Object side telecentric optical system including coaxial epi-illumination system

Abstract

To provide an object side telecentric optical system including a coaxial epi-illumination system with less flare spots.SOLUTION: The object side telecentric optical system includes a coaxial epi-illumination system in which an object side lens group and an image surface side lens group are arranged. A coaxial epi-illumination optical element is arranged between the lens groups, which reflects light incident from an optical axis side to an object side and transmits light from the object to an image surface side. The coaxial epi-illumination system satisfies the following conditional expression. (1-1)m1 / M>0.0, (1-2)f1 / f2<1.5 and (1-3)|Pm| / Pp<1.2. In the above expression, m1 represents magnification ratio of the object side lens group, M represents magnification ratio of the entire lens system, f1 represents focal distance of the object side lens group, f2 represents focal distance of the image side lens group, |Pm| represents an absolute value obtained by adding the power of a lens having negative power of the lenses composing the object side lens group, Pp represents a value obtained by adding the power of a lens having positive power of the lenses composing the object side lens group.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an object-side telecentric optical system equipped with a coaxial epi-illumination system that irradiates an object with illumination light coaxially with a lens optical axis. [Background technology]

[0002] In an object-side telecentric optical system equipped with a coaxial epi-illumination system, the chief ray is parallel to the optical axis on the object side, so even if there is an error in the depth of field direction, there is little change in the dimensions of the image, and this is why it is used in applications that require dimensional accuracy, such as measurements, the transfer of fine patterns, and the mounting positioning of electronic components. As shown in FIG. 1, an object-side telecentric optical system equipped with a coaxial epi-illumination system has an object-side lens group and an image-plane-side lens group arranged along an optical axis directed from the object plane side to the image plane (image sensor) side, and an aperture is arranged between each lens group at the image-plane-side focal position of the object-side lens group, thereby forming an object-side telecentric optical system. In addition, between the aperture and the object-side lens group, a beam splitter BS and a half mirror are arranged as optical elements for coaxial epi-illumination that reflect the light incident from the light source arranged in a direction perpendicular to the optical axis X toward the object side and transmit the light from the object toward the image plane side. Furthermore, since the object side is telecentric, the entrance pupil position becomes infinite, and telecentric illumination with illumination light parallel to the optical axis can be easily obtained.

[0003] However, when the illumination light emitted from the light source and reflected to the object side by the beam splitter passes through each lens constituting the object side lens group, a part of the light is reflected by the back surface of each lens, and the lens reflected light is reflected on the image sensor, resulting in a phenomenon called a flare spot. This causes a problem of uneven brightness in which the center of the image is brighter than the periphery, resulting in a decrease in image contrast. In order to reduce the reflected light from the lens that adversely affects the image, a lens design that satisfies optical performance is performed, and a simulation of the flare spot is performed, and the work of optimizing the radius of curvature of each lens is repeated, thereby preventing the occurrence of flare spots and achieving optical performance (Patent Document 1). However, it was difficult to prevent the occurrence of flare spots due to the reflected light from the object side surface of the beam splitter because the beam splitter is constructed of a flat surface. In addition, during optical design, the optical conditions for reducing the reflected light from the object side of the beam splitter were unknown, which caused a problem that the design took a lot of time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-251081 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors of the present application used flare spot simulation software to analyze the relationship between the flare spots in various optical systems and the magnification, focal length, and lens power constituting the optical systems, and thereby found conditions under which the flare spots can be reduced. The present invention is based on the findings of the inventors obtained through such simulations, and realizes an object-side telecentric optical system equipped with a coaxial epi-illumination system that can reliably reduce the occurrence of flare spots caused by reflected light from a beam splitter surface, which has been difficult to correct, regardless of the optical magnification, and can provide good image recognition. [Means for solving the problem]

[0006] The problem of the present invention can be solved by the following aspects (1) or (2).

[0007] (Aspect 1) This object-side telecentric optical system is equipped with a coaxial epi-illumination system in which an object-side lens group and an image-side lens group are arranged along the optical axis from the object side to the image surface side, and a coaxial epi-illumination optical element is arranged between each lens group to reflect light incident from the side of the optical axis to the object side and transmit light from the object to the image surface side, and is characterized in that the object-side telecentric optical system equipped with a coaxial epi-illumination system satisfies the following conditional expressions (1-1) to (1-3): (1-1) m1 / M >0.0 (1-2) f1 / f2<1.5 (1-3) |P m | / P p <1.2 however, m1: Magnification of the object-side lens group M: Magnification of the entire lens system f1: focal length of the object-side lens group f2: focal length of the image-side lens group |P m |: Absolute value obtained by adding the power of lenses having negative power among the lenses constituting the object-side lens group P p : The sum of the powers of the lenses having positive power among the lenses constituting the object-side lens group

[0008] (Aspect 2) This object-side telecentric optical system is equipped with a coaxial epi-illumination system in which an object-side lens group and an image-side lens group are arranged along the optical axis from the object side to the image surface side, and a coaxial epi-illumination optical element is arranged between each lens group for reflecting light incident from the side of the optical axis to the object side and transmitting light from the object to the image surface side, and is characterized in that the object-side telecentric optical system equipped with a coaxial epi-illumination system satisfies the following conditional expressions (2-1) to (2-3): (1-1) m1 / M >0.0 (1-2) f1 / f2<1.0 (1-3) |P m | / P p <1.0 however, m1: Magnification of the object-side lens group M: Magnification of the entire lens system f1: focal length of the object-side lens group f2: focal length of the image-side lens group |P m |: Absolute value obtained by adding the power of lenses having negative power among the lenses constituting the object-side lens group P p : The sum of the powers of the lenses having positive power among the lenses constituting the object-side lens group Effect of the Invention

[0009] By setting the conditions of the present invention, when carrying out optical design, attention needs to be paid only to reducing reflected light from each surface constituting the object-side lens group, which makes the design easier and makes it possible to realize an object-side telecentric optical system equipped with a coaxial epi-illumination system with few flare spots. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of an object-side telecentric optical system equipped with a coaxial epi-illumination system according to the present invention. [Diagram 2] 1A and 1B are explanatory diagrams of flare spots in an object-side telecentric optical system equipped with a coaxial epi-illumination system; [Diagram 3] 1A is a lens configuration diagram of the first embodiment of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 4] 1A is a lens configuration diagram of the second embodiment of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Diagram 5] 1A is a lens configuration diagram of the third embodiment of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 6] 1A is a lens configuration diagram of Example 4 of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 7] 13A is a lens configuration diagram of the fifth embodiment of the present invention, and FIG. 13B is a reflected light illuminance distribution diagram. [Figure 8] 13A is a lens configuration diagram of the sixth embodiment of the present invention, and FIG. 13B is a reflected light illuminance distribution diagram. [Figure 9] 13A is a lens configuration diagram of the seventh embodiment of the present invention, and FIG. 13B is a reflected light illuminance distribution diagram. [Figure 10] 13A is a lens configuration diagram of the eighth embodiment of the present invention, and FIG. 13B is a reflected light illuminance distribution diagram. [Figure 11] FIG. 1A is a lens configuration diagram of Comparative Example 1 of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 12] 1A is a lens configuration diagram of Comparative Example 2 of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 13] 1A is a lens configuration diagram of Comparative Example 3 of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. [Figure 14] 1A is a lens configuration diagram of Comparative Example 4 of the present invention, and FIG. 1B is a reflected light illuminance distribution diagram. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. However, the drawings are merely examples of the embodiments, and the present invention is not limited thereto.

[0012] 1. Object-side telecentric optical system The present invention relates to an object-side telecentric optical system equipped with a coaxial epi-illumination system that reliably reduces the occurrence of flare spots caused by reflected light from a beam splitter surface and provides good image recognition. 1 is an explanatory diagram showing an example of an object-side telecentric optical system equipped with a coaxial epi-illumination system according to the present invention. Along an optical axis X extending from the object surface side to the image surface (image sensor), an object-side lens group, a coaxial epi-illumination system consisting of a light source and a beam splitter BS arranged in a direction perpendicular to the optical axis X, an aperture arranged at the image surface side focal position of the object-side lens group, and an image-side lens group are arranged in this order. In addition, a cover glass CG for protecting the image sensor is arranged between the image-side lens group and the image surface (image sensor). The beam splitter BS is an optical element for coaxial epi-illumination that reflects light incident from the light source to the object side and transmits the reflected light from the object surface to the image surface side.

[0013] 2. Lens construction In the object-side telecentric optical system equipped with the coaxial epi-illumination system of the present invention, both the object-side lens group and the image-side lens group are composed of lens groups with different lens magnifications m, focal lengths f, and lens powers. In addition, an intersection plane Sn (n is a natural number) between the optical axis X and the intersection is defined along the optical axis X from the object side to the image surface side. Based on these, a flare spot exponent H indicating the strength of the flare spot is calculated.

[0014] 3. Flare Spot Index The strength of the flare spot in the object-side telecentric optical system equipped with the coaxial epi-illumination system of the present invention is defined as the flare spot index H. Specifically, the flare spot index H is calculated by dividing the central illuminance h o is normalized to 1.0, the central illuminance H of the reflected light from the beam splitter surface. p This is the ratio of Figure 2 is an explanatory diagram of a flare spot in an object-side telecentric optical system equipped with a coaxial epi-illumination system. A flare spot occurs when illumination light emitted from a light source is reflected by the object side of the beam splitter, passes through an image-side lens, and is projected onto an image plane (image sensor). It also includes reflected light in which a part of the illumination light is reflected toward the image plane at the image-plane side intersection surface of the object-side lens when illumination light emitted from a light source and reflected toward the object side by the beam splitter BS passes through an object-side lens group and is illuminated onto the object plane. EXAMPLES

[0015] Next, embodiments that exhibit the effects of the present invention will be described as examples, and a summary is shown in Table 1. Examples 1 to 6 are object-side telecentric optical systems equipped with a coaxial epi-illumination system designed to satisfy all of formulas (1-1) to (1-3), and Examples 7 and 8 are object-side telecentric optical systems equipped with a coaxial epi-illumination system designed to satisfy all of formulas (2-1) to (2-3). Comparative Examples 1 to 4 are object-side telecentric optical systems equipped with a coaxial epi-illumination system that does not satisfy any one of the formulas (1-1) to (1-3) and the formulas (2-1) to (2-3).

[0016] [Table 1]

[0017] <Example 1> The lens configuration of Example 1 is shown in Table 2. In this lens configuration, the magnification of the object-side lens group is m1=-0.403, the magnification of the entire lens system is M=-0.800, and m1 / M=0.504, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=69.507, the focal length of the image-side lens group is f2=-139.069, and f1 / f2=-0.500, which satisfies the condition of formula (1-2). The powers of the lenses constituting the object-side lens group are L1=12.986, L2=-9.469, L3=16.535, L4=-22.480, L5=12.601, and L6=11.438, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=31.949, the power sum P of the lens group having a positive power constituting the object-side lens group p =53.559, |P m | / P p =0.597, which satisfies the condition of equation (1-3).

[0018] [Table 2]

[0019] Figure 3 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.014.

[0020] <Example 2> The lens configuration of Example 2 is shown in Table 3. In this lens configuration, the magnification of the object-side lens group is m1=-0.462, the magnification of the entire lens system is M=-0.500, and m1 / M=0.923, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=86.288, the focal length of the image-side lens group is f2=230.805, and f1 / f2=-0.374, which satisfies the condition of formula (1-2). The powers of the lenses constituting the object-side lens group are L1=5.208, L2=18.719, L3=-18.697, and L4=16.145, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=18.607, the power sum P of the lens group having a positive power constituting the object-side lens group p =40.072, |P m| / P p =0.464, which satisfies the condition of equation (1-3).

[0021] [Table 3]

[0022] Figure 4 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.025.

[0023] <Example 3> The lens configuration of Example 3 is shown in Table 4. In this lens configuration, the magnification of the object-side lens group is m1=-0.345, the magnification of the entire lens system is M=-0.500, and m1 / M=0.690, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=74.684, the focal length of the image-side lens group is f2=59.857, and f1 / f2=1.248, which satisfies the condition of formula (1-2). The powers of the lenses constituting the object-side lens group are L1=4.528, L2=21.711, L3=-19.325, and L4=21.190, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=19.325, the power sum P of the lens group having a positive power constituting the object-side lens group p =47.429, |P m | / P p =0.407, which satisfies the condition of equation (1-3).

[0024] [Table 4]

[0025] Figure 5 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (ho is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.029.

[0026] <Example 4> The lens configuration of Example 4 is shown in Table 5. In this lens configuration, the magnification of the object-side lens group is m1=-1.226, the magnification of the entire lens system is M=-3.998, and m1 / M=0.307, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=53.874, the focal length of the image-side lens group is f2=-81.723, and f1 / f2=-0.873, which satisfies the condition of formula (1-2). Furthermore, the powers of the lenses constituting the object-side lens group are L1=11.961, L2=-16.637, L3=15.838, L4=11.549, L5=16.371, and L6=-31.958, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=48.595, the power sum P of the lens group having a positive power constituting the object-side lens group p =55.719, |P m | / P p =0.872, which satisfies the condition of equation (1-3).

[0027] [Table 5]

[0028] Figure 6 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.040.

[0029] <Example 5> The lens configuration of Example 5 is shown in Table 6. In this lens configuration, the magnification of the object-side lens group is m1=-1.148, the magnification of the entire lens system is M=-3.000, and m1 / M=0.383, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=52.176, the focal length of the image-side lens group is f2=-80.997, and f1 / f2=-0.644, which satisfies the condition of formula (1-2). Furthermore, the powers of the lenses constituting the object-side lens group are L1=13.151, L2=-18.259, L3=16.105, L4=10.953, L5=19.354, and L6=-34.204, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=52.463, the power sum P of the lens group having a positive power constituting the object-side lens group p =59.562, |P m | / P p =0.881, which satisfies the condition of equation (1-3).

[0030] [Table 6]

[0031] Figure 7 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.044.

[0032] <Example 6> The lens configuration of Example 6 is shown in Table 7. In this lens configuration, the magnification of the object-side lens group is m1=-0.993, the magnification of the entire lens system is M=-0.200, and m1 / M=0.497, which satisfies the condition of formula (1-1). In addition, the focal length of the object-side lens group is f1=51.455, the focal length of the image-side lens group is f2=-141.047, and f1 / f2=-0.365, which satisfies the condition of formula (1-2). Furthermore, the powers of the lenses constituting the object-side lens group are L1=14.738, L2=10.520, L3=23.958, and L4=-40.577, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=40.577, the power sum P of the lens group having a positive power constituting the object-side lens group p =49.215, |P m | / P p =0.824, which satisfies the condition of equation (1-3).

[0033] [Table 7]

[0034] Figure 8 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.045.

[0035] <Example 7> The lens configuration of Example 7 is shown in Table 8. In this lens configuration, the magnification of the object-side lens group is m1=-2.745, the magnification of the entire lens system is M=-1.000, and m1 / M=2.746, which satisfies the condition of formula (2-1). In addition, the focal length of the object-side lens group is f1=58.828, the focal length of the image-side lens group is f2=77.878, and f1 / f2=0.755, which satisfies the condition of formula (2-2). Furthermore, the powers of the lenses constituting the object-side lens group are L1=15.593, L2=14.372, L3=31.630, and L4=-73.436, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=73.436, the power addition value P of the lens group having a positive power constituting the object-side lens group p =61.594, |P m | / P p= 1.192, which satisfies the condition of equation (2-3).

[0036] [Table 8]

[0037] Figure 9 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.090.

[0038] <Example 8> The lens configuration of Example 8 is shown in Table 9. In this lens configuration, the magnification of the object-side lens group is m1=-0.585, the magnification of the entire lens system is M=-8.000, and m1 / M=0.731, which satisfies the condition of formula (2-1). In addition, the focal length of the object-side lens group is f1=62.364, the focal length of the image-side lens group is f2=55.911, and f1 / f2=1.115, which satisfies the condition of formula (2-2). The powers of the lenses constituting the object-side lens group are L1=7.875, L2=18.367, L3=26.381, and L4=-57.753, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=57.753, the power sum P of the lens group having a positive power constituting the object-side lens group p =52.623, |P m | / P p = 1.097, which satisfies the condition of equation (2-3).

[0039] [Table 9]

[0040] Figure 10 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h ois normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.122.

[0041] <Comparative Example 1> The lens configuration of Comparative Example 1 is shown in Table 10. In this lens configuration, the magnification of the object-side lens group is m1=0.666, the magnification of the entire lens system is M=-5.000, and m1 / M=-1.331, which does not satisfy either the condition of formula (1-1) or formula (2-1). Furthermore, the focal length of the object-side lens group is f1=105.155, the focal length of the image-side lens group is f2=43.167, and f1 / f2=2.436, which does not satisfy either the condition of formula (1-2) or the condition of formula (2-2). The powers of the lenses constituting the object-side lens group are L1=5.476, L2=5.135, L3=14.132, L4=24.711, and L5=-63.735, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=63.735, the power addition value P of the lens group having a positive power constituting the object-side lens group p =49.454, |P m | / P p =1.289, which does not satisfy the conditions of either equation (1-3) or equation (2-3).

[0042] [Table 10]

[0043] Figure 11 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.158.

[0044] <Comparative Example 2> The lens configuration of Comparative Example 2 is shown in Table 11. In this lens configuration, the magnification of the object-side lens group is m1=2.551, the magnification of the entire lens system is M=-8.000, and m1 / M=-3.189, which does not satisfy either of the conditions of formula (1-1) or formula (2-1). Furthermore, the focal length of the object-side lens group is f1=69.811, the focal length of the image-side lens group is f2=52.064, and f1 / f2=1.341, which satisfies the condition of formula (1-2) but does not satisfy the condition of formula (2-2). The powers of the lenses constituting the object-side lens group are L1=9.120, L2=19.995, L3=28.644, and L4=-72.994, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=72.994, the power sum P of the lens group having a positive power constituting the object-side lens group p =57.779, |P m | / P p =1.263, which does not satisfy the conditions of either equation (1-3) or equation (2-3).

[0045] [Table 11]

[0046] Figure 12 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.164.

[0047] <Comparative Example 3> The lens configuration of Comparative Example 3 is shown in Table 12. In this lens configuration, the magnification of the object-side lens group is m1=1.364, the magnification of the entire lens system is M=-8.000, and m1 / M=-1.705, which does not satisfy either of the conditions of formula (1-1) or formula (2-1). Furthermore, the focal length of the object-side lens group is f1=71.596, the focal length of the image-side lens group is f2=46.791, and f1 / f2=1.530, which does not satisfy either the condition of formula (1-2) or the condition of formula (2-2). The powers of the lenses constituting the object-side lens group are L1=8.807, L2=18.780, L3=31.515, and L4=-80.360, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=80.360, the power addition value P of the lens group having a positive power constituting the object-side lens group p =59.102, |P m | / P p =1.360, which does not satisfy the conditions of either equation (1-3) or equation (2-3).

[0048] [Table 12]

[0049] Figure 13 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.168.

[0050] <Comparative Example 4> The lens configuration of Comparative Example 4 is shown in Table 13. In this lens configuration, the magnification of the object-side lens group is m1=0.605, the magnification of the entire lens system is M=-5.000, and m1 / M=-1.209, which does not satisfy either of the conditions of formula (1-1) or formula (2-1). Furthermore, the focal length of the object-side lens group is f1=129.611, the focal length of the image-side lens group is f2=48.133, and f1 / f2=2.693, which does not satisfy either the condition of formula (1-2) or the condition of formula (2-2). The powers of the lenses constituting the object-side lens group are L1=5.581, L2=8.116, L3=16.083, L4=-35.774, and L5=-14.389, respectively. The absolute value of the power sum of the lens group having negative power constituting the object-side lens group is |P m |=50.163, the power sum P of the lens group having a positive power constituting the object-side lens group p =29.780, |P m | / P p =1.684, which does not satisfy the conditions of either equation (1-3) or equation (2-3).

[0051] [Table 13]

[0052] Figure 14 shows the optical path of reflected light in this lens configuration (a), and the illuminance of reflected light from an object surface with a reflectance of 5% at the center of the image plane (h o is normalized to 1.0, and (b) shows the distribution of illuminance reflected from an object surface with a reflectance of 5% and from a beam splitter surface. The calculated flare spot exponent H is 0.229. [Industrial Applicability]

[0053] According to the present invention, it is possible to provide an object-side telecentric optical system equipped with a coaxial epi-illumination system with few flare spots. [Explanation of symbols]

[0054] X optical axis L1, L2, L3, L4, L5, L6, L7, L8, L9 lens group

Claims

1. An object-side telecentric optical system having a coaxial epi-illumination system in which an object-side lens group and an image-side lens group are arranged along an optical axis from an object side toward an image side, and a coaxial epi-illumination optical element is arranged between each lens group for reflecting light incident from a side of the optical axis toward the object side and transmitting light from the object toward the image side, An object-side telecentric optical system equipped with a coaxial epi-illumination system, characterized in that the following conditional expressions (1-1) to (1-3) are satisfied: (1-1) m １ / M >0.0 (1-2) f １ / f ２ <1.5 (1-3) |P ｍ | / P ｐ <1.2 however, m １ : Magnification of the object-side lens group M: Magnification of the entire lens system f １ : Focal length of the object-side lens group f ２ : Focal length of the image-side lens group |P ｍ |: Absolute value obtained by adding the power of lenses having negative power among the lenses constituting the object-side lens group P ｐ : The sum of the powers of the lenses having positive power among the lenses constituting the object-side lens group

2. An object-side telecentric optical system having a coaxial epi-illumination system in which an object-side lens group and an image-side lens group are arranged along an optical axis from an object side toward an image side, and a coaxial epi-illumination optical element is arranged between each lens group for reflecting light incident from a side of the optical axis toward the object side and transmitting light from the object toward the image side, An object-side telecentric optical system equipped with a coaxial epi-illumination system, characterized in that the following conditional expressions (2-1) to (2-3) are satisfied: (2-1) m １ / M >0.0 (2-2) f １ / f ２ <1.0 (2-3) |P ｍ | / P ｐ <1.0 however, m １ : Magnification of the object-side lens group M: Magnification of the entire lens system f １ : Focal length of the object-side lens group f ２ : Focal length of the image-side lens group |P ｍ |: Absolute value obtained by adding the power of lenses having negative power among the lenses constituting the object-side lens group P ｐ : The sum of the powers of the lenses having positive power among the lenses constituting the object-side lens group

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