JP2000089119A - Optical system and image-forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system having lesser number of parts and a thin thickness for linearly focalizing light from a point light source and an image-forming device using the same. SOLUTION: This is an optical system having at least a curved reflecting surface 7, and converting the light, which is emitted from almost a point light source 2 eccentrically placed in an across-section crossing the reflecting surface 7 and travels in the cross section, into approximately parallel light, and also almost converging the light from the light source going outside of the cross-section on one line 4 positioned in the cross-section. In such a manner, it is possible to realize an optical system having lesser number of parts and the thin thickness for focalizing the light from the point light source and an image-forming device using the same. Such an image-forming device is, for example, used as an electronic camera of one-piece design or an attachable and detachable printer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical system and an image forming apparatus using the optical system, and more particularly to an optical system for an image forming apparatus such as an electronic camera having a printer and the image forming apparatus. It is.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using a liquid crystal shutter array has been proposed in Japanese Patent Application Laid-Open No. 8-300731. In this image forming apparatus, a slit 34 is provided so as to surround a light source lamp 32 having a filament 33 as shown in a vertical sectional view in FIG. Is provided with a rotating color filter 31 composed of a red color filter 40r, a green color filter 40g, and a blue color filter 40b. An off-axis parabolic mirror 35 is disposed with the filament 33 as a focal point. The light source lamp 32 rotates around the slit 34. With such an arrangement, the white light emitted from the filament 33 of the light source lamp 32 passes through one of the color filters of the rotating color filter 31 to become a light flux of the color of the color filter, and the off-axis parabolic mirror 3
5 is reflected and becomes parallel light. The parallel light is reflected by the flat mirror 3
The light is reflected at 6 and enters the one-dimensional liquid crystal shutter array 37 substantially perpendicularly, and the transmittance is controlled for each pixel arranged in the one-dimensional direction (main scanning direction) based on the image signal. The light beam transmitted through the liquid crystal shutter array 37 is condensed linearly on the photosensitive member 39 by the cylindrical lens 38. The photoconductor 39 is moved in a sub-scanning direction perpendicular to the main scanning direction.

Accordingly, the image signal supplied to the liquid crystal shutter array 37 in synchronization with the rotation of the rotating color filter 31 is sequentially switched to a red image signal, a green image signal, and a blue image signal of one scanning line, and By moving the photoconductor 39 in synchronization with the scanning, a color image can be formed on the photoconductor 39.

[0004]

In the optical system of such an image forming apparatus, a light source lamp 32 is disposed above an off-axis parabolic mirror 35, as is apparent from FIG. Since the light source 39 is disposed under the light source 39, the distance from the light source lamp 32 to the photoconductor 39 is increased.
When such an image forming apparatus is used, for example, as a printer for an electronic camera equipped with a printer (Japanese Patent Application Laid-Open No. 10-13844), an increase in the thickness of the optical system undesirably leads to an increase in the size of the camera itself. Also, the components constituting the optical system require two off-axis parabolic mirrors 35 and a cylindrical lens 38, even if the plane reflecting mirror 36 is excluded. Leads to up.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an optical system having a small number of parts for condensing light from a point light source linearly and having a small thickness. An object of the present invention is to provide an image forming apparatus using an optical system.

[0006]

An optical system according to the present invention that achieves the above object has at least a curved reflecting surface, and is provided by a light source having a substantially point-like shape which is eccentrically arranged in one section crossing the reflecting surface. Converts light traveling in the cross-section into substantially parallel light, and
The light from the light source to the outside of the cross section is substantially converged on one straight line located in the cross section.

In this case, it is desirable that the straight line is substantially orthogonal to the substantially parallel light in the cross section.

It is desirable that the light from the light source be substantially converged on the straight line in another section crossing the reflecting surface and orthogonal to the section and the straight line.

[0009] The reflecting surface can be configured as a back mirror or a front mirror. In the case of a back mirror, it has a curved surface shape of at least one of a refracting surface and a reflecting surface, and in the case of a front mirror, the curved surface shape of the reflecting surface has a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity. It is desirable to be.

The rotationally asymmetric surface shape is desirably a plane-symmetric free-form surface shape having only one plane of symmetry.

In the image forming apparatus of the present invention, pixels are arranged in parallel on the optical path emitted from the above-described optical system toward the linear convergence position in parallel with the linear direction of the convergence position.
A one-dimensional optical shutter array is arranged, a photoreceptor is arranged so as to be movable through the linear converging position, and the transmittance of each pixel of the one-dimensional optical shutter array is controlled based on a video signal, and the control is performed. It is characterized in that the movement of the photosensitive member is controlled synchronously.

In this case, the image of the subject may be integrated or detachably attached to an imaging device capable of taking an image of the subject and converting the image into a video signal so as to form an image of the taken subject.

Hereinafter, the reason and operation of the above configuration in the present invention will be described in order. An optical system according to the present invention for achieving the above object has at least a curved reflecting surface, and transmits light traveling in the cross section from a substantially point-like light source eccentrically arranged in one cross section across the reflecting surface. Convert to parallel light,
Further, the optical system is characterized in that light traveling from the light source to the outside of the cross section is substantially converged on one straight line located in the cross section.

With such a configuration, since one optical component can be used and the point light source can be disposed eccentrically in the same plane as the optical component, the thickness for condensing light from the point light source linearly can be obtained. Optical system can be realized. And
Since the number of parts is small, it is possible to realize an inexpensive optical system in which position adjustment during assembly is easy.

A straight line on which light converges one-dimensionally is
It is desirable that the light from the light source is substantially orthogonal to the light traveling in parallel in one cross section, and that the light from the light source is on the straight line in another cross section that crosses the reflecting surface and is orthogonal to the cross section and the straight line. It is desirable that the shape be such that it converges substantially.

The above-mentioned reflecting surface of the optical system of the present invention can be in the form of a back mirror or a front mirror. And in the case of a back mirror, the curved surface shape of at least one of a refraction surface and a reflection surface, in the case of a front mirror,
It is desirable that the curved surface of the reflecting surface has a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity. The rotationally asymmetric surface shape is desirably a plane-symmetric free-form surface shape having only one plane of symmetry.

Here, when a ray that is emitted from the point light source, is reflected by the optical system, passes through the center of the stop, and reaches the center of a linear image is defined as an axial chief ray, at least the reflection surface is at least with respect to the axial chief ray. If it is not decentered, the incident ray and the reflected ray of the axial chief ray will take the same optical path, and the axial chief ray will be blocked in the optical system. As a result, an image is formed only by the light flux whose central portion is shielded, and the center becomes dark or the image is not formed at the center at all.

When the reflecting surface is decentered with respect to the axial principal ray, at least one of the reflecting surface and the refracting surface constituting the optical system of the present invention is preferably a rotationally asymmetric surface. The reason will be described in detail below. First, a coordinate system to be used and a rotationally asymmetric surface will be described. An optical axis defined by a straight line until the on-axis principal ray intersects the first surface of the optical system is defined as a Z axis, and is orthogonal to the Z axis and within an eccentric plane of each surface constituting the optical system. An axis is defined as a Y axis, and an axis orthogonal to the optical axis and orthogonal to the Y axis is defined as an X axis. The ray tracing direction will be described in terms of forward ray tracing from the light source to the image plane.

In general, in a spherical lens system composed of only spherical lenses, spherical aberration caused by a spherical surface and aberrations such as coma and field curvature are mutually corrected on several planes, and the aberration as a whole is reduced. Configuration.

On the other hand, in order to favorably correct aberrations with a small number of surfaces, a rotationally symmetric aspherical surface or the like is used. This is to reduce various aberrations generated on the spherical surface. However, in a decentered optical system, it is impossible to correct rotationally asymmetric aberration generated by decentering by a rotationally symmetric optical system. The rotationally asymmetric aberrations caused by this eccentricity include distortion, field curvature, astigmatism and coma which also occur on the axis.

First, the rotationally asymmetric field curvature will be described. For example, light rays incident on a concave mirror decentered from an object point at infinity are reflected and imaged on the concave mirror, but after the light rays hit the concave mirror, the rear focal length to the image plane is
When the image field side is air, the radius of curvature becomes half of the radius of curvature of the portion hit by the light beam. Then, as shown in FIG. 8, an image plane inclined with respect to the axial principal ray is formed. As described above, it is impossible to correct rotationally asymmetric curvature of field with a rotationally symmetric optical system.

In order to correct the tilted curvature of field by the concave mirror M itself, which is its source, the concave mirror M is constituted by a rotationally asymmetric surface. In this example, the curvature is strong in the positive direction of the Y axis ( If the refractive power is increased) and the curvature is decreased (the refractive power is decreased) in the negative direction of the Y axis, the correction can be made. In addition, by arranging a rotationally asymmetric surface having the same effect as the above configuration in the optical system separately from the concave mirror M, a flat image surface can be obtained with a small number of components. In addition, the rotationally asymmetric surface is preferably a rotationally asymmetric surface shape having no rotationally symmetric axis both inside and outside the surface, which is preferable in terms of increasing the degree of freedom and correcting aberrations.

Next, rotationally asymmetric astigmatism will be described. As described above, the eccentrically arranged concave mirror M
In this case, astigmatism as shown in FIG. 9 also occurs for axial rays. Astigmatism can be corrected by appropriately changing the curvature in the X-axis direction and the curvature in the Y-axis direction of the rotationally asymmetric surface, as described above. Also in this case, astigmatism can be corrected with a small number of components by arranging a rotationally asymmetric surface having the same effect as the above configuration in the optical system separately from the concave mirror M.

Further, rotationally asymmetric coma will be described. Similarly to the above description, in the concave mirror M arranged eccentrically, coma as shown in FIG. To correct the coma aberration, the inclination of the surface can be changed as the distance from the origin of the X axis of the rotationally asymmetric surface increases, and the inclination of the surface can be appropriately changed depending on the sign of the Y axis. Also in this case, by arranging a rotationally asymmetric surface having the same effect as the above configuration in the optical system separately from the concave mirror M, it is possible to correct coma with a small number of components.

The rotationally asymmetric surface used in the present invention is preferably a plane-symmetric free-form surface having only one plane of symmetry. Here, the free-form surface used in the present invention is:
It is defined by the following equation (a). Note that the Z axis of the definition formula is the axis of the free-form surface.

[0026] Here, the first term of the equation (a) is a spherical term, and the second term is a free-form surface term.

In the spherical term, c: curvature of the vertex k: conic constant (conical constant) r = √ (X ² + Y ² ).

The free-form surface term is Here, C _j (j is an integer of 2 or more) is a coefficient.

The free-form surface generally includes an XZ plane,
Although neither YZ plane has a plane of symmetry, in the present invention, X
By setting all the odd-order terms to 0, a free-form surface having only one symmetry plane parallel to the YZ plane is obtained. For example, in the above definition formula (a), C ₂ , C ₅ , C ₇ ,
_{C 9, C 12, C 14} , C 16, C 18, C 20, C 23, C 25, C
₂₇ , C ₂₉ , C ₃₁ , C ₃₃ , C ₃₅ ...

By setting all odd-numbered terms of Y to 0, a free-form surface having only one symmetry plane parallel to the XZ plane is obtained. For example, in the above definition formula, C ₃ ,
_{C 5, C 8, C 10} , C 12, C 14, C 17, C 19, C 21, C
₂₃ , C ₂₅ , C ₂₇ , C ₃₀ , C ₃₂ , C ₃₄ , C ₃₆ ...

One of the directions of the symmetry plane is a symmetry plane, and the eccentricity in the corresponding direction, for example, the eccentricity direction of the optical system with respect to the symmetry plane parallel to the YZ plane is in the Y-axis direction. By making the eccentric direction of the optical system the X-axis direction with respect to the symmetric plane parallel to the XZ plane, it is possible to effectively correct rotationally asymmetric aberrations caused by the eccentricity while improving the productivity. Becomes possible.

Further, the above-mentioned definition formula (a) is shown as one example as described above, and the present invention uses a rotationally asymmetric surface having only one plane of symmetry to produce rotation caused by eccentricity. It is characterized by correcting asymmetric aberrations and at the same time improving productivity, and it goes without saying that the same effect can be obtained for any other definitional expressions.

First, parameters are defined here. As shown in FIG. 11, the eccentric direction of the eccentric optical system S is Y
When taken in the axial direction, a light beam with a minute height d in the YZ plane parallel to the axial principal ray of the decentered optical system S is incident from the object side, and the light beam emitted from the decentered optical system S is The angle formed when the axial principal ray is projected on the YZ plane is δy, and δy / d
Is a power Py of the decentered optical system S in the Y direction, and a light beam having a minute height d in the X direction parallel to the axial principal ray of the decentered optical system and orthogonal to the YZ plane is incident from the object side. Δx is the angle formed when the ray projected from S and the plane orthogonal to the YZ plane of the axial principal ray and projected onto a plane containing the axial principal ray are formed.
Δx / d is the power Px of the decentered optical system S in the X direction. The reciprocals of these powers are defined as the focal length Fy of the eccentric optical system in the Y direction and the focal length Fx of the eccentric optical system in the X direction, respectively.

When the section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system according to the present invention is a YZ plane, the free-form surface constituting the optical system has The curvature of the free-form surface in the YZ plane at the position where the light beam strikes is CY1, and the curvature in the plane orthogonal to the YZ plane is CX1, Y.
The curvature in the YZ plane at the position where the light enters the free-form surface on the light source side of the light beam incident on the free-form surface from the light source in the Z-plane in the plane orthogonal to the CY2, YZ plane Is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, the curvature in the plane perpendicular to the YZ plane is CX6, , Y from the light source
OP1 denotes the optical path length from the refraction surface to the reflection surface of the light beam incident farthest from the light source among the light beams incident on this optical system in the -Z plane; The optical path length is OP2.

When the optical system of the present invention is constituted by a back mirror and its refracting surface is constituted by a free-form surface as in Example 1 described later, 0.4 ≦ Fx / Fy ≦ 0.9 (1) It is desirable to satisfy 0.4 which is the lower limit of this conditional expression
Is exceeded, the power in the X direction becomes too strong, and the imaging characteristics of convergent light deteriorate. If the upper limit of 0.9 is exceeded, it becomes difficult to design an optical system having a bright F-number.

It is desirable that the following condition is satisfied: 0.5 ≦ CY2 / CY6 ≦ 2.0 (2) 0.5 which is the lower limit of this conditional expression
Is exceeded, on the free-form surface, the Y component power on the light source side becomes too strong, and the angular characteristics of the parallel light flux are significantly deteriorated. When the value exceeds the upper limit of 2.0, the Y component power on the side far from the light source on the free-form surface becomes too strong,
The angle characteristic of the parallel light beam is significantly deteriorated.

More preferably, it is desirable to satisfy the following condition: 0.8 ≦ CY2 / CY6 ≦ 1.5 (3)

It is desirable that the following condition is satisfied: 0.5 ≦ CX2 / CX6 ≦ 2.0 (4) 0.5 which is the lower limit of this conditional expression
Is exceeded, the X component power on the light source side on the free-form surface becomes too strong, and it becomes difficult to correct the aberration of the converged light flux.
If the upper limit of 2.0 is exceeded, on the free-form surface, the X-component power on the side away from the light source becomes too strong, and it becomes difficult to correct the aberration of the converged light flux.

More preferably, it is desirable to satisfy the following condition: 0.8 ≦ CX2 / CX6 ≦ 1.8 (5)

It is desirable that the following condition is satisfied: 0.5 ≦ OP1 / OP2 ≦ 17.0 (6) 0.5 which is the lower limit of this conditional expression
Is exceeded, the Y component power on the light source side on the free-form surface becomes too strong on the free-form surface while being balanced with the conditional expressions (2) and (3), and the angular characteristics of the parallel light flux are significantly deteriorated. When the value exceeds the upper limit of 17.0, the Y component power on the side far from the light source on the free-form surface becomes too strong while balancing with the conditional expressions (2) and (3), and the angular characteristic of the parallel light beam is significantly deteriorated. I do.

Next, the optical system of the present invention is constituted by a back mirror,
When the reflecting surface is formed of a free-form surface as in Example 2 described later, it is desirable to satisfy the following condition: 0.4 ≦ Fx / Fy ≦ 0.9 (7) 0.4 which is the lower limit of this conditional expression
Is exceeded, the focal length in the X direction becomes too short, and the imaging characteristics of convergent light deteriorates. If the upper limit of 0.9 is exceeded, it becomes difficult to design an optical system having a bright F-number.

It is desirable to satisfy both of the following expressions: CY1 <CY2, CY1 <CY6 (8) When CY1 is larger than CY2, it becomes difficult to correct the spherical aberration on the light source side on the free-form surface, and the angular characteristics of the parallel light beam are significantly deteriorated. If CY1 is larger than CY6, it becomes difficult to correct spherical aberration on the free-form surface away from the light source,
The angle characteristics of the parallel light beam are significantly deteriorated.

It is desirable that the following condition is satisfied: 0.5 ≦ CY2 / CY6 ≦ 2.0 (9) 0.5 which is the lower limit of this conditional expression
Is exceeded, the Y-component power on the light source side on the free-form surface becomes too strong, and the parallelism of the parallel light flux is significantly deteriorated. If the upper limit of 2.0 is exceeded, the power of the Y component on the side of the free-form surface away from the light source becomes too strong, and the parallelism of the parallel light beam is significantly deteriorated.

More preferably, it is desirable to satisfy the following condition: 0.8 ≦ CY2 / CY6 ≦ 1.5 (10)

It is desirable that the following condition is satisfied: 0.5 ≦ CX2 / CX6 ≦ 2.0 (11) 0.5 which is the lower limit of this conditional expression
Is exceeded, the X component power on the light source side on the free-form surface becomes too strong, and it becomes difficult to correct the aberration of the converged light flux.
If the upper limit of 2.0 is exceeded, on the free-form surface, the X-component power on the side away from the light source becomes too strong, and it becomes difficult to correct the aberration of the converged light flux.

More preferably, it is desirable to satisfy 0.8 ≦ CX2 / CX6 ≦ 1.8 (12).

It is desirable that the following condition is satisfied: 15.0 ≦ OP1 / OP2 ≦ 30.0 (13) 15. lower limit of this conditional expression
When the value exceeds 0, the Y component power on the light source side on the free-form surface becomes too strong on the free-form surface while being balanced with the conditional expressions (9) and (10), and the angle characteristic of the parallel light beam is significantly deteriorated. When the value exceeds the upper limit of 30.0, the Y component power on the side far from the light source on the free-form surface becomes excessively strong on the free-form surface while being balanced with the conditional expressions (9) and (10), and the angular characteristic of the parallel light flux is significantly deteriorated. I do.

Next, the optical system of the present invention is constituted by a surface mirror,
When the reflecting surface is formed of a free-form surface as in Example 3 described later, it is desirable to satisfy 0.4 ≦ Fx / Fy ≦ 0.9 (14). 0.4 which is the lower limit of this conditional expression
Is exceeded, the focal length in the X direction becomes too short, and the imaging characteristics of convergent light deteriorate. If the upper limit of 0.9 is exceeded, it becomes difficult to design an optical system having a bright F-number.

It is desirable that the following condition is satisfied: 0.5 ≦ CY6 / CY2 ≦ 2.0 (15) 0.5 which is the lower limit of this conditional expression
Is exceeded, the Y-component power on the light source side on the free-form surface becomes too strong, and the parallelism of the parallel light flux is significantly deteriorated. If the upper limit of 2.0 is exceeded, the power of the Y component on the side of the free-form surface away from the light source becomes too strong, and the parallelism of the parallel light beam is significantly deteriorated.

More preferably, it is desirable to satisfy the following condition: 0.8 ≦ CY6 / CY2 ≦ 1.5 (16)

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical system according to the present invention will be described, and then embodiments of an image forming apparatus using the optical system will be described. 1 to 3 show a horizontal sectional view (a) and a vertical sectional view (b) of Examples 1 to 3, respectively, of an optical system according to the present invention. The horizontal cross section is YZ as shown in each figure.
Plane, and the vertical section is an XZ plane. The optical system 1 of these embodiments has one cross section (YZ) crossing the reflection surface 7 thereof.
When a ray emitted from a point light source 2 eccentrically arranged in the plane and reflected by the optical system 1 and passing through the center of the stop 3 and reaching the center of a linear image 4 is defined as an axial principal ray 5, an axial principal ray 5 converts the light traveling in the YZ plane into substantially parallel light, and converts the light from the point light source 2 out of the YZ plane into a linear image 4 located in the YZ plane. This is an optical system that converges to.

The optical system 1 according to the first embodiment shown in FIG. 1 has a refraction surface 6 composed of a rotationally asymmetric free-form surface having only the YZ plane represented by the above-mentioned equation (a) as a symmetric surface and a reflection composed of a spherical surface. The optical system 1 according to the second embodiment shown in FIG. 2 has a refracting surface 6 composed of a spherical surface and a reflecting surface composed of a rotationally asymmetric free-form surface having only a YZ plane as a symmetric surface. 7 is a back mirror composed of the optical system 1 of the third embodiment shown in FIG.
Is a surface mirror composed of a reflecting surface 7 consisting of a rotationally asymmetric free-form surface having the YZ plane as the only symmetric plane.

The constituent parameters of these embodiments will be described later. In each embodiment, as shown in FIGS. 1 to 3, a virtual surface for indicating the eccentric arrangement position of the refraction surface 6, the reflection surface 7, and the stop 3 is shown. Passes through the intersection of the surface on which the light from the point light source 2 first enters (the refracting surface 6 in the first and second embodiments and the reflecting surface 7 in the third embodiment) and the axial chief ray 5, and The direction of travel along the on-axis principal ray 5 is defined as the positive direction of the Z-axis, and the plane including the Z-axis and the on-axis principal ray 5 is defined as Y. −Z plane, the direction perpendicular to the YZ plane passing through the origin, and the direction from the front of the paper of FIG.
The axis constituting the right-handed orthogonal coordinate system with the axis is defined as the Y axis.

In the first to third embodiments, each surface is decentered in the YZ plane, and the only symmetric plane of each rotationally asymmetric free-form surface is the YZ plane.

For the eccentric surface, the amount of eccentricity (X, Y, and Z in the X, Y, and Z directions, respectively) at the top of the surface from the origin of the coordinate system and the center axis of the surface The inclination angles (α, β, and γ (°), respectively) of the X axis, the Y axis, and the Z axis of (the Z axis in equation (a)) are given. In this case, the positive α and β mean counterclockwise with respect to the positive direction of each axis, and the positive γ means clockwise with respect to the positive direction of the Z axis.

In a case where a specific surface (including a virtual surface) and a surface following the specific surface (including a virtual surface) among the optically acting surfaces constituting the optical system of each embodiment constitute a coaxial optical system, a surface interval is given. In addition, the refractive index of the medium and the Abbe number are given according to a conventional method.

The shape of the surface of the free-form surface used in the present invention is defined by the above equation (a), and the Z axis of the definition expression is the axis of the free-form surface. The term relating to a free-form surface on which no data is described is zero. For the refractive index, d
Lines (wavelength 587.56 nm) are shown. The unit of the length is mm.

As another definition of the free-form surface, there is a Zernike polynomial given by the following expression (b).
The shape of this surface is defined by the following equation. The Z axis of the defining equation is the axis of the Zernike polynomial. The definition of the rotationally asymmetric surface is defined by polar coordinates of the height of the Z axis with respect to the XY plane, A is the distance from the Z axis in the XY plane, R is the azimuth around the Z axis, and the Z axis It can be expressed by the rotation angle measured from.

X = R × cos (A) y = R × sin (A) Z = D ₂ + D ₃ Rcos (A) + D ₄ Rsin (A) + D ₅ R ² cos (2A) + D ₆ (R ² −1 ^{_{) + D 7 R 2 sin (}} 2A) + D 8 R 3 cos (3A) + D 9 (3R 3 -2R) cos (A) + D 10 (3R 3 -2R) sin (A) + D 11 R 3 sin (3A) + D ^{_{12 R 4 cos (4A) +}} D 13 (4R 4 -3R 2) cos (2A) + D 14 (6R 4 -6R 2 +1) + D 15 (4R 4 -3R 2) sin (2A) + D 16 R 4 sin (4A ^{_{) + D 17 R 5 cos (}} 5A) + D 18 (5R 5 -4R 3) cos (3A) + D 19 (10R 5 -12R 3 + 3R) cos (A) + D 20 (10R 5 -12R 3 + 3R) sin (A) ^{_{+ D 21 (5R 5 -4R 3}} ) sin (3A) + D 22 R 5 sin (5A) + D 23 R 6 cos (6A) + D 24 (6R 6 -5R 4) cos (4A) + D 25 (15R 6 -20R 4 ^{+ 6R 2) cos (2A)} + D 26 (20R 6 -30R 4 + 12R 2 -1) + D 27 (15R 6 -20R 4 + 6R 2) sin (2A) ^{_{D 28 (6R 6 -5R 4)}} sin (4A) + D 29 R 6 sin (6A) ····· ··· (b) In addition, to design an optical system symmetric with respect to the X-axis direction, D
_{4, D 5, D 6,} D 10 0, D 11, D 12, D 13, D 14,
_{D 20, D 21, D 22} ... to use.

As another example, the following definition formula (c)
Is raised. Z = ΣΣC _nm XY As an example, when k = 7 (seventh-order term) is considered, when expanded, it can be expressed by the following equation. _{Z = C 2 + C 3 y} + C 4 | x | + C 5 y 2 + C 6 y | x | + C 7 x 2 + C 8 y 3 + C 9 y 2 | x | + C 10 yx 2 + C 11 | x 3 | + C 12 y 4 ^{_{+ C 13 y 3 | x |}} + C 14 y 2 x 2 + C 15 y | x 3 | + C 16 x 4 + C 17 y 5 + C 18 y 4 | x | + C 19 y 3 x 2 + C 20 y 2 | x 3 | + C ^{_{21 yx 4 + C 22 | x}} 5 | + C 23 y 6 + C 24 y 5 | x | + C 25 y 4 x 2 + C 26 y 3 | x 3 | + C 27 y 2 x 4 + C 28 y | x 5 | + C 29 x ^{_{6 + C 30 y 7 + C}} 31 y 6 | x | + C 32 y 5 x 2 + C 33 y 4 | x 3 | + C 34 y 3 x 4 + C 35 y 2 | x 5 | + C 36 yx 6 + C 37 | x 7 | (C) In the embodiment of the present invention, the surface shape is expressed by a free-form surface using the above equation (a).
It goes without saying that the same operation and effect can be obtained by using the expression (c).

The configuration parameters of the first to third embodiments are shown below. “FFS” in these tables is a free-form surface, “HR”
P "indicates a virtual plane. NAx and NAy are the numerical aperture in the X direction and the numerical aperture in the Y direction.

Example 1 Fx = 36.2 mm Fy = 54.9 mm NAx = 0.10 NAy = 0.45 Surface number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ (light source) 50.00 1 ∞ (HRP) 2 FFS Eccentricity (1) 1.5168 64.2 3 -97.13 (Reflective surface) Eccentricity (2) 1.5168 64.2 4 FFS Eccentricity (1) 5 ∞ (Aperture surface) -50.00 Eccentricity (3) Image plane ∞ FFS C ₄ -1.6627 × 10 ^-3 C ₆ -7.0381 × 10 ^-3 C ₈ -2.0022 × 10 ^-5 C ₁₀ -1.7667 × 10 ^-5 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α -17.59 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 0.00 Z 5.47 α -15.18 β 0.00 γ 0.00 eccentricity (3) X 0.00 Y 30.33 Z -50.00 α -29.49 β 0.00 γ 0.00 Fx / Fy = 0.66 CY2 / CY6 = 1.309 CX2 / CX6 = 1.609 OP1 / OP2 = 0.96.

Example 2 Fx = 37.3 mm Fy = 49.3 mm NAx = 0.10 NAy = 0.45 Surface number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ (light source) 50.00 1 ∞ (HRP) 2 -331.72 Eccentricity (1) 1.5168 64.2 3 FFS (Reflective surface) Eccentricity (2) 1.5168 64.2 4 -331.72 Eccentricity (1) 5 ∞ (Aperture surface) -50.00 Eccentricity (3) Image plane ＦＦ FFS C ₄ -4.9298 × 10 ^-3 C ₆ -3.3677 × 10 ^-3 C ₈ -7.3001 × 10 ^-6 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α 8.54 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 0.00 Z 8.91 α -6.22 β 0.00 γ 0.00 Eccentricity (3) X 0.00 Y 30.63 Z -50.00 α -29.19 β 0.00 γ 0.00 Fx / Fy = 0.76 CY2 / CY6 = 1.000 CX2 / CX6 = 1.061 OP1 / OP2 = 22.16.

Example 3 Fx = 34.1 mm Fy = 48.3 mm NAx = 0.10 NAy = 0.45 Surface number Curvature radius Surface spacing Eccentricity Refractive index Abbe number Object surface ∞ (light source) 50.00 1 ∞ (HRP) 2 FFS (reflective surface) Eccentricity (1) 3∞ (aperture surface) -50.00 Eccentricity (2) Image plane ∞ 0.00 FFS C ₄ -7.6001 × 10 ^-3 C ₆ -5.0013 × 10 ^-3 C ₈ 2.0017 × 10 ^-6 C ₁₀ 1.2811 × 10 ^-5 C ₁₃ -4.1741 × 10 ^-7 Eccentricity (1) X 0.00 Y 0.00 Z 0.00 α -15.29 β 0.00 γ 0.00 Eccentricity (2) X 0.00 Y 29.56 Z -50.00 α -30.59 β 0.00 γ 0.00 Fx / Fy = 0.71 CY6 / CY2 = 1.315.

By combining the optical system and the liquid crystal shutter array as in the above embodiments, for example, a printer (image forming apparatus) for an electronic camera can be constructed. Part 1
FIG. 4 shows a schematic configuration of the example. FIG. 4A is a plan view, and FIG. 4B is a vertical sectional view. Basically, except for the optical system, it is substantially the same as the conventional example of FIG. In this case,
The optical system of the first embodiment is used as the optical system 1 for condensing the light from the point light source in a straight line, and the light source 12 includes a red LED (light emitting diode), a green LED, and a blue LED. A point light source that is brought into close proximity to two point light sources is used, and is disposed at the position of the point light source 2 (FIG. 1) of the optical system 1. A plane reflecting mirror 13 that bends the optical path by 90 ° in the one-dimensional converging optical path of the optical system 1 is arranged, and pixels are arranged in the linear direction in the optical path between the plane reflecting mirror 13 and the linear convergence position 4. One-dimensional liquid crystal shutter array 14
A photoreceptor 15 such as an instant photographic film is movably disposed at the linear convergence position 4.

In such a configuration, while the lighting of the red, green, and blue LEDs of the light source 12 is switched, the liquid crystal shutter array 14 is synchronized with the lighting.
Are sequentially switched to a red image signal, a green image signal, and a blue image signal of one scanning line, and the photoconductor 15 is moved in synchronization with the scanning of each scanning line.
A color image can be formed on the photoconductor 15 by moving the photoconductor 15 in the direction of the arrow perpendicular to the parallel direction of the photoconductors 4.

The printer as described above is provided in, for example, a thin plan view A of an attachment portion 21 integrally or detachably attached to the back of the electronic camera 20 as shown in a perspective view in FIG. The image of the subject photographed through the objective optical system 10 can be printed out immediately or later on a photoreceptor 15 such as a film for instant photography. Note that reference numeral 22 in FIG.
Denotes a shutter button, and 23 denotes a lighting device.

FIG. 6 shows a schematic system configuration diagram for this purpose. An image of the subject is photographed by the CCD 11 through the objective optical system 10, and the image signal is input to the CPU 16. C
The PU 16 has a memory 19, a light source 12, a liquid crystal shutter array 14, a drive motor 17, an LCD (liquid crystal display) 2.
4 is connected, and an image photographed by the CCD 11 is displayed on the LCD 24. This display image is displayed on the eyepiece optical system 25.
And the photographer can observe it as a finder image. The memory 19 stores a video signal captured by the CCD 11. When printing out an image photographed by a printer, the CPU 16 calls up the stored image from the memory 19, and based on the video signal, the light source 12, the liquid crystal shutter array 14, and the drive motor for driving the photoconductor 15. As described above, the operation of the light source 12 and the liquid crystal shutter array 14 is synchronously controlled while the photosensitive member 15 is being fed by the drive roller 18 coupled to the output shaft of the drive motor 17 by controlling the drive motor 17.

The optical system 1 of the present invention shown in the above embodiment has at least a curved reflecting surface 7 and is eccentrically arranged in one section (YZ plane) crossing the reflecting surface 7. It has the characteristics of converting light traveling from the point light source 2 into its cross section into substantially parallel light, and converging light traveling from the light source 2 to the outside of the cross section on a linear image 4 located in the cross section. Since the point light source 2 can be arranged eccentrically in the same plane as the optical system 1, the optical system has a small thickness, a small number of parts, easy position adjustment during assembly, and is inexpensive. Instead of such an optical system, an optical system having similar optical characteristics that can be easily adjusted in position and is inexpensive using one internal reflector can also be configured. An example is shown in FIG. FIG.
4A is a plan view of the optical system 41, and FIG. 4B is a vertical sectional view thereof. The optical system 41 is made of a single transparent body, and has a first surface 42 on which divergent light from the point light source 1 is incident, and a second surface 43 that refracts the first surface 42 and internally reflects light incident on the transparent body. The third surface 43 and the third surface 44 for internally reflecting the light internally reflected on the second surface 43 and refracting and emitting the light internally reflected on the fourth surface 45 to form a linear image 4. Surface 45 for internally reflecting light internally reflected by
These reflecting surfaces 43, 44, and 45 are all eccentrically arranged with respect to the axial principal ray 5, and the first surface 4
The second to fourth surfaces 45 have a co-curved surface shape. For example, the first surface 42, the third surface 44, and the fourth surface 45 each have a rotationally asymmetric free-form surface having only one symmetric surface expressed by the above-described formula (a). And the second surface is constituted by a rotationally symmetric aspherical surface or a spherical surface.
Here, the reflection surfaces of the second surface 43 and the fourth surface 45 are mirror surfaces, and the reflection surface of the third surface 44 is a total reflection surface or only the reflection area is a mirror surface.

The optical system 4 composed of a transparent body having such a configuration
4, a light source in which three point light sources of a red LED (light emitting diode), a green LED, and a blue LED are placed very close to each other at the position of the point light source 1 as in the case of FIG. A one-dimensional liquid crystal shutter array 14 in which pixels are arranged in a linear direction in the one-dimensional convergent light path emitted from the system 41 is disposed. By arranging the body 15 so as to be movable, a printer that similarly forms a color image can be configured. in this case,
There is no need for a plane reflecting mirror that bends the optical path by 90 °. When the printer using the optical system 41 is arranged in the attachment portion 21 (FIG. 5) integrally or detachably attached to the back of the electronic camera 20, it is desirable to provide the printer at, for example, a slightly thicker end B thereof. .

In any of the above image forming apparatuses, it is assumed that a point light source or a plurality of minute light sources are arranged close to each other to emit divergent light. At a position (reflection point) of a polygon mirror or a galvano mirror, and a micro-section parallel light beam deflected and reflected in the YZ section from that position is incident on the optical systems 1 and 41. Can also. In that case, it is not necessary to arrange the one-dimensional liquid crystal shutter array in the one-dimensional convergent light path, and the light beam incident on the polygon mirror or the galvanometer mirror may be modulated according to the video signal.

Instead of a light source arranged in close proximity to a three-color point light source, a white lamp may be used, and a rotating color filter may be arranged therearound, as in the prior art of FIG. Of course.

The optical system of the present invention and the image forming apparatus using the optical system have been described based on the embodiments.
The present invention is not limited to these embodiments, and various modifications are possible.

The above-described optical system of the present invention and an image forming apparatus using the optical system can be configured, for example, as follows. [1] At least a curved reflecting surface, and converts light traveling in the cross section from a substantially point-like light source eccentrically arranged in one cross section crossing the reflecting surface into substantially parallel light, and the light source The light traveling out of the cross-section from the
An optical system characterized by being substantially converged on two straight lines.

[2] The optical system according to the above item 1, wherein the straight line is substantially orthogonal to substantially parallel light in the cross section.

[3] The light from the light source substantially converges on the straight line in another section crossing the reflecting surface and orthogonal to the section and the straight line. Optical system.

[4] The optical system as described in any one of [1] to [3] above, wherein the reflection surface comprises a back mirror.

[5] The optical system as described in [4] above, wherein at least one of the refracting surface and the reflecting surface of the back mirror has a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity. .

[6] The optical system as described in [5] above, wherein the rotationally asymmetric surface shape is a plane-symmetric free-form surface shape having only one plane of symmetry.

[7] The optical system as described in any one of [1] to [3] above, wherein the reflection surface comprises a surface mirror.

[8] The optical system according to the above item 7, wherein the curved surface of the reflecting surface has a rotationally asymmetric surface shape for correcting aberrations caused by eccentricity.

[0082]

[9] The optical system according to the above item 6, wherein the refracting surface of the back mirror is a rotationally asymmetric free-form surface having the one cross section as a sole symmetric surface.

[10] The reflection surface of the back mirror is 1
7. The optical system according to the above item 6, wherein the optical system comprises a rotationally asymmetric free-form surface having one cross section as a sole symmetric surface.

[11] The reflecting surface of the surface mirror is 1
9. The optical system according to the above item 8, wherein the optical system comprises a rotationally asymmetric free-form surface having two cross sections as the only symmetric surfaces.

[12] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the focal length of the optical system in the YZ plane is defined as Fy, Y
-The focal length of the optical system in a plane perpendicular to the Z plane is Fx
The optical system according to the above item 9, wherein the following condition is satisfied: 0.4 ≦ Fx / Fy ≦ 0.9 (1)

[13] A section including the principal ray on the axis of incidence and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the light is incident on the free-form surface in the YZ plane. Y at the position of incidence on the free-form surface closest to the light source in the light beam
The curvature in the Z plane is CY2, the curvature in the plane perpendicular to the YZ plane is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, The following 9 or 12 characterized by satisfying a condition of 0.5 ≦ CY2 / CY6 ≦ 2.0 (2), where CX6 is a curvature in a plane perpendicular to the YZ plane. Optical system.

[14] A section including the principal ray on the axis of incidence and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the free-form surface is incident from the light source within the YZ plane. Y at the position of incidence on the free-form surface closest to the light source in the light beam
The curvature in the Z plane is CY2, the curvature in the plane perpendicular to the YZ plane is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, When the curvature in a plane orthogonal to the YZ plane is CX6, the following condition is satisfied: 0.5 ≦ CX2 / CX6 ≦ 2.0 (4) 1
3. The optical system according to 3.

[15] A section including the principal axis on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the light source enters the optical system in the YZ plane in the YZ plane. When the optical path length from the refraction surface to the reflection surface of the light beam incident farthest from the light source among the incident light beams is OP1, and the optical path length from the refraction surface to the reflection surface of the light beam incident most on the light source side is OP2, 0. 5 ≦ OP1 / OP2 ≦ 17.0 (6) The above conditions 9, 12, and 13 are satisfied.
Or the optical system according to 14.

[16] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the focal length of the optical system in the YZ plane is defined as Fy, Y
-The focal length of the optical system in a plane perpendicular to the Z plane is Fx
Wherein the optical system satisfies the following condition: 0.4 ≦ Fx / Fy ≦ 0.9 (7)

[17] A section including the principal ray on the axis of incidence and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the free curved surface is incident from the light source within the YZ plane. The curvature in the YZ plane at the position where the axial chief ray hits is CY
1. The curvature in a plane orthogonal to the YZ plane is CX1, and YZ at the position closest to the light source among the light rays incident from the light source in the YZ plane on the free curved surface is the light source side. The curvature in the plane is CY2, and the curvature in the plane orthogonal to the YZ plane is CX.
2. When the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, and the curvature in the plane orthogonal to the YZ plane is CX6, CY1 <CY2, CY1 <CY6 ... (8) Both of the above conditions 10 and 16 are satisfied.
Optical system as described.

[18] A section including the principal axis on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the free-form surface is incident from the light source within the YZ plane. Y at the position of incidence on the free-form surface closest to the light source in the light beam
The curvature in the Z plane is CY2, the curvature in the plane perpendicular to the YZ plane is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, When the curvature in a plane orthogonal to the YZ plane is CX6, the following condition is satisfied: 0.5 ≦ CY2 / CY6 ≦ 2.0 (9) 18. The optical system according to 17.

[19] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the free-form surface is incident on the free-form surface from the light source within the YZ plane. Y at the position of incidence on the free-form surface closest to the light source in the light beam
The curvature in the Z plane is CY2, the curvature in the plane perpendicular to the YZ plane is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, When the curvature in a plane orthogonal to the YZ plane is CX6, the following condition is satisfied: 0.5 ≦ CX2 / CX6 ≦ 2.0 (11) 1
19. The optical system according to 7 or 18.

[20] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the light source enters the optical system in the YZ plane in the YZ plane. 14. When the optical path length from the refraction surface to the reflection surface of the light beam incident farthest from the light source in the incident light beam is OP1, and the optical path length from the refraction surface to the reflection surface of the light beam incident on the light source side is OP2, 0 ≦ OP1 / OP2 ≦ 30.0 (13)
20. The optical system according to 7, 18, or 19.

[21] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the focal length of the optical system in the YZ plane is defined as Fy, Y
-The focal length of the optical system in a plane perpendicular to the Z plane is Fx
Wherein the optical system satisfies the following condition: 0.4 ≦ Fx / Fy ≦ 0.9 (14).

[22] A section including the principal ray on the incident axis and the principal ray on the exit axis from the light source to the optical system is defined as a YZ plane, and the free-form surface is incident from the light source in the YZ plane. Y at the position of incidence on the free-form surface closest to the light source in the light beam
The curvature in the Z plane is CY2, the curvature in the plane perpendicular to the YZ plane is CX2, the curvature in the YZ plane at the position farthest from the light source and incident on the free-form surface is CY6, 23. When the curvature in a plane orthogonal to the YZ plane is CX6, the following condition is satisfied: 0.5 ≦ CY6 / CY2 ≦ 2.0 (15) Optical system.

[23] A single internal reflector formed of a transparent medium, having a curved shape and having a plurality of eccentrically arranged reflecting surfaces for internally reflecting light beams in the medium, A rotation that has at least an incident surface for entering the body and an exit surface for emitting a light beam out of the internal reflector, and that corrects aberration caused by eccentricity of at least one of the reflecting surface, the incident surface, and the exit surface; It has an asymmetric surface shape, and a light beam incident on the internal reflector from a substantially point light source disposed on the incident side of the incident surface reflects the plurality of reflecting surfaces in order and exits from the exit surface. An optical system characterized by being substantially converged on one straight line.

[24] The internal reflector has four working surfaces, and the first surface receives divergent light from the light source,
The surface refracts light on the first surface and internally reflects light incident on the internal reflector, and the third surface reflects light internally reflected on the second surface and light reflected internally on the fourth surface. 23. The light emitting device according to the above 23, wherein the light is refracted and emitted, and the fourth surface reflects the light internally reflected by the third surface.
Optical system as described.

[25] A pixel in which pixels are juxtaposed in an optical path emitted from the optical system according to any one of the above items 1 to 24 toward a linear convergence position in parallel with the linear direction of the convergence position.
A one-dimensional optical shutter array is arranged, a photoreceptor is arranged so as to be movable through the linear converging position, and the transmittance of each pixel of the one-dimensional optical shutter array is controlled based on a video signal, and the control is performed. An image forming apparatus, wherein movement of the photosensitive member is controlled in synchronization.

[26] It is characterized in that it is integrally or detachably attached to an imaging device capable of taking an image of a subject and converting it into a video signal, so as to form the image of the taken subject. 26. The image forming apparatus according to the above item 25.

[0100]

As is apparent from the above description, according to the present invention, an optical system having a small number of components for condensing light from a point light source linearly and having a small thickness, and an image forming apparatus using the optical system. Can be realized. Such an image forming apparatus can be used, for example, as an integral or detachable printer with an electronic camera.

[Brief description of the drawings]

FIG. 1 is a horizontal sectional view and a vertical sectional view of an optical system according to a first embodiment of the present invention.

FIG. 2 is a horizontal sectional view and a vertical sectional view of Embodiment 2 of the optical system according to the present invention.

FIG. 3 is a horizontal sectional view and a vertical sectional view of Embodiment 3 of the optical system according to the present invention.

FIG. 4 is a plan view and a vertical sectional view showing a schematic configuration of a printer according to the present invention.

FIG. 5 is a perspective view of an electronic camera to which the printer of FIG. 4 is attached.

FIG. 6 is a schematic system configuration diagram of an electronic camera to which a printer is attached.

FIG. 7 is a plan view and a vertical sectional view of another example of the optical system according to the present invention.

FIG. 8 is a conceptual diagram for explaining field curvature generated by an eccentric reflecting surface.

FIG. 9 is a conceptual diagram for explaining astigmatism generated by a decentered reflecting surface.

FIG. 10 is a conceptual diagram for explaining coma generated by a decentered reflecting surface.

FIG. 11 is a diagram for explaining the definition of the power of the decentered optical system and the optical surface.

FIG. 12 is a diagram illustrating a schematic configuration of an example of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical system 2 ... Point light source 3 ... Stop 4 ... Linear image (linear convergence position) 5 ... On-axis chief ray 6 ... Refraction surface 7 ... Reflection surface 10 ... Objective optical system 11 ... CCD 12 ... Light source 13 ... Plane reflector 14 ... One-dimensional liquid crystal shutter array 15 ... Photoconductor 16 ... CPU 17 ... Drive motor 18 ... Drive roller 19 ... Memory 20 ... Electronic camera 21 ... Attachment part 22 ... Shutter button 23 ... Lighting device 24 ... LCD 25 ... Eyepiece Optical system 41 Optical system 42 First surface 43 Second surface 44 Third surface 45 Fourth surface M concave mirror S decentered optical system

Claims (3)

[Claims] 1. A light source having at least a curved reflecting surface, converting light traveling into the cross section from a substantially point light source eccentrically arranged in one cross section crossing the reflecting surface into substantially parallel light, and
An optical system, wherein light traveling from the light source to the outside of the cross section is substantially converged on one straight line located in the cross section. 2. A one-dimensional optical shutter array in which pixels are arranged in parallel with a linear direction of the convergence position in an optical path emitted from the optical system according to claim 1 toward a linear convergence position, and A photoconductor is disposed so as to be movable through a shape converging position, the transmittance of each pixel of the one-dimensional optical shutter array is controlled based on a video signal, and the photoconductor is moved in synchronization with the control. An image forming apparatus comprising: 3. An image pickup apparatus capable of taking an image of a subject and converting the image into a video signal, integrally or detachably attached to the image pickup apparatus,
The image forming apparatus according to claim 2, wherein the image forming apparatus is configured to form the image of the photographed subject.