JP5888856B2 - Imaging device - Google Patents

Description

  The present invention relates to an image pickup apparatus suitable for obtaining image information by forming image information on a light receiving means composed of a light receiving portion long in one direction by an imaging optical system. For example, the present invention is suitable for an image reading apparatus suitable for an image scanner or a digital copying machine, which uses a scanning optical system unit to read image information of a document, or a camera for imaging a subject on solid-state imaging.

  2. Description of the Related Art Conventionally, an image reading apparatus such as a video camera or a digital still camera or an image scanner forms image information on a light receiving means by an imaging optical system, and obtains image information from a signal obtained by the light receiving means. In a camera, an image reading apparatus, or the like, when imaging target image information on a light receiving means, a light beam having a wavelength other than the visible range, particularly ultraviolet light or infrared light, may reach the light receiving means. Then, the spectral characteristic of the image information imaged on the light receiving means is different from that observed.

  For example, the color of the image information obtained by the light receiving means is different from the color of the image information actually observed. An imaging optical system in which means for reducing the color difference at this time is provided in the optical path is known (Patent Documents 1 and 2). In Patent Document 1, the infrared light is removed by depositing an optical film that cuts infrared light on the lens surface of the lens constituting the imaging optical system, and the image information on the document surface is read with high accuracy. An original reading apparatus is disclosed. Patent Document 2 discloses an image reading apparatus in which a spectral characteristic adjusting unit having a polymer multilayer film that transmits or reflects only a specific wavelength is provided in an optical path.

JP 2000-304918 A JP 2006-74575 A

  The method of forming a desired multilayer film on a lens surface having a curvature and shielding infrared light does not require a new optical element and is advantageous for downsizing the entire apparatus. Is difficult to form uniformly. On the other hand, the method in which an optical element in which a multilayer film for cutting infrared light is applied to a transparent parallel substrate is disposed in the optical path can easily form the multilayer film and cut infrared light relatively easily. In general, the method of cutting infrared light using an optical element in which a multilayer film is formed differs in the half-value wavelength at which the transmittance becomes half (50%) depending on the incident angle of the light beam to the optical element due to the optical properties of the multilayer film. come.

  Therefore, when such an optical element having a multilayer film is used in an imaging optical system, the half-value wavelength for cutting infrared light differs between the optical axis and off-axis positions. Will be different.

  As a result, it becomes difficult to obtain good image quality over the entire screen. For example, color image information read by the imaging optical system in the image reading apparatus has different colors at the screen center and the screen periphery, making it difficult to read the image information with high accuracy. In addition, in the camera, the color is different between the center of the screen and the periphery of the screen, making it difficult to obtain a high-quality color image.

  For this reason, in an imaging optical system that reduces the incidence of infrared light on the light receiving means by using a spectral characteristic adjustment means using a multilayer film in the optical path, light beams of various angles of view are incident on the imaging optical system. Even so, it is important that the half-wavelength shift amount of the infrared cut is small over the entire screen.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging apparatus in which the amount of shift of the half-wavelength of infrared cut depending on the angle of view is small, and image information with good image quality can be obtained over a wide range from the screen center to the screen periphery.

In order to achieve the above object, an imaging apparatus according to the present invention is an imaging apparatus having an imaging optical system that collects a light beam from an object, and a light receiving unit that receives the light beam from the object. The light receiving unit has a rectangular shape that is long in a first direction perpendicular to the optical axis of the imaging optical system, and is disposed in the optical path from the object to the light receiving unit, and changes the spectral characteristics of the light beam from the object. An adjusting means including a multilayer film surface to be formed, wherein an angle formed by the optical axis and a surface normal of the multilayer film surface in a cross section perpendicular to the first direction is α, and the optical axis and the light receiving unit When the angle formed by the incident off-axis chief ray is θ,
0.3θ <α < 80 °
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain an imaging apparatus in which the amount of shift of the half-wavelength of infrared cut depending on the angle of view is small, and image information with good image quality can be obtained over a wide range from the screen center to the screen periphery.

1 is a schematic diagram of a main part of an image reading apparatus according to a first embodiment of the present invention. It is explanatory drawing of the spectral characteristic of a spectral characteristic adjustment means. It is explanatory drawing of the incident angle change by rotation of a spectral characteristic adjustment means. It is explanatory drawing of the spectral characteristic of a spectral characteristic adjustment means. It is explanatory drawing of the change of the rotation angle of a spectral characteristic adjustment means, and an incident angle difference. It is explanatory drawing about derivation | leading-out of amount of asses. FIG. 6 is a schematic diagram of a main part of a camera according to a second embodiment. It is explanatory drawing of the spectral characteristic of a spectral characteristic adjustment means.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The image pickup apparatus of the present invention forms image information such as a subject or document data on a document surface on a light receiving means such as a one-dimensional sensor or an image sensor having a rectangular light receiving portion that is long in one direction by an imaging optical system. A camera or an image reading device for obtaining image information.

The imaging apparatus has spectral characteristic adjusting means in which a multilayer film having a function of changing the spectral characteristic of an incident light beam and emitting it in an optical path is applied to a parallel plate. The spectral characteristic adjusting means is arranged in one direction (horizontal direction in the case of a camera or main scanning direction in the case of an image reading apparatus) and is set to an optical axis with an axis perpendicular to the optical axis of the imaging optical system as a rotation axis. It is inclined and arranged. The angle between the optical axis and the surface normal of the spectral characteristic adjusting means is α, and the angle between the optical axis and the most off-axis principal ray (the principal ray of the light incident on the periphery of the screen) of the light flux incident on the light receiving means. Is θ,
0.3θ <α
Is satisfied.

  In the case of an image reading apparatus, the light receiving means has a configuration in which a plurality of one-dimensional sensors in which a plurality of pixels are arranged in the main scanning direction are arranged in the sub-scanning direction orthogonal to the optical axis and orthogonal to the main scanning direction. . In the case of a camera, the light receiving means consists of a rectangular image sensor that is long in the horizontal direction.

[Example 1]
FIG. 1 is a schematic view of a main part when the image pickup apparatus according to the first embodiment of the present invention is applied to a carriage-integrated image reading apparatus (flatbed scanner).

  In FIG. 1, reference numeral 1 denotes a main body of the image reading apparatus. Reference numeral 102 denotes an original platen glass on which an original 101 is placed. Reference numeral 108 denotes a carriage which holds an illumination light source 107 as illumination means, a plurality of reflection mirrors (103a to 103e) 103, an imaging optical system (imaging lens) 105, a spectral characteristic adjustment means 104, a reading means 106, and the like. ing. The carriage 108 scans in the sub-scanning direction (A direction) in FIG. 1 by a sub-scanning mechanism Mo such as a motor, and the reading unit 106 reads the image information of the document 101 two-dimensionally. The carriage 108 may be moved in the sub scanning direction relative to the document table glass 101.

  The read image information is sent to an external device such as a personal computer through an interface (not shown). The illuminating means 107 is composed of cold cathode tubes or halogen lamps arranged in the main scanning direction shown in the drawing, and the reflecting mirrors 103a to 103e respectively bend the light path of the light beam from the document 101 inside the carriage 108 in order. The imaging lens 105 forms an image of a light beam from a one-dimensional direction or a rectangular area of the document 101 on the surface of the reading unit 106 formed of a line sensor or an image sensor.

The reading means 106 has at least three line sensors (one-dimensional sensors) in which a plurality of pixels are arranged in the main scanning direction for receiving R, G, and B light, respectively, as a plurality of light receiving units . The direction in which the pixels of the reading unit 106 are arranged (the direction perpendicular to the paper surface) is the main scanning direction (the first direction perpendicular to the optical axis of the imaging optical system 105) . In other words, the plurality of rectangular light receiving sections that are long in the first direction are arranged in a second direction perpendicular to the optical axis of the imaging optical system 105 and the first direction. The spectral characteristic adjusting means 104 is formed by forming a multilayer film on a transparent substrate, and the multilayer film constituting surface has an axis parallel to the main scanning direction in the optical path between the imaging lens 105 and the reading means 106. It rotates about the center and is arranged at a predetermined angle α with respect to the optical axis 105a. The spectral characteristic adjusting unit 104 may be disposed anywhere in the optical path between the document 101 and the reading unit 106.

  The spectral characteristic adjusting unit 104 attenuates light (infrared light) in a wavelength region having a wavelength of about 700 nm or more, so that the R row of one line sensor of the reading unit 106 receives infrared light that is not originally in the visible region. Thus, the color of the output image is prevented from differing from the color of the document. The spectral characteristic adjusting means 104 in this embodiment is set so as to reduce the light in the infrared region, and the spectral transmittance with respect to incident light at 0 ° and 23 ° is as shown in FIG. Is happening.

  This is because the optical path length and the refraction angle in the spectral characteristic adjusting means 104 change as the angle of view (incident angle) is added, and generally the half-value wavelength of the light beam with the incident angle is shorter than that of normal incidence. Tend to move to the side. Here, a technical reason for disposing the spectral characteristic adjusting unit 104 by rotating around an axis parallel to the main scanning direction will be described.

When the multilayer film constituting surface of the spectral characteristic adjusting means 104 is arranged perpendicular to the optical axis in a cross section perpendicular to the main scanning direction (first direction), the main scanning of the imaging optical system 105 in this embodiment is performed. Depending on the angle of view, an incident angle difference of about 23 ° occurs from the optical axis to the outermost axis. From FIG. 2, the half-value wavelength of the spectral characteristic adjusting means 104 is about 675 nm at an incident angle of 0 °, and about 639 nm at an incident angle of 23 °. There is a possibility that the image will have a different color off-axis.

Therefore, if the multilayer film constituting surface of the spectral characteristic adjusting means is arranged by being rotated by 10 ° about an axis parallel to the main scanning direction, the incident angle on the axis is 10 ° and the off-axis angle is as shown in FIG. The incident angle is 24.7 °. The difference between the incident angle on the axis and the off-axis with respect to the spectral characteristic adjusting unit 104 is as small as 14.7 °. The spectral transmittance when the incident angle is 10 ° and 24.7 ° is as shown in FIG. 4. When the angle of view is 0 °, the half-value wavelength is 668 nm, and when the angle of view is 23 °, the half-value wavelength is 655 nm. As a result, the shift of the half-value wavelength in the main scanning direction is about 13 nm as the shift of the infrared cut wavelength, and is reduced by 50% or more compared to the case where the spectral characteristic adjusting means 104 is not rotated.

  The incident angle φ of the principal ray at the most off-axis field angle θ in the main scanning direction with respect to the spectral characteristic adjusting means 104 is relative to the tilt angle α.

When this is graphed, it is as shown in FIG. In FIG. 5, the vertical axis represents the on-axis-off-axis incident angle difference when the spectral characteristic adjusting unit 104 is tilted, and the horizontal axis is the tilt angle of the spectral characteristic adjusting unit 104.

  The graph plots the correlation when the angle of view is 30 °, when the angle of view is 20 °, and when the angle of view is 10 °. As the spectral characteristic adjusting means 104 is tilted, the difference between the on-axis and off-axis incident angles becomes smaller. I understand. In order to reduce the incident angle difference, that is, the half-value wavelength shift to 70%, it is effective to set the tilt angle α to α≈0.3θ. When it is reduced by about%, the color unevenness in the output image is more effectively reduced.

  Although the half-value wavelength shift in the sub-scanning direction is worsened by inclining the spectral characteristic adjusting unit 104, generally, the line sensors of the image reading apparatus have a plurality of line sensors of each color arranged in the sub-scanning direction. If the color unevenness in the main scanning direction can be improved, the correction is easy.

  However, when the light beam incident on the spectral characteristic adjusting means 104 is not parallel light, if it is too tilted, astigmatism (astigmatism) occurs, and the imaging performance is deteriorated. It is desirable to set so that The amount of asperity is represented here by the difference in wavefront aberration between the main scanning direction and the sub-scanning direction. 6A and 6B, the surface normal angle of the spectral characteristic adjusting unit 104 with respect to the optical axis 105a at the position of the spectral characteristic adjusting unit 104 is α, and the thickness of the spectral characteristic adjusting unit 104 is d. . The refractive index for light having a wavelength of 587.6 nm is denoted by nd, and the axial luminous flux incident on the spectral characteristic adjusting means 104 is denoted by NAi.

  At this time, the optical path length of the marginal ray 701 in the main scanning direction of the axial principal ray with the light of wavelength 587.6 nm in the spectral characteristic adjusting means 104 is

Similarly, the optical path length of the marginal ray 702 in the sub-scanning direction is the average of the upper and lower sides.

It can be expressed as. Therefore, the amount of asphalt is obtained by dividing the absolute value of this difference by the wavelength.

It is represented by In order not to deteriorate the imaging performance, it is desirable that the asphalt amount in this optical system is 5λ or less.

  In this embodiment, since d = 1.1 mm, Nd = 1.516, Nai = 0.4782 ° and α = 10 °, the asphalt amount is about 1λ, which can be considered to be within the allowable range.

[Example 2]
FIG. 7A is a main part schematic diagram when the image pickup apparatus according to the second embodiment of the present invention is applied to a digital camera. In FIG. 7A, light from the subject passes through the imaging lens 801 and is a light receiving means 802 such as a film or a two-dimensional sensor (image sensor) (as shown in FIG. 7, the direction of the horizontal axis 804 (first The image is formed into a rectangular shape that is long in the direction) . The spectral characteristic adjusting means 803 in the optical path between the object (not shown) and the light receiving means 802 is arranged to rotate 10 ° about a horizontal axis 804.

  Here, when the spectral characteristic adjusting means 803 is arranged perpendicular to the optical axis 801a, the incident angle at the position intersecting with the optical axis 801a is 0 ° and the vertical end is 1 ° as shown in FIG. 7B. And an incident angle difference of 1 ° is generated. On the other hand, at the most off-axis passing position corresponding to the four corners of the light receiving means 802, the angle is 30.01 °, and the incident angle difference is 30.01 ° with respect to the axis.

  The spectral transmittance of the spectral characteristic adjusting means 803 in this embodiment is as shown in FIG. 8 in the case of normal incidence, and the half-value wavelength is about 675 nm when the incident angle is 0 °. When the incident angle with respect to the spectral characteristic adjusting unit 803 is increased, the half-value wavelength is shifted to the short wavelength side as in the case of the first embodiment. At this time, as shown in FIG. 10, when the incident angle is 1 °, it is about 674.3 nm, and when the incident angle is 30.01 °, it is about 654 nm, the cut wavelength difference in the vertical direction is 0.7 nm, and the cut wavelength in the diagonal direction. The difference is 21 nm. Due to this cut wavelength difference, there is a possibility that the output image has a large color unevenness in the diagonal direction compared to the vertical direction.

Therefore, when the spectral characteristic adjusting means 803 is rotated around an axis parallel to the horizontal direction, the incident angle θmax at the position 806 where the incident angle becomes the largest after the rotation is obtained geometrically. That is, in the spectral characteristic adjusting unit 803 when the spectral characteristic adjusting unit 803 is arranged perpendicular to the optical axis 801a, the incident angle of the light incident on the long side direction end is θ _H , and the light incident on the short side end. and incident angle θ _V of. At this time,

It becomes.

When the spectral characteristic adjusting means 803 is rotated by 10 ° as the angle α as shown in FIG. 8A, the incident angle θ at the position 805 having the smallest incident angle is θ = α−θ _V = 9 °, and the most incident angle is. The incident angle θmax at the increasing position 806 is 31.34 °. Also, alpha> when theta _V, incidence angle difference in a narrow direction angle of view whereas the 2 [Theta] _V, the angle of incidence of the smallest position 805 of the incident angle and the position 806 corresponding to the four corners of the light receiving means 802 The difference Δθ is

It becomes.

Thus a narrow vertical angle of view against to the 2 ° incidence angle difference of 9 ° and 11 °, the incident angle of the smallest position 805 of the incident angle and the position 806 corresponding to the four corners of the light receiving means 802 The difference Δθ is 22.34 °.

  From Table 1, the cut wavelength of the spectral characteristic adjusting means 803 is about 669 nm when the incident angle is 9 °, about 667.5 nm when the incident angle is 11 °, and about 653.6 nm when the incident angle is 31.34 °. The cut wavelength difference in the vertical direction is 0.7 nm, and the cut wavelength difference in the diagonal direction is 21 nm. Therefore, the cut wavelength difference in the vertical direction is 1.5 nm, and the cut wavelength difference in the diagonal direction is 15.4 nm. By rotating the spectral characteristic adjusting means 803, the half-value wavelength difference in the horizontal direction with a wide angle of view is reduced. It can be improved to about 74%.

  Considering to improve the unevenness of the tint by reducing the unevenness of the half-value wavelength in the light receiving means 802, it is effective if it can be reduced to about 80% in the direction where the difference in the incident angle is the largest, and the effect is further increased. For this purpose, it is appropriate to set it to 70 or less. The larger the angle at which the spectral characteristic adjusting means 803 is tilted, the more in-plane half-value wavelength unevenness can be improved. It is conceivable that the deterioration occurs as in the first embodiment. For this reason, what is necessary is just to set it as the tolerance | permissible_range as the imaging device.

  As described above, according to each embodiment, it is possible to reduce a spectral distribution unevenness due to an angle of view while using a parallel plate optical filter, and to obtain a camera and an image reading apparatus that can obtain high-quality image information.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 101 Document 102 Original plate glass 103 Folding mirror 104 Spectral characteristic adjustment means 105 Imaging lens 106 Reading means 107 Light source means 108 Carriage 801 Imaging lens 802 Light receiving means 803 Spectral characteristic adjustment means

Claims (5)

An imaging apparatus having an imaging optical system that collects a light beam from an object, and a light receiving unit that receives the light beam from the object,
The light receiving portion has a rectangular shape that is long in a first direction perpendicular to the optical axis of the imaging optical system,
Adjusting means including a multilayer film surface arranged in an optical path from the object to the light receiving unit and changing a spectral characteristic of a light beam from the object;
An angle formed between the optical axis and a surface normal of the multilayer film surface in a cross section perpendicular to the first direction is α, and an angle formed between the optical axis and the most off-axis principal ray incident on the light receiving unit. θ,
0.3θ <α <80 °
An imaging device characterized by satisfying the following condition: 0.67θ <α <80 °
The imaging apparatus according to claim 1 , wherein the following condition is satisfied. The light receiving unit, an imaging apparatus according to claim 1 or 2, characterized in that it comprises a plurality of pixels arranged in the first direction. The imaging apparatus according to claim 3 , comprising a plurality of the light receiving units, wherein the plurality of light receiving units are arranged in a second direction perpendicular to the optical axis and the first direction. Illuminating means for illuminating the object, an imaging apparatus according to the light beam to any one of claims 1 to 4, characterized in that it has a, a reflecting member for guiding the image forming optical system from the object.