JP2005257771A - Optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system which is not easily influenced by surface roughness even when an aspheric lens is used, can be easily manufactured and is not easily influenced by environmental changes such as a temperature change. <P>SOLUTION: The optical system 10 is constituted of a 1st lens 20 and a glass-made 2nd lens 30 having positive refractive power which are successively arranged from the object side and the shapes of all optical faces of the 1st and 2nd lenses 20, 30 are rotationally symmetrical about the optical axis. The 1st lens 20 has a meniscus shape turning its convex surface to the image surface side, the optical surface of the object side has an aspherical shape and both the optical surfaces of the object side and image surface side of the 2nd lens 30 are spherical shapes. When it is defined that the half field angle of a beam made incident on the optical system is θ[rad.], the image height of a beam emitted from the optical system is Y[mm] and the focal distance of the optical system is f[mm], the following inequality (1) is satisfied. The inequality (1) is -0.10<(Y-f×θ)/Y<0.10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical system in which an image height is substantially equal to a product of an incident half angle of view and a focal length, and more particularly to an optical system telecentric on the image plane side.

Conventionally, an f-θ optical system is used for a scanning optical system including a deflector such as an LBP (Laser Beam Printer), a laser fax machine, or a digital copying machine, in which an image height needs to be proportional to an incident half field angle. in use.
In recent years, there has been an increasing demand for cost reduction and miniaturization of such a scanning optical system, and in response to this, many proposals have been made regarding techniques related to scanning optical systems including aspherical scanning lenses (for example, patents). See references 1 and 2.)
Patent Documents 1 and 2 disclose a technique relating to a scanning optical system having a two-lens configuration in which parallel light is incident on the main scanning direction of a plastic aspherical scanning lens and a scanning optical system corresponding to a wide angle of view. As a result, not only the above-mentioned cost reduction and downsizing but also the field curvature and f-θ characteristics can be improved.
JP-A-5-5853 JP-A-8-327898

In general, aspherical lenses manufactured by glass molding, injection molding, etc., have a local error from the design value at the time of mold manufacture, compared to spherical glass lenses manufactured by polishing optical surfaces. Due to the above, a slight distortion (surface roughness) is generated on the optical surface.
Therefore, the smaller the diameter of the incident light beam with respect to the lens effective diameter of the aspheric lens, the more easily affected by the surface roughness, and the local f-θ characteristic deviation and the pixel omission due to blur are likely to occur. There's a problem.

However, the above-mentioned patent document does not mention any means for solving the above-mentioned problem caused by the surface roughness generated on the optical surface of the aspheric lens, and of course, no countermeasure is taken.
In general, the scanning lens has a problem that it is difficult to perform accurate scanning because a back focus error causes a magnification error.

  The object of the present invention is to take the above-mentioned problems into consideration, and even when an aspherical lens is used, the influence of surface roughness is small and can be easily manufactured. Further, the influence of environmental changes such as temperature changes. It is to provide an optical system with less.

In order to solve the above-described problems, the invention according to claim 1 is configured by arranging at least two lenses of a first lens and a glass-made second lens having a positive refractive power in order from the object side. In the optical system in which the shapes of all the optical surfaces of the first lens and the second lens are rotationally symmetric with respect to the optical axis, the first lens has a meniscus shape with a convex surface facing the image surface side, and The object-side optical surface of the first lens has an aspherical shape, the object-side optical surface and the image-side optical surface of the second lens both have a spherical shape, and a half image of a light beam incident on the optical system. When the angle is defined as θ [rad.], The image height of the light beam emitted from the optical system is defined as Y [mm], and the focal length of the optical system is defined as f [mm], the following equation (1) is satisfied. Features.
−0.10 <(Y−f × θ) / Y <0.10 (1)

As described above, in general, an aspherical lens manufactured by a glass mold method or the like has a slight distortion (surface) on its optical surface due to a local error from a design value at the time of mold manufacture. (Roughness) has occurred.
When the first lens has a meniscus shape with the convex surface facing the image surface side, the light beam diameter on the object-side optical surface of the first lens is compared with the light beam diameter on the optical surface on the image surface side. The light beam diameter on the optical surface on the object side is larger.
Here, when the first lens has a meniscus shape with the convex surface facing the image surface side, the ratio between the effective diameter φ _L1 of the optical surface on the object side of the first lens and the beam diameter φ _B1 on the optical axis on this surface and φ _B1 / φ _L1, when comparing the ratio φ _B1 '/ φ _L1' 'of the light flux diameter phi _B1 on the optical axis in the plane as the' effective diameter phi _L1 of the optical surface on the image plane side of the first lens The value of φ _B1 / φ _L1 on the object side is larger.

Therefore, as in the first aspect of the invention, the optical surface on the object side among the optical surfaces of the meniscus-shaped first lens with the convex surface facing the image surface side, that is, closer to the light source and with respect to the effective diameter of the optical surface. By making the surface on the side with a large ratio of the light beam diameter an aspherical surface, the influence of the light beam on the surface roughness can be reduced, and a local f-θ characteristic shift or pixel omission due to blurring can be reduced. Occurrence can be suppressed, and the optical system can be easily manufactured.
A spherical glass lens manufactured by polishing an optical surface has a smaller surface roughness than that of an aspheric lens. Therefore, by using such a spherical glass lens as the second lens, it is difficult to be adversely affected by the surface roughness. An optical system can be obtained.

The surface roughness of the aspheric optical surface on the object side can be reduced by making the first lens made of resin.
Such an optical system is applied to a general scanning optical system, that is, an optical system that scans an image plane while changing a half angle of view with a substantially parallel incident light beam having a small diameter with respect to the effective diameter of the optical surface. In this case, the scanning speed of the image plane in the vicinity of the optical axis and in the peripheral portion can be kept substantially constant.
Further, when such an optical system is applied to an optical system that gives different signals to the light flux depending on, for example, the incident angle of view, the angular resolution of the signals that can be placed at the entire image height can be made substantially equal.

  According to a second aspect of the present invention, in the optical system according to the first aspect, the image plane side is telecentric.

For example, when the light receiving portion of the photodetector is not exposed on the surface of the photodetector and is covered with an outer wall or the like, such as a CCD (Charge Coupled Device), The vignetting by the outer wall occurs, and there is a problem that it is not possible to receive all of the incident light beam. On the other hand, since the light is incident substantially perpendicularly, the influence of the vignetting can be suppressed.
Further, by making the image surface side telecentric, a change in image height caused by a slight error in the arrangement of the light receiving surfaces can be prevented, and an optical system with a precise magnification can be obtained.

According to a third aspect of the present invention, in the optical system according to the second aspect, when the thickness on the optical axis from the object-side optical surface to the image-side optical surface of the first lens is defined as d. The following equation (2) is satisfied.
0.040 <d / f <0.55 (2)

  As described in the third aspect of the invention, by making d / f larger than the lower limit of the expression (2), the field curvature in the f-θ optical system can be suppressed, and d / f is set to (2). By making it smaller than the upper limit of the expression, the axial thickness of the first lens can be suppressed, and the lens can be easily molded.

According to a fourth aspect of the present invention, in the optical system according to the second or third aspect, the optical system comprises two lenses, the first lens and the second lens, and the paraxial power of the first lens. _Is defined as P _L1 , and the paraxial power of the second lens is defined as P _L2 , the following expression (3) is satisfied.
-2.8 <P _L1 / P _L2 <10.0 (3)

As in the invention described in claim 4, by making P _L1 / P _L2 smaller than the upper limit of the expression (3), the distance on the optical axis between the first lens and the second lens does not become too long, By making P _L1 / P _L2 larger than the lower limit of the expression (3), the distance on the optical axis between the second lens and the image plane does not become too long, and the optical surface on the image plane side of the entrance pupil and the first lens. Can be corrected satisfactorily while ensuring a sufficient distance from each other.
In order to further enhance the above action, it is more preferable to satisfy the following range.
-1.4 <P _L1 / P _L2 <5.0

According to a fifth aspect of the present invention, in the optical system according to any one of the second to fourth aspects, the optical system includes two lenses, the first lens and the second lens. When the distance on the optical axis from the optical surface on the image plane side of the lens to the optical surface on the object side of the second lens is defined as Δl, the following expression (4) is satisfied.
0.0 <Δl / f <2.0 (4)

As in the fifth aspect of the invention, by setting Δl / f within the range of the expression (4), the paraxial power P _L1 of the first lens does not become too large, and the entrance pupil and the image plane of the first lens The curvature of field can be corrected well while ensuring a sufficient distance from the optical surface on the side.

According to a sixth aspect of the present invention, in the optical system according to any one of the second to fifth aspects, the optical system includes two lenses, the first lens and the second lens. The effective diameter of the optical surface on the object side of the lens is φ _L1 , the diameter of the light beam incident on the optical surface on the object side of the first lens is φ _B1 , and the effective diameter of the optical surface on the object side of the second lens is φ _L2 satisfies the following expression (5) when the diameter of the light beam incident on the object-side optical surface of the second lens is defined as φ _B2 .
1.4 <(φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) <18.0 (5)

As in the sixth aspect of the invention, by making (φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) smaller than the upper limit of the expression (5), the object-side optics of the first lens that is aspherical It is possible to reduce the influence of the passing light flux by the local surface roughness existing on the surface, and by making (φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) larger than the lower limit of the equation (5) The paraxial power P _L2 of the second lens does not become too small, and the field curvature can be corrected well.
In order to further enhance the above action, it is more preferable to satisfy the following range.
2.0 <(φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) <6.0

According to a seventh aspect of the present invention, in the optical system according to any one of the second to sixth aspects, the optical system includes two lenses, the first lens and the second lens. lens is made of plastic, when the paraxial power of the first lens defined P _L1, the paraxial power of the second lens and P _L2, and satisfies the following equation (6).
-2.8 <P _L1 / P _L2 <1.2 (6)

In general, plastics have a higher refractive index temperature dependency than glass, so in an optical system using plastic lenses, the focal length is designed because the refractive index of the lens changes due to changes in environmental temperature. There is a problem of deviating from the value.
For example, in the case of an optical system in which light receiving elements are discontinuously arranged, such as a CCD, by using a plastic lens, the refractive index of the lens changes due to environmental temperature changes, and the focal length deviates from the design value. The imaging position deviates from the design value, and the light is not condensed on the light receiving element.
Therefore, when the first lens is made of plastic as in the invention described in claim 7, the refractive index of the first lens is changed by setting P _L1 / P _L2 within the range of the expression (6). Even in this case, the deviation of the focal length due to the environmental temperature change can be made sufficiently small, and the deviation of the imaging position from the design value, the curvature of field, etc. can be corrected well.
In order to further enhance the above action, it is more preferable to satisfy the following range.
-1.4 <P _L1 / P _L2 <0.6

According to an eighth aspect of the present invention, in the optical system according to the seventh aspect, when the thickness on the optical axis from the object-side optical surface to the image-side optical surface of the first lens is defined as d. The following expression (7) is satisfied.
0.075 <d / f <0.550 (7)

In general, the refractive index of plastic is lower than that of glass. Therefore, if the lens thickness on the optical axis is equal to the focal length, the plastic lens has a larger Petzval sum than the glass lens.
Therefore, when a plastic lens is used as the first lens as in the invention described in claim 8, the curvature of field can be corrected well by making d / f larger than the lower limit of the expression (7), and the upper limit. By making it smaller, the thickness of the first lens on the optical axis does not become too thick and can be easily manufactured.

  According to the present invention, even when an aspherical lens is used, an optical system that is less affected by surface roughness, can be easily manufactured, and is less affected by environmental changes such as temperature changes can be obtained.

The best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 1, the optical system 10 of the present embodiment includes a single first lens 20 and a second single lens 30 made of glass having positive refractive power, and each optical axis l1. 12 are arranged in order from the object side, and one or a plurality of optical elements (not shown) such as a collimator are arranged in front of the first lens 20 so that the image surface side is telecentric. Designed to.
Reference numeral F1 indicates the object side focal point of the optical system 10, reference numeral F2 indicates the image plane side focal point, and reference numeral 40 indicates the image plane. Although not shown, a light source is disposed in front of the first lens 20.

The first lens 20 has a meniscus shape in which both the paraxial curvatures of the optical surface 21 on the object side and the optical surface 22 on the image surface side are negative, with the convex surface facing the image surface side, and the optical surface 21 on the object side. Has an aspherical shape. The optical surface 22 on the image plane side of the first lens 20 may be spherical or aspherical, but in this embodiment, it is spherical.
In the second lens 30, both the object-side optical surface 31 and the image-side optical surface 32 are spherical.
As described above, the shapes of all the optical surfaces 21, 22, 31, and 32 of the first lens 20 and the second lens 30 are rotationally symmetric with respect to the optical axes l1 and l2.

The light beam emitted from the light source passes through an optical element such as a collimator disposed between the light source and the first lens 20 to be collimated, and reaches the optical surface 21 on the object side of the first lens 20.
Here, when the first lens 20 has a meniscus shape with a convex surface facing the image surface side, the effective diameter φ _L1 of the optical surface 21 on the object side of the first lens 20 and the light beam diameter φ on the optical axis on this surface. the ratio φ _B1 / φ _L1 of _B1, the ratio φ _B1 '/ φ _L1' of the optical axis in this plane and beam diameter phi _B1 'effective diameter phi _L1 on the image plane side of the optical surface 22 of the first lens 20 When comparing ′, the value of φ _B1 / φ _L1 on the object side is larger.
Therefore, among the optical surfaces of the meniscus first lens 20 with the convex surface facing the image surface, the object-side optical surface 21, that is, closer to the light source and on the side where the ratio of the light beam diameter to the effective diameter of the optical surface is larger. By making the surface aspherical, the light beam is emitted from the optical surface 22 on the image plane side of the first lens 20 in a state where the influence of the light beam on the surface roughness is reduced.

  The light beam emitted from the optical surface 22 on the image plane side of the first lens 20 is refracted by the optical surface 31 on the object side and the optical surface 32 on the image plane side of the second lens 30, and the principal ray thereof is the optical axis. The light beam is emitted from the optical surface 32 on the image plane side of the second lens 30 in a state parallel to l2, and the light beam is condensed on the image plane 40 in a state where the principal ray is incident on the image plane 40 perpendicularly. become.

A plurality of light beams emitted from the light source are incident on the first lens 20 as parallel lights at different angles of view, and after passing through the first lens 20 and the second lens 30, are collected on the image plane at different image heights. Although the optical system 10 of the present embodiment is lighted, the half field angle of the incident light beam is θ [rad.], The image height of the light beam emitted from the optical system 10 is Y [mm], and the optical system 10 When the focal length is defined as f [mm], it is designed to satisfy the following equation (1), so that the image height is approximately equal to the product of the focal length and the angle of view incident on the optical system. I have to.
−0.10 <(Y−f × θ) / Y <0.10 (1)

Further, since the image plane side is telecentric, the light beam is incident substantially perpendicular to the image plane 40. For example, when the optical system 10 of the present embodiment is applied to a CCD, the photodetector The influence of vignetting when entering the light receiving element can be suppressed, and the amount of light can be secured.
When the thickness on the optical axis l1 from the optical surface 21 on the object side to the optical surface 22 on the image plane side of the first lens 20 is defined as d, the design is performed so as to satisfy the following expression (2). As a result, the curvature of field in the f-θ optical system can be suppressed, and the axial thickness of the first lens 20 can be suppressed, which facilitates lens molding.
0.040 <d / f <0.55 (2)

Further, when the paraxial power of the first lens 20 is defined as P _L1 and the paraxial power of the second lens 30 is defined as P _L2 , the first lens 20 and the first lens 20 are designed so as to satisfy the following expression (3). The distance on the optical axis between the second lens 30 and the distance on the optical axis between the second lens 30 and the image plane 40 are not too long, and the distance between the entrance pupil and the optical surface on the image plane side of the first lens. It is possible to satisfactorily correct the field curvature while ensuring sufficient.
-2.8 <P _L1 / P _L2 <10.0 (3)

In addition, when the distance on the optical axis from the optical surface 22 on the image plane side of the first lens 20 to the optical surface 31 on the object side of the second lens 30 is defined as Δl, it is designed to satisfy the following equation (4). , The paraxial power P _L1 of the first lens 20 does not become too large, and the curvature of field is corrected well while ensuring a sufficient distance between the entrance pupil and the optical surface on the image plane side of the first lens. I can do it.
0.0 <Δl / f <2.0 (4)

The effective diameter of the object-side optical surface 21 of the first lens 20 is φ _L1 , the beam diameter of the light beam incident on the object-side optical surface 21 of the first lens 20 is φ _B1 , and the object-side optical surface 21 of the second lens 30 is object-side. By designing so that the effective diameter of the optical surface 31 is φ _L2 and the diameter of the light beam incident on the object-side optical surface 31 of the second lens 30 is φ _B2 , the following equation (5) is satisfied. The influence of the incident light flux due to the local surface roughness present on the object-side optical surface 21 of the first lens 20 that is an aspherical surface can be reduced, and the paraxial power P _L2 of the second lens 30 can be reduced. Is not too small, and the field curvature can be corrected well.
1.4 <(φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) <18.0 (5)

Further, when the first lens 20 is made of plastic, the paraxial power of the first lens 20 is defined as P _L1 , and the paraxial power of the second lens 30 is defined as P _L2 , the first lens 20 is designed to satisfy the following formula (6). Thus, even when the refractive index of the first lens 20 changes due to a change in the temperature of the environment, the deviation of the focal length can be made sufficiently small, the deviation of the image height from the design value with respect to the incident angle of view, and the image plane. The curvature can be corrected well.
-2.8 <P _L1 / P _L2 <1.2 (6)

In addition, when the first lens 20 is made of plastic, when the thickness on the optical axis from the object-side optical surface 21 to the image-side optical surface 22 of the first lens 20 is defined as d, By designing so as to satisfy (7), the curvature of field can be corrected satisfactorily, and the thickness of the first lens 20 on the optical axis does not become too thick and can be easily manufactured.
0.075 <d / f <0.550 (7)

Next, Examples 1 to 7 will be described.
2-8 is sectional drawing of the optical system in each Example.
In the first, third, fifth, and sixth embodiments, the first lens L1 is made of glass, the object-side optical surface is aspherical, and the image-side optical surface is spherical. The first lens L1 is made of plastic, and both the object-side optical surface and the image-side optical surface are aspherical.
The second lens L2 is made of glass in all of Examples 1 to 7, and both the object-side optical surface and the image-side optical surface are spherical.

表１〜表７中のＮＡは開口数、ｆは焦点距離、λは設計波長、Ｎλは設計波長における屈折率、ｍは結像倍率、θは光学系への入射半画角、ｒは曲率半径、ｄは光軸方向に前後する２つの面の光軸方向の位置を表している。また、プラスチック製の第１レンズの温度変化による屈折率変化量Δnは、Δｎ＝−9.00000×10^-5[１／℃]である。 Tables 1 to 7 show lens data of each example.

In Tables 1 to 7, NA is the numerical aperture, f is the focal length, λ is the design wavelength, Nλ is the refractive index at the design wavelength, m is the imaging magnification, θ is the half angle of incidence on the optical system, and r is the curvature. The radius, d, represents the position in the optical axis direction of the two surfaces that move back and forth in the optical axis direction. Further, the refractive index change amount Δn due to the temperature change of the first plastic lens is Δn = −9.00000 × 10 ⁻⁵ [1 / ° C.].

但し、面の頂点に接する平面からの変形量をｘ(mm)、光軸に垂直な方向の高さをｈ(mm)、曲率半径をr(mm)、κを円錐係数、Ａ_2iを非球面係数とする。 The object-side optical surface of the first lens in Examples 1, 3, 5, and 6, and the object-side optical surface and the image-side optical surface of the first lens in Examples 2, 4, and 7, respectively, Are formed as aspherical surfaces that are rotationally symmetric with respect to the optical axis and are defined by mathematical formulas in which the coefficients shown in Tables 1 to 7 are substituted.

However, the amount of deformation from the plane in contact with the vertex of the surface is x (mm), the height in the direction perpendicular to the optical axis is h (mm), the radius of curvature is r (mm), κ is the cone coefficient, and A _2i is non Spherical coefficient.

Table 8 shows the values of the above formulas (1) to (5) in Examples 1 to 7.

9A is a graph showing the f-θ characteristic in Example 1, FIG. 9B is a graph showing telecentricity in Example 1, and FIG. 9C is a graph showing field curvature in Example 1. FIG. It is.
In each example, in the graph showing the f-θ characteristic, the horizontal axis represents (Y−f × θ) / Y in the equation (1), and the vertical axis represents the image height Y. In the graph indicating telecentricity, the horizontal axis indicates the image height Y, and the vertical axis indicates the incident angle of the principal ray on the image plane. Of the graphs showing the field curvature, the graph shown on the left shows the field curvature, the vertical axis shows the image height, the graph shown on the right shows the distortion (distortion), and the vertical axis shows the image height. Indicates.

  The first embodiment satisfies the expressions (1) to (5), and as shown in FIGS. 9A to 9C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. Since the maximum value divided by the image height Y is 0.014, the maximum value of the incident angle to the image plane is 0.2 °, and the maximum value of the field curvature is 0.003 mm, f− An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I understand that there is.

10A is a graph showing the f-θ characteristics in Example 2, FIG. 10B is a graph showing telecentricity in Example 2, and FIG. 10C is a graph showing field curvature in Example 2. FIG. It is.
The second embodiment satisfies the expressions (1) to (5). As shown in FIGS. 10A to 10C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.02, the maximum angle of incidence on the image plane is 0.2 °, and the maximum value of field curvature is 0.003 mm. An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I understand that there is.

11A is a graph showing the f-θ characteristic in Example 3, FIG. 11B is a graph showing telecentricity in Example 3, and FIG. 11C is a graph showing field curvature in Example 3. It is.
The third embodiment satisfies the expressions (1) to (5). As shown in FIGS. 11A to 11C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.02, the maximum angle of incidence on the image plane is 0.5 °, and the maximum value of field curvature is 0.002 mm. An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I know that there is.

12A is a graph showing the f-θ characteristic in Example 4, FIG. 12B is a graph showing telecentricity in Example 4, and FIG. 12C is a graph showing field curvature in Example 4. FIG. It is.
The fourth embodiment satisfies the expressions (1) to (5), and as shown in FIGS. 12A to 12C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.016, the maximum value of the incident angle to the image plane is 0.4 °, and the maximum value of the field curvature is 0.014 mm. An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I understand that there is.

13A is a graph showing the f-θ characteristic in Example 5, FIG. 13B is a graph showing telecentricity in Example 5, and FIG. 13C is a graph showing field curvature in Example 5. It is.
The fifth embodiment satisfies the expressions (1) to (5). As shown in FIGS. 13A to 13C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.033, the maximum incident angle to the image plane is 0.1 °, and the maximum value of the field curvature is 0.092 mm. An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I understand that there is.

14A is a graph showing the f-θ characteristic in Example 6, FIG. 14B is a graph showing telecentricity in Example 6, and FIG. 14C is a graph showing field curvature in Example 6. It is.
In Example 6, the expressions (1) to (5) are satisfied. As shown in FIGS. 14A to 14C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.002, the maximum angle of incidence on the image plane is 0.4 °, and the maximum value of field curvature is 0.023 mm. An optical system that has good performance in all aspects of θ characteristics, telecentricity, and field curvature, and that is easy to mold because the optical surface closest to the light source is aspherical, and that is less affected by surface roughness. I understand that there is.

15A is a graph showing the f-θ characteristic in Example 7, FIG. 15B is a graph showing telecentricity in Example 7, and FIG. 15C is a graph showing field curvature in Example 7. It is.
The seventh embodiment satisfies the expressions (1) to (5), and as shown in FIGS. 15A to 15C, the deviation from the product of the focal position of the image height Y and the incident angle to the optical system is detected. The maximum value divided by the image height Y is 0.053, the maximum value of the incident angle to the image plane is 0.5 °, and the maximum value of the field curvature is 0.002 mm. It can be seen that the optical system has a light condensing performance, and the optical surface closest to the light source is aspherical, so that it is easy to mold, and is less affected by surface roughness.

16A is a graph showing the f-θ characteristics when the environmental temperature is increased by 30 ° C. in Example 7, FIG. 16B is a graph showing the telecentricity in Example 7, and FIG. 10 is a graph showing field curvature in Example 7.
When the environmental temperature rises by 30 ° C. in Example 7, the expression (6) is further satisfied, and as shown in FIGS. 16A to 16C, the focal position of the image height Y and the incident angle to the optical system. The maximum value obtained by dividing the deviation from the product by the image height Y is 0.053, the maximum angle of incidence on the image plane is 0.5 °, and the maximum value of the field curvature is 0.004 mm. It is. In addition, since the value obtained by dividing the focal length change Δf when the environmental temperature rises by 30 ° C. by the designed focal length f is Δf / f = 1.1 × 10 ⁻⁴ , the focal length change due to the environmental temperature change It can be seen that this is a precise optical system with a sufficiently small influence.

It is principal part sectional drawing which shows the structure of an optical system. FIG. 3 is a cross-sectional view of a main part showing a configuration of an optical system in Example 1. FIG. 6 is a cross-sectional view of a principal part showing a configuration of an optical system in Example 2. FIG. 6 is a cross-sectional view of a principal part showing a configuration of an optical system in Example 3. FIG. 6 is a cross-sectional view of a principal part showing a configuration of an optical system in Example 4. FIG. 10 is a cross-sectional view of a principal part showing a configuration of an optical system in Example 5. FIG. 10 is a main part sectional view showing a configuration of an optical system in Example 6; FIG. 10 is a cross-sectional view of a principal part showing a configuration of an optical system in Example 7. 2 is a graph (a) representing f-θ characteristics, a graph (b) representing telecentricity, and a graph (c) representing field curvature. 7 is a graph (a) representing f-θ characteristics in Example 2, a graph (b) representing telecentricity, and a graph (c) representing field curvature. 6 is a graph (a) representing f-θ characteristics in Example 3, a graph (b) representing telecentricity, and a graph (c) representing field curvature. 6 is a graph (a) representing f-θ characteristics in Example 4, a graph (b) representing telecentricity, and a graph (c) representing field curvature. 10 is a graph (a) representing f-θ characteristics, a graph (b) representing telecentricity, and a graph (c) representing field curvature in Example 5. FIG. It is the graph (a) showing the f-theta characteristic in Example 6, the graph (b) showing telecentricity, and the graph (c) showing curvature of field. It is the graph (a) showing the f-theta characteristic in Example 7, the graph (b) showing telecentricity, and the graph (c) showing curvature of field. It is the graph (a) showing the f-theta characteristic in Example 7, the graph (b) showing telecentricity, and the graph (c) showing curvature of field.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical system 20 1st lens 21 Optical surface 22 of an object side Optical surface 30 of an image surface side 2nd lens 31 Optical surface 32 of an object side Optical surface 40 of an image surface side Image surface

Claims (8)

In order from the object side, at least two lenses of a first lens and a glass-made second lens having a positive refractive power are arranged, and shapes of all optical surfaces of the first lens and the second lens are arranged. In an optical system in which is rotationally symmetric about the optical axis,
The first lens has a meniscus shape with a convex surface facing the image surface side, and the object-side optical surface of the first lens has an aspheric shape,
The object-side optical surface and the image-side optical surface of the second lens are both spherical.
When the half angle of view of the light beam incident on the optical system is defined as θ [rad.], The image height of the light beam emitted from the optical system is defined as Y [mm], and the focal length of the optical system is defined as f [mm]. An optical system characterized by satisfying the following formula (1).
−0.10 <(Y−f × θ) / Y <0.10 (1)   The optical system according to claim 1, wherein the image plane side is telecentric. The following equation (2) is satisfied, where d is a thickness on the optical axis from the object-side optical surface to the image-side optical surface of the first lens. Optical system.
0.040 <d / f <0.550 (2) The optical system is composed of two lenses, the first lens and the second lens,
When the paraxial power of the first lens defined P _L1, the paraxial power of the second lens and P _L2, the optical system according to claim 2 or 3 and satisfies the following expression (3) .
-2.8 <P _L1 / P _L2 <10.0 (3) The optical system is composed of two lenses, the first lens and the second lens,
The following equation (4) is satisfied when an interval on the optical axis from the optical surface on the image plane side of the first lens to the optical surface on the object side of the second lens is defined as Δl. The optical system as described in any one of 2-4.
0.0 <Δl / f <2.0 (4) The optical system is composed of two lenses, the first lens and the second lens,
The effective diameter of the optical surface on the object side of the first lens is φ _L1 , the diameter of the light beam incident on the optical surface on the object side of the first lens is φ _B1 , and the effective diameter of the optical surface on the object side of the second lens is The following expression (5) is satisfied, where the diameter is defined as φ _L2 and the diameter of the light beam incident on the object-side optical surface of the second lens is defined as φ _B2 . The optical system according to one item.
1.4 <(φ _L2 × φ _B1 ) / (φ _L1 × φ _B2 ) <18.0 (5) The optical system is composed of two lenses, the first lens and the second lens,
The first lens is made of plastic;
The paraxial power P _L1 of the first lens, when the paraxial power of the second lens is defined as P _L2, any one of claims 2-6 characterized by satisfying the following expression (6) The optical system described in 1.
-2.8 <P _L1 / P _L2 <1.2 (6) The following expression (7) is satisfied when the thickness on the optical axis from the object-side optical surface of the first lens to the image-side optical surface is defined as d. Optical system.
0.075 <d / f <0.550 (7)

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