JP3332890B2 - Optical element and imaging device having the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element and an image pickup apparatus having the same, and more particularly, to an optical system having an optical element having a plurality of reflecting surfaces to form an object image on a predetermined surface. It is suitable for a video camera, a still video camera, a copying machine, and the like, which are miniaturized.

[0002]

2. Description of the Related Art Conventionally, various photographing optical systems using a reflecting surface such as a concave mirror or a convex mirror have been proposed. FIG.
FIG. 2 is a schematic diagram of a so-called mirror optical system including one concave mirror and one convex mirror.

In the mirror optical system shown in FIG. 1, an object light beam 104 from an object is reflected by a concave mirror 101, converges toward the object side, is reflected by a convex mirror 102, and is reflected by an image plane.
Image at 103.

This mirror optical system is based on a so-called Cassegrain-type reflection telescope, and the optical path of a long-lens telephoto lens system composed of a refractive lens is folded by using two opposing reflection mirrors. The purpose is to shorten the entire length of the optical system.

[0005] For the same reason, in the objective lens system constituting the telescope, for the same reason, in addition to the Cassegrain type, there are known many types in which the entire length of the optical system is shortened by using a plurality of reflecting mirrors.

As described above, a compact mirror optical system is obtained by efficiently folding the optical path by using a reflecting mirror instead of a lens of a photographic lens having a longer overall lens length than before.

However, a mirror optical system such as a Cassegrain type reflection telescope generally has a problem that a part of the object beam is vignetted by the convex mirror 102. This problem is caused by the presence of the convex mirror 102 in the area where the object light beam 104 passes.

In order to solve this problem, the reflecting mirror is used eccentrically so as to prevent the passing area of the object light beam 104 from being blocked by other parts of the optical system, ie, the principal ray of the light beam.
A mirror optical system that separates 106 from the optical axis 105 has also been proposed.

FIG. 25 is a schematic diagram of a mirror optical system disclosed in US Pat. No. 3,674,334. The above vignetting is performed by using a part of a reflection mirror rotationally symmetric with respect to the optical axis. Solving the problem.

The mirror optical system shown in FIG. 1 includes a concave mirror 111, a convex mirror 113, and a concave mirror 112 in the order in which light beams pass, and they originally have an optical axis 114 as shown by two-dot broken lines in the figure.
This is a reflection mirror rotationally symmetric with respect to. Concave mirror
111 is used only on the upper side of the paper with respect to the optical axis 114, the convex mirror 113 is used only on the lower side of the paper with respect to the optical axis 114, and the concave mirror 112 is used only on the lower side of the paper with respect to the optical axis 114.
Is separated from the optical axis 114 to constitute an optical system in which vignetting of the object light beam 115 is eliminated.

FIG. 26 is a schematic view of a mirror optical system disclosed in US Pat. No. 5,063,586. The mirror optical system shown in the figure solves the above problem by decentering the central axis of the reflection mirror itself with respect to the optical axis and separating the principal ray of the object light beam from the optical axis.

In FIG. 1, when the vertical axis of the object plane 121 is defined as an optical axis 127, the center coordinates and the center axis of the respective reflecting surfaces of the convex mirror 122, concave mirror 123, convex mirror 124, and concave mirror 125 in the order of passage of the light flux The axes 122a, 123a, 124a and 125a connecting the center of the reflecting surface and the center of curvature of the surface are eccentric with respect to the optical axis 127. In this figure, by appropriately setting the amount of eccentricity and the radius of curvature of each surface at this time, vignetting of the object light beam 128 by each reflection mirror is prevented, and the object image is efficiently formed on the image forming surface 126. I have.

In addition, US Pat. No. 4,737,021 and US Pat. No. 4,265,510 also disclose a configuration in which a part of a reflection mirror rotationally symmetric with respect to the optical axis is used to avoid vignetting, or the central axis of the reflection mirror is used as a light source. A configuration is disclosed in which the shaft is eccentric with respect to the shaft to avoid vignetting.

[0014] These reflection type photographing optical systems have a large number of constituent parts, and it is necessary to assemble each optical part with high accuracy in order to obtain necessary optical performance. In particular, since the relative position accuracy of the reflection mirrors is severe, it is necessary to adjust the positions and angles of the reflection mirrors.

As one method for solving this problem, a method has been proposed in which, for example, a mirror system is divided into one block to avoid errors in assembling optical components during assembly.

Heretofore, optical prisms such as a pentagonal roof prism and a Porro prism used for a finder system or the like have been used as a single block having a large number of reflecting surfaces.

In these prisms, since a plurality of reflecting surfaces are integrally formed, the relative positional relationship between the reflecting surfaces is made with high accuracy, and it is not necessary to adjust the positions of the reflecting surfaces. However, the main function of these prisms is to reverse the image by changing the traveling direction of the light beam, and each reflecting surface is formed of a plane.

On the other hand, an optical system in which a reflecting surface of a prism has a curvature is also known.

FIG. 27 is a schematic view of a main part of an observation optical system disclosed in US Pat. No. 4,775,217. This observation optical system is an optical system for observing an external scenery and observing a display image displayed on an information display body while overlapping the scenery.

In this observation optical system, the display light flux 145 emitted from the display image of the information display body 141 is reflected on the surface 142, goes to the object side, and enters the concave half mirror surface 143. After being reflected by the half mirror surface 143, the display light beam 145 becomes a substantially parallel light beam due to the refracting power of the concave surface 143. After refraction and transmission through the surface 142, an enlarged virtual image of the display image is formed and the observer's image is formed. The light enters the pupil 144 to make the viewer recognize the displayed image.

On the other hand, the object light beam 146 from the object is
The light enters a surface 147 substantially parallel to 2 and is refracted to reach a concave half mirror surface 143. A semi-transmissive film is deposited on the concave surface 143, and a part of the object light beam 146 transmits through the concave surface 143 and
After being refracted and transmitted through 2, the light enters the pupil 144 of the observer. Thus, the observer visually recognizes the display image in the outside scenery while overlapping.

FIG. 28 is a schematic view of a main part of an observation optical system disclosed in Japanese Patent Application Laid-Open No. 2-279516. This observation optical system is also an optical system for observing an external scenery and observing a display image displayed on an information display body in an overlapping manner.

In this observation optical system, the display light beam 154 emitted from the information display body 150 is applied to the flat surface 15 forming the prism Pa.
7 and enters the prism Pa and enters the parabolic reflecting surface 151. The display light beam 154 is reflected by the reflection surface 151 to become a convergent light beam and forms an image on the focal plane 156. At this time, the reflective surface 151
The display light beam 154 reflected by the light source 2 forms the prism Pa
The light reaches the focal plane 156 while being totally reflected between the two parallel planes 157 and 158, thereby achieving a reduction in the thickness of the entire optical system.

Next, the display light beam 154 emitted as divergent light from the focal plane 156 is incident on a parabolic half mirror 152 while being totally reflected between the planes 157 and 158, and is reflected on the half mirror plane 152. Simultaneously, the refracting power forms an enlarged virtual image of the display image and forms a substantially parallel light flux, which passes through the surface 157 and enters the observer's pupil 153,
This allows the viewer to recognize the display image.

On the other hand, the object light beam 155 from the outside
The light passes through a surface 158b constituting Pb, passes through a parabolic half mirror 152, passes through a surface 157, and enters the pupil 153 of the observer. The observer visually recognizes the displayed image in an overlapping manner in the outside scenery.

Further, as examples of using an optical element on the reflecting surface of a prism, for example, Japanese Patent Application Laid-Open Nos.
There is an optical head for an optical pickup disclosed in Japanese Patent No. 139612 or the like. These devices reflect light from a semiconductor laser on a Fresnel surface or a hologram surface, form an image on a disk surface, and guide reflected light from the disk to a detector.

[0027]

The above-mentioned US Pat. No. 3,674,33
No. 4, U.S. Pat.No. 5,063,586, U.S. Pat.
In each of the mirror optical systems having the eccentric mirror disclosed in the specification of Japanese Patent No. 265,510, each reflecting mirror is arranged with a different amount of eccentricity, so that the mounting structure of each reflecting mirror becomes very complicated and the mounting accuracy is reduced. It is very difficult to secure.

The conventional reflection type photographing optical system has a configuration suitable for a so-called telephoto lens system having a long overall optical system and a small angle of view. In addition, when obtaining a photographing optical system that requires an angle of view of a standard lens to an angle of view of a wide-angle lens, the number of reflecting surfaces required for aberration correction increases, so higher component accuracy and higher assembly accuracy are required. And the cost or the whole tends to be large.

Further, the observation optical systems disclosed in the above-mentioned US Pat. No. 4,775,217 and Japanese Patent Application Laid-Open No. 2-279516 are all displayed on an information display which is arranged away from the pupil of the observer. Focusing on pupil imaging and changing the direction of travel of light to efficiently transmit the displayed image to the observer's pupil, and a technology for actively correcting aberrations with a reflective surface with curvature Is not disclosed directly.

Further, Japanese Patent Application Laid-Open Nos. 5-12704 and 6-1396
The optical systems for optical pickups disclosed in Japanese Patent Publication No. 12 and the like are all limited to the use of a detection optical system, and are not applicable to an imaging optical system, particularly to an imaging apparatus using an area-type imaging device such as a CCD. The image performance was not satisfactory.

According to the present invention, there is provided an optical element capable of reducing the size of the entire mirror optical system and reducing the disposition accuracy (assembly accuracy) of the reflection mirror, which is often present in the mirror optical system, and an imaging device having the same. The purpose is to provide a device.

Further, by providing a plurality of reflecting surfaces, giving an appropriate refractive power to the plurality of reflecting surfaces, and eccentrically arranging each reflecting surface, the optical path is bent into a desired shape, and the entire length in the predetermined direction is reduced. It is an object of the present invention to provide an optical element which is shortened and an imaging device including the optical element.

[0033]

According to a first aspect of the present invention, there is provided an optical element, comprising: a center of an image plane, a stop, an entrance pupil or an exit pupil, or a center of a first surface or a center of a final surface of an optical system. When the path of the light beam passing therethrough is used as a reference axis, the surface has at least three curved reflecting surfaces inclined with respect to the reference axis, and the curved reflecting surface is an aspheric surface having only one symmetric surface that defines a pair of symmetric surfaces. And an intermediate image is formed inside the element.

According to a second aspect of the present invention, in the first aspect of the present invention, each of the plurality of curved reflecting surfaces uses a local coordinate system xyz having an origin at an intersection between each curved reflecting surface and a reference axis, and a, b, a When t is a coefficient representing the surface shape, A = (a + b) · (y ² · cos ² t + x ² ) B = 2a · b · cos t [1 + {(ba) · y · sin t / (2a ・ b)} + [1 + {(ba)
・ Y ・ sin t / (a ・ b)}-{y ² / (a ・ b)}-{4a ・ b ・ cos ² t + (a + b) ² sin
² t} x ² / (4a ² b ² cos ² t)] ^1/2 ] and z = A / B + C ₀₂ y ² + C ₂₀ x ² + C ₀₃ y ³ + C ₂₁ x ² y + C ₀₄ y ⁴ + C ₂₂ x ² y ² + C ₄₀
It is characterized in that which is defined by x ^4.

According to a third aspect of the present invention, in the first or second aspect, the at least three curved reflecting surfaces sequentially deflect a light beam.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, a curved surface refraction surface is provided.

According to a fifth aspect of the present invention, in the first, second or third aspect, the curved reflecting surface is provided on a surface of a surface reflecting mirror.

According to a sixth aspect of the present invention, in the first, second or third aspect, the curved reflecting surface is provided on a surface of a transparent body.

In the optical system according to the present invention, the path of the light beam passing through the center of the image plane and either the stop, the entrance pupil or the exit pupil, or the center of the first surface or the center of the last surface of the optical system is referred to. Two optical elements each having a curved reflecting surface inclined with respect to a reference axis when the axis is an axis, and the curved reflecting surface being an aspheric surface having only one symmetric surface defining a pair of symmetric surfaces. A stop between the two optical elements, wherein an optical element on the object side of the two optical elements forms an intermediate image of the object, and the stop is moved to the optical element on the object side. Is formed on the object side of the first curved reflecting surface counted from the light incident side, and has at least three curved reflecting surfaces inclined with respect to the reference axis as a whole.

The image pickup apparatus according to the eighth aspect of the present invention is characterized in that:
An optical element according to claim 6 or an optical system according to claim 7 is provided.

According to a ninth aspect of the present invention, there is provided the image forming apparatus according to the first aspect.
An optical element according to any one of claims 1 to 6, or an optical system according to claim 7 is provided.

The optical system according to the tenth aspect has a curved reflecting surface inclined with respect to the reference axis, and the curved reflecting surfaces are a, b, and b.
t as the coefficient representing the surface shape, A = (a + b) · (y 2 · cos 2 t + x 2) B = 2a · b · cos t [1 + {(ba) · y · sin t / ( 2a ・ b)} + [1 + {(ba) ・ y ・ sin t / (a ・ b)}-{y ² / (a ・ b)}-{4a ・ b ・ cos ² t + (a + b) ² sin ² t} x ² / (4a ² b ² cos ² t)] ^1/2 ] and z = A / B + C ₀₂ y ² + C ₂₀ x ² + C ₀₃ y ³ + C ₂₁ x ² y + C ₀₄ y ⁴ + C ₂₂ x ² y ² + C ₄₀ x ⁴
An optical element on the object side of the two optical elements forms an intermediate image of the object, and the optical element on the curved surface of the optical element on the object side. An image is formed on the object side of the reflection surface.

The invention of claim 11 is the invention of claim 8, 9 or 10.
In the invention, each of the optical elements has a plurality of the curved reflecting surfaces, and the plurality of curved reflecting surfaces sequentially deflect a light beam.

According to a twelfth aspect of the present invention, in any one of the eighth, ninth, tenth and eleventh aspects of the present invention, the twelfth aspect has a curved refracting surface.

According to a thirteenth aspect, in the twelfth aspect, the reflecting surface is provided on a surface of a surface reflecting mirror.

According to a fourteenth aspect, in the twelfth aspect, the reflection surface is provided on a surface of a transparent body.

The invention of claim 15 is the invention of claim 8, 9 or 10.
In the invention, the stop is arranged on the object side of the optical element on the object side.

According to a sixteenth aspect of the present invention, there is provided an imaging apparatus including the optical system according to any one of the first to fifteenth aspects.

The image forming apparatus according to the seventeenth aspect is the first aspect.
The optical system according to any one of (1) to (15) is provided.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments, the way of expressing the configuration data of the embodiments and the common items of the entire embodiments will be described.

FIG. 1 shows an optical element of the present invention (hereinafter referred to as “optical system”).
Also called. FIG. 4 is an explanatory diagram of a coordinate system that defines configuration data of FIG. In the embodiment of the present invention, the i-th surface is defined as the i-th surface along one light ray (shown by a dashed line in FIG. 1 and referred to as a reference axis light ray) traveling from the object side to the image plane.

In FIG. 1, a first surface R1 is a stop, a second surface R2 is a refracting surface coaxial with the first surface, a third surface R3 is a reflecting surface tilted with respect to the second surface R2, and a fourth surface R4. , A fifth surface R5 is a reflecting surface shifted and tilted with respect to each front surface, and a sixth surface R6 is a fifth surface
This is a refraction surface shifted and tilted with respect to R5. Second side
Each surface from R2 to the sixth surface R6 is formed on one optical element made of a medium such as glass, plastic or the like, and is shown as an optical element 10 in FIG.

Therefore, in the configuration shown in FIG. 1, the medium from the object surface (not shown) to the second surface R2 is air, the medium from the second surface R2 to the sixth surface R6 is a common medium, and the medium from the sixth surface R6 to the second surface R6 is not shown. The medium up to the seventh surface R7 is composed of air.

Since the optical system of the present invention is a decentered optical system, the surfaces constituting the optical system do not have a common optical axis. Therefore, in the embodiment of the present invention, first, an absolute coordinate system having the origin at the center of the effective ray diameter on the first surface is set.

In the embodiment of the present invention, the first
The center point of the effective ray diameter of the surface is defined as the origin, and the path of a light beam (reference axis light beam) passing through the origin and the center of the final imaging plane is defined as the reference axis of the optical system. Further, the reference axis in this embodiment has a direction (direction). The direction is the direction in which the reference axis ray travels during imaging.

In the embodiment of the present invention, the reference axis serving as the reference of the optical system is set as described above. However, how to determine the reference axis of the optical system depends on optical design, integration of aberrations, or optical system. It is only necessary to adopt an axis that is convenient for expressing each surface shape that constitutes. However, in general, the path of the light beam passing through the center of the image plane and either the stop, the entrance pupil or the exit pupil, or the center of the first surface or the center of the last surface of the optical system is referred to as a reference axis serving as a reference of the optical system. Set to.

That is, in the embodiment of the present invention, the reference axis passes through the first surface, that is, the center point of the effective beam diameter of the stop surface.
The reference axis is set such that the light ray (reference axis light ray) reaching the center of the final imaging plane is refracted and reflected by each refraction surface and reflection surface. The order of each surface is set in the order in which the reference axis rays are refracted and reflected.

Accordingly, the reference axis finally reaches the center of the image plane while changing its direction along the set order of each surface according to the law of refraction or reflection.

The tilt surfaces constituting the optical system of each embodiment of the present invention are basically all tilted in the same plane. Therefore, each axis of the absolute coordinate system is determined as follows.

Z axis: Reference axis passing through the origin to the second surface R2 Y axis: Straight line passing through the origin and forming 90 ° counterclockwise with respect to the Z axis in the tilt plane (in the paper plane of FIG. 1) : Straight lines passing through the origin and perpendicular to each of the Z and Y axes (straight lines perpendicular to the plane of FIG. 1). Also, to express the surface shape of the i-th surface that constitutes the optical system, the shape of that surface in the absolute coordinate system , The reference axis and the i-th
The configuration data of the present invention is displayed because it is easier to understand the shape of the surface by setting the local coordinate system having the origin at the point where the surface intersects and expressing the surface shape of the surface in the local coordinate system. In the embodiment, the surface shape of the i-th surface is represented by a local coordinate system.

The tilt angle of the i-th surface in the YZ plane is an angle θ with the counterclockwise direction being positive with respect to the Z axis of the absolute coordinate system.
i (unit: °). Therefore, in the embodiment of the present invention, the origin of the local coordinates of each surface is on the YZ plane in FIG. Also
There is no plane eccentricity in the XZ and XY planes. Further, the y, z axes of the local coordinates (x, y, z) on the ith plane are inclined at an angle θi in the YZ plane with respect to the absolute coordinate system (X, Y, Z). Set as follows.

Z-axis: an angle θ that passes through the origin of the local coordinate system and is counterclockwise in the YZ plane with respect to the Z direction of the absolute coordinate system.
i-axis straight line y-axis: straight line passing through the origin of local coordinates and making 90 ° counterclockwise in the YZ plane with respect to z-direction x-axis: straight line passing through the origin of local coordinates and perpendicular to the YZ plane Di is a scalar quantity representing the distance between the origin of the local coordinates of the i-th surface and the (i + 1) -th surface, and Ndi and νdi are the i-th surface and (i + 1) -th surface.
+1) The refractive index and Abbe number of the medium between the surfaces.

In the embodiments of the present invention, a sectional view of the optical system and numerical data are shown.

The embodiment of the present invention has a spherical surface and a rotationally asymmetric aspheric surface. Spherical portion of which I wrote the radius of curvature R _i as a spherical shape. The sign of the radius of curvature R _i is first
The case where the center of curvature is on the first surface side along the reference axis (dashed line in FIG. 1) that advances from the surface to the image surface is defined as minus, and the case where it is on the imaging surface side is defined as plus.

The spherical surface has a shape represented by the following equation:

[0066]

(Equation 1)

The optical system of the present invention has at least one rotationally asymmetric aspherical surface, and its shape is represented by the following equation (where a, b, and t are counts relating to the shape): A = ( a + b) ・ (y ²・ cos ² t + x ² ) B = 2a ・ b ・ cos t [1 + {(ba) ・ y ・ sin t / (2a ・ b)} + [1 + {(ba ) ・ Y ・ sin t / (a ・ b)}-{y ² / (a ・ b)}-{4a ・ b ・ cos ² t + (a + b) ² sin ² t} x ² / (4a ² b ² cos ² t)] ^1/2 ] and z = A / B + C ₀₂ y ² + C ₂₀ x ² + C ₀₃ y ³ + C ₂₁ x ² y + C ₀₄ y ⁴ + C ₂₂ x ² y ² + C ₄₀ × ^{4 Since the} above-mentioned curved surface equation has only even-order terms with respect to x, the curved surface defined by the above-mentioned curved surface expression has a plane-symmetric shape with the yz plane as a symmetric surface. Further, when the following condition is satisfied, the shape is plane-symmetric with respect to the xz plane. Therefore, if the following conditions are not satisfied, the shape will not be plane-symmetric with respect to the xz plane, and there will be only one plane of symmetry, the yz plane, and not more than two planes.

[0068] If the _{C 03 = C 21 = 0,} t = 0 Furthermore _{C 02 = C 20 C 04 =} C 40 = C 22/2 is satisfied represents a rotation-symmetrical shape. If the above conditions are not satisfied, the shape is non-rotationally symmetric.

In the embodiments of the present invention,
C ₀₂ = C ₂₀ = 0, and is configured by adding a higher-order asymmetric aspherical surface to the basic shape of a quadratic surface.

In each embodiment of the present invention, as shown in FIG. 1, the first surface is a stop. Also, horizontal half angle of view
u _Y is the maximum angle of view of the light beam incident on the stop R1 in the YZ plane of FIG. 1, and the vertical half angle of view u _X is the maximum angle of view of the light beam incident on the stop R1 in the XZ plane. Also, the stop R1 which is the first surface
Is shown as the aperture diameter. This is related to the brightness of the optical system. Since the entrance pupil is located on the first surface, the aperture diameter is equal to the entrance pupil diameter.

The effective image range on the image plane is shown as an image size. The image size is represented by a rectangular area in which the size in the y direction of the local coordinates is horizontal and the size in the x direction is vertical.

The examples show the size of the optical system. The size is a size determined by the effective beam diameter.

The lateral aberration chart is shown for the embodiment in which the configuration data is given. The lateral aberration diagram shows that for each embodiment, the horizontal angle of incidence and the vertical angle of incidence on the stop R1 are (u _Y , u _X ),
_{(0, u X), (} - u Y, u X), (u Y, 0), (0,0), (- u Y, 0) and showing lateral aberration of the light flux incident angle made. In the lateral aberration diagram, the horizontal axis represents the height of incidence on the pupil, and the vertical axis represents the amount of aberration. In each embodiment, since each surface is basically a plane-symmetrical shape with the yz plane as a plane of symmetry, the plus and minus directions of the vertical angle of view are the same even in the lateral aberration diagram, so that the drawing is simplified. For this reason, a lateral aberration diagram in the minus direction is omitted.

Hereinafter, each embodiment will be described.

[Embodiment 1] FIGS. 2 and 3 are sectional views of an optical system according to Embodiment 1 of the present invention in the YZ plane. This embodiment is an imaging optical system having a horizontal angle of view of 52.6 degrees and a vertical angle of view of 40.6 degrees. FIG.
Also shows the optical path. Figure 3 shows the pupil ray (off-axis chief ray)
FIG. The configuration data of the present embodiment is as follows.

[0076]

[Outside 1]

[0077]

[Outside 2]

In FIG. 2, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, in the order of passage of light rays from the object, there are a concave refracting surface (incident surface) R2 having negative refracting power and four reflecting surfaces of a concave mirror R3, a reflecting surface R4, a reflecting surface R5, and a concave mirror R6 and a positive reflecting surface. A convex refraction surface (exit surface) R7 having a refractive power of? R1 is a stop (entrance pupil) arranged on the object side of the optical element 10, 3 is an optical correction plate such as a quartz low-pass filter or an infrared cut filter, and R10 is a final image forming plane, and is an image pickup device such as a CCD. ) Is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

The two refracting surfaces are both rotationally symmetric spherical surfaces, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation in this embodiment will be described. The luminous flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop R1, and the surfaces R3, R4
After being reflected by, an image is once formed near the surface R4, and then the surfaces R5 and R
The light is reflected one after another at 6, exits from the exit surface R 7, and is re-imaged on the final imaging surface R 10 via the optical correction plate 3. The object ray forms an intermediate image near the surface R4, and the pupil ray forms an intermediate image between the surface R5 and the surface R6.

In the present embodiment, the direction of the reference axis incident on the optical element 10 and the direction of the reference axis emerging therefrom are parallel and the same direction. Further, the reference axes including the incoming and outgoing light are all placed in the plane of the paper (YZ plane).

As described above, the optical element 10 is formed as a lens unit having desired optical performance and having a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

In this embodiment, focusing on a short-distance object is performed by moving the entire optical system with respect to the imaging surface R10 of the imaging device. Particularly in this embodiment,
Since the direction of the reference axis incident on the optical element 10 and the direction of the reference axis exiting from the optical system 10 are parallel and the same direction, they move parallel to the direction of the reference axis exiting the entire optical system (Z-axis direction). By doing so, the focusing operation can be performed in the same manner as in the conventional lens system.

FIG. 4 is a lateral aberration diagram of the optical system of this embodiment.
Shown in In this embodiment, a well-balanced aberration correction state is obtained.

The effect of this embodiment will be described.

In the case of this embodiment in which the entrance pupil is located near the first surface R2 of the optical element 10, the convergence of the first curved reflecting surface R3, especially when counted from the object side, is given to the compact optical system. Has contributed. This is to make the optical system even thinner by forming an intermediate image of the pupil ray (principal ray) at a stage close to the entrance surface, and to converge the off-axis principal ray that has exited the stop R1 before it spreads greatly. The increase in the effective diameter of each surface after the first reflecting surface R3 due to the wide angle of the system is suppressed.

In particular, as shown in FIG. 3, the apparent stop center 6 '(the entrance pupil to the surface R3) when the first reflecting surface R3 is viewed from the reflecting surface.
And an imaginary point 8 ′ on the yz plane containing the bent reference axis inside the optical system is used as the spheroidal surface with the focal point, so that the off-axis chief ray is imaged at the point 8 inside with almost no aberration. As a result, the thickness of the optical element 10 can be reduced, and off-axis aberrations can be suppressed at an initial stage.

This will be described.

It is preferable that a, b, and t representing the base shape of the first reflecting surface R3 satisfy the following conditions: a · b> 0 (1) 0.9 <t / | θ | <1.5 (2) 0.9 <| a | / d <2.0 (3) 0.9 <| b | / d <2.0 (4) where d is the first from the center of the diaphragm measured along the reference axis.
This is the distance to the reflection surface R3.

Conditional expression (1) defines the properties of the base surface shape. When this value is positive, the spheroid has two focal points in the yz plane, and the light emitted from one focal point is obtained. A real image can be formed at the other focus with almost no aberration. a, b, t represent two focal positions on the ellipsoid.

Conditional expression (2) indicates that one focal point is the first reflecting surface R3.
From the condition that the entrance pupil 6 'of this surface becomes
If the upper and lower limits of (2) are not satisfied, one of the focal points does not fall on the reference axis, and off-axis rays do not form an image at an internal point, or even if the image is formed, aberrations become large, which is not good.

The same holds true for conditional expression (3). If the upper and lower limits are deviated, the distance between the first reflecting surface R3 and the focal point is greatly different from the distance from the first reflecting surface R3 to the entrance pupil 6 'of this surface. In addition, off-axis rays do not form an image at an internal point, or even if an image is formed, the occurrence of aberration increases, which is not good.

Conditional expression (4) is a condition for achieving both the reduction in thickness of the optical system and the correction of aberrations. The conditional expression (4) considers d as the width of the optical system in the Z direction, and restricts the position of the intermediate image point in comparison with d. It is. Beyond the upper limit, if the focal point on the exit side of the first reflecting surface R3 is long, the off-axis light beam does not easily converge and the optical system becomes large due to the spread of the off-axis light beam when the optical system is widened. Not good. Conversely, if the value exceeds the lower limit, the refractive power of the first reflecting surface becomes too strong, and aberration is generated particularly off-axis, which is not good.

The above is the description of the shape condition of the first reflecting surface R3 which is a spheroid.

In this embodiment, the entrance surface R2 and the exit surface R7 of the optical element 10 have a refractive power (optical power). In the present embodiment, the occurrence of various off-axis aberrations is reduced by making the incident surface R2 a concentric concave surface with respect to the off-axis principal ray. Further, the exit surface R7 is formed as a convex surface, thereby preventing the back focus from becoming too long. On the other hand, if the incident surface R2 is made convex, off-axis rays converge on this surface, so that the first reflecting surface R3 can be prevented from becoming large.

Further, the shape of the exit surface R7 is such that the off-axis principal ray (pupil ray) to this surface is changed on the exit side (image side) in accordance with the angle of incidence.
Are determined to be almost parallel, that is, telecentric. This is because when using an image sensor such as a CCD,
Since there is a gap between the color filter of the CCD and the light receiving surface, it is effective to prevent the color separation performance from being changed by the incident angle to the image sensor. If the optical system is made telecentric on the image side, both the principal rays of the on-axis and off-axis light beams are substantially parallel to the optical axis, and the angle of incidence on the CCD is substantially constant over the entire light receiving surface.

Further, in this embodiment, the reflecting surface is a surface having only one symmetric surface, whereas the shape of the input / output surface is rotationally symmetric with respect to the reference axis. This is to make it possible to accurately measure the reference axis when manufacturing and evaluating the optical system. Further, by making the refracting surface rotationally symmetric, it is possible to reduce the occurrence of asymmetric chromatic aberration.

This embodiment has the following effects.

In the conventional optical system shown in FIG. 28, the reflection surfaces on the entrance side and the exit side have a refracting power, but the reflection between them merely serves as a so-called light guide for guiding a light beam. In the present embodiment, by forming at least three reflecting surfaces having a refractive power integrally, it is possible to obtain a compact and free shape having a function of bending the optical axis and a function of correcting aberration, and to achieve a high performance with a compact shape. An optical system is obtained.

In the present embodiment, the object ray is shifted to the position 7
, And the pupil rays are intermediately imaged at the position 8 respectively. As described above, in the present embodiment, each light beam is intermediately imaged at a stage closer to the incident surface as compared with the conventional imaging optical system,
On the image side from the stop R1, the size of each surface where the effective range is determined by the object beam and the pupil beam is suppressed, and the size of the cross section of the optical system has been successfully reduced.

Further, in this embodiment, the reference axis 5 bent inside the optical system is included in the same plane, that is, in the plane of FIG. As a result, the direction (X
Direction) is reduced in size.

Each of the reflecting surfaces constituting the optical system is a so-called eccentric reflecting surface in which the normal line at the intersection between the reference axis and the reflecting surface does not coincide with the direction of the reference axis. This prevents vignetting that occurs in conventional mirror optical systems,
As a result, a more flexible arrangement can be obtained, and a space-efficient optical element having a compact and free shape can be formed.

The shape of each reflecting surface is two orthogonal surfaces.
These are planes with different radii of curvature within (yz plane, xz plane). This is to suppress the eccentric aberration caused by the eccentric arrangement of each reflecting surface. By making this reflecting surface asymmetrical, various aberrations are corrected well and desired optical performance is achieved. .

In this embodiment, the stop R1 is arranged immediately before the entrance surface R2. In the case of a conventional photographing optical system, a stop (entrance pupil) is often arranged inside the optical system, and the larger the distance from the stop to the entrance surface located closest to the object side, the larger the effective beam diameter of the entrance surface. However, there is a problem that the size increases with an increase in the angle of view. In the present embodiment,
By arranging R1 on the object side of the photographing optical system (light beam incident side of the optical system), the enlargement of the photographing optical system that occurs when the optical system is widened is suppressed.

As a feature of the reflection optical system, the directions of the reference axis to be incident and the reference axis to be emitted can be variously changed by combining the arrangement of the respective surfaces.

[Embodiment 2] FIG. 5 is a sectional view of an optical system according to Embodiment 2 of the present invention in the YZ plane. This embodiment has a horizontal angle of view of 6
It is a shooting optical system with 3.4 degrees and a vertical angle of view of 49.6 degrees. FIG. 5 also illustrates the optical path. The configuration data of this embodiment is shown below.

[0107]

[Outside 3]

[0108]

[Outside 4]

In FIG. 5, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, there are five reflecting surfaces of a concave refracting surface (incident surface) R2 and a concave mirror R3, a convex mirror R4, a concave mirror R5, a reflecting surface R6, and a concave mirror R7 having negative refracting power in the order of passage of light rays from the object. And a convex refractive surface (exit surface) R8 having a positive refractive power. R1 is a stop arranged on the object side of the optical element 10, and R9 is a final image forming surface, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

Each of the two refracting surfaces is a rotationally symmetric spherical surface, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation in this embodiment will be described. The luminous flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop (entrance pupil) R1, is reflected by the surface R3, and is once formed between the surfaces R3 and R4. Statue and
Next, the light is reflected on the surfaces R4, R5, R6, and R7 one after another, and
And re-images on the final imaging plane R9.

As described above, the optical element 10 is formed as a lens unit having a desired optical performance and a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

In this embodiment, the direction of the reference axis incident on the optical element 10 and the direction of the reference axis emerging therefrom are parallel and opposite to each other. In addition, all reference axes including incident and outgoing light are on the paper surface (YZ plane).

In this embodiment, focusing on a short-distance object is performed by moving the entire optical system with respect to the imaging surface R9 of the imaging device. Particularly in this embodiment, since the direction of the reference axis entering the optical element 10 and the direction of the reference axis exiting from the optical system 10 are parallel, the direction of the reference axis exiting the entire optical system (Z-axis direction) , The focusing operation can be performed similarly to the conventional lens system.

FIG. 6 is a lateral aberration diagram of the optical system of this embodiment.
Shown in

The effect of this embodiment will be described. This embodiment has the same effect as the first embodiment.

In addition, in the present embodiment, since both the input and output surfaces of the optical element 10 are arranged on one side of the optical element, the optical system can be made thinner in the X direction and also have a small overall length in the Z axis (+) direction. be able to.

Since the present embodiment has a configuration in which one reflecting surface is added to reverse the direction of the reference axis light beam as compared with the first embodiment, the distribution of the refracting power and the ability to correct the asymmetric aberration on each surface. By appropriately performing the above, it is possible to improve the imaging performance and further widen the angle of view.

[Embodiment 3] FIG. 7 is a sectional view in the YZ plane of an optical system according to Embodiment 3 of the present invention. This embodiment has a horizontal angle of view of 4
This is a photographic optical system with a 0.0 degree vertical angle of view of 52.0 degrees. FIG. 7 also illustrates the optical path. The configuration data of this embodiment is shown below.

[0120]

[Outside 5]

[0121]

[Outside 6]

In FIG. 7, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, in order of passage of light rays from the object, there are six convex refracting surfaces (incident surfaces) R2, concave mirrors R3, convex mirrors R4, concave mirrors R5, reflecting surfaces R6, concave mirrors R7, and convex mirrors R8 having a positive refractive power. Reflection surface and convex refraction surface (exit surface) R9 having positive refractive power
Is formed. R1 is a stop (entrance pupil) arranged on the object side of the optical element 10, and R10 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

Each of the two refracting surfaces is a rotationally symmetric spherical surface, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation of this embodiment will be described. The luminous flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop (entrance pupil) R1, is reflected by the surface R3, and is once formed between the surfaces R3 and R4. Image, then surface R
The light is sequentially reflected at 4, R5, R6, R7, and R8, exits from the exit surface R9, and is re-imaged on the final imaging surface R10.

As described above, the optical element 10 is formed as a lens unit having desired optical performance and having a positive refractive power as a whole by the refractive power of the input / output surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

FIG. 8 shows a lateral aberration diagram of the present embodiment.

In this embodiment, the direction of the reference axis incident on the optical element 10 and the direction of the reference axis emerging therefrom are orthogonal to each other. In addition, all reference axes including incident and outgoing light are on the paper surface (YZ plane).

With this configuration, the thickness of the portion occupied by the back focus of the optical system and the package and circuit portion of the image sensor such as a CCD can be integrated in the Y direction, so that the thickness in the X direction can be reduced. At the same time, a reduction in thickness in the Z direction indicated by D in FIG. 7 can be achieved.

[Embodiment 4] FIG. 9 is a sectional view of an optical system according to Embodiment 4 of the present invention in the YZ plane. This embodiment has a horizontal angle of view of 6
It is a shooting optical system with 3.4 degrees and a vertical angle of view of 49.6 degrees. FIG. 9 also illustrates the optical path. The configuration data of this embodiment is shown below.

[0130]

[Outside 7]

[0131]

[Outside 8]

In FIG. 9, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, in the order of passage of light rays from the object, four reflecting surfaces of a concave refracting surface (incident surface) R2 having a negative refracting power, a concave mirror R3, a convex mirror R4, a concave mirror R5, a reflecting surface R6, and a positive surface A convex refractive surface (exit surface) R7 having a refractive power is formed. R1 is a stop (entrance pupil) arranged on the object side of the optical element 10, and R8 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

The two refracting surfaces are both rotationally symmetric spherical surfaces, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation of this embodiment will be described. The luminous flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop (entrance pupil) R1, is reflected by the surface R3, and is once formed between the surfaces R3 and R4. Image, then surface R
4, R5, R6 reflected one after another, emitted from the exit surface R7,
The image is re-imaged on the final image plane R8.

As described above, the optical element 10 is formed as a lens unit having desired optical performance and a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

FIG. 10 shows a lateral aberration diagram of the present embodiment.

In this embodiment, the direction of the reference axis incident on the optical element 10 and the reference axis emerging therefrom form an angle of about 45 °. This is an example in which the reference axis is bent so that the light rays on each surface do not interfere with each other so that the incident angle of the light beam on each reflection surface becomes small, so that the emission reference axis is not parallel or perpendicular to the incident reference axis It is.

Even in this case, all the reference axis rays including the incident reference axis and the exit reference axis are on the same plane (YZ plane) in order to keep the entire optical system thin in the X direction.

[Embodiment 5] FIG. 11 is a sectional view of an optical system according to Embodiment 5 of the present invention, taken along the XZ plane, and a side view thereof. FIG. 12 is a perspective view of the fifth embodiment, and also illustrates an optical path. This embodiment is an imaging optical system having a horizontal angle of view of 56.8 degrees and a vertical angle of view of 44 degrees.

In the present embodiment, the definition of the local coordinate system is changed because there are two types of tilts on each plane, that is, an XZ plane and an XY plane. First, when the tilt angle of the i-th surface in the XZ plane is viewed from the positive direction of the Y-axis, an angle φi with the clockwise direction being positive (unit:
degree), the tilt angle in the XY plane as viewed from the positive direction of the Z-axis, with the counterclockwise direction as the positive angle θi (degrees)
Expressed by Further, each axis of the local coordinate (x, y, z) on the i-th surface is first set at the origin (Xi, Yi, Z) with respect to the absolute coordinate system (X, Y, Z).
After moving to i), it is assumed that it is inclined at an angle φi in the XZ plane and finally inclined at an angle θi in the XY plane. Specifically, the following settings are made.

Origin (Xi, Yi, Zi) z: Angle φi in the XZ plane with respect to the Z direction which is the optical axis direction of the first surface, and direction inclined at angle θi in the XY plane y: YZ with respect to the z direction A direction x that forms 90 ° in the plane counterclockwise in the plane: a direction perpendicular to the YZ plane with the vertex position of the reflection surface as the origin, configuration data of the present embodiment is as follows.

[0142]

[Outside 9]

[0143]

[Outside 10]

In FIG. 11, reference numeral 10 denotes an optical element having one flat reflecting surface and a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. A convex refractive surface (incident surface) having a positive refractive power is arranged on the surface of the optical element 10 in the order of passage of light rays from the object.
R2 and flat reflecting surface R3, concave mirror R4, convex mirror R5, concave mirror R6
Six reflecting surfaces of a reflecting surface R7 and a concave mirror R8 and a convex refracting surface (exit surface) R9 having a positive refractive power are formed. R1 is a stop (entrance pupil) arranged on the object side of the optical element 10, and R10 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located.
Reference numeral 5 denotes a reference axis of the photographing optical system.

The two refracting surfaces are both rotationally symmetric spherical surfaces, and the reflecting surfaces of all the curved surfaces are surfaces having only one symmetric surface.

Next, the image forming operation in this embodiment will be described. The luminous flux 1 from the object coming from the Z (-) direction is regulated by the stop (entrance pupil) R1 and then incident on the entrance surface R2 of the optical element 10 to be subjected to a converging action, and then to a plane reflecting surface.
After being reflected by R3 and deflected in the X (-) direction, it is reflected by surface R4 to form an image once, then reflected by surfaces R5, R6, R7, R8 one after another, and exits from surface R9 to X ( (+) Direction, and the final image plane R1
Re-image on 0.

The object ray forms an intermediate image between the plane R4 and the plane R5, and the pupil ray forms an intermediate image between the plane R6 and the plane R7.

As described above, the optical element 10 is formed as a lens unit having desired optical performance and having a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

FIG. 13 shows a lateral aberration diagram of the optical system of this embodiment.

In the case of this embodiment, the incident surface R2 of the optical element 10
Has a relatively strong positive refracting power, condensing on-axis and off-axis light beams to prevent the plane reflecting surface R3 from becoming large, and thus further reducing the overall thickness of the optical system. I have.

In this embodiment, the incident reference axis (Z axis)
The reference axis ray after the reflection surface R3 is bent in a plane (XY plane) perpendicular to the plane. (Approximately 80% of the length of the reference axis in the optical element 10 is on the XY plane).

In the above embodiments, the incident reference axis,
Although all the reference axes including the emission reference axis are included in a plane (YZ plane), it may be preferable that the incident reference axis is not parallel to the plane due to the layout of the imaging optical system. Therefore, in the case of the present embodiment, as in the other embodiments, the thickness can be reduced in the direction perpendicular to the plane including the bent reference axis in the optical system (in this case, the Z-axis direction). Therefore, a thin photographing optical system can be configured, and the degree of freedom in incorporating the optical system into a camera or the like is further expanded.

In this embodiment, the incident reference axis (Z axis)
Almost all other reference axis rays are bent in a plane perpendicular to the plane (XY plane). That is, in the present embodiment, approximately 80% of the length of the reference axis in the optical element 10 is placed on the XY plane, whereby the thickness of the optical element 10 in the Z direction is reduced.

In this embodiment, the incident reference axis is arranged perpendicular to the plane on which most of the reference axes in the optical element are mounted, but the emission reference axis may be perpendicular. In that case,
What is necessary is just to arrange | position a plane reflection surface just before an emission surface. In this case, the thickness can be reduced in the direction perpendicular to the plane on which most of the reference axes are mounted, and the degree of freedom in the layout of the imaging device is created.

Further, it is possible to arrange both the incident reference axis and the emission reference axis perpendicular to the plane on which most of the reference axes are mounted, and to make the incoming and outgoing optical axes parallel while taking a free layout. A focusing operation similar to that of the conventional lens system can be performed.

[Embodiment 6] FIG. 14 is a sectional view in the YZ plane of an optical system according to Embodiment 6 of the present invention. This embodiment has a horizontal angle of view of 5
It is a shooting optical system with 2.0 degrees and vertical angle of view of 40.0 degrees. FIG. 14 also shows the optical path. In all of the embodiments described above, the optical element in which the refraction surface and the reflection surface are formed on the surface of the transparent body is used. However, a plurality of reflection surfaces may be configured by a surface mirror inside the hollow block. . This embodiment is an embodiment in which a mirror surface is provided on the inner surface of a hollow block to constitute an optical element.

The configuration data of this embodiment is as follows.

[0158]

[Outside 11]

[0159]

[Outside 12]

In FIG. 14, reference numeral 60 denotes a hollow block (optical element) having a reflection surface formed of a plurality of curved surfaces formed therein. On the inner surface of the optical element 60, four reflecting surfaces of a concave mirror R2, a reflecting surface R3, a reflecting surface R4, and a concave mirror R5 are formed in the order of passage of light rays from the object. R1 is a stop (entrance pupil) arranged on the object side of the optical element 60, R6 is a final image plane, and the CCD
The imaging surface of the imaging device is located. Reference numeral 5 denotes a reference axis of the photographing optical system. All reference axes are on the paper (YZ plane).

It is to be noted that all reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation of this embodiment will be described. The light flux 1 from the object is incident on the optical element 60 after the amount of incident light is regulated by the stop (entrance pupil) R1, is reflected by the reflection surface R2, and forms an image once near the reflection surface R3. Then face R
After being reflected one after another at R3 and R5, the light exits from the optical element 60 and is re-imaged on the final image plane R6.

The object ray forms an intermediate image between the plane R2 and the plane R3, and forms a reduced image again on the final image plane. The pupil ray forms an intermediate image near the surface R3.

As described above, the optical element 60 functions as a lens unit having a desired optical performance and a positive refractive power as a whole due to the refractive power of the plurality of curved reflecting mirrors therein.

FIG. 15 shows a lateral aberration diagram of the optical system of this embodiment.

In this embodiment, only the surface reflecting mirror is used, and there is an advantage that chromatic aberration does not occur because there is no refracting surface. When a surface mirror is used as in this embodiment,
In order to prevent the occurrence of an error in the position between the surfaces, it is preferable to form each reflecting surface integrally.

[Embodiment 7] FIG. 16 is a sectional view in the YZ plane of an optical system according to Embodiment 7 of the present invention. This embodiment has a horizontal angle of view of 5
It is a shooting optical system with 2.0 degrees and vertical angle of view of 40.0 degrees. FIG. 16 also shows the optical path. This embodiment is an example in which an optical system is configured by a hollow block (optical element) having a plurality of surface reflecting mirrors and two refraction lenses.

The configuration data of this embodiment is as follows.

[0169]

[Outside 13]

[0170]

[Outside 14]

In FIG. 16, reference numeral 60 denotes a hollow block (optical element) having a plurality of curved reflecting surfaces formed therein. 71,
Reference numeral 72 denotes a convex lens (refractive optical system), which is disposed at the entrance and exit of the optical element 60, respectively. On the inner surface of the optical element 60, four reflecting surfaces of a concave mirror R4, a convex mirror R5, a concave mirror R6, and a reflecting surface R7 are formed in the order of passage of light rays from the object. R1 is a stop (entrance pupil) arranged on the object side of the convex lens 71, and R10 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system. All reference axes are on the paper (YZ plane).

The optical element 60, the convex lenses 71 and 72
These constitute one element of the optical system 70.

Next, the image forming operation in this embodiment will be described. The light flux 1 from the object is restricted by the stop (entrance pupil) R1 and then refracted by the refraction surfaces R2 and R3 of the convex lens 71, converges, enters the optical element 70, and enters the reflection surface R4.
After being reflected at the surface, an image is once formed near the reflecting surface R5 and then
After being sequentially reflected by R5, R6, and R7, the light exits from the optical element 70, enters the convex lens 72, is refracted by the refraction surfaces R8, R9, and is re-imaged on the final imaging surface R10. Object ray is surface R4
And the surface R5, and then form a reduced image on the final imaging surface R10. The pupil ray forms an intermediate image between the plane R6 and the plane R7.

As described above, the optical system 70 has the refractive power of the plurality of curved mirrors in the optical element 60 and the two convex lenses 7.
With the refractive powers of 1, 72, the lens unit functions as a lens unit having desired optical performance and having a positive refractive power as a whole.

FIG. 17 shows a lateral aberration diagram of the optical system of this embodiment.

In this embodiment, the refraction system is disposed on each of the entrance side and the exit side of the optical element 60 using the hollow mirror surface, so that the refraction caused by the small refractive index (= 1.0) in the reflection in the air. It compensates for the lack of power.

Further, if a surface reflecting mirror is used, dust or the like adhering to the surface is likely to appear as a shadow on the screen during photographing. In this embodiment, however, the two convex lenses 71 and 72 and the optical element 60 are formed integrally. This prevents dust from entering.

Further, in this embodiment, a convex lens is arranged on the light incident side of the optical system to converge the light rays, thereby preventing the first reflecting surface R4 of the optical element 60 from becoming large. The refractive power is supplemented by arranging the convex lens 72 also on the light exit side.

[Eighth Embodiment] FIG. 18 is a sectional view of an optical system according to an eighth embodiment of the present invention in the YZ plane. This embodiment has a horizontal angle of view of 5
It is a photographic optical system with 2.6 degrees and a vertical angle of view of 40.6 degrees. FIG. 18 also shows the optical path.

The configuration data of this embodiment is as follows.

[0181]

[Outside 15]

[0182]

[Outside 16]

In FIG. 18, reference numeral 10 denotes an optical element having two refracting surfaces and a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, in the order of passage of light rays from the object, the four reflecting surfaces of the concave refracting surface (incident surface) R2 and the concave mirror R3, the reflecting surface R4, the reflecting surface R5, and the concave mirror R6 having negative refracting power and the negative reflecting surface. A concave refracting surface (exit surface) R7 having a refractive power of? R1 is a stop (entrance pupil) arranged on the object side of the optical element 10, and R8 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.
All reference axes are on the paper (YZ plane).

Each of the two refracting surfaces is a rotationally symmetric spherical surface, and all the surfaces are symmetrical only with respect to the YZ plane.

Next, the image forming operation in this embodiment will be described. The luminous flux 1 from the object coming from the Z (-) direction is regulated by a stop (entrance pupil) R1 and then incident on the entrance surface R2 of the optical element 10 to undergo a diverging action, and then by the concave mirror R3. The light is reflected and forms an image once, and then reflected one after another on the surfaces R4, R5, and R6, exits from the exit surface R7, and is re-imaged on the final imaging surface R8.

The object ray forms an intermediate image near the plane R4, and the pupil ray forms an intermediate image near the plane R5.

As described above, the optical element 10 is formed as a lens unit having desired optical performance and having a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

FIG. 19 shows a lateral aberration diagram of the optical system of this embodiment.

In this embodiment, the incidence surface R2 is a spherical concave refraction surface, and the off-axis principal ray is concentric on the object side to reduce the occurrence of various off-axis aberrations. Also, the surface R7, which is the exit surface, is a concave concave refracting surface, so that axial rays are concentric on the image side, thereby suppressing spherical aberration and axial chromatic aberration.

[Embodiment 9] FIG. 20 is a sectional view in the YZ plane of an optical system according to Embodiment 9 of the present invention. This embodiment has a horizontal angle of view of 6
This is a shooting optical system with a 3.4 ° vertical angle of view of 49.6 °. FIG. 20 also shows the optical path. The configuration data of the optical system is as follows.

[0191]

[Outside 17]

[0192]

[Outside 18]

In FIG. 20, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, there are five reflecting surfaces of a convex refracting surface (incident surface) R2 and a concave mirror R3, a convex mirror R4, a concave mirror R5, a reflecting surface R6, and a concave mirror R7 having a positive refracting power in the order of passage of light rays from the object. And a convex refractive surface (exit surface) R8 having a positive refractive power. R1 is a stop (entrance pupil) disposed on the object side of the optical element 10, and R9 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

Each of the two refracting surfaces is a rotationally symmetric spherical surface, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation in this embodiment will be described. The light flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop (entrance pupil) R1, reflected by the surface R3, forms an image once, and then forms the surfaces R4 and R5. , R
The light is successively reflected at 6, R7, exits from the exit surface R8, and is re-imaged on the final imaging surface R9. The object ray forms an intermediate image between the plane R3 and the plane R4, and the pupil ray forms an intermediate image near the plane R6.

FIG. 21 shows a lateral aberration diagram of the optical system of this embodiment.

In this embodiment, the direction of the reference axis incident on the optical element 10 and the direction of the reference axis emerging therefrom are parallel and opposite. Further, the reference axes including the incoming and outgoing light are all placed in the plane of the paper (YZ plane).

As described above, the optical element 10 is formed as a lens unit having a desired optical performance and a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

In this embodiment, focusing on a short-distance object is performed by moving the entire optical system with respect to the imaging surface R9 of the imaging device. In particular, in the present embodiment, since the direction of the reference axis incident on the optical element 10 and the direction of the reference axis exiting from the optical system 10 are parallel, the direction of the reference axis exiting the entire optical system (Z-axis direction). By moving the lens in parallel, a focusing operation can be performed in the same manner as in a conventional lens system.

In the present embodiment, by making the surface R2, which is the entrance surface, a spherical convex refraction surface, the effective diameter of the first reflection surface R3 becomes large when the off-axis principal ray is converged to have a wide angle of view. Has been prevented. The exit surface R8 is also a spherical convex refraction surface to prevent the back focus from becoming too long, and to control the off-axis rays so that the off-axis chief rays become image-side telecentric.

[Embodiment 10] FIG. 22 shows Embodiment 10 of the present invention.
FIG. 3 is a sectional view of the optical system No. 0 in the YZ plane. This embodiment is an imaging optical system having a horizontal angle of view of 63.4 ° and a vertical angle of view of 49.6 °. FIG.
Also shows the optical path. The configuration data of the optical system is as follows.

[0202]

[Outside 19]

[0203]

[Outside 20]

In FIG. 22, reference numeral 10 denotes an optical element having a plurality of curved reflecting surfaces, which is made of a transparent material such as glass. On the surface of the optical element 10, there are five convex refracting surfaces (incident surfaces) R2, concave mirrors R3, reflecting surfaces R4, reflecting surfaces R5, reflecting surfaces R6, and concave mirrors R7 having a positive refractive power in the order of passage of light rays from the object. A reflection surface and a concave refraction surface (exit surface) R8 having a negative refractive power are formed. R1 is a stop (entrance pupil) disposed on the object side of the optical element 10, and R9 is a final image forming plane, on which an image pickup surface of an image pickup device such as a CCD is located. Reference numeral 5 denotes a reference axis of the photographing optical system.

Each of the two refracting surfaces is a rotationally symmetric spherical surface, and all the reflecting surfaces are surfaces symmetric only with respect to the YZ plane.

Next, the image forming operation in this embodiment will be described. The light flux 1 from the object is incident on the entrance surface R2 of the optical element 10 after the amount of incident light is regulated by the stop (entrance pupil) R1, reflected by the surface R3, forms an image once, and then forms the surfaces R4 and R5. , R
The light is successively reflected at 6, R7, exits from the exit surface R8, and is re-imaged on the final imaging surface R9. The object ray forms an intermediate image between the plane R3 and the plane R4, and the pupil ray forms an intermediate image between the plane R5 and the plane R6.

FIG. 23 shows a lateral aberration diagram of the optical system of this embodiment.

In this embodiment, the direction of the reference axis incident on the optical element 10 and the direction of the reference axis emerging therefrom are parallel and opposite. Further, the reference axes including the incoming and outgoing light are all placed in the plane of the paper (YZ plane).

As described above, the optical element 10 is formed as a lens unit having desired optical performance and having a positive refractive power as a whole by the refractive power of the entrance / exit surface and the refractive power of the plurality of curved reflecting mirrors therein. It is functioning.

In this embodiment, focusing on a short-distance object is performed by moving the entire optical system with respect to the imaging surface R9 of the imaging device. In particular, in this embodiment, since the direction of the reference axis entering the optical element 10 and the direction of the reference axis exiting from the optical system 10 are parallel, the direction of the reference axis exiting the entire optical system (Z-axis direction). By moving the lens in parallel, a focusing operation can be performed in the same manner as in a conventional lens system.

In this embodiment, the entrance surface R2 is formed as a spherical convex refraction surface, thereby preventing the effective diameter of the first reflection surface R3 from increasing when the off-axis principal ray is converged to have a wide angle of view. ing. The exit surface R8 is also a spherical concave refraction surface, so that a long back focus is secured for on-axis rays, and the arrangement is such that off-axis rays are telecentric on the image side.

Although the embodiments of the present invention have been described above, the optical element constituting the present invention is required to have at least three reflecting surfaces each having a curved surface. This is because with an eccentric reflecting surface having two curved surfaces as in the conventional example, it is extremely difficult to correct the aberration of the off-axis light beam even though the aberration of the axial light beam can be corrected. In the present invention, at least three eccentric reflecting surfaces having a refractive power are used, so that the aberration is favorably corrected over the entire surface of the two-dimensional image plane.

Also, a light incident surface and a light emitting surface are provided on the surface of the transparent body.
Examples 1 to 5 and Examples 8 to 1 using an optical element provided with at least three reflection surfaces for internal reflection formed of curved surfaces
At 0, the optical element is configured such that 70% or more of the length of the reference axis in the optical element is in one plane. Specifically, in Examples 1 to 4 and Examples 8 to 10, the reference axes are all in one plane. Thereby, the reflection type optical system of the present invention can be configured to be thinnest in the direction perpendicular to the plane. The fifth embodiment is an example in which an object light beam is incident from a direction orthogonal to a plane where most of the reference axes exist.
Also in this case, since the reference axis of 70% or more is in one plane, an extremely thin optical system can be formed in a direction perpendicular to the plane. Preferably, 80% or more of the reference axes are in one plane.

Next, the values of the conditional expressions (1) to (4) for the reflecting surface of the first curved surface counted from the object side in each embodiment are described below.

[0215]

[Table 1]

In all of the above embodiments, the stop is located closest to the object side of the optical system. However, in the embodiment of the present invention, the pupil actually forms an image in the optical system. The optical element may be divided into two with the image forming position as a boundary, and an aperture may be provided therebetween. In this way, the entrance pupil is formed closest to the object side of the optical system as in the above-described embodiment, so that the optical system is equivalent to the above-described embodiment, and the same effect can be obtained. At this time, the same effect as in the above embodiment can be obtained by forming the entrance pupil at a position closer to the object side than the reflecting surface of the first curved surface, counting from the object side of the optical element where the light beam from the object first enters. Can be

[0219]

According to the present invention, the size of the entire mirror optical system can be reduced by setting each element as described above, and the arrangement accuracy (assembly accuracy) of the reflection mirror, which is common in the mirror optical system, can be improved. It is an object of the present invention to provide an optical element that can be moderated and an imaging device including the optical element.

Further, by having a plurality of reflecting surfaces, giving an appropriate refractive power to the plurality of reflecting surfaces, and eccentrically arranging the respective reflecting surfaces, the optical path is bent into a desired shape and the entire length in a predetermined direction is reduced. It is possible to achieve a shortened optical element and an imaging device including the same.

In addition, according to the present invention, (a-1) the practice of the present invention in which the stop is on the front side of the optical element or the entrance pupil is on the object side of the first reflecting surface counted from the object side of the optical element In the case of the example, the first
The convergence of the reflecting surface contributes to downsizing of the optical system. This is to make the optical system even thinner by forming an intermediate image of the pupil ray (principal ray) at a stage close to the entrance surface, and to converge the off-axis principal ray that has exited the stop R1 before it spreads greatly. This suppresses an increase in the effective diameter of each surface after the first reflecting surface R3 due to the wide angle of the system. (A-2) A spheroid whose two focal points are the apparent stop center (the entrance pupil position with respect to the reflecting surface) when the first reflecting surface is viewed from the reflecting surface and a point on the bent reference axis inside the optical system. With a plane, an off-axis chief ray can be imaged internally with almost no aberration, thereby reducing the thickness of the optical element and suppressing an increase in off-axis aberrations at an initial stage. (A-3) In the embodiment of the present invention, when a refracting power is given to the entrance surface and the exit surface of the optical element, a special effect is produced. For example, by making the incident surface a concentric concave surface with respect to the off-axis principal ray, the occurrence of various off-axis aberrations can be reduced. In addition, if the emission surface is formed as a convex surface, it is possible to prevent the back focus from becoming too long. On the other hand, if the incident surface is made convex, off-axis rays converge on this surface, so that the effective diameter of the first reflecting surface can be prevented from increasing. (A-4) Further, the shape of the exit surface is determined so that the off-axis principal ray (pupil ray) to this surface is substantially parallel, that is, telecentric on the exit side (image side) according to the angle of incidence. Is also good. This is because when using an image sensor such as a CCD,
Since there is a gap between the color filter of the CCD and its imaging surface, it is effective to prevent the color separation performance from being changed by the incident angle to the imaging device. If the optical system is made telecentric on the image side, the principal rays of the on-axis and off-axis light beams are both substantially parallel to the optical axis, and the angle of incidence on the CCD is substantially constant over the entire light receiving surface. (A-5) Further, in the embodiment of the present invention, most of the reflecting surfaces are surfaces having only one symmetric surface, whereas the shapes of the input and output surfaces are rotationally symmetric with respect to the reference axis. .
Thereby, the reference axis can be accurately measured when manufacturing and evaluating the optical system. Further, by making the refracting surface rotationally symmetric, it is possible to reduce the occurrence of asymmetric chromatic aberration. (A-6) In the conventional optical system shown in FIG. 28, the reflection surfaces on the entrance side and the exit side have a refracting power, but the reflection between them merely plays a role of a so-called light guide for guiding a light beam. . In the embodiment of the present invention, by forming at least three reflecting surfaces having refractive power integrally, a compact and free shape having both a function of bending an optical axis and a function of correcting aberration with respect to a two-dimensional image plane is provided. A high-performance imaging optical system capable of achieving the above is obtained. (A-7) In the embodiment of the present invention, the object ray and the pupil ray are each formed into an intermediate image. Then, compared with the conventional photographing optical system, each ray is intermediately imaged at a stage closer to the entrance surface of the optical element, thereby suppressing the effective diameter of each surface on the image side from the stop, and the cross section of the optical system Has succeeded in reducing the size. (A-8) Further, in the embodiment of the present invention, the reference axis bent inside the optical element is included in the same plane, that is, in the YZ plane. As a result, the direction (X
Direction) is reduced in size. (A-9) Each of the reflecting surfaces constituting the optical element is a so-called eccentric reflecting surface in which the normal line at the intersection between the reference axis for input and output and the reflecting surface does not coincide with the direction of the reference axis. This prevents vignetting that occurs in the conventional mirror optical system, and allows a more flexible arrangement, thereby achieving a space-efficient, compact and free-form optical element. (A-10) Further, the shape of each reflecting surface is a surface having a different radius of curvature between two orthogonal surfaces (yz surface and xz surface). This is to suppress the eccentric aberration caused by the eccentric arrangement of each reflecting surface. By making this reflecting surface asymmetrical, various aberrations are corrected well and desired optical performance is achieved. . (A-11) In the present invention, molding can be performed by forming the inside with an optical element filled with a transparent body such as glass, and mass productivity and cost reduction can be achieved. On the other hand, if an optical element having a surface mirror formed inside a hollow block is used as an embodiment, the weight of the optical system can be reduced and the chromatic aberration can be reduced. (A-12) In the present invention, the stop is disposed immediately before the entrance surface of the optical element, or the entrance pupil is on the object side of the first reflection surface counted from the object side of the optical element. In the case of a conventional photographing optical system, the stop is arranged inside the optical system, and the entrance pupil is often located deep inside the optical system, and as the distance from the stop to the entrance surface closest to the object side is larger, However, there has been a problem that the effective beam diameter on the incident surface increases with an increase in the angle of view. In the present embodiment, the stop or the entrance pupil is arranged on the object side of the optical element (the light beam incident side of the optical system), thereby suppressing the enlargement of the photographing optical system that occurs when the optical system is widened. (A-13) When the direction of the reference axis entering the optical system and the direction of the reference axis exiting are made parallel, the entire optical system is moved in parallel to the input / output reference axis, thereby performing the focusing operation in the same manner as the conventional lens system. Can be performed, and the photographing range at that time does not change. (A-14) As a characteristic of the reflection optical system, the directions of the reference axis to be incident and the reference axis to be emitted can be variously changed by combining the arrangement of the respective surfaces.

That is, according to the present invention, various optical elements having different directions of the incident reference axis and the exit reference axis can be configured, so that a layout having a high degree of freedom according to the form of a camera incorporating a photographing optical system can be realized. It is possible to take.
Thus, an optical element having at least one effect and an imaging device including the same can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a coordinate system according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view in the YZ plane of the optical system according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view in the YZ plane of the optical system according to the first embodiment of the present invention.

FIG. 4 is a lateral aberration diagram of the first embodiment.

FIG. 5 is a cross-sectional view in the YZ plane of an optical system according to a second embodiment of the present invention.

FIG. 6 is a lateral aberration diagram of the second embodiment.

FIG. 7 is a cross-sectional view of the optical system according to a third embodiment of the present invention in the YZ plane.

FIG. 8 is a lateral aberration diagram of the third embodiment.

FIG. 9 is a sectional view of the optical system according to a fourth embodiment of the present invention in the YZ plane.

FIG. 10 is a lateral aberration diagram of the fourth embodiment.

FIG. 11 is a sectional view and a side view in the YX plane of an optical system according to a fifth embodiment of the present invention.

FIG. 12 is a perspective view of a fifth embodiment.

FIG. 13 is a lateral aberration diagram of the fifth embodiment.

FIG. 14 is a sectional view of an optical system according to a sixth embodiment of the present invention in the YZ plane.

FIG. 15 is a lateral aberration diagram of the sixth embodiment.

FIG. 16 is a sectional view of the optical system according to a seventh embodiment of the present invention in the YZ plane.

FIG. 17 is a lateral aberration diagram of the seventh embodiment.

FIG. 18 is a sectional view of the optical system according to Example 8 of the present invention in the YZ plane.

FIG. 19 is a lateral aberration diagram of the eighth embodiment.

FIG. 20 is a sectional view of an optical system according to a ninth embodiment of the present invention in the YZ plane.

FIG. 21 is a lateral aberration diagram of the ninth embodiment.

FIG. 22 is a sectional view of the optical system according to a tenth embodiment of the present invention in the YZ plane.

FIG. 23 is a lateral aberration diagram of the tenth embodiment.

FIG. 24 is a basic configuration diagram of a Cassegrain reflection telescope.

FIG. 25 is an explanatory diagram of a first method of separating a principal ray from an optical axis and preventing vignetting in a mirror optical system.

FIG. 26 is an explanatory diagram of a second method of separating a principal ray from an optical axis to prevent vignetting in a mirror optical system.

FIG. 27 is a configuration diagram of an observation optical system having a curvature on a prism reflection surface.

FIG. 28 is a configuration diagram of an observation optical system having a curvature on another prism reflection surface.

[Explanation of symbols]

 Ri surface R1 Aperture Di Surface spacing along reference axis Ndi Refractive index νdi Abbe number

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihiro Namba 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Saruwatari 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Kenshi Akiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Examiner, Canon Inc. Masaaki Moriuchi (56) References JP-A-3-180810 (JP, A) JP-A-2 JP-A-297516 (JP, A) JP-A-5-12704 (JP, A) JP-A-6-139612 (JP, A) JP-A-7-36959 (JP, A) JP-A-7-5364 (JP, A) US Pat. No. 5,063,586 (US, A) US Pat. No. 3,674,334 (US, A) US Pat. No. 4,775,217 (US, A) US Pat. No. 4,812,030 (US, A) US Pat. No. 4,993,818 (US, A) US Pat. No. 5,144,476 (US, A) International public 94/12905 (WO, A1) (58 ) investigated the field (Int.Cl. ^7, DB name) G02B 9/00 - 17/08 G02B 21/02 - 21/04 G02B 25/00 - 25/04

Claims (9)

(57) [Claims] 1. A center of an image plane, a stop or an entrance pupil or an exit.
The center of the pupil or the first surface of the optical system or the center of the last surface
When the path of the light beam passing through the shift is set as a reference axis, the path has at least three curved reflecting surfaces inclined with respect to the reference axis, and the curved reflecting surface defines only one pair of symmetric surfaces.
An optical element having an aspheric surface and forming an intermediate image inside the element. 2. The method according to claim 1, wherein each of the plurality of curved reflecting surfaces is a curved surface.
Local coordinate system with the origin at the intersection of the surface reflection surface and the reference axis
Using xyz, let a, b, t be coefficients representing the surface shape
Can, A = (a + b) · (y 2 · cos 2 t + x 2) B = 2a · b · cos t [1 + {(ba) · y · sin t / (2a · b)} + [ 1 + {(ba)
・ Y ・ sin t / (a ・ b)}-{y ² / (a ・ b)}-{4a ・ b ・ cos ² t + (a + b) ² sin
² t} x ² / (4a ² b ² cos ² t)] ^1/2 ] and z = A / B + C ₀₂ y ² + C ₂₀ x ² + C ₀₃ y ³ + C ₂₁ x ² y + C ₀₄ y ⁴ + C ₂₂ x ² y ² + C ₄₀
claim, characterized in that Ru der those defined by x ⁴ 1
Optical element of. Wherein said at least three optical element according to claim 1 or 2 curved reflecting surface, characterized in that successively deflecting the light beam. 4. The optical element according to claim 1 , wherein said optical element has a curved refraction surface. 5. The optical element according to claim 1, 2 or 3, wherein the curved reflecting surface is provided on the surface of the surface mirror. 6. The optical element according to claim 1, 2 or 3 wherein the curved reflecting surfaces, characterized in that provided on the surface of the transparent body. 7. A center of an image plane, an aperture or an entrance pupil or an exit.
The center of the pupil or the first surface of the optical system or the center of the last surface
When the reference axis the path of light rays through the Zureka have inclined curved reflecting surface with respect to the reference axis, and the curved surface reflecting surface has only one plane of symmetry defining a pair of symmetrical surfaces aspheric And an aperture between the two optical elements, wherein an optical element on the object side of the two optical elements forms an intermediate image of the object, The stop forms an image on the object side of the first curved reflecting surface , counting from the object side of the optical element on the object side.
Characterized by having at least three curved reflecting surfaces
Optical system . 8. An optical element according to claim 1 , wherein:
An imaging apparatus comprising the optical system according to claim 7 . 9. An optical element according to claim 1 ,
An image forming apparatus comprising the optical system according to claim 7 .