group in zooming from the wide angle end to the telephoto end. Is a zoom lens that independently moves, and the second lens group in order from the object side to the image side is a 21st lens having a positive refractive power, a 22nd lens having a positive refractive power, and a 23rd lens having a negative refractive power. The lens consists of a 24th lens with positive refractive power,
When the focal lengths of the first and second lens units are f1 and f2, respectively, and the focal length of the entire system at the wide angle end is fw, 1.4 <f2 / fw <2.3.
1.2 <| f1 | / fw <1.6
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens having a wide angle of view and an excellent optical performance and having a small overall system and an imaging apparatus having the same.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and each lens group in zooming from the wide angle end to the telephoto end. Is a zoom lens that moves independently.

  The first lens group includes, in order from the object side to the image side, an eleventh lens having a positive refractive power, a twelfth lens having a negative refractive power, a thirteenth lens having a negative refractive power, and a fourteenth lens having a positive refractive power. It is configured.

  Alternatively, the first lens group includes, in order from the object side to the image side, an eleventh lens having a negative refractive power, a twelfth lens having a negative refractive power, and a thirteenth lens having a positive refractive power.

  The second lens group, in order from the object side to the image side, includes a 21st lens having a positive refractive power, a 22nd lens having a positive refractive power, a 23rd lens having a negative refractive power, and a 24th lens having a positive refractive power. It is configured.

  FIGS. 1A and 1B are lens cross-sectional views at the wide-angle end (short focal length end) and the telephoto end (long focal length end) of the zoom lens according to Embodiment 1 of the present invention.

  FIGS. 2A and 2B are aberration diagrams when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 1, respectively.

  Embodiment 1 is a zoom lens having a zoom ratio of 2.85, an F number of 3.65 to 5.88, and a shooting field angle of 72.5 ° to 28.8 °.

  3A and 3B are lens cross-sectional views at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 2 of the present invention. 4A and 4B are aberration diagrams when focusing on an infinite object at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 2, respectively. The second embodiment is a zoom lens having a zoom ratio of 2.86, an F number of 3.65 to 5.88, and a shooting field angle of 72.6 ° to 28.8 °.

  5A and 5B are lens cross-sectional views at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 3 of the present invention. FIGS. 6A and 6B are aberration diagrams when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 3, respectively. The third exemplary embodiment is a zoom lens having a zoom ratio of 2.86, an F number of 3.65 to 5.88, and a shooting field angle of 72.4 ° to 28.8 °.

  7A and 7B are lens cross-sectional views at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 4 of the present invention. 8A and 8B are aberration diagrams when focusing on an infinite object at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 4, respectively. The fourth exemplary embodiment is a zoom lens having a zoom ratio of 2.74, an F number of 3.65 to 5.88, and a shooting field angle of 69.0 ° to 28.1 °.

  FIGS. 9A and 9B are lens cross-sectional views at the wide-angle end and the telephoto end of the zoom lens according to Embodiment 5 of the present invention. FIGS. 10A and 10B are aberration diagrams when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 5, respectively. Example 5 is a zoom lens having a zoom ratio of 2.86, an F number of 3.65 to 5.88, and a shooting field angle of 72.5 ° to 28.8 °.

  FIG. 11 is a schematic diagram of a main part of a digital single-lens reflex camera (imaging device) including the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographic lens system used in the imaging apparatus, and in the lens cross-sectional view, the left side is the object side and the right side is the image side.

  In the lens cross-sectional views of Examples 1 to 5 in FIGS. 1, 3, 5, 7, and 9, L1 is a first lens unit having negative refractive power (optical power = reciprocal of focal length), and L2 is This is a second lens unit having a positive refractive power.

  SP is an F number determining member (hereinafter also referred to as “aperture stop”) that functions as an aperture stop that determines (limits) a released F number (Fno) light beam. The aperture stop SP is located on the object side of the second lens unit L2 or in the second lens unit.

  FC is a flare cut stop whose aperture diameter does not change, and is composed of first and second flare cut stops FC1 and FC2, which are positioned on the image side of the second lens unit L2.

  The first and second flare cut stops FC1 and FC2 are arranged close to each other at the wide angle end. In Numerical Example 1 to be described later, it is treated as being in close contact (interval 0) at the wide angle end.

  IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, a photosensitive surface corresponding to an imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed. Yes.

  The arrows indicate the movement trajectories of the lens units, the aperture stop SP, and the first flare cut stop FC1 during zooming from the wide-angle end to the telephoto end.

  In the aberration diagrams, d, g, F, and C are d line, g line, F line, and C line in this order. M and S are a meridional image plane and a sagittal image plane.

  Fno is an F number. Y is the image height.

  In the zoom lens of each embodiment, during zooming from the wide-angle end to the telephoto end zoom position, the first lens unit L1 moves so as to draw a part of a convex locus on the image side. The second lens unit L2 moves to the object side integrally with the aperture stop SP.

  In each embodiment, the zoom positions at the wide-angle end and the telephoto end refer to zoom positions when the zooming lens group (second lens group) is positioned at both ends of the range that can move on the optical axis due to the mechanism.

  In the zoom lens of each embodiment, main zooming is performed by moving the second lens unit L2, and movement of the image point accompanying zooming is corrected by moving the first lens unit L1.

  In each embodiment, focusing is performed by the first lens unit L1.

  In the first and second flare cut stops provided on the image side of the second lens unit L2, the first flare cut stop on the object side moves during zooming, and the second flare cut stop on the image side does not move.

  Specifically, the first flare cut stop FC1 moves to the object side during zooming from the wide angle end to the telephoto end.

  The second flare cut stop FC2 is immovable but may be moved.

  In each embodiment, the two flare cut stops are used as described above to effectively cut off the flare component of the off-axis light beam caused by zooming, and to reduce the fluctuation of flare due to zooming. Have gained.

  The lens configuration of the first lens unit L1 is as follows in order from the object side to the image side in the first to third embodiments of FIGS. 1, 3, 5, and 9.

  An eleventh lens having a positive refractive power having a convex surface on the object side, a twelfth lens having a negative meniscus shape having a convex meniscus shape on the object side, a thirteenth lens having a negative refractive power having a concave shape on the image side, and a convex meniscus shape having a convex surface on the object side. It is composed of a 14th lens having a positive refractive power.

  In Example 4 of FIG. 7, the order is as follows from the object side to the image side.

  The object side surface is convex and the meniscus negative eleventh lens having a negative refractive power, the object side surface is convex and the meniscus negative refracting power twelfth lens, the object side is convex and the meniscus shape has a positive refractive power It consists of a thirteenth lens.

  In each embodiment, the lens configuration of the second lens unit L2 is as follows from the object side to the image side.

  The 21st lens with positive refractive power whose both lens surfaces are convex, the 22nd lens with positive refractive power whose both lens surfaces are convex, the 23rd lens with negative refractive power whose both lens surfaces are concave, and both lenses The surface is composed of a convex 24th lens having a positive refractive power.

  In Examples 1 to 4 of FIGS. 1, 3, 5, and 7, the 22nd lens and the 23rd lens are cemented.

  This facilitates correction of chromatic aberration and further reduces the decentration error of the lens during assembly.

In each embodiment, the focal lengths of the first and second lens units L1 and L2 are f1 and f2, respectively, and the focal length of the entire system at the wide angle end is fw. At this time,
1.4 <f2 / fw <2.3 (1)
1.2 <| f1 | / fw <1.6 (2)
The following conditional expression is satisfied.

  Conditional expression (1) represents an appropriate focal length range for the second lens unit L2 that performs the zooming action, reduces aberration fluctuations during focusing, and is excellent over a wide object distance range. This is to obtain optical performance.

  If the upper limit of conditional expression (1) is exceeded and the refractive power of the second lens unit L2 becomes too weak, it is difficult to reduce the size of the entire lens system. In addition, if the refractive power of the second lens unit L2 becomes too strong beyond the lower limit, the aberration variation accompanying zooming becomes large, which is not good.

  In each embodiment, it is more preferable to set the numerical range of conditional expression (1) as follows.

1.6 <f2 / fw <2.0 (1a)
Conditional expression (2) represents the range of the focal length of the first lens unit L1, and indicates an appropriate refractive power of the first lens unit L1. If the upper limit of conditional expression (2) is exceeded and the refractive power of the first lens unit L1 becomes too weak, it becomes difficult to reduce the size of the entire lens system. If the lower limit of conditional expression (2) is exceeded and the refractive power of the first lens unit L1 becomes too strong, fluctuations in field curvature due to zooming will increase, making it difficult to maintain good optical performance over the entire screen. .

  In each embodiment, it is more preferable to set the numerical range of conditional expression (2) as follows.

1.4 <| f1 | / fw <1.6 (2a)
As described above, according to each embodiment, by appropriately adjusting the refractive power distribution of each lens group, the lens configuration of the second lens group, and the like, it is favorable over a wide zoom range with a wide angle of view (more than 65 degrees at a wide angle of view). It is possible to obtain a zoom lens having a zoom ratio of about 3 while maintaining excellent optical performance.

  In addition, although the number of lenses is as small as 7 to 8 as a whole, an excellent optical performance can be obtained over the entire zoom range, and a zoom lens having a small overall system can be obtained.

In each embodiment, the imaging magnification at the telephoto end of the second lens unit L2 is more preferably β2t. At this time, 1.7 <| β2t | <2.3 (3)
It is good to satisfy the following conditional expression.

  Conditional expression (3) indicates the range of the imaging magnification at the telephoto end of the second lens unit L2. If the lower limit of conditional expression (3) is exceeded, the refractive power of the first lens unit L1 will be insufficient, and the variation in field curvature due to zooming will increase. If the upper limit of conditional expression (3) is exceeded, the refractive power of the first lens unit L1 becomes too strong, and the variation of spherical aberration due to zooming becomes large.

  More preferably, the numerical range of conditional expression (3) is set as follows.

1.75 <| β2t | <2.10 (3a)
In each embodiment, if at least one of the above-described conditional expressions is satisfied, in the negative lead type two-group zoom lens, aberration variation during zooming is small, and good optical performance can be obtained over the entire screen.

  In each embodiment, a converter lens or / and a field lens may be added to the object side of the first lens unit L1 and / or the image side of the second lens unit.

  Next, an embodiment of a single-lens reflex camera system using the zoom lens of the present invention will be described with reference to FIG.

  In FIG. 11, 10 is a single-lens reflex camera body, and 11 is an interchangeable lens equipped with an optical system according to the present invention. Reference numeral 12 denotes recording means such as a film or an image sensor for receiving a subject image formed through the interchangeable lens 11.

  Reference numeral 13 denotes a finder optical system for observing a subject image from the interchangeable lens 11, and reference numeral 14 denotes a rotating quick return mirror for switching and transmitting the subject image from the interchangeable lens 11 to the recording means 12 and the finder optical system 13.

  When the subject image is observed with the viewfinder, the subject image formed on the focusing plate 15 via the quick return mirror 14 is converted into an erect image with the pentaprism 16 and then magnified with the eyepiece optical system 17 for observation.

  At the time of shooting, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed and recorded on the recording means 12. Reference numeral 18 denotes a submirror, and 19 denotes a focus detection device.

  In this way, by applying the optical system of the present invention to an imaging apparatus such as a single-lens reflex camera interchangeable lens, an imaging apparatus having high optical performance can be realized.

  The present invention can be similarly applied to an SLR (Single Lens Reflex) camera having no quick return mirror.

  In the following, numerical examples 1 to 5 corresponding to the first to fifth examples will be described. In each numerical example, i indicates the order of the surfaces from the object side. ri is the radius of curvature of each surface, di is the distance between the i-th surface and the (i + 1) -th surface, and ni and νi are the refractive index and Abbe number based on the d-line, respectively.

  When the aspherical shape is X with the displacement in the optical axis direction at the position of the height h from the optical axis as the reference to the surface vertex,

It is represented by However, R is a paraxial radius of curvature, B, C, D, and E are aspherical coefficients, and constants and coefficients not described in the numerical examples are zero.

[E-X] means [× 10 ^−X ]. f represents a focal length, Fno represents an F number, and ω represents a half angle of view.

  Moreover, the numerical value in each Example is shown in Table-1.

  Table 1 shows numerical values in the respective examples with respect to the conditional expressions (1) to (3) described above.

1 is a cross-sectional view of a lens at a wide-angle end and a telephoto end according to a first embodiment of a zoom lens according to the present invention. Aberration diagram for the infinite object at the wide-angle end and the telephoto end of the zoom lens according to the first exemplary embodiment of the present invention. Cross-sectional view of the zoom lens according to the second embodiment of the present invention at the wide-angle end and the telephoto end Aberration diagram of the zoom lens according to the second embodiment of the present invention when the object is at infinity at the wide-angle end and the telephoto end. Cross-sectional view of the zoom lens according to the third embodiment of the present invention at the wide-angle end and the telephoto end Aberration diagram of the zoom lens according to the third exemplary embodiment of the present invention when the object is at infinity at the wide-angle end and the telephoto end. Cross-sectional view of a zoom lens according to a fourth embodiment of the present invention at the wide-angle end and the telephoto end Aberration diagrams of the zoom lens according to the fourth exemplary embodiment of the present invention when the object is at infinity at the wide-angle end and the telephoto end. Cross-sectional view of the zoom lens according to Embodiment 5 of the present invention at the wide-angle end and the telephoto end Aberration diagram of the zoom lens according to the fifth exemplary embodiment of the present invention when the object is at infinity at the wide angle end and the telephoto end. Schematic diagram of main parts of an imaging apparatus of the present invention

Explanation of symbols

L1 1st lens group L2 2nd lens group SP Aperture FC Flare cut aperture FC1 1st flare cut aperture FC2 2nd flare cut aperture IP Image plane Fno F number Y Image height d d line g g line C C line F F line M Meridional image plane S Sagittal image plane

Claims (9)

A zoom lens composed of a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side to the image side, and each lens group independently moving during zooming from the wide-angle end to the telephoto end The second lens group includes, in order from the object side to the image side, a 21st lens having a positive refractive power, a 22nd lens having a positive refractive power, a 23rd lens having a negative refractive power, and a positive refractive power. Consists of the 24th lens,
When the focal lengths of the first and second lens units are f1 and f2, respectively, and the focal length of the entire system at the wide angle end is fw, 1.4 <f2 / fw <2.3.
1.2 <| f1 | / fw <1.6
A zoom lens satisfying the following conditional expression:   The zoom lens according to claim 1, wherein the 22nd lens and the 23rd lens in the second lens group are cemented.   The first lens group includes, in order from the object side to the image side, an eleventh lens having a positive refractive power, a twelfth lens having a negative refractive power, a twenty-third lens having a negative refractive power, and a fourteenth lens having a positive refractive power. The zoom lens according to claim 1, wherein the zoom lens is configured.   The first lens group includes, in order from the object side to the image side, an eleventh lens having a negative refractive power, a twelfth lens having a negative refractive power, and a thirteenth lens having a positive refractive power. The zoom lens according to claim 1 or 2. When the imaging magnification at the telephoto end of the second lens group is β2t, 1.7 <| β2t | <2.3
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   The zoom lens according to claim 1, wherein a flare cut stop is disposed on the image side of the second lens group.   First and second flare cut stops are disposed on the image side of the second lens group, and the first flare cut stop on the object side moves during zooming, and the second flare cut stop on the image side does not move. The zoom lens according to claim 1, wherein the zoom lens is provided.   The zoom lens according to claim 1, wherein an image is formed on a solid-state image sensor.   An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.