JP2007003653A - Reduction optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance compact reduction optical system and an imaging apparatus equipped therewith. <P>SOLUTION: In contrast to a main lens system ML for forming a subject image, reduction optical system SL is an optical system for forming an image on an imaging device, having a format of smaller image plane size than that of a format image-formed by the main lens system ML by reducing the image formed by the main lens system ML without reimaging it, and has a meniscus-shaped cemented lens LC convex of the object side. The cemented lens LC satisfies the conditional expression: -0.15<(Rf-Rr)/(Rf+Rr)<0.15 (Rf: the radius of curvature of the object-side surface of the cemented lens LC and Rr: the radius of curvature of the image-side surface of the cemented lens LC). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reduction optical system, for example, a reduction optical system that reduces an object image formed by a replaceable main lens system in a digital camera that captures an image of an object with an image sensor or a digital device with an image input function. And an imaging apparatus including the same.

In recent years, with the spread of personal computers, digital cameras that can easily capture images are becoming popular. As digital cameras become more widespread, photographing optical systems with various specifications have been demanded. Since a single-lens reflex camera that records an image on a silver salt film can exchange lenses, the above-described demand can be met if an interchangeable lens for a single-lens reflex camera can be applied to a digital camera. In order to achieve this, Patent Documents 1 to 3 propose a photographing optical system in which a condenser lens is disposed in the vicinity of an image surface of an interchangeable lens and an image formed by the interchangeable lens is re-imaged by a relay lens system. Further, Patent Document 4 proposes a reduction optical system that reduces an image formed by an interchangeable lens without re-imaging.
JP-A 63-205626 JP-A-7-253537 JP-A-8-114742 JP 2000-121932 A

  However, in the optical configurations proposed in Patent Documents 1 to 3, the configuration for re-imaging the image formed by the interchangeable lens leads to an increase in the size of the entire photographing optical system. In the optical configuration proposed in Patent Document 4, correction of various aberrations is completed in the interchangeable lens as the main lens system, and thus it is difficult to sufficiently correct the various aberrations in the reduction optical system to be added. There is a problem.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a high-performance and compact reduction optical system and an image pickup apparatus including the same.

In order to achieve the above object, a reduction optical system according to a first aspect of the present invention reduces a main lens system that forms an image of an object without re-imaging an image formed by the main lens system. A reduction optical system that forms an image on an image pickup device having a screen size format smaller than the screen size of the format that the system forms an image, and has a meniscus-shaped cemented lens on the object side. Conditional expression (1) is satisfied.
-0.15 <(Rf−Rr) / (Rf + Rr) <0.15 (1)
However,
Rf: radius of curvature of the object side of the cemented lens,
Rr: radius of curvature of image side of cemented lens,
It is.

  The reduction optical system according to a second aspect is characterized in that, in the first aspect, the cemented lens is located closest to the object side.

A reduction optical system according to a third aspect is characterized in that, in the first or second aspect, the cemented lens is composed of two lenses and satisfies the following conditional expression (2).
0.001 <(n2-n1) / rc <0.002 (2)
However,
n1: Refractive index of the lens located on the object side of the cemented surface,
n2: refractive index of the lens located on the image side of the cemented surface,
rc: radius of curvature of the joint surface,
It is.

  A reduction optical system according to a fourth invention is characterized in that, in any one of the first to third inventions, the cemented lens includes a positive meniscus lens and a negative meniscus lens.

A reduction optical system according to a fifth invention is characterized in that, in any one of the first to fourth inventions, the cemented lens satisfies the following conditional expression (3).
0.3 <tm / ts <0.5 (3)
However,
tm: core thickness of the cemented lens,
ts: axial thickness of the entire reduction optical system,
It is.

  A reduction optical system according to a sixth invention is characterized in that, in any one of the first to fifth inventions, the lens located closest to the image side has an aspherical surface.

  In a reduction optical system according to a seventh aspect of the present invention, in any one of the first to sixth aspects, the number of constituent lenses of the cemented lens is two, and the total number of constituent lenses is three. Features.

The reduction optical system according to an eighth aspect of the present invention is characterized in that, in any one of the first to seventh aspects, the following conditional expression (4) is satisfied.
rr <0.8 (4)
However,
rr: Reduction rate,
rr = SY / LY,
SY: 1/2 of the diagonal length of the image sensor screen,
LY: Maximum image height of the image formed only by the main lens system for the image sensor in the format in which the main lens system forms an image,
It is.

  A reduction optical system according to a ninth aspect of the present invention is characterized in that, in any one of the first to eighth aspects of the invention, the format in which the main lens system forms an image is 135 systems.

  An image pickup apparatus according to a tenth aspect includes the reduction optical system according to any one of the first to ninth aspects, and is capable of mounting the main lens system mounted in a replaceable manner.

  According to the present invention, the reduction optical system has a meniscus cemented lens that is convex on the object side, and the cemented lens satisfies a predetermined condition, thereby realizing a high-performance and compact reduction optical system. can do. Since the image pickup apparatus includes the reduction optical system according to the present invention, the main lens system can be exchanged. For example, an interchangeable lens for a silver salt single-lens reflex camera can be applied to a digital camera. Moreover, since it becomes possible to use the interchangeable lens of the format of 135 system which is the most widespread, the interchangeable lens of a new format is not necessary. Therefore, the system of the interchangeable lens digital camera can be configured at low cost.

  Hereinafter, a reduction optical system, a photographing optical system, an image pickup apparatus and the like embodying the present invention will be described with reference to the drawings. In general, a reduction optical system is a lateral magnification when arranged behind a main lens system having an imaging function: βs = ys / ym (ym: maximum image height of the main lens system, ys: main lens system and additional optics) This is an additional optical system in which the maximum image height of the photographing optical system combined with the system is smaller than 1. If only the main lens system is used for an image sensor with a small format, the angle of view will be narrowed. The same angle of view can be obtained. Therefore, if a reduction optical system that reduces an image formed by the main lens system is used as in each embodiment described later, the lens of the main lens system can be exchanged. For example, for a silver salt single-lens reflex camera It becomes possible to apply an interchangeable lens to a digital camera. In addition, since the image becomes brighter when the reduction ratio is reduced, it is possible to use a wide-angle lens for a silver-salt single-lens reflex camera as a wide-angle lens for a substantially bright digital camera while using an image sensor with a small format. become.

  FIG. 7 is a schematic cross-sectional view showing a schematic optical configuration example of a camera CU (corresponding to a digital camera, a digital device with an image input function, etc.) used for still image shooting or moving image shooting of a subject. The camera CU includes a camera body CB and an interchangeable lens CL. The interchangeable lens CL corresponds to an interchangeable lens for a silver salt single-lens reflex camera, and includes a main lens system ML that forms an image of a subject. The camera body CB is an imaging device that can be mounted with a replaceable main lens system ML, and includes a reduction optical system SL, a shutter SY, an imaging element SR, an EVF finder FR, and a display device DP (for example, LCD: Liquid). Crystal Display) etc.

  The reduction optical system SL is an optical system that reduces an image formed by the main lens system ML without re-imaging, and can change a subject image (IM: image plane) in combination with the main lens system ML. A zoom lens system ZL to be formed (corresponding to a photographing optical system functioning as a variable magnification optical system) is configured. In the zoom lens system ZL including the main lens system ML and the reduction optical system SL, a plurality of lens groups move along the optical axis AX, and zooming is performed by changing the distance between the lens groups. As the imaging element SR, for example, a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor having a plurality of pixels is used. The optical image formed by the zoom lens system ZL (on the light receiving surface SS of the image sensor SR) is converted into an electrical signal by the image sensor SR. The signal generated by the image sensor SR is used for displaying a subject image by the display device DP.

  1 to 3 are lens configuration diagrams respectively corresponding to the zoom lens systems ZL constituting the first to third embodiments, and the lens arrangement at the wide angle end (W) is shown in an optical section. FIG. 8 is a lens configuration diagram of a single main lens system ML commonly used in the first to third embodiments, and shows a lens arrangement at the wide angle end (W) in an optical section. . In each lens configuration diagram, the surface with ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side (the surface with ri marked with * is an aspheric surface). In addition, the axial upper surface interval with di (i = 1, 2, 3,...) Is a variable interval that changes during zooming among the i-th axial upper surface interval counted from the object side. In each lens configuration diagram, arrows m1, m2, m3, and m4 indicate the first lens group GR1, the second lens group GR2, the third lens group GR3, and the third lens group in zooming from the wide-angle end (W) to the telephoto end (T). The movement of the four lens groups GR4 is schematically shown, and the arrow on the most image side indicates the fifth lens group GR5 and a parallel plane plate PT (such as an optical low-pass filter and an infrared cut filter arranged as necessary). The optical filter (corresponding to the cover glass or the like of the image sensor SR) indicates that the position is fixed during zooming. The image sensor SR is 4/3 type compatible.

  The zoom lens system ZL of the first to third embodiments (FIGS. 1 to 3) has, in order from the object side, positive power (power: an amount defined by the reciprocal of the focal length). GR1, the second lens group GR2 having negative power, the stop ST, the third lens group GR3 having positive power, the fourth lens group GR4 having positive power, and the fifth having positive power. Lens group GR5, and has a five-component zoom configuration in which zooming is performed by changing the distance between the lens groups. The zoom lens system ZL is composed of the main lens system ML and the reduction optical system SL as described above, and the reduction optical system SL is formed by the main lens system ML in contrast to the main lens system ML that forms an object. The image is reduced without re-imaging. In any of the embodiments, the main lens system ML having the same configuration is used, and the stop ST disposed between the second lens group GR2 and the third lens group GR3 is the third lens group GR3. At the same time, the zoom is moved (arrow m3).

  The main lens system ML (FIG. 8) used in the first to third embodiments (FIGS. 1 to 3) is a positive / negative / positive / positive lens composed of the first to fourth lens groups GR1 to GR4. The four-component zoom lens system alone has good optical performance, and is configured to be easily replaceable as the interchangeable lens CL of the camera CU. On the other hand, the reduction optical system SL is mounted in a fixed state on the camera body CB as a positive power fifth lens group GR5 which is the final group of the zoom lens system ZL. The lens configuration of each embodiment will be described in detail below.

  Each lens group of the main lens system ML in the first to third embodiments (FIGS. 1 to 3) is configured as follows. The first lens group GR1 includes, in order from the object side, a cemented lens including a negative meniscus lens concave on the image side and a biconvex positive lens, and a positive meniscus lens convex on the object side. The second lens group GR2 includes, in order from the object side, a negative meniscus lens concave on the image side whose object side surface is an aspheric surface, a biconcave negative lens, a biconvex positive lens, and a negative meniscus concave on the object side. And a lens. The third lens group GR3 includes, in order from the object side, two biconvex positive lenses and a biconcave negative lens. The third lens group GR3 has a third lens group on the object side for zooming. A stop ST that moves together with GR3 is disposed. The fourth lens group GR4 includes, in order from the object side, a biconvex positive lens and a negative meniscus lens that is concave on the image side and includes a double-sided aspheric surface.

  In the first to third embodiments (FIGS. 1 to 3), the reduction optical system SL constituting the fifth lens group GR5 is configured as follows. In the first embodiment (FIG. 1), in order from the object side, a cemented lens LC composed of a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and the object side whose image side surface is an aspheric surface. And a positive meniscus lens convex. In the second embodiment (FIG. 2), in order from the object side, a cemented lens LC composed of a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and an object side whose both surfaces are aspherical surfaces. And a convex positive meniscus lens. In the third embodiment (FIG. 3), in order from the object side, a cemented lens LC composed of a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and an object side whose image side surface is an aspheric surface. And a positive meniscus lens convex.

  In any embodiment, the reduction optical system SL has a meniscus cemented lens LC convex on the object side. In order to lower the light beam height in the reduction optical system, a relatively thick meniscus lens (or lens block) convex toward the object side is effective, and the cemented lens is effective for correcting chromatic aberration. Therefore, if the reduction optical system has a meniscus cemented lens convex on the object side, a high-performance and compact reduction optical system can be realized. If the reduction optical system is provided in the imaging apparatus, for example, an interchangeable lens for a silver salt single-lens reflex camera can be used interchangeably with a digital camera or the like. If the imaging device is used in devices such as a digital camera and a portable information device, it can contribute to thinning, lightness, compactness, low cost, high performance, high functionality, etc. of these devices. Further, if the shape and the like of the cemented lens satisfy predetermined conditions, aberration performance and the like can be further improved while maintaining a good balance with downsizing and cost reduction as described below. It becomes possible.

It is desirable that the following conditional expression (1) is satisfied.
-0.15 <(Rf−Rr) / (Rf + Rr) <0.15 (1)
However,
Rf: radius of curvature of the object side of the cemented lens,
Rr: radius of curvature of image side of cemented lens,
It is.

  Since the role of the meniscus cemented lens is to reduce the height of the light beam, it is desirable that aberrations are not generated as much as possible. That is, it is desirable that the aberration generated on the front surface (that is, the object side surface) of the cemented lens is canceled by the aberration generated on the rear surface (that is, the image side surface) of the cemented lens. For this purpose, it is necessary that the curvature of both surfaces of the cemented lens is close. From this viewpoint, the conditional expression (1) defines a preferable condition range for the shape factor of the cemented lens. If the condition range of the conditional expression (1) is not satisfied, the residual aberration increases, so that it is difficult to correct it with another lens.

It is further desirable to satisfy at least one of the following conditional expressions (1a) and (1b).
-0.10 <(Rf−Rr) / (Rf + Rr) <0.14 (1a)
-0.05 <(Rf−Rr) / (Rf + Rr) <0.13 (1b)
The conditional expressions (1a) and (1b) define a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1).

  In any of the embodiments, the reduction optical system SL has a meniscus cemented lens LC convex on the object side on the most object side. As described above, when the meniscus cemented lens is disposed closest to the object side, aberration correction (particularly correction of field curvature) can be performed efficiently, and the entire reduction optical system can be made compact. Accordingly, it is preferable to dispose a meniscus cemented lens convex on the object side as the lens located closest to the object side in the reduction optical system.

It is desirable that the cemented lens is composed of two lenses and satisfies the following conditional expression (2).
0.001 <(n2-n1) / rc <0.002 (2)
However,
n1: Refractive index of the lens located on the object side of the cemented surface,
n2: refractive index of the lens located on the image side of the cemented surface,
rc: radius of curvature of the joint surface,
It is.

  Conditional expression (2) defines a preferable condition range regarding the power of the cemented surface of the cemented lens. By satisfying conditional expression (2), axial chromatic aberration and lateral chromatic aberration can be corrected in a well-balanced manner. If the upper limit of conditional expression (2) is exceeded, the amount of chromatic aberration of magnification increases, making it difficult to sufficiently correct this. Conversely, if the lower limit of conditional expression (2) is exceeded, the effect of correcting axial chromatic aberration will not be sufficient.

It is further desirable to satisfy at least one of the following conditional expressions (2a) and (2b).
0.0011 <(n2-n1) / rc <0.0015 (2a)
0.0012 <(n2-n1) / rc <0.0013… (2b)
The conditional expressions (2a) and (2b) define more preferable condition ranges based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2).

  In any of the embodiments, the object side convex meniscus cemented lens LC includes a positive meniscus lens and a negative meniscus lens. Therefore, assuming that the refractive index difference between the front and rear surfaces is (n2−n1)> 0, the joint surface has a convex shape (rc> 0) on the object side. Thus, if the meniscus cemented lens is composed of a positive meniscus lens and a negative meniscus lens, axial chromatic aberration and lateral chromatic aberration can be corrected in a balanced manner, and in particular, lateral chromatic aberration can be corrected more effectively. It can be corrected. In addition, since the lens shape is easy to manufacture, it is effective in reducing the cost.

It is desirable to satisfy the following conditional expression (3).
0.3 <tm / ts <0.5 (3)
However,
tm: core thickness of the cemented lens,
ts: axial thickness of the entire reduction optical system,
It is.

  Conditional expression (3) defines a preferable condition range regarding the core thickness of the object side convex meniscus cemented lens. If the lower limit of conditional expression (3) is exceeded, the core thickness of the cemented lens will be reduced, and the function of reducing the beam height will be insufficient. On the other hand, if the upper limit of conditional expression (3) is exceeded, the core thickness of the cemented lens is increased, so that the function of lowering the light beam height is increased. However, since field curvature occurs, it is difficult to correct this.

It is further desirable to satisfy at least one of the following conditional expressions (3a) and (3b).
0.35 <tm / ts <0.47 (3a)
0.37 <tm / ts <0.45 (3b)
The conditional expressions (3a) and (3b) define more preferable condition ranges based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3).

  In any of the embodiments, an aspherical surface is disposed on the lens closest to the image plane. A lens located near the image plane is effective for correcting the curvature of field, and by introducing an aspherical surface to the lens, the curvature of field can be corrected more efficiently. Therefore, it is preferable that the lens located closest to the image side in the reduction optical system has an aspherical surface.

  In any of the embodiments, the reduction optical system SL includes, in order from the object side, a cemented lens LC including a positive meniscus lens convex on the object side and a negative meniscus lens concave on the image side, and a positive meniscus convex on the object side. And a lens. Thus, if the number of lenses constituting the cemented lens is two and the number of lenses constituting the entire system is three, the reduction optical system can be reduced in weight, size, and cost while effectively correcting chromatic aberration. can do. In addition, aberration correction can be performed more effectively by using all three lenses as meniscus lenses.

For example, when considering that an interchangeable lens for a silver salt single-lens reflex camera is applied to a digital camera, the reduction optical system is configured so that aberration performance is balanced at a lateral magnification of a predetermined range: βs (<1). There is a need. From this viewpoint, it is desirable that the reduction optical system satisfies the following conditional expression (4). Further, when the image formed by the main lens system is reduced without re-imaging, if the reduction optical system satisfies the conditional expression (4), further effective performance enhancement can be achieved.
rr <0.8 (4)
However,
rr: Reduction rate,
rr = SY / LY,
SY: 1/2 of the diagonal length of the image sensor screen,
LY: Maximum image height of the image formed only by the main lens system for the image sensor in the format in which the main lens system forms an image,
It is.

  The zoom lens system ZL constituting each embodiment uses a refractive lens that deflects incident light by refraction (that is, a lens that deflects at the interface between media having different refractive indexes). However, the usable lens is not limited to this. For example, a diffractive lens that deflects incident light by diffracting action, a refractive / diffractive hybrid lens that deflects incident light by combining diffractive action and refracting action, and a refractive index distribution that deflects incident light by a refractive index distribution in the medium A mold lens or the like may be used. However, it is desirable to use a homogeneous material lens having a uniform refractive index distribution, because the refractive index distribution type lens whose refractive index changes in the medium increases the cost of its complicated manufacturing method. Further, in the zoom lens system ZL constituting each embodiment, a stop ST is used as an optical element in addition to the lens, but a light flux restricting plate (for example, a flare cutter) or the like for cutting unnecessary light is used. You may arrange | position as needed.

  Hereinafter, the configuration of the zoom lens system embodying the present invention will be described more specifically with reference to construction data and the like. Examples 1 to 3 listed here are numerical examples corresponding respectively to the first to third embodiments described above, and are optical configuration diagrams showing the first to third embodiments (FIGS. 1 to 3). 3) shows the lens configurations of the corresponding first to third embodiments.

  Tables 1 to 6 show construction data of Examples 1 to 3, and Tables 7 and 8 show construction data of the main lens system ML alone (FIG. 8) commonly used in Examples 1 to 3. Table 9 shows values corresponding to the conditional expressions of the respective examples. In the basic optical configurations (i: surface number) shown in Table 1, Table 3, Table 5, and Table 7, ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side. The radius of curvature (mm) and di (i = 1, 2, 3,...) Indicate the axial distance (mm) between the i-th surface and the (i + 1) -th surface counted from the object side. Ni (i = 1, 2, 3,...) And νi (i = 1, 2, 3,...) Are refractive indexes (Nd ) And Abbe number (νd). Further, the axial top surface distance di that changes during zooming is a variable air distance from the wide-angle end (shortest focal length state, W) to the middle (intermediate focal length state, M) to the telephoto end (longest focal length state, T). , F, FNO respectively indicate the focal length (mm) and the F number of the entire system corresponding to each focal length state (W), (M), (T).

The surfaces marked with * in the data of the radius of curvature ri are aspherical surfaces (aspherical refractive optical surfaces, surfaces having a refractive action equivalent to aspherical surfaces, etc.), and represent the following aspherical surface shapes: It is defined by the formula (AS). In Table 2, Table 4, Table 6, and Table 8, aspherical data of Examples 1 to 3 and main lens system ML are shown. However, the coefficient of the term without description is 0, and E−n = × 10 ⁻ⁿ for all data.
X (H) = (C0 · H ² ) / {1 + √ (1−ε · C0 ² · H ² )} + Σ (Aj · H ^j ) (AS)
However, in the formula (AS)
X (H): Amount of displacement in the optical axis AX direction at the position of height H (based on the surface vertex),
H: height in a direction perpendicular to the optical axis AX,
C0: paraxial curvature (= 1 / ri),
ε: quadric surface parameter,
Aj: j-order aspheric coefficient,
It is.

  4 to 6 are aberration diagrams corresponding to Examples 1 to 3, respectively. FIG. 9 is an aberration diagram of the main lens system ML alone. (W) is a wide angle end, (M) is a middle, and (T ) Are various aberrations in the infinite focus state at the telephoto end {spherical aberration, astigmatism, distortion aberration in order from the left. FNO is the F number, and Y ′ (mm) is the maximum image height (corresponding to the distance from the optical axis AX) on the light receiving surface SS of the image sensor SR. }. In the spherical aberration diagram, a solid line d represents spherical aberration (mm) with respect to the d line, and a broken line SC represents an unsatisfactory sine condition (mm). In the astigmatism diagram, the broken line DM represents the meridional surface, and the solid line DS represents each astigmatism (mm) with respect to the d-line on the sagittal surface. In the distortion diagram, the solid line represents the distortion (%) with respect to the d-line.

  The main lens system ML commonly used in each embodiment corresponds to a 135 system with a focal length of 24 to 105 mm (a 35 mm film format and a maximum image height of a full size is 21.5 mm). Even if it is a positive / negative / positive / positive four-component zoom lens system alone, it has good optical performance. When a subject image is formed with an interchangeable lens for the 135 system with respect to an image sensor having a screen size of the 135 system, the periphery of the screen becomes dark due to vignetting. In order to avoid this, an image sensor having a screen size format smaller than the screen size of the 135 system, that is, a so-called APS-C size format is known. In the APS-C size format, the maximum image height is 14.2 mm, and the aberration diagram of FIG. 9 shows the optical performance corresponding to the APS-C size.

  The reduction optical system of each embodiment reduces the image formed by the main lens system ML without re-imaging with respect to the main lens system ML that forms an image of the subject, and the APS on which the main lens system ML forms an image. The image is formed on an image sensor having a screen size format smaller than the screen size of the C format (if the vignetting is acceptable, the screen size to be reduced may be the format of the 135 system). . Here, 4/3 type (four thirds system) is assumed as the format of the small screen size. In the 4/3 type format, the maximum image height is 10.8 mm (reduction ratio: 0.76), and the aberration diagrams of FIGS. 4 to 6 show the optical performance corresponding to the 4/3 type.

  As can be seen by comparing the aberration of the main lens system ML alone (FIG. 9) and the aberrations of Examples 1 to 4 (FIGS. 4 to 6), the aberration characteristics are clearly shown by the reduction optical system of each Example. It has been improved. In addition, the F number is small, and a total bright imaging optical system (zoom lens system ZL) is realized. If the brightness of the photographic optical system is improved, the shutter speed can be increased, so that camera shake can be effectively suppressed.

Each embodiment shows a reduction example in which an APS-C format is imaged on a 4/3 type image pickup device, but is not limited thereto, and includes the following examples and other examples.
An example of imaging 135 full format on a 4 / 3-type image sensor,
An example in which an APS-C format is imaged on a 2/3 type image sensor,
An example of imaging a 645 format onto an image sensor that supports 135 format,
An example in which 66 format is imaged on an image sensor compatible with 135 format.

The lens block diagram of 1st Embodiment (Example 1). The lens block diagram of 2nd Embodiment (Example 2). The lens block diagram of 3rd Embodiment (Example 3). FIG. 6 is an aberration diagram of Example 1. FIG. 6 is an aberration diagram of Example 2. FIG. 6 is an aberration diagram of Example 3. FIG. 2 is a schematic diagram illustrating a schematic optical configuration example of a camera equipped with an imaging device. FIG. 3 is a lens configuration diagram of a main lens system commonly used in each embodiment (Examples 1 to 3). Aberration diagram of the main lens system alone.

Explanation of symbols

CU camera CB camera body (imaging device)
CL interchangeable lens ZL zoom lens system (photographing optical system)
ML Main lens system SL Reduction optical system GR1 First lens group GR2 Second lens group GR3 Third lens group GR4 Fourth lens group GR5 Fifth lens group ST Aperture LC Joint lens PT Parallel plane plate SY Shutter FR EVF finder SR Imaging element SS Photosensitive surface IM Image surface AX Optical axis

Claims (10)

The main lens system that forms an image of the subject is reduced without re-imaging the image formed by the main lens system, and has a screen size format smaller than the screen size of the format in which the main lens system forms an image. A reduction optical system that forms an image on an image sensor, comprising a meniscus cemented lens convex on the object side, and the cemented lens satisfies the following conditional expression (1):
-0.15 <(Rf−Rr) / (Rf + Rr) <0.15 (1)
However,
Rf: radius of curvature of the object side of the cemented lens,
Rr: radius of curvature of image side of cemented lens,
It is.   The reduction optical system according to claim 1, wherein the cemented lens is located closest to the object side. The reduction optical system according to claim 1 or 2, wherein the cemented lens is composed of two lenses and satisfies the following conditional expression (2):
0.001 <(n2-n1) / rc <0.002 (2)
However,
n1: Refractive index of the lens located on the object side of the cemented surface,
n2: refractive index of the lens located on the image side of the cemented surface,
rc: radius of curvature of the joint surface,
It is.   The reduction optical system according to claim 1, wherein the cemented lens includes a positive meniscus lens and a negative meniscus lens. The reduction optical system according to any one of claims 1 to 4, wherein the cemented lens satisfies the following conditional expression (3):
0.3 <tm / ts <0.5 (3)
However,
tm: core thickness of the cemented lens,
ts: axial thickness of the entire reduction optical system,
It is.   The reduction optical system according to claim 1, wherein the lens located closest to the image side has an aspherical surface.   The reduction optical system according to claim 1, wherein the number of constituent lenses of the cemented lens is two, and the number of constituent lenses of the entire system is three. The reduction optical system according to claim 1, wherein the following conditional expression (4) is satisfied:
rr <0.8 (4)
However,
rr: Reduction rate,
rr = SY / LY,
SY: 1/2 of the diagonal length of the image sensor screen,
LY: Maximum image height of the image formed only by the main lens system for the image sensor in the format in which the main lens system forms an image,
It is.   The reduction optical system according to claim 1, wherein the main lens system forms an image in a 135 system.   An imaging apparatus comprising: the reduction optical system according to claim 1, wherein the main lens system mounted in a replaceable manner is mountable.

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