JP2013045098A - Erecting equal-magnification lens array unit and image reading apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an influence of stray light between adjacent lenses in an erecting equal-magnification lens array unit.SOLUTION: An erecting equal-magnification lens array unit 13 has a first lens array 17, a second lens array 18 and a connection portion 19. The first lens array has a plurality of first lenses 20. The first lenses are arranged in a first direction. The second lens array has a plurality of second lenses. The respective optical axes of the second lenses overlap with the respective optical axes of the first lenses. The second lenses are arranged in the first direction. An opening is formed in a connection portion 19. The opening is formed between the first and second lenses of which the optical axes overlap with each other.

Description

  The present invention relates to an erecting equal-magnification lens array unit used in an image reading apparatus such as a scanner or a facsimile or an image forming apparatus such as an LED printer.

  A reduction optical system or an erecting equal-magnification optical system is used in an image reading apparatus such as a scanner or a facsimile or an image forming apparatus such as an LED printer. In particular, the erecting equal-magnification optical system is characterized in that the overall size of the apparatus can be easily reduced as compared with the case where a reduction optical system is used.

  Conventionally, an erecting equal-magnification optical system is formed by inserting rod-shaped lenses such as SELFOC (registered trademark, Nippon Sheet Glass) and rod lenses through an opaque black resin so as to be arranged in an array. Since each lens has an erecting equality, the erecting equality is maintained even when arranged in an array.

  The above-mentioned Selfoc and rod lens are provided with a light collecting property by changing the refractive power from the center to the periphery of the rod. Thus, since it is necessary to manufacture by a special method compared with a normal lens, manufacture is difficult and manufacturing cost is high. Thus, an erecting equal-magnification optical system using a lens array plate having convex surfaces arranged in an array has been proposed (see Patent Document 1).

  An erecting equal-magnification optical system using Selfoc has a narrow depth of field. In an image reading apparatus such as a scanner, by placing an object from which an image is read on a cover glass that is kept at a constant distance from the optical system, the distance between the object from which the image is read and the optical system is reduced. Kept at the desired distance. In this way, by keeping the distance between the object and the optical system at a desired distance, it is possible to read an image with less blur even at a narrow depth of field.

  However, depending on the object to be read, the reading surface may leave without being in close contact with the cover glass. In such a case, the blur of the read image is large due to the narrow depth of field. Thus, an erecting equal-magnification optical system with an expanded depth of field has been proposed (see Patent Document 2).

  Moreover, when using SELFOC, the lenses are optically separated by embedding rod-shaped lenses in black resin. However, in Patent Document 1 and Patent Document 2, since the lenses are not optically separated, there is a possibility that noise is mixed in an optical image formed by stray light.

  In view of this, there has been proposed a configuration that suppresses stray light when a formed equal-magnification optical system is formed using a lens array that is not optically separated (see Patent Documents 3 to 5).

JP 2006-014081 A JP 2010-164974 A JP 2000-253205 A JP 2000-284158 A JP 2010-286741 A

  In the imaging element of Patent Document 3, a diamond-shaped concave portion is formed in a substrate serving as a lens array, and the concave portion is filled with a light-absorbing substance. In the lens array assembly of Patent Document 4, a bottomed groove is formed between the lens portions in the lens array, and the bottomed groove is covered with a light shielding material. Thus, in any of Patent Documents 3 and 4, the configuration is complicated, and the labor for manufacturing is large.

  In the erecting equal-magnification lens array plate disclosed in Patent Document 5, a first light shielding wall is provided to surround the first lens. However, when such a light shielding wall is provided, it is difficult to increase the depth of field.

  Accordingly, an object of the present invention made in view of such circumstances is to provide an erecting equal-magnification lens array unit capable of expanding the depth of field and suppressing stray light.

を満たすことを特徴とするものである。 In order to solve the above-described problems, an erecting equal-magnification lens array unit according to the present invention is
A first lens array having a plurality of first lenses, wherein the plurality of first lenses are arranged along a first direction perpendicular to the optical axis of the first lens;
A second lens array having a plurality of second lenses each having an optical axis superimposed on each of the first lenses, wherein the plurality of second lenses are arranged along a first direction;
A light shielding portion in which an opening is formed between the first and second lenses whose optical axes overlap each other,
Each optical system formed by the first lens and the second lens whose optical axes overlap each other is an erecting equal-magnification optical system,
r is the radius of the first lens side of the aperture, p is the pitch between adjacent first lenses, L ₀ is the object distance from the predetermined first lens to the object plane, and L ₁ is the first When the thickness of the lens, n is the refractive index of the first lens, and s is an arbitrary integer,

It is characterized by satisfying.

を満たす正立等倍レンズアレイユニットを備える
ことを特徴とするものである。 In order to solve the above-described problems, an image reading apparatus according to the present invention includes:
A first lens array having a plurality of first lenses and having a plurality of first lenses disposed along a first direction perpendicular to the optical axis of the first lens; and each of the first lenses A second lens array having a plurality of second lenses on which optical axes are superposed and having a plurality of second lenses arranged along a first direction; and first and second optical axes that overlap each other. Each of the optical systems formed by the first lens and the second lens whose optical axes overlap each other is an erecting equal-magnification optical system, The first lens side radius of the aperture, p is the pitch between adjacent first lenses, L ₀ is the predetermined object distance from the first lens to the object plane, and L ₁ is the first lens When the thickness, n is the refractive index of the first lens, and s is an arbitrary integer,

An erecting equal-magnification lens array unit that satisfies the following conditions is provided.

  According to the erecting equal-magnification lens array unit according to the present invention configured as described above, the light that can be stray light is blocked by the light blocking portion, so that the incident on the second lens is suppressed. Is possible.

1 is a perspective view illustrating an appearance of an image reading unit having an erecting equal-magnification lens array unit according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of an image reading unit taken along a plane perpendicular to the main scanning direction in FIG. 1. It is a perspective view which shows the external appearance of an erecting equal-magnification lens array unit. It is a figure which shows the positional relationship of a unit optical system, an image surface, and an object surface. It is a figure for _{demonstrating} the definition of (theta) _g with respect to a unit optical system. It is a fragmentary sectional view of the unit optical system by the plane perpendicular | vertical to the 1st direction in FIG. It is a figure for demonstrating the change of the image formation position on an image surface when the object plane is displaced from the ideal position in the conventional erecting equal-magnification lens array unit. It is a figure which shows the positional relationship of the 1st lens and translucent hole for calculating the aperture by the side of the 1st lens of a translucent hole. FIG. 6 is a graph showing a relationship of an allowable image shift amount with respect to a depth of field in order to explain that the image shift amount varies depending on the degree of overlap.

  Hereinafter, embodiments of an erecting equal-magnification lens array unit to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a perspective view of an image reading unit having an erecting equal-magnification lens array unit according to an embodiment of the present invention. The image reading unit 10 is provided in an image scanner (not shown). The image reading unit 10 can read an image of a subject (not shown) arranged on the image reading surface ics in a straight line along the main scanning direction. By continuously reading linear images while displacing the image reading unit 10 in the sub-scanning direction perpendicular to the main scanning direction, a two-dimensional image of the subject is read.

  Next, the configuration of the image reading unit 10 will be described with reference to FIG. FIG. 2 is a diagram schematically showing a cross section of a portion indicated by a two-dot chain line in FIG. 1 which is a plane perpendicular to the main scanning direction. However, unlike FIG. 1, a cover glass 11 is provided. The direction from the back surface to the front surface in FIG. 2 is the main scanning direction, the direction from left to right is the sub-scanning direction, and the direction from top to bottom is the optical axis direction.

  The image reading unit 10 includes a cover glass 11, an illumination system 12, an erecting equal-magnification lens array unit 13, an image sensor 14, and a position defining member 15. The cover glass 11, the illumination system 12, the erecting equal-magnification lens array unit 13, and the image sensor 14 are fixed by the position defining member 15 so that their positions and postures are maintained in the state described below.

  A hole 16 is formed in the position defining member 15. The hole 16 has a first chamber r1 and a second chamber r2. The first chamber r1 is formed so as to have a longer width in the sub-scanning direction than the second chamber r2.

  The cover glass 11 is attached to the end of the hole 16 on the first chamber r1 side. An illumination system 12 is disposed in the first chamber r1. In addition, the illumination system 12 is arrange | positioned in the position which does not overlap with the 2nd chamber part r2 seeing from an optical axis direction. The illumination system 12 is provided so that the illumination light emitted from the illumination system 12 is emitted in the direction of the cover glass 11. That is, the posture and position of a light source (not shown) and an illumination optical system (not shown) constituting the illumination system 12 are determined.

  The erecting equal-magnification lens array unit 13 is inserted into the second chamber r2. In addition, the imaging element 14 is fixed to the end of the hole 16 on the second chamber r2 side.

  The normal of the plane of the cover glass 11, the optical axis of each optical system (not shown in FIG. 2) provided in the erecting equal-magnification lens array unit 13, and the normal of the light receiving surface of the imaging device 14 The posture is adjusted so as to be parallel to the direction.

  In the configuration as described above, illumination light emitted from the illumination system 12 is irradiated to a subject (not shown) through the cover glass 11. Reflected light with respect to illumination light from the subject passes through the cover glass 11. The reflected light of the subject is imaged on the light receiving surface of the image sensor 14 by the erecting equal-magnification lens array unit 13. The formed optical image is picked up by the image pickup device 14, and an image signal which is an electric signal is generated.

  The image sensor 14 is a CCD line sensor, a CMOS line sensor, or the like, and generates a one-dimensional image signal. The generated one-dimensional image signal is transmitted to a signal processing circuit (not shown) and subjected to predetermined image processing. A two-dimensional image signal is generated by generating a one-dimensional image signal of a plurality of frames generated while displacing the image reading unit 10.

  Next, a detailed configuration of the erecting equal-magnification lens array unit 13 will be described with reference to FIG. The erecting equal-magnification lens array unit 13 includes a first lens array 17, a second lens array 18, and a connecting portion 19 (light shielding portion).

  The first lens array 17 is provided with a plurality of first lenses 20. The plurality of first lenses 20 are positioned so that their optical axes are parallel to each other. In addition, the first lens 20 is disposed so as to be in close contact with each other along a first direction perpendicular to the optical axis of the first lens 20.

  The second lens array 18 is provided with a plurality of second lenses 21 (see FIG. 2). The postures of the plurality of second lenses 21 are determined so that the optical axes are parallel to each other. Further, the second lens 21 is arranged so as to be aligned along a direction perpendicular to the optical axis of the second lens 21.

  The first lens array 17 and the second lens array 18 are connected by a connecting portion 19. The positions of the first lens array 17 and the second lens array 18 are aligned so that the optical axis of each first lens 20 and the optical axis of any second lens 21 overlap.

  A plurality of light transmitting holes 22 (openings) are formed in the connecting portion 19. The light transmitting hole 22 penetrates from the first lens 20 toward the second lens 21. Note that the surface of the connecting portion 19 on the first lens 20 side functions as a stop, and shields light incident on surfaces other than the light transmitting hole 22. Therefore, the unit optical system 23 is configured by the first lens 20, the light transmitting hole 22, and the second lens 21.

  The first lens 20 and the second lens 21 are designed so that each unit optical system 23 is an erecting equal-magnification optical system and substantially telecentric on the object side. Composed. The conditions that are substantially telecentric will be described later.

  In the present embodiment, the unit optical system 23 is provided with erecting equality by forming the first surface of the first lens 20 and the both surfaces of the second lens 21 to be convex surfaces. Note that the second surface of the first lens 20 may be a convex surface, a concave surface, or a flat surface.

Furthermore, each unit optical system 23 is designed and formed to satisfy the following expression (1).
0.5 ≦ y ₀ /D≦1.0 (1)

As shown in FIG. 4, y ₀ is the field radius of the unit optical system 23, that is, the radius of the range on the object plane os of light that can be taken in by the unit optical system 23. Note that the distance L ₀ from the unit optical system 23 to the object plane os is determined in advance, and the distance between the glass surface on which the document serving as the subject is placed and the unit optical system 23 is the determined distance L ₀ . Thus, the image scanner is formed. D is the diameter of the unit optical system 23.

Furthermore, each unit optical system 23 is designed and formed to satisfy the following expression (2).
D / (8 × L ₀ ) <tan θ _g (2)

Here, L ₀ is a predetermined object distance from the unit optical system 23 to the object plane os. As shown in FIG. 5, θ _g is a unit optical system 23 of a light ray passing through the center of gravity cg of a minute optical image fi in which one point on the object plane os is imaged on the image plane is by the unit optical system 23. Is the angle of incidence on.

Furthermore, since each unit optical system 23 is substantially telecentric, it is designed and formed to satisfy the following expression (3).
tan θ _g <δ / Δz (3)

  However, δ is an image shift amount allowed in advance for the unit optical system 23. The image shift amount is the light of the unit optical system 23 at one point on the object plane that forms an image at an arbitrary point on the image plane by displacing the object from the unit optical system 23 by the depth of field. The amount of displacement in the direction perpendicular to the axis.

  For example, when the erecting equal-magnification lens array unit 13 is used as the imaging optical system of the image sensor 14, when the image shift amount δ is equal to or less than the pixel pitch, the captured image is different from the unit optical system 23. The blur caused by the shift of the image formation point on the image plane corresponding to the same point on the object cannot be recognized. Therefore, the allowable image shift amount δ is determined according to an imaging element or a light receiving device to be used, or a shift amount that can be perceived by humans.

  Next, the shape of the light transmitting hole 22 will be described in detail. As shown in FIG. 6, the inner surface of the light transmission hole 22 is formed in a shape along the side surfaces of two truncated cones having the same center line cl. Further, the light transmitting hole 22 is formed so that the diameter of the light transmitting hole 22 on the first lens 20 side is smaller than the diameter on the second lens 21 side. The formation position of the light transmission hole 22 is determined so that the center line cl overlaps with the optical axes of the first lens 20 and the second lens 21.

  In particular, the radius r of the aperture of the light transmitting hole 22 on the first lens 20 side is determined to a value that allows an integer s that satisfies the following expression (4) to exist.

In the equation (4),
r is a radius of the light transmitting hole 22 on the first lens 20 side,
p is the pitch (distance) between the adjacent first lenses 20,
L ₁ is the thickness of the first lens 20,
n is the refractive index of the first lens 20.

  Further, the inner surface of the light transmitting hole 22 is subjected to processing for suppressing reflection of light and processing for absorbing light. For example, as a process for suppressing the reflection of light, there are a process called graining for roughening the surface by sandblasting or the like, and a process for suppressing the progress of reflected light by processing the surface into a screw shape. Examples of the light absorbing treatment include application of the inner surface with a light absorbing paint.

  According to the erecting equal-magnification lens array unit of the present embodiment having the above-described configuration, the diameter of the light transmission hole 22 on the first lens 20 side is formed so as to satisfy the expression (4). The amount of light incident on the second lens 21 can be further reduced. The suppression of stray light incidence according to equation (4) will be described in detail below with reference to FIG.

  A light ray can travel in all directions from an arbitrary point on the object plane os, and can enter the first surfaces of all the first lenses 20. When the light beam incident on the first surface exits from the second surface of the first lens 20, the light beam becomes stray light. Therefore, it is preferable to form the light transmitting holes 22 so that such stray light can be reduced as much as possible.

Emitted from the reference point sp on the object plane os intersecting the optical axis of any of the first lens 20 ₀ will be considered first ray b1 incident on the first surface of the first lens 20 ₁ adjacent. The angle of incidence on the first lens 20 ₁ of the first light beam b1 theta _0, the incident angle of the first light beam b1 incident on the first lens 20 ₁ and theta _1.

The following equation (5) is established according to Snell's law.
n × sin θ ₁ = sin θ ₀ (5)

  From the geometric relationship, the following relationships (6) and (7) are established.

However, in Formula (7), d is the distance between the position where the first light ray b1 reaches the second surface and the optical axis of the _first lens 201. The following equation (8) is obtained by modifying the equation (7).

d = L ₁ × tan θ ₁ (8)

Further, assuming that tan θ ₀ = sin θ ₀ and tan θ ₁ = sin θ ₁ and transforming equation (8) using equations (5) and (6), the following equation (9) is obtained.

Accordingly, the distance between the optical axis lx ₀ of arrival position of the first lens 20 ₀ on the second surface of the first light beam b1 is obtained by the following equation (10).

Light-transmitting hole 22 first ray b1 is, (the s to arbitrary integer) first from the lens 20 ₀ (s-1) pieces and the s corresponding to distant first lens _{20 s-1,} 20 _s if reached during the _s-1, 22 _s, the incident stray light is prevented to light-transmitting hole _{22 s-1, 22 s} of the first light beam b1.

The distance from the optical axis lx ₀ to the far edge of the light transmitting hole 22 _s-1 is r + (s−1) × p. Further, up to the side edge close to that of light-transmitting hole 22 _s, the distance from the optical axis lx ₀ is s × p-r.

Therefore, Expression (4) is obtained as a condition for causing the first light ray b1 to reach between the light transmitting holes 22 _s-1 and 22 _s . In the present embodiment, since the light transmitting hole 22 is formed so as to satisfy the expression (4), it is possible to reduce the amount of incident stray light as described above.

  In the present embodiment, since the aperture of the light transmitting hole 22 on the first lens 20 side is smaller than the aperture of the second lens 21 side, stray light from the first lens 20 of the other unit optical system 23 is It is possible to prevent the incident on the second lens 21.

  In the first lenses 20 that are in close contact with each other, stray light may be incident from the side surfaces of the adjacent first lenses 20. Due to the mixing of such stray light, the influence of noise on the image to be formed becomes large. However, as in the present embodiment, stray light can be suppressed by suppressing the incidence of stray light to the second lens 21 using the light transmitting hole 22, and the influence of image noise can be reduced. .

  In the present embodiment, the inner surface of the light transmitting hole 22 is subjected to a process for suppressing light reflection and a process for absorbing light, so that it passes through the opening on the first lens 20 side and passes through the opening of the light transmitting hole 22. Propagation of stray light incident on the inner surface to the second lens 21 can be prevented.

  In this embodiment, it is possible to form an erecting equal-magnification lens array unit that can be formed using a normal lens and has an expanded depth of field as the entire array. The effect of increasing the depth of field for the entire array will be described in detail below.

  As shown in FIG. 7A, in the conventional erecting equal-magnification lens array unit 13 ′, the object placed at the position of the ideal object plane os with respect to the distance to the image plane is is the unit optical system. 23 ′ forms an equal-size erect image on the image plane is. An image formed by the plurality of unit optical systems 23 'is projected as one whole image without causing a positional shift (see FIG. 7A).

  However, as shown in FIG. 7B, when the object plane os is displaced from the ideal position, the equality in the image plane is of each unit optical system 23 ′ is lost, and the same one-point image plane in the object plane os. The imaging positions at is are different between adjacent unit optical systems 23 '. Therefore, the image projected by the entire erecting equal-magnification lens array unit 13 'is blurred. Therefore, the depth of field of the erecting equal-magnification lens array unit as a whole becomes shallow.

  In general, as the incident angle of the principal ray on the object side increases, the change in the magnification of the lens with respect to the displacement of the object surface increases. In the entire erecting equal-magnification lens array unit, the larger the change in magnification, the greater the deviation of the imaging position of the same point on the object plane by the adjacent lenses.

  Therefore, ideally, when the incident angle of the chief ray is zero, the magnification does not change with respect to the displacement of the object plane. Therefore, even if the object plane is displaced from the ideal position, the image is formed at the same position on the image plane without shifting the imaging position by one point of the separate lens on the object plane. That is, if the individual optical systems constituting the lens array are object-side telecentric, the depth of field of the entire lens array can be kept deep. As described above, the erecting equal-magnification lens array unit 13 of the present embodiment can increase the subject depth as the entire lens array.

  Further, according to the present embodiment, the first lenses 20 are disposed so as to be in close contact with each other along the first direction. With such a configuration, it is possible to form an image having no missing portion along the first direction.

  In the present embodiment, as described above, since each unit optical system 23 is substantially telecentric on the object side, the amount of light transmitted from a point located outside the diameter of the unit optical system 23 is low. Therefore, if there is a gap between the adjacent unit optical systems 23, the image of the point on the object plane os on the extension of the gap becomes extremely dark, and the image may be lost. However, as described above, since the first lens 20 is in close contact along the first direction, it is possible to obtain an image having no gap along the first direction without such a gap.

Further, according to the present embodiment, the unit optical system 23 is formed so that 0.5 ≦ y ₀ / D. Therefore, since all the points on the object plane can be included in the field of view of any of the unit optical systems 23, partial omission of the image is prevented.

By the way, as y ₀ / D becomes larger, the unit optical system 23 includes the object plane at a distance from the optical axis in the field of view. Therefore, when y ₀ / D increases, the number of unit optical systems 23 that form an image on one point on the object plane increases, and the influence of the deviation of images formed by different unit optical systems 23 increases.

Therefore, in the present embodiment, the unit optical system 23 is formed so that y ₀ / D ≦ 1. Therefore, the number of unit optical systems 23 that image one point on the object plane is limited to two or less, and the influence of image shift can be reduced.

Further, in the present embodiment, each unit optical system 23 is formed so as to satisfy the expression (2) (D / 8L ₀ <tan θ _g ), so that uneven brightness is suppressed as described below. Is possible.

  As is known in the art, an image by an optical system such as a lens is darkest as the intersection between the image plane and the optical axis is brightest and away from the optical axis. Therefore, unevenness in brightness occurs in the formed image. In the case of a digital camera, it is possible to reduce brightness unevenness by changing the amplification factor for each image area.

  However, when the amount of light in the region away from the optical axis is extremely low, it is necessary to increase the amplification factor, and the influence of noise also increases. Therefore, it is preferable that the ratio of the light amount to the light amount on the optical axis is designed to exceed about 50% at any position.

In the case of the erecting equal-magnification lens array unit 13 of the present embodiment, it is only necessary to obtain a light amount exceeding about 50% by combining the light beams transmitted through the two adjacent unit optical systems 23. The amount of light exceeding 25% may be obtained from the system 23. If the incident angle θ _g satisfies the following expression (11), light having a light quantity exceeding 25% of the vicinity of the optical axis can be transmitted at any position within the field of view of the single unit optical system 23.

The left side of the equation (11) is D / 8L ₀ , and each unit optical system 23 is formed so as to satisfy the equation (2). Therefore, the brightness unevenness is sufficiently compensated by the amplification process. It is possible to suppress.

In the present embodiment, each unit optical system 23 is formed so as to satisfy the expression (3) (tan θ _g <δ / Δz). That is, as the angle calculated by the depth of field Δz is acceptable image shift amount δ and tolerance is becomes the maximum angle of theta _g, unit optical system 23 is designed.

  As described above, this condition is a condition that the unit optical system 23 is substantially telecentric on the object side. By satisfying such a condition, it is possible to suppress the deviation of the image forming position of the image formed by the adjacent unit optical system 23 to an extent that it is difficult to visually recognize.

Next, define the overlapping degree m the ratio of the diameter D of the unit optical system 23 with respect to the viewing radius y _0, the relationship between the overlapping degree m and the image shift amount [delta], is described below with reference to numerical values. When the incident angle of light emitted from an arbitrary point on the object surface is θ, the following equations (12) and (13) are established.

  Using the equations (12), (13) and m, the following equation (14) is derived.

As is apparent from the equation (14), the image shift amount δ increases as the overlapping degree m changes from 1/2. FIG. 9 shows the relationship between the depth of field Δz and the image shift amount δ by taking m = 0.65 and m = 2.7 as an example. Note that D = 2.0 and L ₀ = 9.

  As the image shift amount δ increases, the resolution of the erecting equal-magnification lens array unit 13 as a whole decreases, and the deviation of the imaging position of the point on the same object plane imaged by the adjacent unit optical system 23 increases. Become. As shown in FIG. 9, at the same depth of field Δz, the image shift amount δ is smaller in the case of m = 0.65 than in the case of m = 2.7. Therefore, it can be seen that the larger the difference between m and 1/2, the greater the displacement of the imaging position.

  For example, when the allowable image shift amount is 0.05 mm of the pixel pitch of the image sensor 14 used as an example, m = 2.7 and the depth of field Δz is 0.1 mm. On the other hand, when m = 0.65, the depth of field Δz is 0.65 mm. Thus, it can be seen that the depth of field Δz determined based on the allowable image shift amount is deeper as the overlapping degree m is closer to ½.

  Next, the effects of the present invention will be described by way of examples. However, the present examples are merely examples for explaining the effects of the present invention, and do not limit the present invention.

  Using the lens data shown in Tables 1 and 2, a unit optical system 23 of Example 1 was created. A surface corresponding to the surface number in Table 1 is shown in FIG.

However, in Table 1,
* 1 indicates an aspherical surface, and the aspherical surface is given by the following equation (15).
* 2 is SCHOTT AG bk7.
* 3 is ZEONEX (registered trademark) E48R of ZEON CORPORATION.
* 4 is the aperture.

In the equation (15),
Z is the depth from the tangent plane to the surface vertex,
r is the radius of curvature,
h is the height from the optical axis,
k is the conic constant,
A is the fourth-order aspheric coefficient,
B is the sixth-order aspheric coefficient,
C is the 8th-order aspheric coefficient,
D is a 10th-order aspheric coefficient.
Table 2 shows the conic constant k and aspheric coefficients A, B, C, and C.

  Using the lens data shown in Table 3 and Table 4, the unit optical system 23 of Example 2 was created. The surface corresponding to the surface number in Table 3 is the same as in Table 1.

However, in Table 3,
* 1 indicates an aspherical surface, and the aspherical surface is given by the above-described equation (15). Table 4 shows the conic constant k and the aspherical coefficients A, B, C, and C.
* 2 is SCHOTT AG bk7.
* 3 is ZEONEX (registered trademark) E48R of ZEON CORPORATION.
* 4 is the aperture.

  Using the lens data shown in Tables 5 and 6, a unit optical system 23 of Example 3 was created. The surface corresponding to the surface number in Table 5 is the same as in Table 1.

However, in Table 5,
* 1 indicates an aspherical surface, and the aspherical surface is given by the above-described equation (15). Table 6 shows the conic constant k and the aspherical coefficients A, B, C, and C.
* 2 is SCHOTT AG bk7.
* 3 is ZEONEX (registered trademark) E48R of ZEON CORPORATION.
* 4 is the aperture.

  As shown as the fourth surface in Table 1, Table 3, and Table 5, the second surface of the first lens 20 may be flat (see Example 1), concave (see Example 2), or convex (see Example). 3) It can be seen that it can be formed so as to have an erecting equality.

The field radius y ₀ of the unit optical system 23 and the diameter D of the unit optical system 23 in Examples 1 to 3 were measured, and the ratio of the field radius y ₀ to the diameter D was calculated. The calculation results are shown in Table 7.

As shown in Table 7, it can be seen that the unit optical system 23 satisfying 0.5 ≦ y ₀ /D≦1.0 can be formed.

The depth of field Δz was calculated based on the field radius y ₀ of the unit optical system 23 and the diameter D of the unit optical system 23 in Examples 1 to 3. The allowable image shift amount δ is 0.05 mm. The calculation results are shown in Table 8.

  The depth of field when a conventional Selfoc lens or rod lens is used is ± 0.4. On the other hand, as shown in Table 8, ± 2.6 in Example 1 and ± 1. 74 and ± 2.6 in Example 3, indicating that the depth of field is increased compared to the conventional case.

  It was calculated whether or not the light transmitting hole 22 satisfying the expression (4) can be designed for the unit optical system 23 of Examples 1 to 3. The calculation results are shown in Table 9.

  As shown in Table 9, the radius r of the light transmission hole 22 on the first lens 20 side is 0.125 in Example 1, 0.23 in Example 2, and 0.13 in Example 3. , An integer s satisfying the equation (4) may exist. Thus, it turns out that the light transmission hole 22 which reduces the light quantity of a stray light can be designed by satisfy | filling (4) Formula with respect to the unit optical system 23 of Example 1- Example 3. FIG.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

For example, in the above embodiment, the unit optical system 23 is formed so as to satisfy the expression (2) (D / 8L ₀ <tan θ _g ), but is designed and formed so as to satisfy 0 <tan θ _g. It may be configured.

Even if tan θ _g <D / 8L ₀ , the unit optical system 23 having a deep depth of field can be formed. However, when tan θ _g = 0, the width of the light beam needs to be zero. In that case, the amount of light reaching the image plane is substantially zero. Therefore, tan θ _g needs to be at least a value exceeding zero.

DESCRIPTION OF SYMBOLS 10 Image reading part 11 Cover glass 12 Illumination system 13, 13 'Erecting equal magnification lens array unit 14 Image pick-up element 15 Position-defining member 16 Hole part 17 1st lens array 18 2nd lens array 19 Connection part 20 1st Lens 21 Second lens 22 Translucent hole 23, 23 'Unit optical system cg Center of gravity position cl Center line fi Minute optical image ics Image reading surface is Image surface os Object surface r1, r2 First chamber, second Murobe

Claims (4)

A first lens array having a plurality of first lenses, wherein the plurality of first lenses are arranged along a first direction perpendicular to an optical axis of the first lenses;
A second lens array including a plurality of second lenses each having an optical axis superimposed on each of the first lenses, wherein the plurality of second lenses are arranged along the first direction;
A light shielding portion in which an opening is formed between the first and second lenses whose optical axes overlap each other,
Each optical system formed by the first lens and the second lens whose optical axes overlap each other is an erecting equal magnification optical system,
r is a radius of the aperture on the side of the first lens, p is a pitch between the first lenses adjacent to each other, L ₀ is a predetermined object distance from the first lens to the object plane, L ₁ Is the thickness of the first lens, n is the refractive index of the first lens, and s is an arbitrary integer,

An erecting equal-magnification lens array unit characterized by satisfying   2. The erecting equal-magnification lens array unit according to claim 1, wherein a diameter of the opening on the first lens side is smaller than a diameter on the second lens side. Erect life-size lens array unit.   3. The erecting equal-magnification lens array unit according to claim 1 or 2, wherein the inner surface of the opening is subjected to surface treatment for preventing light reflection. unit.   An image reading apparatus comprising the erecting equal-magnification lens array unit according to any one of claims 1 to 3.

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