JP2013015718A - Catadioptric system and imaging device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catadioptric system in which various aberrations are satisfactorily corrected over a wide wavelength range, and which has high optical performance in a wide observation area.SOLUTION: The catadioptric system includes a first imaging optical system that has a catadioptric part for collecting a light flux from an object and a second imaging optical system that receives the light flux from the first imaging optical system to form an intermediate image and has a refraction part for focusing the intermediate image on an image plane. In the catadioptric system, the first imaging optical system has first and second optical elements using rear surface reflection. The second imaging optical system has a twenty-first lens group having a positive refractive power, an aperture stop, and a twenty-second lens group having a positive refractive power. The first optical element, the second optical element and the twenty-second lens group are configured appropriately.

Description

  The present invention relates to a catadioptric optical system suitable for enlarging and observing a sample (object) and an imaging apparatus having the same.

  In the current pathological examination, a pathological specimen (sample) is directly observed with the human eye using an optical microscope. In recent years, a so-called virtual microscope that takes a pathological specimen as image data and observes it on a display has been used. In a virtual microscope, image data of a pathological specimen can be observed on a display, so that a plurality of persons can observe it simultaneously. In addition, the use of this virtual microscope has many advantages such as sharing image data with a distant pathologist for diagnosis. However, this method has a problem that it takes time to capture a pathological specimen and capture it as image data.

  One of the causes of time consuming is that a pathological specimen in a large imaging range must be captured as image data using a narrow imaging region of a microscope. When the imaging area of the microscope is small, it is necessary to capture a plurality of times or to capture a single image by connecting the images while scanning. 2. Description of the Related Art In order to reduce the number of times of image pickup and reduce the time for capturing image data, an optical system (image pickup optical system) having a wide image pickup area is required. In addition, in observing a pathological specimen, a wide imaging region is required, and at the same time, an optical system having high resolution in the visible region (wide wavelength region) is desired.

  A microscope objective lens suitable for observation of a living cell or the like that is composed of a refractive optical system and has excellent aberration reduction over the entire visible light region is known (Patent Document 1). Also, an ultra-wideband ultraviolet microscope imaging system having a high resolving power over a wide ultraviolet wavelength band using a catadioptric optical system for inspecting defects present in an integrated circuit or a photomask is known (Patent Document 2). . Further, a catadioptric optical system suitable for manufacturing a semiconductor element by exposing a fine pattern over a wide area is known (Patent Document 3).

Shoko 60-034737 Special table 2007-514179 Special WO00 / 039623

  In general, an imaging optical system for a virtual microscope is required to have high optical performance by satisfactorily correcting various aberrations such as chromatic aberration, spherical aberration, coma aberration, and astigmatism over a wide field of view.

  Although the microscope objective lens disclosed in Patent Document 1 reduces various aberrations well over the entire visible light region, the size of the observation region is not always sufficient. Moreover, although the wide-band microscope catadioptric imaging system disclosed in Patent Document 2 reduces aberrations well over a wide wavelength band and has high resolution, the size of the field of view is not always sufficient. Further, the catadioptric imaging optical system disclosed in Patent Document 3 has high resolution over a wide area, but the width of the wavelength range in which aberrations are well corrected is not necessarily sufficient.

  In order to observe a sample in an enlarged manner, it is effective to use an aspherical optical surface while appropriately selecting an optical material to be used in order to obtain a high optical performance over a wide wavelength range with a large observation region. However, even if an aspherical optical surface is used while simply selecting an optical material, it is difficult to satisfactorily correct various aberrations over a wide wavelength range and to obtain high optical performance over a wide observation region. In particular, in a catadioptric optical system, in order to obtain high optical performance in a wide wavelength region and in a wide observation region, an aspherical optical surface is appropriately positioned in the optical system while appropriately selecting an optical material that performs catadioptric refraction. It is important to provide

  An object of the present invention is to provide a catadioptric optical system that corrects various aberrations well over a wide wavelength range and has high optical performance in a wide observation region, and an imaging apparatus having the same.

The catadioptric optical system of the present invention includes a first imaging optical system including a catadioptric unit that collects a light beam from an object, and forms an intermediate image by receiving the light beam from the first imaging optical system. A catadioptric optical system having a second imaging optical system including a refracting unit that forms the intermediate image on an image plane,
The first imaging optical system includes a first optical element having a light transmission portion around the optical axis, a reflection portion provided on the object side surface of the outer peripheral portion of the light transmission portion, and a back reflection portion. A second optical element having a light transmission portion around the optical axis, a reflection portion provided on the image side surface of the outer peripheral portion of the light transmission portion, and a back reflection portion. The optical element and the second optical element are arranged so that the back surface reflection portions of each other face each other,
The second imaging optical system includes, in order from the object side to the image surface side, a 21st lens group having a positive refractive power, an aperture stop, and a 22nd lens group having a positive refractive power.
The light beam from the object is sequentially transmitted through the light transmission part of the first optical element, the back surface reflection part of the second optical element, the back surface reflection part of the first optical element, and the light transmission of the second optical element. Exits to the second imaging optical system through a section,
The back surface reflecting portion of the first optical element and the back surface reflecting portion of the second optical element are aspherical,
The materials of the first optical element and the second optical element are the same, the Abbe number and refractive index of the material are νdM and NdM, respectively, and the positive lens with the shortest focal length included in the twenty-second lens group is used. When the Abbe number and refractive index of the material are νd22p and Nd22p, respectively, and the Abbe number and refractive index of the negative lens material having the shortest focal length included in the 22nd lens group are νd22n and Nd22n, respectively.
νd22n <νd22p <νdM
NdM <Nd22p
NdM <Nd22n
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a catadioptric optical system that satisfactorily corrects various aberrations over a wide wavelength region and has high optical performance in a wide observation region.

It is a schematic sectional drawing which shows the structure of the imaging device of a present Example. 1 is a schematic diagram of a main part of a catadioptric optical system of Example 1. FIG. 2 is a lateral aberration diagram of the catadioptric optical system of Example 1. FIG. FIG. 6 is a schematic diagram of a main part of a catadioptric optical system of Example 2. 6 is a lateral aberration diagram of the catadioptric optical system of Example 2. FIG. FIG. 6 is a schematic diagram of a main part of a catadioptric optical system of Example 3. 6 is a lateral aberration diagram of the catadioptric optical system of Example 3. FIG. FIG. 6 is a schematic diagram of a main part of a catadioptric optical system of Example 4. 6 is a lateral aberration diagram of the catadioptric optical system of Example 4. FIG.

  Hereinafter, the catadioptric optical system of the present invention and an image pickup apparatus having the same will be described. The imaging apparatus 1000 of the present invention includes a light source unit 101, an illumination optical system 102 that illuminates an object 103 with a light beam from the light source unit 101, and a catadioptric optical system 104 that forms an image of the object 103. Further, an image sensor 105 that photoelectrically converts an object image formed by the catadioptric optical system 104, an image processing system 106 that generates image information from data from the image sensor 105, and image data generated by the image processing system 106 are displayed. Display means 107. In addition, a storage unit 110 that stores image information processed by the image processing system 106 is provided.

  The catadioptric optical system 104 of the present invention receives the first imaging optical system G1 including a catadioptric unit that collects the light beam from the object and the light beam from the first imaging optical system G1, and forms an intermediate image IM. And a second imaging optical system G2 including a refracting unit that forms an intermediate image IM on the image plane. Further, the catadioptric optical system 104 of the present invention images a visual field region having a diameter of 3 mm or more on the surface of the object 103.

  FIG. 1 is a schematic diagram of a main part of an imaging apparatus according to the present invention. FIG. 2 is a schematic view of the essential portions of Embodiment 1 of the catadioptric optical system of the present invention. FIG. 3 is a lateral aberration diagram of the catadioptric optical system of Example 1 of the present invention. FIGS. 4 and 5 are a schematic diagram and a lateral aberration diagram of the essential portions of Embodiment 2 of the catadioptric optical system of the present invention. FIGS. 6 and 7 are a schematic diagram and a lateral aberration diagram of the essential portions of Embodiment 3 of the catadioptric optical system of the present invention. FIGS. 8 and 9 are a schematic diagram and a lateral aberration diagram of the essential portions of Embodiment 4 of the catadioptric optical system of the present invention.

  Hereinafter, with reference to FIG. 1, the structure of the imaging device 1000 having the catadioptric optical system 104 of the present invention will be described. The imaging apparatus 1000 collects the light from the light source unit 101 by the illumination optical system 102 and uniformly illuminates the object 103 as a sample. The light used at this time is visible light (for example, light having a wavelength of 400 nm to 700 nm, including at least light in a wavelength range of 486 nm to 656 nm). The imaging optical system includes a catadioptric optical system 104 having a reflecting part and a refracting part for forming an image of the object 103 on the image sensor 105.

  Data (image information) acquired by the image sensor 105 is generated by the image processing system 106, and the generated image data is displayed on the display means 107 or the like. In addition, it is stored in the storage means 110. The image processing system 106 corrects aberrations that could not be corrected by the catadioptric optical system 104, or connected image data at different imaging positions to combine them into a single piece of image data. Is done.

  The configuration of the catadioptric optical system 104 of the present invention will be described with reference to the lens cross-sectional views of FIGS. 2, 4, 6 and 8. 2, 4, 6, and 8, 104 is a catadioptric optical system, and 103 is an object surface as a sample. Reference numeral 105 denotes an image sensor, which is disposed on the image plane. AS is an aperture stop, and IM is an intermediate image. AX is the optical axis of the catadioptric optical system 104.

  The catadioptric optical system 104 includes a first imaging optical system G1 including a reflective surface that converts a light beam from the object 103 into focused light. Further, it receives the focused light from the first imaging optical system G1, forms an intermediate image IM on a predetermined surface, and includes a refractive surface that forms the intermediate image IM on the image sensor 105, an aperture stop AS, and a light shielding portion SH. A second imaging optical system G2 is included.

  The first imaging optical system G1 includes a first optical element (Mangin mirror) M1 and a second optical element (Mangin mirror) M2 in order from the object side. The second imaging optical system G2 includes a twenty-first lens group G21, an aperture stop AS, and a twenty-second lens group G22 in order from the object side.

  Here, the aperture stop AS may be provided on the first imaging optical system G1 side. In the lens cross-sectional view, an on-axis light beam and an off-axis light beam from the object plane 103 to the image plane 105 are schematically shown. The first optical element M1 of the first imaging optical system G1 has a convex surface on the object 103 side, a light transmitting portion M1T having a positive refractive power around the optical axis, and the object side of the peripheral portion (outer peripheral side). The surface M1a is provided with a reflective film to form a back surface reflecting portion. The second optical element M2 has a meniscus shape with a concave surface facing the object side.

  Then, a light transmissive portion M2T having a negative refractive power is provided around the optical axis, and a reflective film is applied to the image-side surface M2b of the peripheral portion to form a back surface reflective portion. The first optical element M1 and the second optical element M2 are arranged so that the back surface reflecting portions M1a and M2b face each other. In the second imaging optical system G2, a light shielding plate SH that shields a light beam near the optical axis among light beams from the object 103 and prevents the light from entering the image sensor 105 is disposed at or near the aperture stop AS.

  In the catadioptric optical system 104, the light beam emitted from the illumination optical system 102 and emitted from the object 103 passes through the central transmission part M1T of the first optical element M1. Thereafter, the light enters the refracting surface M2a of the second optical element M2, is then reflected by the back surface reflecting portion M2b, passes through the refracting surface M2a, and enters the refracting surface M1b of the first optical element M1. Then, it reflects with the back surface reflection part M1a of the 1st optical element M1.

  Then, it passes through the refractive surface M1b, passes through the central transmission part M2T of the second optical element M2, and exits toward the second imaging optical system G2. Further, by using the same optical material as the optical material of the first and second optical elements M1 and M2 of the first imaging optical system G1, the secondary spectrum generated in the first imaging optical system G1 is reduced. The chromatic aberration is corrected well.

  Here, both the back surface reflection part M1a of the first optical element M1 and the back surface reflection part M2b of the second optical element M2 included in the first imaging optical system G1 are formed of an aspherical shape. As a result, spherical aberration, coma and the like are favorably corrected while suppressing the occurrence of chromatic aberration. Further, even with a high NA (aperture ratio), various aberrations are satisfactorily reduced over a wide visible wavelength band. Note that the aspheric shape may be one of the rear surface reflecting surfaces M1a and M2b.

  In addition, the back surface reflecting portion M1a of the first optical element M1 and the back surface reflecting portion M2b of the second optical element M2 are both reflecting surfaces having positive refractive power. As a result, the increase in Petzval sum when the positive refractive power of the lens of the second imaging optical system G2 is increased to shorten the total length of the optical system is reduced. This is because the effect on the Petzval sum is opposite between the reflecting surface and the refracting surface. The second imaging optical system G2 receives the focused light from the first imaging optical system G1, and forms an intermediate image on a predetermined surface. It has a 21st lens group (lens group) G21 having a positive refractive power for condensing light from the intermediate image IM, and an 22nd lens group (lens group) G22 having an aperture stop AS and a positive refractive power.

  The object 103 is enlarged and imaged on the image sensor 105. The light-shielding part SH does not reflect the light from the object 103 by the first optical element M1 and the second optical element M2, and the central transmission part M1T of the first and second optical elements M1 and M2. , And reaching the image sensor 105 directly through M2T.

  The twenty-second lens group G22 includes lenses (lens components) L1 to L8 (lens components) L8 or lenses L1 to L9.

In the present embodiment, the materials of the first optical element M1 and the second optical element M2 are the same, and the Abbe number and refractive index of the materials are νdM and NdM, respectively. The Abbe number and refractive index of the material of the positive lens (lens A) having the shortest focal length included in the 22nd lens group G22 are denoted by νd22p and Nd22p, respectively. The Abbe number and refractive index of the material of the negative lens (lens B) with the shortest focal length included in the 22nd lens group G22 are denoted by νd22n and Nd22n, respectively. At this time,
νd22n <νd22p <νdM (1)
NdM <Nd22p (2)
NdM <Nd22n (3)
The following conditional expression is satisfied.

  Conditional expression (1) is mainly for correcting axial chromatic aberration. If the left inequality sign in conditional expression (1) does not hold, axial chromatic aberration remains, making it difficult to obtain good optical performance. When the right inequality sign does not hold, the secondary spectrum generated in the first imaging optical system G1 becomes large, and it is difficult to correct it well by the second imaging optical system G2.

  Conditional expression (2) and conditional expression (3) are conditions for reducing the amount of spherical aberration generated mainly in the lenses A and B of the second imaging optical system. If conditional expressions (2) and (3) do not hold, it will be difficult to correct spherical aberration, and it will also be difficult to correct field curvature.

  In each embodiment, the lens B is disposed closer to the image side than the lens A. Accordingly, since the negative lens B is arranged after the light beam is focused by the positive lens A, the effective diameter of the negative lens B can be reduced, and the absolute value of the power of the negative lens B can be increased. Accordingly, the off-axis light beam can be greatly diverged by the negative lens B, and the observation field of view can be easily enlarged.

  The second imaging optical system G2 includes an aspheric lens (optical element) (negative lens B) having a negative refractive power including an aspheric concave surface in which the absolute value of the radius of curvature decreases from the lens center to the lens periphery. Have.

  In each embodiment, the image-side surface of the fourth lens L4 has an aspherical shape. The fourth lens L4 corresponds to the negative lens B. The second imaging optical system G2 includes a concave aspherical surface whose absolute value of the radius of curvature decreases as the distance from the optical axis increases, so that off-axis rays are greatly displaced away from the optical axis. This makes it easy to enlarge the observation field of view.

  Further, at least one concave aspheric lens is provided in the 22nd lens group G22 on the image side of the aperture stop AS. This facilitates large displacement of off-axis rays in the direction away from the optical axis, and facilitates expansion of the observation field. This also facilitates downsizing of the lens outer shape and the entire lens length.

In each embodiment, the refractive indexes and Abbe numbers of the materials of the first optical element M1 and the second optical element M2 are νdM and NdM, respectively. At this time,
−0.001 <(NdM−1.5) / νdM <0.002 (4)
The following conditional expression is satisfied.

  Conditional expression (4) is for reducing chromatic aberration occurring in the first imaging optical system G1. If the lower limit value of conditional expression (4) is not reached, suitable optical materials are reduced. If the upper limit of conditional expression (4) is exceeded, the remaining chromatic aberration increases, which is not preferable.

  In the catadioptric optical system of each embodiment, the same optical material is used as the optical material of the two optical elements M1 and M2 constituting the first imaging optical system G1. As a result, the value of the secondary spectrum generated in the first imaging optical system G1 is reduced, and it is easy to satisfactorily correct chromatic aberration.

  In each embodiment, it is more preferable to satisfy one or more of the following conditions. Let the partial dispersion ratio of the material of the second optical element M2 be θgFM2. Let θgF22 be the partial dispersion ratio of the material of the positive lens (lens A) with the shortest focal length included in the twenty-second lens group G22. The focal lengths of the first imaging optical system G1 and the second imaging optical system G2 are f1 and f2, respectively. The focal lengths of the 21st lens group G21 and the 22nd lens group G22 are fG21 and fG22, respectively. At this time, it is preferable to satisfy one or more of the following conditions.

| ΘgF22−θgFM2 | ≦ 0.03 (5)
0.005 <| f1 / f2 | <0.800 (6)
0.005 <| fG21 / f2 | <0.500 (7)
0.01 <| fG22 / f2 | <1.80 (8)
0.1 <fG21 / fG22 <0.8 (9)
Here, the partial dispersion ratio and the Abbe number of the material of the optical element (lens) used in this example are as follows. The refractive indexes of the Fraunhofer line for g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng, NF, Nd, and NC, respectively. To do. The partial dispersion ratio θgF for the Abbe number νd, g-line and F-line is as follows.

νd = (Nd−1) / (NF−NC)
θgF = (Ng−NF) / (NF−NC)
Conditional expression (5) is for correcting the chromatic aberration generated in the first imaging optical system G1 by the second imaging optical system G2 over the entire visible region covering the wavelength range of 486 nm to 656 nm. Satisfying conditional expression (5) facilitates obtaining color information of an object over the entire visible region without losing resolution. Deviating from the range of conditional expression (5) is not preferable because the secondary spectrum of chromatic aberration increases.

  In the catadioptric optical system of each embodiment, the observation visual field region on the object 103 is set to φ3 mm or more. If the field of view is less than this, the number of times of imaging when the entire sample is divided and imaged increases, and the time taken for the entire imaging becomes long. By setting the field of view to φ3 mm or more, the number of division imaging is reduced, so that the imaging time can be easily reduced. Further, it is more preferable that the visual field area is φ10 mm or more, and batch imaging of the sample becomes possible, so that the imaging time can be greatly shortened.

  Conditional expression (6) relates to the ratio of the focal lengths of the first imaging optical system G1 and the second imaging optical system G2. If the upper limit of conditional expression (6) is exceeded and the focal length of the first image-forming optical system G1 becomes too long, pupil dropout increases and image degradation occurs, or the size of G1 becomes too large. Absent. If the absolute value of the focal length of the first imaging optical system G1 is too small beyond the lower limit value of conditional expression (6), it is difficult to correct chromatic aberration and curvature of field, which is not preferable.

  Conditional expression (7) relates to the ratio of the focal lengths of the 21st lens group G21 and the second imaging optical system G2. If the upper limit of conditional expression (7) is exceeded and the focal length of the 21st lens group G21 becomes too long, the total length of the optical system becomes too long, which is not preferable. If the absolute value of the focal length of the twenty-first lens group G21 is too small beyond the lower limit value of conditional expression (7), the lens arrangement space in the twenty-first lens group becomes narrow, and the lens may not be arranged. This is not preferable.

  Conditional expression (8) relates to the ratio of the focal lengths of the 22nd lens group G22 and the second imaging optical system G2. If the upper limit of conditional expression (8) is exceeded and the focal length of the 22nd lens group G22 becomes too long, the total length of the optical system becomes too long, which is not preferable. Further, if the absolute value of the focal length of the 22nd lens group G22 becomes too small beyond the lower limit value of the conditional expression (8), the lens arrangement space in the 21st lens group G21 may become too narrow to arrange the lens. This is not preferable.

  Conditional expression (9) relates to the ratio of the focal lengths of the 21st lens group G21 and the 22nd lens group G22. If the upper limit of conditional expression (9) is exceeded and the focal length of the twenty-first lens group G21 becomes too long compared to the focal length of the twenty-second lens group G22, the magnification of the optical system becomes too small and a desired magnification (for example, 4 to 12 times). If the lower limit of conditional expression (9) is exceeded and the focal length of the twenty-first lens group G21 becomes too short compared to the focal length of the twenty-second lens group G22, the magnification of the optical system becomes too large, and a desired magnification (for example, 4 to 12 times).

The second imaging optical system sets the focal length of an aspherical lens having an aspherical lens having a negative refractive power including an aspherical concave surface in which the absolute value of the radius of curvature decreases from the lens center to the lens periphery, fL4, The paraxial radii of curvature of the object-side and image-side surfaces of the aspheric lens are RL41 and RL42, respectively, and the focal length of the 22nd lens group G22 is fG22. At this time,
RL41 / RL42 <−1.0 (10)
−1.0 <fL4 / fG22 <−0.1 (11)
The following conditional expression is satisfied.

  Conditional expression (10) defines the lens shape of the aspherical lens. By satisfying conditional expression (10), the radius of curvature of the image side (second surface side) surface is made smaller than the radius of curvature of the object side (first surface side) surface of the aspherical lens. As a result, off-axis rays emitted from the refracting surface on the image side of the aspherical lens can be greatly repelled, and the observation field is expanded.

  Conditional expression (11) defines the power (refractive power) of the aspherical lens. By satisfying conditional expression (11), it becomes easy to increase the power of the aspherical lens, the off-axis rays emitted from the aspherical lens can be greatly repelled, and the viewing field is expanded. . If the lower limit of conditional expression (11) is not reached, the power of the aspherical lens is too small, and it becomes difficult to expand the observation field. If the upper limit of conditional expression (11) is exceeded, the power of the aspherical lens will be too great, making it difficult to correct aberrations. More preferably, the numerical ranges of conditional expressions (10) and (11) are set as follows.

−10.00 <RL41 / RL42 <−1.05 (10a)
−0.8 <fL4 / fG22 <−0.2 (11a)
As described above, according to each embodiment, it is possible to obtain a catadioptric optical system having a wide field region with high NA and reduced aberration over the entire visible light region.

Next, the catadioptric optical system of each example is described.
[Example 1]
In the first embodiment, the first imaging optical system G1 includes a first optical element (Mangin mirror) M1 and a second optical element (Mangin mirror) M2. The second imaging optical system G2 includes a twenty-first lens group G21, a twenty-second lens group G22, and an aperture stop AS. The twenty-second lens group G22 includes lenses (optical elements) L1 to L8. The second imaging optical system G2 uses a lens made of three or more kinds of optical materials.

  An aspherical surface is used for the fourth fourth lens L4 counted from the object side of the 22nd lens group G22 located on the image side of the aperture stop AS. The fourth lens L4 is a biconcave negative lens (lens B), and the image-side concave surface (the 30th surface in Table 1) has an aspherical shape. This aspherical surface is shaped such that the absolute value of the radius of curvature decreases as the distance from the optical axis increases within the cross section including the optical axis. This aspherical surface makes it easy to displace the off-axis light beam in the direction away from the optical axis, thereby facilitating the expansion of the observation field.

  This also contributes to shortening the total lens length and reducing the lens diameter on the object side of the aspherical surface. Furthermore, the fact that the fourth lens L4 has a biconcave shape and that the fourth lens L4 is disposed at a place where the effective beam diameter is smaller than the front and rear lenses also displaces the off-axis light beam in the direction away from the optical axis. This makes it easier to enlarge the observation field of view.

  In the aspherical surface on the image side of the fourth lens L4 of the present embodiment, the sag amount of the aspherical surface with respect to the spherical surface having the paraxial radius of curvature is 1.2 mm at the effective diameter end.

  In the present embodiment, the ratio of paraxial radii of curvature of both surfaces of the fourth lens L4 is RL41 / RL42 = −2.128, which satisfies the conditional expression (10). The ratio of the focal length fL4 of the fourth lens L4 and the focal length fG22 of the twenty-second lens group G22 is fL4 / fG22 = −0.522, which satisfies the conditional expression (11). In the present embodiment, the positive lens A having the shortest focal length among the positive lenses located on the image side from the aperture stop AS is the biconvex second lens L2. The partial dispersion ratio θgF22 of the material of the second lens L2 is 0.548.

  On the other hand, the partial dispersion ratio θgFM2 of the material of the second optical element M2 is 0.530. Therefore, | θgF22−θgFM2 | = 0.018, which satisfies the conditional expression (5). For this reason, it is easy to reduce the secondary spectrum.

  In the catadioptric optical system 104 of Example 1, the numerical aperture on the object side is 0.7, the magnification is 4 times, the object height Y at the object 103 is 10.6 mm, and the observation field area is φ (diameter) 21. .2 mm. The observation visual field region satisfies φ3 mm or more and also satisfies φ10 mm or more. On the other hand, the image height Y ′ at the image plane 105 is 42.4 mm, and the image plane size is a diameter φ84.8 mm. Both the object side and the image side are almost telecentric, and the ratio of the void in the pupil is suppressed to 20% or less in terms of the area ratio. Further, the wavefront aberration in white light covering the visible wavelength range of 486 nm to 656 nm is suppressed to 50 mλrms or less.

  FIG. 3 shows lateral aberrations on the image plane (imaging device surface) of Example 1, and the aberrations are well corrected in a wide wavelength band in the visible range both on and off the axis. The value of conditional expression (4) regarding the optical materials of the first and second optical elements M1 and M2 is −0.0002, which is within the range of conditional expression (4).

[Example 2]
The catadioptric optical system of Example 2 will be described. Portions that are not particularly described are the same as those in the first embodiment.

  The first and second imaging optical systems G1 and G2 constituting the catadioptric optical system 104, and the configurations and optical functions of the 21st lens group G21 and the 22nd lens group G22 constituting the second imaging optical system G2 are examples. It is almost the same as 1. An aspherical surface is used for the fourth lens L4 of the twenty-second lens group G22 located on the image side of the aperture stop AS. The fourth lens L4 is a biconcave negative lens (lens B), and the image-side concave surface (the 31st surface of Numerical Example 2) has an aspherical shape.

  This aspherical surface is shaped such that the absolute value of the radius of curvature decreases as the distance from the optical axis increases within the cross section including the optical axis. The fourth lens L4 is disposed at a location where the effective beam diameter is smaller than the front and rear lenses.

  In the aspherical surface on the image side of the fourth lens L4 of the present embodiment, the sag amount of the aspherical surface with respect to the spherical surface having the paraxial radius of curvature is 0.11 mm at the effective diameter end. In this embodiment, the value of conditional expression (10) is RL41 / RL42 = −8.081, which satisfies conditional expression (10). Moreover, since the value of fL4 / fG22 in the conditional expression (11) is −0.402, the conditional expression (11) is satisfied.

  In the present embodiment, the positive lens A having the shortest focal length in the 22nd lens group G22 is a biconvex third lens L3. The partial dispersion ratio θgF22 of the material of the third lens L3 is 0.546, while the partial dispersion ratio θgFM2 of the material of the second optical element M2 is also 0.546. Therefore, | θgF22−θgFM2 | = 0.000, which satisfies the conditional expression (5).

  In the catadioptric optical system 104 of Example 2, the numerical aperture on the object side is 0.7, the magnification is 4 times, the object height Y at the object 103 is 10.6 mm, and the observation field area is φ21.2 mm. is there. The observation visual field region satisfies φ3 mm or more and also satisfies φ10 mm or more. On the other hand, the image height Y ′ on the image plane 105 is 42.4 mm, and the image plane size is φ84.8 mm. Both the object side and the image side are almost telecentric, and the ratio of the void in the pupil is suppressed to 20% or less in terms of the area ratio. Further, the wavefront aberration in white light covering the visible wavelength range of 486 nm to 656 nm is suppressed to 60 mλrms or less.

  FIG. 5 shows lateral aberrations on the image surface (imaging device surface) of Example 2, and aberrations are well corrected in a wide wavelength band in the visible range both on and off the axis. The value of conditional expression (4) regarding the optical materials of the first and second optical elements M1 and M2 is +0.0003, which is within the range of conditional expression (4).

[Example 3]
The catadioptric optical system of Example 3 will be described. Portions that are not particularly described are the same as those in the first embodiment.

  The first and second imaging optical systems G1 and G2 constituting the catadioptric optical system 104, and the configurations and optical functions of the 21st lens group G21 and the 22nd lens group G22 constituting the second imaging optical system G2 are examples. It is almost the same as 1. An aspherical surface is used for the fourth lens L4 of the twenty-second lens group G22 located on the image side of the aperture stop AS. The fourth lens L4 is a biconcave negative lens (lens B), and the image-side concave surface (the 31st surface of Numerical Example 3) has an aspherical shape.

  This aspherical surface is shaped such that the absolute value of the radius of curvature decreases as the distance from the optical axis increases within the cross section including the optical axis. The fourth lens L4 is disposed at a location where the effective beam diameter is smaller than the front and rear lenses.

  In the aspherical surface on the image side of the fourth lens L4 of the present embodiment, the sag amount of the aspherical surface with respect to the spherical surface having the paraxial curvature radius is 0.87 mm at the effective diameter end. In this embodiment, the value of conditional expression (10) is RL41 / RL42 = −4.402, which satisfies conditional expression (10). Further, since the value of fL4 / fG22 in the conditional expression (11) is −0.387, the conditional expression (11) is satisfied.

  In the present embodiment, the positive lens A having the shortest focal length in the 22nd lens group G22 is a biconvex third lens L3. The partial dispersion ratio θgF22 of the material of the third lens L3 is 0.546, while the partial dispersion ratio θgFM2 of the material of the second optical element M2 is also 0.546. Therefore, | θgF22−θgFM2 | = 0.000, which satisfies the conditional expression (5).

  In the catadioptric optical system 104 of Example 3, the numerical aperture on the object side is 0.7, the magnification is 5.9 times, the object height Y at the object 103 is 10.6 mm, and the observation field area is φ21. 2 mm. The observation visual field region satisfies φ3 mm or more and also satisfies φ10 mm or more. On the other hand, the image height Y ′ on the image plane 105 is 62.5 mm, and the image plane size is a diameter φ125 mm. Both the object side and the image side are almost telecentric, and the ratio of the void in the pupil is suppressed to 20% or less in terms of the area ratio. Further, the wavefront aberration in white light covering the visible wavelength range of 486 nm to 656 nm is suppressed to 60 mλrms or less.

  FIG. 7 shows lateral aberrations on the image plane (imaging device surface) of Example 3, and the aberrations are corrected well in a wide wavelength band in the visible range both on and off the axis. The value of conditional expression (4) regarding the optical materials of the first and second optical elements M1 and M2 is +0.0003, which is within the range of conditional expression (4).

[Example 4]
The catadioptric optical system 104 of Example 4 will be described. Portions that are not particularly described are the same as those in the first embodiment.

  The first and second imaging optical systems G1 and G2 constituting the catadioptric optical system 104, and the configurations and optical functions of the 21st lens group G21 and the 22nd lens group G22 constituting the second imaging optical system G2 are examples. It is almost the same as 1. In the present embodiment, the twenty-second lens group G22 is different in that it is composed of lenses L1 to L9.

  An aspherical surface is used for the fourth lens L4 of the twenty-second lens group G22 located on the image side of the aperture stop AS. The fourth lens L4 is a biconcave negative lens (lens B), and the image-side concave surface (the 33rd surface of Numerical Example 4) has an aspherical shape. This aspherical surface is shaped such that the absolute value of the radius of curvature decreases as the distance from the optical axis increases within the cross section including the optical axis. The fourth lens L4 is disposed at a location where the effective beam diameter is smaller than the front and rear lenses. In the aspherical surface on the image side of the fourth lens L4 of the present embodiment, the sag amount of the aspherical surface with respect to the spherical surface having the paraxial radius of curvature is 2.06 mm at the effective diameter end.

  In this embodiment, the value of conditional expression (10) is RL41 / RL42 = −1.175, which satisfies conditional expression (10). Further, since the value of fL4 / fG22 in the conditional expression (11) is −0.463, the conditional expression (11) is satisfied. In the present embodiment, the positive lens A having the shortest focal length in the twenty-second lens group G22 is a biconvex positive lens L3. The partial dispersion ratio θgF22 of the material of the third lens L3 is 0.560, while the partial dispersion ratio θgFM2 of the material of the second optical element M2 is 0.546. Therefore, | θgF22−θgFM2 | = 0.014, which satisfies the conditional expression (5).

  In the catadioptric optical system 104 of Example 4, the numerical aperture on the object side is 0.7, the magnification is 11.9 times, the object height Y at the object 103 is 10.6 mm, and the observation field area is φ21. 2 mm. The observation visual field region satisfies φ3 mm or more and also satisfies φ10 mm or more. On the other hand, the image height Y ′ on the image plane 105 is 126 mm, and the image plane size is a diameter φ252 mm. Both the object side and the image side are almost telecentric, and the ratio of the void in the pupil is suppressed to 20% or less in terms of the area ratio. Further, the wavefront aberration in white light covering the visible wavelength range of 486 nm to 656 nm is suppressed to 40 mλrms or less.

  FIG. 9 shows lateral aberrations on the image plane (imaging element surface) of Example 4, and the aberrations are well corrected in a wide wavelength band on the axis and off the axis. The value of conditional expression (4) regarding the optical materials of the first and second optical elements M1 and M2 is +0.0003, which is within the range of conditional expression (4).

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention may be applied to a catadioptric optical system in which the aperture stop AS is disposed between the first and second optical elements M1 and M2.

  Further, for example, even in an optical system in which an actual aperture stop is not disposed in the second imaging optical system, as long as the optical system is configured so that the chief ray crosses the optical axis in the second imaging optical system. The present invention can be applied by regarding the intersection of the principal ray and the optical axis as the aperture stop position. Further, the present invention can be applied to an imaging apparatus that scans a large screen and an imaging apparatus that does not scan.

  Hereinafter, numerical examples of the respective examples will be shown. The surface number is the order of the optical surfaces counted from the object surface (sample surface) to the image surface. r is the radius of curvature of the i-th optical surface. d is the i-th and (i + 1) -th interval (the sign is positive when measured from the object side to the image plane side (when light travels) and negative in the reverse direction). Nd and νd indicate the refractive index and Abbe number of the material for a wavelength of 587.6 nm, respectively.

  The shape of the aspheric surface is represented by a general aspherical expression shown in the following expression. In the following formula, Z is the coordinate in the optical axis direction, c is the curvature (the reciprocal of the radius of curvature r), h is the height from the optical axis, k is the cone coefficient, A, B, C, D, E, F, G, H, J... Are aspherical coefficients of 4th order, 6th order, 8th order, 10th order, 12th order, 14th order, 16th order, 18th order, 20th order,.

“ ^EX ” means “10 ^−X ”. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.

[Numerical Example 1]

Surface number r d Nd νd
Object plane ∞ 13.39
1 736.61 24.08 1.4875 70.2
2 -9661.75 97.67
3 -118.31 9.38 1.4875 70.2
4 -170.29 -9.38 1.4875 70.2 Reflecting surface
5 -118.31 -97.67
6 -9661.75 -24.08 1.4875 70.2
7 736.61 24.08 1.4875 70.2 Reflecting surface
8 -9661.75 97.67
9 -118.31 9.38 1.4875 70.2
10 -170.29 10.00
11 -458.41 5.89 1.6425 58.4
12 -119.83 3.29
13 -54.79 5.00 1.6477 33.8
14 -998.82 11.55 1.6204 60.3
15 -54.52 0.73
16 79.77 7.04 1.6204 60.3
17 483.74 34.05
18 59.02 11.53 1.7620 40.1
19 109.31 0.50
20 65.70 20.52 1.4875 70.4
21 -118.81 24.84
22 ∞ 20.00 Aperture stop
23 -49.26 33.31 1.8052 25.4
24 -79.27 0.50
25 122.53 26.67 1.6385 55.4
26 -86.46 0.50
27 57.90 15.51 1.4875 70.4
28 78.67 17.39
29 -124.44 5.74 1.5673 42.9
30 58.49 15.64
31 -147.56 8.96 1.7570 47.8
32 -75.81 11.90
33 -59.72 8.10 1.6034 38.0
34 272.55 9.12
35 -178.62 19.27 1.7205 34.7
36 -68.40 0.50
37 1362.89 16.90 1.5111 60.5
38 -142.77 10.50

(Aspheric coefficient)
Face number
1,7 k = 0.00E + 00 A = 6.72E-09 B = 6.14E-14 C = 2.27E-17 D = -9.74E-22
E = 1.18E-25 F = -5.31E-30 G = 2.75E-34 H = 0.00E + 00 J = 0.00E + 00
4,10 k = 0.00E + 00 A = 5.58E-09 B = 2.43E-13 C = 9.28E-18 D = 1.61E-22
E = 2.65E-26 F = -9.34E-31 G = 5.28E-35 H = 0.00E + 00 J = 0.00E + 00
17 k = 0.00E + 00 A = 6.69E-07 B = -6.19E-11 C = 3.77E-14 D = -1.71E-16
E = 1.20E-19 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
19 k = 0.00E + 00 A = 9.53E-07 B = 2.89E-10 C = 2.54E-14 D = -5.14E-18
E = 5.40E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
26 k = 0.00E + 00 A = 4.94E-07 B = 1.25E-11 C = 2.56E-15 D = -9.15E-19
E = 1.58E-22 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
30 k = 0.00E + 00 A = 1.32E-06 B = 1.83E-10 C = -1.01E-13 D = -2.77E-18
E = -2.19E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
38 k = 0.00E + 00 A = -6.34E-07 B = 9.02E-12 C = -3.52E-14 D = 9.31E-18
E = -1.34E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00

[Numerical Example 2]
Surface number r d Nd νd
Object plane ∞ 13.39
1 914.69 10.00 1.5182 58.9
2 -3746.87 108.16
3 -119.33 10.30 1.5182 58.9
4 -171.61 -10.30 1.5182 58.9 Reflecting surface
5 -119.33 -108.16
6 -3746.87 -10.00 1.5182 58.9
7 914.69 10.00 1.5182 58.9 Reflecting surface
8 -3746.87 108.16
9 -119.33 10.30 1.5182 58.9
10 -171.61 10.50
11 -166.20 6.28 1.6031 60.6
12 -78.85 2.58
13 -59.36 5.00 1.6989 30.1
14 165.70 8.66 1.5831 59.4
15 -60.59 12.89
16 91.17 32.10 1.7440 44.8
17 32606.75 20.79
18 64.72 23.38 1.7440 44.8
19 -93.02 13.04 1.6989 30.1
20 924.91 8.49
21 -124.32 5.86 1.7200 50.2
22 -106.70 24.20
23 ∞ 38.00 Aperture stop
24 286.56 12.00 1.7200 50.2
25 -348.88 0.50
26 482.47 15.14 1.7618 26.5
27 -133.69 4.39
28 69.00 21.22 1.6230 58.2
29 -674.14 3.68
30 -351.10 5.00 1.6989 30.1
31 43.45 52.65
32 -48.16 5.00 1.5174 52.4
33 122.81 2.31
34 138.39 17.97 1.7200 50.2
35 -156.35 0.50
36 149.52 8.70 1.7440 44.8
37 301.27 19.30
38 245.18 18.02 1.7440 44.8
39 -537.83 10.00

(Aspheric coefficient)
Face number
1,7 k = 0.00E + 00 A = 7.23E-09 B = 2.58E-13 C = 4.55E-18 D = -3.30E-23
E = 1.43E-25 F = -1.32E-29 G = 6.00E-34 H = 0.00E + 00 J = 0.00E + 00
4,10 k = 0.00E + 00 A = 4.67E-09 B = 2.22E-13 C = 9.16E-18 D = 2.18E-22
E = 1.80E-26 F = -1.31E-31 G = 2.63E-35 H = 0.00E + 00 J = 0.00E + 00
17 k = 0.00E + 00 A = 4.59E-07 B = 5.81E-11 C = 4.24E-15 D = 5.46E-18
E = -2.20E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
20 k = 0.00E + 00 A = 1.16E-06 B = 2.27E-10 C = 7.60E-14 D = -1.40E-17
E = 1.70E-20 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
27 k = 0.00E + 00 A = 2.36E-07 B = -7.77E-12 C = -6.93E-16 D = 3.97E-19
E = -1.99E-23 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
31 k = 0.00E + 00 A = -1.17E-08 B = 2.80E-11 C = 1.26E-13 D = -8.64E-17
E = 9.63E-20 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
32 k = 0.00E + 00 A = 9.61E-07 B = 3.85E-10 C = 2.59E-13 D = -4.59E-17
E = 7.72E-20 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00

[Numerical Example 3]
Surface number r d Nd νd
Object plane ∞ 13.39
1 894.62 10.00 1.5182 58.9
2 -3308.82 107.32
3 -121.36 10.05 1.5182 58.9
4 -171.86 -10.05 1.5182 58.9 Reflecting surface
5 -121.36 -107.32
6 -3308.82 -10.00 1.5182 58.9
7 894.62 10.00 1.5182 58.9 Reflecting surface
8 -3308.82 107.32
9 -121.36 10.05 1.5182 58.9
10 -171.86 10.50
11 -149.75 6.17 1.6031 60.6
12 -72.32 2.52
13 -57.02 5.00 1.6989 30.1
14 221.17 8.36 1.5831 59.4
15 -61.63 7.69
16 84.63 23.57 1.7440 44.8
17 1668.62 20.73
18 63.81 22.15 1.7440 44.8
19 -82.25 14.70 1.6989 30.1
20 -10648.41 1.10
21 66.41 7.06 1.7200 50.2
22 66.75 28.00
23 ∞ 35.87 Aperture stop
24 224.09 14.11 1.7200 50.2
25 -304.53 0.50
26 18489.00 28.22 1.7618 26.5
27 -137.85 9.00
28 78.13 23.03 1.6230 58.2
29 -431.72 7.18
30 -245.67 5.00 1.6989 30.1
31 55.81 54.58
32 -56.99 5.00 1.5 174 52.4
33 157.80 5.26
34 216.64 15.80 1.7200 50.2
35 -256.66 30.52
36 203.73 26.28 1.7440 44.8
37 448.63 14.60
38 769.29 16.73 1.7440 44.8
39 -262.77 10.00

(Aspheric coefficient)
Face number
1,7 k = 0.00E + 00 A = 6.23E-09 B = 1.93E-13 C = 1.31E-17 D = -1.14E-21
E = 2.38E-25 F = -1.87E-29 G = 7.29E-34 H = 0.00E + 00 J = 0.00E + 00
4,10 k = 0.00E + 00 A = 4.61E-09 B = 2.16E-13 C = 9.13E-18 D = 1.60E-22
E = 2.52E-26 F = -6.70E-31 G = 4.31E-35 H = 0.00E + 00 J = 0.00E + 00
17 k = 0.00E + 00 A = 6.04E-07 B = 7.98E-11 C = -4.25E-14 D = 2.72E-17
E = -2.20E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
20 k = 0.00E + 00 A = 1.22E-06 B = 2.94E-10 C = 9.95E-14 D = -2.62E-17
E = 2.70E-20 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
27 k = 0.00E + 00 A = 1.45E-07 B = 1.45E-11 C = -2.48E-15 D = 4.29E-19
E = -1.62E-23 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
31 k = 0.00E + 00 A = 4.76E-07 B = 7.53E-11 C = 7.80E-14 D = -1.11E-18
E = 2.06E-20 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
32 k = 0.00E + 00 A = 6.64E-07 B = 2.24E-10 C = 7.37E-14 D = 1.27E-17
E = 8.86E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00

[Numerical Example 4]

Surface number r d Nd νd
Object plane ∞ 12.74
1 929.59 16.68 1.5182 58.9
2 -2124.78 105.79
3 -125.51 10.27 1.5182 58.9
4 -175.80 -10.27 1.5182 58.9 Reflecting surface
5 -125.51 -105.79
6 -2124.78 -16.68 1.5182 58.9
7 929.59 16.68 1.5182 58.9 Reflecting surface
8 -2124.78 105.79
9 -125.51 10.27 1.5182 58.9
10 -175.80 10.50
11 1132.81 6.49 1.6031 60.6
12 -93.83 2.23
13 -86.97 5.00 1.6989 30.1
14 116.48 14.08 1.5831 59.4
15 -94.65 0.50
16 76.10 6.68 1.7440 44.8
17 148.42 19.33
18 81.92 19.77 1.7440 44.8
19 -73.01 11.74 1.6989 30.1
20 286.30 0.50
21 65.24 6.10 1.7200 50.2
22 69.87 10.09
23 5605.17 13.63 1.7200 50.2
24 -105.76 28.00
25 ∞ 38.01 Aperture stop
26 -113.02 21.78 1.7618 26.5
27 -100.45 0.50
28 153.22 40.00 1.5955 39.2
29 667.82 11.46
30 124.30 40.00 1.7000 48.1
31 -1047.78 23.04
32 -194.89 5.00 1.7552 27.5
33 165.93 98.96
34 -128.49 15.38 1.4875 70.2
35 181.46 3.72
36 203.94 40.00 1.6700 47.2
37 -262.34 55.81
38 -118.99 16.84 1.6364 35.4
39 -2492.75 26.40
40 -394.11 24.00 1.6935 50.8
41 -190.32 0.50
42 300.72 45.50 1.5145 54.7
43 -764.68 92.99

(Aspheric coefficient)
Face number
1,7 k = 0.00E + 00 A = 3.08E-09 B = 1.51E-13 C = 7.83E-18 D = 2.63E-22
E = -2.42E-26 F = 3.68E-30 G = -8.49E-35 H = 0.00E + 00 J = 0.00E + 00
4,10 k = 0.00E + 00 A = 3.40E-09 B = 1.53E-13 C = 6.19E-18 D = 6.03E-23
E = 2.34E-26 F = -1.01E-30 G = 4.55E-35 H = 0.00E + 00 J = 0.00E + 00
17 k = 0.00E + 00 A = 4.12E-07 B = 3.61E-11 C = -3.90E-14 D = 1.45E-16
E = -1.06E-19 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
20 k = 0.00E + 00 A = 1.15E-06 B = 1.65E-10 C = 2.22E-14 D = -6.04E-18
E = 6.59E-21 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
27 k = 0.00E + 00 A = -2.21E-08 B = -3.09E-12 C = 2.81E-16 D = -5.93E-20
E = 1.77E-23 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
33 k = 0.00E + 00 A = 6.23E-07 B = 3.54E-11 C = 3.83E-16 D = 1.41E-18
E = -3.34E-22 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00
34 k = 0.00E + 00 A = 2.15E-07 B = 2.13E-11 C = 1.25E-15 D = 1.92E-20
E = -2.21E-23 F = 0.00E + 00 G = 0.00E + 00 H = 0.00E + 00 J = 0.00E + 00

DESCRIPTION OF SYMBOLS 101 Light source 102 Illumination optical system 103 Sample 104 Catadioptric optical system 105 Imaging element AS Aperture stop G1 First imaging optical system G2 Second imaging optical system G21, G22 Lens group L1 to L9 Lens M1 First optical element M2 First 2 optical elements

Claims (6)

A first imaging optical system including a catadioptric unit that collects a light beam from an object and an intermediate image formed by receiving the light beam from the first imaging optical system, and forming the intermediate image on an image plane A catadioptric optical system having a second imaging optical system including a refractive part to be
The first imaging optical system includes a first optical element having a light transmission portion around the optical axis, a reflection portion provided on the object side surface of the outer peripheral portion of the light transmission portion, and a back reflection portion. A second optical element having a light transmission portion around the optical axis, a reflection portion provided on the image side surface of the outer peripheral portion of the light transmission portion, and a back reflection portion. The optical element and the second optical element are arranged so that the back surface reflection portions of each other face each other,
The second imaging optical system includes, in order from the object side to the image surface side, a 21st lens group having a positive refractive power, an aperture stop, and a 22nd lens group having a positive refractive power.
The light beam from the object is sequentially transmitted through the light transmission part of the first optical element, the back surface reflection part of the second optical element, the back surface reflection part of the first optical element, and the light transmission of the second optical element. Exits to the second imaging optical system through a section,
The back surface reflecting portion of the first optical element and the back surface reflecting portion of the second optical element are aspherical,
The materials of the first optical element and the second optical element are the same, the Abbe number and refractive index of the material are νdM and NdM, respectively, and the positive lens with the shortest focal length included in the twenty-second lens group is used. When the Abbe number and refractive index of the material are νd22p and Nd22p, respectively, and the Abbe number and refractive index of the negative lens material having the shortest focal length included in the 22nd lens group are νd22n and Nd22n, respectively.
νd22n <νd22p <νdM
NdM <Nd22p
NdM <Nd22n
A catadioptric optical system satisfying the following conditional expression:   2. The catadioptric optical system according to claim 1, wherein the negative lens is disposed closer to the image side than the positive lens. −0.001 <(NdM−1.5) / νdM <0.002.
The catadioptric optical system according to claim 1 or 2, wherein the following conditional expression is satisfied. When the focal lengths of the first imaging optical system and the second imaging optical system are f1 and f2, respectively, and the focal lengths of the 21st lens group and the 22nd lens group are fG21 and fG22, respectively.
0.005 <| f1 / f2 | <0.800
0.005 <| fG21 / f2 | <0.500
0.01 <| fG22 / f2 | <1.80
0.1 <fG21 / fG22 <0.8
The catadioptric optical system according to claim 1, wherein the following conditional expression is satisfied.   The first optical element has a meniscus shape with a convex object side surface, and the second optical element has a meniscus shape with a concave object side surface. The catadioptric optical system according to item 1.   6. A light source means, an illumination optical system that illuminates an object with a light beam from the light source means, a catadioptric optical system according to claim 1, and an image formed by the catadioptric optical system. An image pickup apparatus, comprising: an image pickup device that photoelectrically converts a captured object image; and an image processing system that generates image information from data from the image pickup device.