JP5361480B2 - Optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system that suppresses the deterioration of imaging performance, in the optical system and can simultaneously observe a front object and a substantially-lateral object. <P>SOLUTION: A first lens group having a negative refractive power, a second lens group including a reflective-refractive lens, and a third lens group having an aperture diaphragm and positive refractive power are arranged sequentially from the front object side. The reflective-refractive lens has a first surface formed at the front object side, a second surface formed at an image side, and a third surface formed on the entire peripheral surface between the first surface and the second surface. The first surface has a first transmission surface formed around the optical axis and a first reflection surface that faces the image side and is formed around the first transmission surface. The first surface is defined by an aspherical surface having a concave shape in the vicinity of the optical axis and a convex shape in the vicinity of the first reflection surface. The second surface has a second transmission surface formed around the optical axis and a second reflection surface that faces the front object side and is formed around the second transmission surface. The third surface is a transmission surface. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an optical system capable of observing a substantially lateral object simultaneously with observing a front object.

  Conventionally, there has been known an optical system capable of simultaneously observing a front object and a substantially lateral object. Here, the substantially lateral side includes not only the lateral side of the optical system itself but also the diagonally forward and diagonally rear sides of the optical system.

  Among such optical systems, there is known a configuration in which light from a substantially lateral object side is reflected twice inside and then emitted to the image side. (For example, refer to Patent Document 1).

International Publication No. 2003/042743

  However, the optical system described in Patent Document 1 emits light from a substantially lateral object side to the image side after being reflected by two members. Therefore, if the accumulated tolerance between these members and the lens barrel that holds these members increases, the other member tends to be eccentric with respect to one member during assembly, and the imaging performance There was a problem that was easily deteriorated.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an optical system capable of suppressing deterioration in imaging performance.

In order to achieve the above object, an optical system of the present invention is an optical system for observing a front object and a substantially lateral object, and has a negative refractive power in order from the front object side. A lens group, a second lens group including a catadioptric lens, an aperture stop, and a third lens group having a positive refractive power are disposed, and the catadioptric lens is formed on the front object side. A first surface, a second surface formed on the image side, and a third surface formed on the entire circumferential surface between the first surface and the second surface, the first surface Has a first transmission surface formed around the optical axis, and a first reflection surface facing the image side and formed around the first transmission surface . surface shape is concave on the object side around the optical axis, and the surface shape of the first reflecting surface near a convex surface shape toward the object side, the second It is being formed around the optical axis, and a second transmission surface of the concave shape on the image side, and a second reflecting surface which is formed around the be oriented in front of the object side the second transmission surface The third surface is a transmission surface.

  In the optical system of the present invention, after light from the front object side is incident on the first transmission surface, the light is emitted from the second transmission surface to the image side, and light from the substantially object side is emitted. It is preferable that after entering the third surface, the light is sequentially reflected by the second reflecting surface and the first reflecting surface and emitted from the second transmitting surface to the image side.

Moreover, it is preferable that the optical system of the present invention satisfies the following conditional expression.
2 <R _{21 1} / f _{F 21} <30
Where f _{F 21} is a focal length of the catadioptric lens with respect to a paraxial ray among light from the front object side, and R _{21 1} is a paraxial radius of curvature of the first surface of the catadioptric lens.

Moreover, it is preferable that the optical system of the present invention satisfies the following conditional expression.
1 / f _{S twenty one Mid} <1 / f _{S twenty one Max}
Where f _{S twenty one Mid} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through an intermediate angle of view among the light from the substantially lateral object side, and f _{S twenty one Max} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through the maximum angle of view among light from the substantially lateral object side.

Moreover, it is preferable that the optical system of the present invention satisfies the following conditional expression.
f _{S twenty one Mid} <0
Where f _{S twenty one Mid} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through an intermediate angle of view among the light from the substantially object side.

Moreover, it is preferable that the optical system of the present invention satisfies the following conditional expression.
f _{S Mid} <f _{S Max}
Where f _{S Mid} is a focal length of the optical system with respect to light from which the principal ray passes through an intermediate angle of view among the light from the substantially lateral object side, and f _{S Max} is the focal length of the optical system with respect to the light whose principal ray passes through the maximum angle of view among the light from the substantially lateral object side.

  According to the present invention, it is possible to provide an optical system capable of suppressing deterioration in imaging performance.

It is a schematic diagram which shows the optical path of the light from the substantially object side, (a) is the catadioptric member of the optical system of a prior art example, and its surrounding optical path, (b) is the optical system of a present Example. It is a catadioptric member (catadioptric lens) and the optical path around it. It is a schematic diagram which shows the angle of view regarding the light which injects from the substantially object side with respect to the catadioptric lens which the optical system of a present Example has. It is a schematic diagram which shows the relationship between the principal ray of the light which injects from the substantially object side with respect to the catadioptric lens which the optical system of a present Example has, and its vicinity ray, (a) is a catadioptric lens being abbreviated. (B) shows the case where the catadioptric lens has a negative focal length with respect to the light from the substantially object side when the light from the lateral object side has a positive focal length. ing. It is a schematic diagram showing the optical path around the catadioptric lens of the optical system of the present embodiment of the light from which the principal ray passes the maximum angle of view among the light from the substantially object side, (a) is a conditional expression ( 1 is a catadioptric lens satisfying 1), and (b) is a catadioptric lens not satisfying conditional expression (1). 1 is a cross-sectional view along the optical axis showing the configuration and optical path of an optical system according to Example 1. FIG. It is sectional drawing which follows the optical axis which shows the surface of the optical system shown in FIG. FIG. 7 is an enlarged view of a part of the optical system shown in FIGS. 5 and 6 (a catadioptric lens in the second lens group). 8A and 8B are aberration curve diagrams in the case where a light ray traveling from the object side in front of the optical system illustrated in FIGS. 5 to 7 to the imaging surface is traced, in which FIG. 5A is a coma aberration related to a meridional surface, and FIG. Aberration, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 8 is an aberration curve diagram in the case where a light ray traveling from the object side to the imaging surface of the optical system shown in FIGS. 5 to 7 is traced, (a) coma aberration relating to the meridional surface, and (b) sagittal surface. (C) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 134 °, 123 °, 112 °, 101 °, and 90 ° in order from the top. FIG. 6 is a cross-sectional view along the optical axis showing the configuration and optical path of an optical system according to Example 2. It is sectional drawing in alignment with the optical axis which shows the surface and surface interval of an optical system shown in FIG. FIG. 12 is an aberration curve diagram in the case where a light ray traveling from the object side in front of the optical system shown in FIGS. 10 and 11 to the imaging surface is tracked, (a) coma aberration relating to the meridional surface, and (b) coma relating to the sagittal surface. Aberration, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 12 is an aberration curve diagram in the case where a ray traveling from the object side to the imaging surface of the optical system shown in FIGS. 10 and 11 is traced, (a) coma aberration relating to the meridional surface, and (b) sagittal surface. (C) shows astigmatism. Each figure shows aberrations in the case of half angle of view of 120 °, 112 °, 101 °, 90 °, and 85 ° in order from the top. FIG. 6 is a cross-sectional view along the optical axis showing the configuration and optical path of an optical system according to Example 3. It is sectional drawing which follows the optical axis which shows the surface and surface spacing of the optical system shown in FIG. FIGS. 14A and 14B are aberration curve diagrams in the case where a light ray traveling from the object side in front of the optical system illustrated in FIGS. 14 and 15 to the imaging surface is traced, where FIG. 14A is a coma aberration related to a meridional surface, and FIG. Aberration, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIGS. 14A and 14B are aberration curve diagrams in the case where a light ray traveling from the object side to the imaging surface of the optical system illustrated in FIGS. 14 and 15 is traced, where FIG. 14A is a coma aberration related to a meridional surface, and FIG. (C) shows astigmatism. Each figure shows the aberrations in the case of the half field angles of 125 °, 116 °, 106 °, 95 °, and 85 ° in order from the top. FIG. 6 is a cross-sectional view along the optical axis showing the configuration and optical path of an optical system according to Example 4. It is sectional drawing in alignment with the optical axis which shows the surface and surface interval of an optical system shown in FIG. FIGS. 18A and 19B are aberration curve diagrams in the case where a light ray traveling from the object side in front of the optical system illustrated in FIGS. Aberration, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 20 is an aberration curve diagram in the case where a light ray traveling from the object side to the imaging surface of the optical system illustrated in FIGS. 18 and 19 is traced, (a) is coma aberration related to the meridional surface, and (b) is a sagittal surface. (C) shows astigmatism. Each figure shows the aberrations in the case of the half field angles of 125 °, 116 °, 106 °, 95 °, and 85 ° in order from the top.

  Prior to the description of the embodiments of the optical system of the present invention, the operational effects of the configuration of this embodiment will be described with reference to the drawings.

  The optical system of the present embodiment, in order from the front object side, includes a first lens group having a negative refractive power, a second lens group including a catadioptric lens, an aperture stop, and a third lens having a positive refractive power. And a lens group.

  The catadioptric lens included in the second lens group includes the first surface formed on the front object side, the second surface formed on the image side, and the first surface and the second surface. And a third surface formed on the peripheral surface.

The first surface has a first transmission surface that is formed around the optical axis and a first reflection surface that faces the image side and is formed in an annular shape around the first transmission surface. The first surface is a surface shape in the vicinity of the optical axis center is concave on the object side around an optical axis, the surface shape in the vicinity of the first reflecting surface is an aspherical surface shape such that the convex surface on the object side. For this reason, the first surface has a negative lens function for light rays that pass through the vicinity of the center, and has a positive lens function for light rays that are reflected by the first reflection surface. The second surface is formed around the optical axis, and has a concave second transmissive surface on the image surface side and an annular shape formed around the second transmissive surface facing the front object side. It has two reflective surfaces. The third surface is a transmission surface.

  Note that light incident on the catadioptric lens from the front object side is incident on the first transmission surface and then emitted from the second transmission surface to the image side. In addition, the light incident from the substantially object side is incident on the third surface, then sequentially reflected by the second reflecting surface and the first reflecting surface, and emitted from the second transmitting surface to the image side. It has become.

  As described above, in the optical system of the present embodiment, the member that reflects and refracts light from the substantially object side is configured by one member, unlike the optical system of the conventional example. That is, the reflectively refracting member of this embodiment is not air but glass or the like between the reflecting surfaces.

  Here, the difference between the catadioptric member of the optical system of the present embodiment and the catadioptric member of light from the substantially object side in the optical system of the conventional example will be described with reference to FIG. FIG. 1 is a schematic diagram showing an optical path of light from a substantially object side, (a) is a catadioptric member of an optical system of a conventional example and the optical path in the vicinity thereof, and (b) is the present embodiment. It is the catadioptric member of the optical system of an example, and the optical path in the periphery. Here, the catadioptric member means a member that utilizes a light reflecting action and a refractive action.

As shown in FIG. 1A, the catadioptric member r of the optical system of the conventional example is composed of a first reflecting member ra and a second reflecting member rb. The first reflection member ra has a transmission surface ra ₁ formed around the optical axis, and a reflection surface ra ₂ formed in an annular shape around the transmission surface and facing the image side. The second reflection member rb has a transmission surface rb ₁ formed around the optical axis, and a reflection surface rb ₂ formed in an annular shape around the transmission surface and facing the front object side. Thus, since the first reflecting member ra and the second reflecting member rb each have only one reflecting surface, the two reflecting surfaces of the catadioptric member r are formed by different members.

On the other hand, as shown in FIG. 1B, the catadioptric member of the optical system of the present embodiment is configured only by the catadioptric lens RL. That is, in the present embodiment, the two reflecting surfaces of the catadioptric lens RL are constituted by one member. The catadioptric lens RL is formed on the front object side, the first surface RLa on which light from the front object side is incident, the second surface RLb formed on the image side, the first surface, and the first surface A third surface RLc that is formed on the entire circumferential surface between the two surfaces and on which light from the substantially object side is incident. The first surface RLa of the lens RL has a first transmission surface RLa ₁ formed around the optical axis and a first reflection formed in an annular shape around the first transmission surface RLa ₁ facing the image side. Surface RLa ₂ . The second surface RLb is a second transmission surface RLb ₁ formed around the optical axis, and a second reflection surface facing the front object side and formed annularly around the second transmission surface RLb ₁ RLb ₂ .

Note that the catadioptric lens RL of the optical system of this embodiment may be a cemented lens. Further, the first reflection surface RLa ₂ and the second reflection surface RLb ₂ of the catadioptric lens RL are formed by vapor deposition. Specifically, for example, the first transmitting surface RLa _1, on which a mask of the first transmission surface RLa ₁ the same shape, subjected to a mirror coating on the entire first surface RLa, then peeled off the mask. If such a method is used, since the masked portion is not mirror-coated, the first transmission surface RLa ₁ can be used as the transmission surface even after the first reflection surface RLa ₂ is formed. In addition, the method of forming the first reflective surface RLa ₂ and the second reflecting surface RLb ₂ is not limited to the above method. Further, the third surface RLc of the catadioptric lens RL may be formed to have the same size as the front object side diameter and the image side diameter, or the image side diameter may be larger than the front object side diameter. You may form small or large.

  As shown in FIG. 1, the catadioptric member of the optical system of the present embodiment is constituted by a catadioptric lens RL that is a single member. That is, the catadioptric lens RL is filled with a medium different from air between the two reflecting surfaces. Accordingly, the catadioptric lens RL can refract light from the substantially object side on the third surface RLc formed between the two reflecting surfaces. Therefore, the interval between the two reflecting surfaces can be made smaller than when the space between the two reflecting surfaces is filled with air. Specifically, for example, in the case of the optical system described as Example 1 in Patent Document 1 which is one of the conventional examples, the distance between the two reflecting surfaces on the optical axis is from the front object side. In contrast, the optical system of this embodiment can be reduced to about 1.4 times the focal length of the light.

  Thus, even when the catadioptric lens RL of the optical system of the present embodiment is configured to have the same angle of view as the catadioptric member r of the optical system of the conventional example, light from the front object side is used. The thickness in the direction along the optical axis can be made very thin.

The optical system of the present embodiment is preferably configured to satisfy the following conditional expression (1).
2 <R _{21 1} / f _{F 21} <30 (1)
However, f _{F 21} is the focal length of the catadioptric lens for paraxial rays of light from the front object side, R _{21 1} is the paraxial radius of curvature of the first surface of the catadioptric lens.

The conditional expression (1) is in a plane with the catadioptric lens, concave to the object side surface shape in the vicinity of the center is around the optical axis, a convex shape on the object side is a surface shape in the vicinity of the first reflecting surface The paraxial radius of curvature of the first surface formed in an aspherical shape is defined. If the lower limit of conditional expression (1) is not reached, the paraxial radius of curvature of the first surface becomes too small with respect to the focal length of the catadioptric lens. That is, the paraxial curvature of the first surface becomes too large. In this case, the refractive power of the first surface changes rapidly from negative to positive from the paraxial position to the first reflecting surface. That is, in the first surface, since the inclination at the inflection point changing from the concave surface to the convex surface becomes too large, it is difficult to process the aspherical shape in the catadioptric lens. On the other hand, if the upper limit value of conditional expression (1) is exceeded, the paraxial radius of curvature of the first surface becomes too large. That is, the paraxial curvature of the first surface becomes too small. In this case, since the negative refractive power by the first surface is reduced, it is necessary to increase the negative refractive power of the second surface and the negative refractive power of the first lens group. As a result, spherical aberration is deteriorated.

  Here, the definition of the angle of view of light incident from substantially the object side to the catadioptric lens of the optical system of the present embodiment will be described using the schematic diagram of FIG.

  The chief ray of light incident from the substantially object side is incident on the third surface RLc of the catadioptric lens RL. The angle formed by the chief ray and the optical axis LC on the front object side is catadioptric. This is a half angle of view with respect to the object side substantially on the side of the lens RL.

Further, in the case of such a catadioptric lens RL, it is not possible to observe a front object, that is, an object present on the optical axis LC via the third surface RLc. Therefore, the angle of view has a minimum angle of view θ _Min and a maximum angle of view θ _Max . At this time, the minimum angle of view θ _Min is an angle θ _Min formed by the principal ray of the light on the foremost object side and the optical axis in the range that can be observed through the third surface RLc. On the other hand, the maximum angle of view θ _Max is an angle θ _Max formed by the principal ray of the most image-side light and the optical axis in the range that can be observed through the third surface RLc. An intermediate angle between them is an intermediate angle of view θ _Mid .

  Next, with reference to FIG. 3, the definition of the focal length of light incident from substantially the object side to the catadioptric lens of the optical system of the present embodiment will be described. FIG. 3 is a schematic diagram showing the relationship between the principal ray of light incident from the substantially object side and its neighboring rays with respect to the catadioptric lens of the optical system of the present embodiment. FIG. When the lens has a positive focal length with respect to the light from the substantially object side, (b) shows the case where the catadioptric lens has a negative focal length with respect to the light from the approximately object side. , Respectively.

First, with respect to the third surface RLc of the approximately lateral catadioptric lens RL, and the principal ray L _Sc of the light from the approximately-lateral-object side, the chief ray L _Sc parallel to near light distance is Δh of It is assumed that L _Sp is incident (see FIG. 3A).

At this time, if the catadioptric lens RL has a positive focal length, the principal ray L _Sc and the near ray L _Sp are emitted from the second surface RLb of the catadioptric lens RL as shown in FIG. Then, the light is condensed at a predetermined point on the image side with respect to the second surface RLb of the catadioptric lens RL. If the angle formed by these light rays when condensing is θ ′, the focal length f is within the range where tan θ ′ = θ ′. ₂₁ can be defined by the following relational expression.
f _{S 21} = Δh / θ '

On the other hand, if the catadioptric lens RL has a negative focal length, as shown in FIG. 3B, the principal ray L _Sc and the near ray L _Sp are emitted from the second surface RLb of the catadioptric lens RL. It diverges. At this time, if the optical path after the principal ray L _Sc is emitted from the second surface RLb and the optical path after the neighboring ray L _Sp is emitted from the second surface RLb are respectively extended to the object side, they intersect at a predetermined point. . If the angle formed when these extended optical paths intersect is θ ″, the focal length f is within the range where tan θ ″ = θ ″ holds. ₂₁ can be defined by the following relational expression.
f _{S 21} = -Δh / θ "

Moreover, it is preferable that the optical system of the present embodiment is configured to satisfy the following conditional expression (2).
1 / f _{S twenty one Mid} <1 / f _{S twenty one Max} (2)
Where f _{S twenty one Mid} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through the intermediate angle of view among light from the substantially object side, and f _{S twenty one Max} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through the maximum angle of view among light from the substantially object side.

  Conditional expression (2) defines the refractive power of the catadioptric lens with respect to light having the maximum angle of view among light from substantially the object side. When this conditional expression (2) is not satisfied, the catadioptric lens has a refractive power with respect to light incident at the maximum angle of view in a negative direction larger than that with respect to light incident at the intermediate angle of view.

  Here, the effect by satisfying conditional expression (2) is demonstrated using FIG. FIG. 4 is a schematic diagram showing an optical path around the catadioptric lens of the optical system of the present embodiment, of the light from the substantially side object side, the principal ray passing through the maximum angle of view. The catadioptric lens shown in FIG. 4 (a) satisfies the conditional expression (2), and the catadioptric lens shown in FIG. 4 (b) does not satisfy the conditional expression (2). The same components as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

As shown in FIG. 4, when the catadioptric lens RL is configured to satisfy the conditional expression (2) (see FIG. 4A), it is configured not to satisfy the conditional expression (2) (FIG. 4B). The range in which the second reflecting surface RLb ₂ is formed can be made smaller than in the case of (see).

Moreover, it is preferable that the optical system of the present embodiment is configured to satisfy the following conditional expression (3).
f _{S twenty one Mid} <0 (3)
Where f _{S twenty one Mid} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through the intermediate angle of view among light from the substantially object side.

  This conditional expression (3) is a conditional expression for prescribing the refractive power of the catadioptric lens with respect to light from the substantially lateral object side. Specifically, the catadioptric lens is a substantially lateral object. It is a conditional expression that prescribes having negative refractive power with respect to light from the side.

  The optical system of the present embodiment is characterized in that the third lens group on the image side from the aperture stop has a positive refractive power. In addition, the light from the substantially object side does not pass through the first lens group. Therefore, in order to balance the positive refractive power of the third lens group, the second lens group needs to have a negative refractive power. Therefore, if the catadioptric lens is configured so as to satisfy the conditional expression (3), the optical system is a combination of a negative lens group and a positive lens group with respect to light from the substantially object side. Aberration correction can be balanced.

Moreover, it is preferable that the optical system of the present embodiment is configured to satisfy the following conditional expression (4).
f _{S Mid} <f _{S Max} ... (4)
Where f _{S Mid} is a focal length of the optical system with respect to light from which the principal ray passes through the intermediate angle of view among the light from the substantially object side, and f _{S Max} is the focal length of the optical system with respect to light from which the principal ray passes through the maximum angle of view among light from substantially the object side.

  Conditional expression (4) is a conditional expression for defining the focal length of the catadioptric lens with respect to light from the substantially object side. More specifically, among the focal lengths of the catadioptric lens, a conditional expression that specifies that the focal length for light from an object near the maximum angle of view is longer than the focal length for light from an object near the intermediate angle of view. It is.

  When using the optical system of the present embodiment and observing a side wall or the like that is substantially parallel to the optical axis of light from the front object side as a substantially lateral object, inevitably, the side of the catadioptric lens is substantially lateral. An object located in the direction of the maximum angle of view is positioned farther from the catadioptric lens than an object located in the direction of the intermediate angle of view. Therefore, if it is configured to satisfy the conditional expression (4), it is easy to prevent a focus shift.

  Hereinafter, optical systems according to the first to fourth embodiments will be described with reference to the drawings.

The numbers shown as subscripts in the optical system sectional views r ₁ , r ₂ ,... And d ₁ , d ₂ ,. doing.

In the numerical data, s is the surface number, r is the radius of curvature of each surface, d is the surface spacing, nd is the refractive index at the d-line (wavelength 587.5600 nm), νd is the Abbe number at the d-line, and K is the cone coefficient. , A ₄ , A ₆ , A ₈ , and A ₁₀ indicate aspherical coefficients, respectively.

In the aspheric coefficient of the numerical data, E represents a power of 10. For example, “E-10” represents 10 minus the first power. Each aspheric shape is expressed by the following equation using each aspheric coefficient in each embodiment. However, the coordinate in the direction along the optical axis is Z, and the coordinate in the direction perpendicular to the optical axis is Y.
Z = (Y ² / r) / [1+ {1− (1 + k) · (Y / r) ² } ^1/2 ]
+ A ₄ Y ⁴ + A ₆ Y ⁶ + A ₈ Y ⁸ + A ₁₀ Y ¹⁰ +...

  FIG. 5 is a cross-sectional view taken along the optical axis, showing the configuration and optical path of the optical system according to the present embodiment. FIG. 6 is a cross-sectional view along the optical axis, showing the surfaces of the optical system shown in FIG. FIG. 7 is an enlarged view of a part of the optical system shown in the present embodiment (a catadioptric lens in the second lens group).

  FIG. 8 is an aberration curve diagram in the case where a light ray traveling from the object side in front of the optical system shown in FIGS. 5 to 7 to the imaging surface is traced. FIG. 8A is a coma aberration related to the meridional surface, and FIG. The coma relating to the sagittal surface, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 9 is an aberration curve diagram in the case where a light ray traveling from the object side on the substantially lateral side of the optical system shown in FIGS. 5 to 7 to the imaging surface is traced. FIG. 9A is a coma aberration related to the meridional surface. ) Shows coma with respect to the sagittal surface, and (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 134 °, 123 °, 112 °, 101 °, and 90 ° in order from the top. The meridional plane is the plane containing the optical axis and principal ray of the optical system (plane parallel to the paper), and the sagittal plane is the plane containing the optical axis and perpendicular to the meridional plane (plane perpendicular to the paper). means. Since the optical system of the present embodiment is symmetric with respect to the meridional surface, the aberration amount for the sagittal surface is omitted from the negative value with respect to the horizontal axis. In the graph showing coma aberration, the vertical axis represents the aberration amount (unit: mm), and the horizontal axis represents the aperture ratio (−1 to 1). The wavelength corresponding to each line is shown at the right end in the figure. For example, the wavelength corresponding to the solid line is 656.27 nm. In the diagram showing astigmatism, the vertical axis represents the angle (unit deg), and the horizontal axis represents the focal position (unit mm). The solid line (y in the figure) represents the amount of aberration at a wavelength of 546.07 nm with respect to the sagittal surface, and the broken line (x in the figure) represents the meridional surface.

First, the configuration of the optical system of the present embodiment will be described with reference to FIGS. The optical system of the present embodiment includes, on the optical axis LC of light from the front object side, in order from the front object side, a first lens group G ₁ having a negative refractive power, a second lens group G ₂ , An aperture stop S and a third lens group G ₃ having a positive refractive power are disposed.

The first lens group G ₁ includes, in order from the front object side, a lens L ₁₁ that is a plano-concave lens with a concave surface facing the image side.

The second lens group G ₂ includes, in order from the front object side, a lens L ₂₁ that is a catadioptric lens and a lens L ₂₂ that is a flat lens. The aperture stop S is disposed integrally with the lens L _{22 on} the image side surface of the lens L ₂₂ .

The third lens group G ₃ includes, in order from the front object side, a lens L ₃₁ that is a plano-convex lens having a convex surface directed toward the image side, a cemented lens, and a lens L ₃₄ that is a biconvex lens having an aspheric surface on the image side. And a lens L ₃₅ which is a flat lens. The cemented lens includes a lens L ₃₂ that is a biconvex lens and a lens L ₃₃ that is a biconcave lens.

  The shape of these lenses is a shape in the vicinity of the optical axis of light from the front object side.

Catadioptric lens L ₂₁ is includes a first surface L ₂₁ a which light from the front-object side is incident is formed in front of the object side, a second surface L ₂₁ b formed on the image side And the third surface L ₂₁ c. The third surface L ₂₁ c is formed on the entire circumferential surface between the first surface L ₂₁ a and the second surface L ₂₁ b, and light from the substantially object side is incident on the third surface L ₂₁ c.

The first surface L ₂₁ a is formed in an annular shape around the first transmission surface L ₂₁ a ₁ that faces the image side and the first transmission surface L ₂₁ a ₁ that is formed around the optical axis. having a first reflective surface L ₂₁ a _2. The first surface L ₂₁ a has a surface shape near the optical axis that is concave on the object side with the optical axis as the center, and a surface shape near the first reflection surface L ₂₁ a ₂ has a convex shape on the object side. The aspherical surface is formed. Second surface L ₂₁ b is be formed around the optical axis, and the second transmitting surface L ₂₁ b ₁ of the concave shape on the image side, the second transmitting surface L ₂₁ b be oriented in front of the object side ₁ has a second reflecting surface L ₂₁ b ₂ formed in an annular shape around ₁ .

Next, the path followed by the light incident on the optical system of this embodiment will be described with reference to FIGS. Light L _F entering from the front-object side to the optical system of this embodiment, first passes through the lens L _11. Then, the light L _F passing through the lens L ₁₁ is incident on the first transmitting surface L ₂₁ a ₁ of the lens L _21. Then, the light L _F incident on the first transmitting surface L ₂₁ a ₁ is emitted from the second transmitting surface L ₂₁ b ₁ of the lens L _21. Light L _F emitted from the second transmitting surface L ₂₁ b ₁ is a lens L _22, passes through the aperture stop S, a lens L ₃₁ ~ lens L ₃₅ in order to be incident on the imaging element or the like.

On the other hand, the light L _S incident on the optical system of the present embodiment from the substantially object side first enters the third surface L ₂₁ c of the lens L ₂₁ . The light L _S incident on the third surface L ₂₁ c is reflected by the second reflecting surface L ₂₁ b ₂ of the lens L ₂₁ . Next, the light L _S reflected by the second reflecting surface L ₂₁ b ₂ is reflected by the first reflecting surface L ₂₁ a ₂ of the lens L ₂₁ . Thereafter, the light L _S reflected by the first reflecting surface L ₂₁ a ₂ is emitted from the second transmitting surface L ₂₁ b ₁ of the lens L ₂₁ . The light L _S emitted from the second transmission surface L ₂₁ b ₁ sequentially passes through the lens L ₂₂ , the aperture stop _S , the lenses L ₃₁ to L ₃₅ , and enters the image sensor and the like.

  Next, the configuration and numerical data of the lenses constituting the optical system according to the present example are shown.

Numerical data 1
Unit mm
Surface data Surface number Curvature radius Surface spacing Refractive index Abbe number s r d nd νd
Object ∞ 8.493
1 ∞ 0.7 1.8830 40.8
2 1.588 0.7
3 (Aspherical surface) -107.841 0.85 1.5163 64.1
4 (Aspherical) 2.131 2.157
5 2.700 2.700
6 ∞ 0.4 1.5163 64.1
7 (Aperture stop) ∞ 1.234
8 ∞ 1.25 1.7725 49.6
9 -2.330 0.1
10 8.269 1.5 1.7292 54.7
11 -1.967 0.4 1.8467 23.8
12 6.730 0.1
13 2.85 1 1.5163 64.1
14 (Aspherical surface) -8.822 0.75
15 ∞ 2 1.5163 64.1
16 ∞ 0
Image plane ∞ 0
The radius of curvature according to the surface number 5 is the radius of curvature of the third surface of the lens L ₂₁ that is a catadioptric lens, that is, a cylindrical surface centered on the optical axis. The interval is the distance from the optical axis to the surface with surface number 5.

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
s r k A ₄ A ₆ A ₈ A ₁₀
3 -107.841 0 2.62089E-02 -3.58125E-03 -6.23702E-06 3.69654E-05
4 2.131 0 1.86065E-02 -1.38914E-03 1.08439E-03 -4.17585E-04
14 -8.822 0 -1.02784E-02 4.71739E-02 -1.54701E-02 2.96788E-03

Total focal length (front): 0.602 mm
F number: 5.6
Half field angle Front object side: 70 °
Near side object side (minimum field angle to maximum field angle): 90 to 135 °
Image height: 1.35mm
Total lens length: 13.14mm
Back focus: 0mm

Next, data relating to the conditional expression in the optical system of the present embodiment will be shown.
R _{21 1} / f _{F 21} : 26.826
f _{S Mid} : 0.830
f _{S Max} : 2.047
1 / f _{S twenty one Mid} : -0.605
1 / f _{S twenty one Max} : -0.204

  FIG. 10 is a cross-sectional view taken along the optical axis, showing the configuration and optical path of the optical system according to the present example. FIG. 11 is a cross-sectional view taken along the optical axis, showing the surface and the surface spacing of the optical system shown in FIG.

  12A and 12B are aberration curve diagrams in the case where a light ray traveling from the object side in front of the optical system shown in FIGS. 10 and 11 to the imaging surface is traced. FIG. 12A is a coma aberration relating to a meridional surface, and FIG. The coma relating to the sagittal surface, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 13 is an aberration curve diagram in the case where a light ray traveling from the object side on the substantially lateral side of the optical system shown in FIGS. 10 and 11 to the imaging surface is traced. FIG. 13A is a coma aberration related to the meridional surface. ) Shows coma with respect to the sagittal surface, and (c) shows astigmatism. Each figure shows aberrations in the case of half angle of view of 120 °, 112 °, 101 °, 90 °, and 85 ° in order from the top.

First, the configuration of the optical system of the present embodiment will be described with reference to FIGS. The optical system of the present embodiment includes, on the optical axis LC of light from the front object side, in order from the front object side, a first lens group G ₁ having a negative refractive power, a second lens group G ₂ , An aperture stop S and a third lens group G ₃ having a positive refractive power are disposed.

The first lens group G ₁ includes a lens L ₁₁ that is a plano-concave lens having a concave surface facing the image side.

The second lens group G ₂ has a lens L ₂₁ that is a catadioptric lens.

The third lens group G ₃ is a lens L ₃₁ that is a positive meniscus lens having a convex surface directed toward the image side in order from the front object side, a lens L ₃₂ that is a biconvex lens, a cemented lens, and a flat lens. and a lens L _35. The cemented lens includes, in order from the front object side, a lens L ₃₃ that is a biconcave lens and a lens L ₃₄ that is a biconvex lens having an aspheric surface on the image side.

  The shape of these lenses is a shape in the vicinity of the optical axis of light from the front object side.

  In addition, since the optical path of the optical system of the present embodiment and the shape of the catadioptric lens are substantially the same as those of the optical system of Embodiment 1, their description is omitted.

  Next, the configuration and numerical data of the lenses constituting the optical system according to the present example are shown.

Numerical data 2
Unit mm
Surface data Surface number Curvature radius Surface spacing Refractive index Abbe number s r d nd νd
Object ∞ 8.517
1 ∞ 0.7 1.8830 40.8
2 1.498 0.7
3 (Aspherical surface) -8.407 0.85 1.5163 64.1
4 (Aspherical) 2.290 2.605
5 2.500 2.500
6 (Aperture stop) ∞ 1.145
7 -8.957 1.25 1.7725 49.6
8 -2.209 0.1
9 3.795 1.45 1.7292 54.7
10 -3.196 0.1
11 -3.131 0.4 1.8467 23.8
12 2.098 1.2 1.5163 64.1
13 (Aspherical surface) -6.267 0.75
14 ∞ 2 1.5163 64.1
15 ∞ 0
Image plane ∞ 0
The radius of curvature according to the surface number 5 is the radius of curvature of the third surface of the lens L ₂₁ that is a catadioptric lens, that is, a cylindrical surface centered on the optical axis. The interval is the distance from the optical axis to the surface with surface number 5.

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
s r k A ₄ A ₆ A ₈ A ₁₀
3 -8.407 0 4.18039E-02 -7.90749E-03 3.92149E-04 6.03174E-05
4 2.290 0 3.46914E-02 -2.63649E-02 7.09801E-03 -7.50164E-04
13 -6.267 0 2.07916E-02 2.02383E-02 4.69558E-02 -1.46362E-02

Total focal length (front): 0.610 mm
F number: 5.6
Half field angle Front object side: 70 °
Near side object side (minimum field angle to maximum field angle): 80 to 125 °
Image height: 1.35mm
Total lens length: 13.25mm
Back focus: 0mm

Next, data relating to the conditional expression in the optical system of the present embodiment will be shown.
R _{21 1} / f _{F 21} : 2.487
f _{S Mid} : 0.802
f _{S Max} : 1.734
1 / f _{S twenty one Mid} : -0.822
1 / f _{S twenty one Max} : -0.437

  FIG. 14 is a cross-sectional view taken along the optical axis, showing the configuration and optical path of the optical system according to the present example. FIG. 15 is a cross-sectional view taken along the optical axis, showing the surface and the surface spacing of the optical system shown in FIG.

  FIG. 16 is an aberration curve diagram in the case where a light ray traveling from the object side in front of the optical system shown in FIGS. 14 and 15 to the imaging surface is traced. FIG. 16A is a coma aberration relating to the meridional surface, and FIG. The coma relating to the sagittal surface, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 17 is an aberration curve diagram in the case where a light ray traveling from the object side on the substantially lateral side of the optical system shown in FIGS. 14 and 15 to the imaging surface is traced, (a) is a coma aberration related to the meridional surface, (b) ) Shows coma with respect to the sagittal surface, and (c) shows astigmatism. Each figure shows the aberrations in the case of the half field angles of 125 °, 116 °, 106 °, 95 °, and 85 ° in order from the top.

First, the configuration of the optical system of the present embodiment will be described with reference to FIGS. The optical system of the present embodiment includes, on the optical axis LC of light from the front object side, in order from the front object side, a first lens group G ₁ having a negative refractive power, a second lens group G ₂ , An aperture stop S and a third lens group G ₃ having a positive refractive power are disposed.

The first lens group G ₁ includes, in order from the front object side, a lens L ₁₁ that is a plano-concave lens with a concave surface facing the image side.

The second lens group G ₂ includes, in order from the front object side, a lens L ₂₁ that is a catadioptric lens, and a lens L ₂₂ that is a flat lens with a convex surface facing the front object side. The aperture stop S is disposed integrally with the lens L22 on the image side surface of the lens L22.

The third lens group G ₃ includes, in order from the front object side, a lens L ₃₁ that is a plano-convex lens having a convex surface directed toward the image side, a cemented lens, and a lens L ₃₄ that is a biconvex lens having an aspheric surface on the image side. And a lens L ₃₅ which is a flat lens. Cemented lens, in order from the front-object side, a lens L ₃₂ is a negative meniscus lens having a convex surface directed toward the object side, a lens L ₃₃ is a positive meniscus lens having a convex surface directed toward the object side.

  The shape of these lenses is a shape in the vicinity of the optical axis of light from the front object side.

  In addition, since the optical path of the optical system of the present embodiment and the shape of the catadioptric lens are substantially the same as those of the optical system of Embodiment 1 and Embodiment 2, description thereof is omitted.

  Next, the configuration and numerical data of the lenses constituting the optical system according to the present example are shown.

Numerical data 3
Unit mm
Surface data Surface number Curvature radius Surface spacing Refractive index Abbe number s r d nd νd
Object ∞ 8.464
1 ∞ 0.7 1.8830 40.8
2 1.6 0.7
3 (Aspherical surface) -30.168 0.85 1.5163 64.1
4 (Aspherical) 2.188 2.072
5 2.700 2.700
6 ∞ 0.4 1.5163 64.1
7 (Aperture stop) ∞ 1.086
8 ∞ 1.25 1.7725 49.6
9 -2.247 0.1
10 9.804 0.4 1.8467 23.8
11 1.618 1.5 1.7292 54.7
12 10.502 0.1
13 2.857 1 1.5163 64.1
14 (Aspherical) -16.622 0.75
15 ∞ 2 1.5163 64.1
16 ∞ 0
Image plane ∞ 0
The radius of curvature according to the surface number 5 is the radius of curvature of the third surface of the lens L ₂₁ that is a catadioptric lens, that is, a cylindrical surface centered on the optical axis. The interval is the distance from the optical axis to the surface with surface number 5.

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
s r k A ₄ A ₆ A ₈ A ₁₀
3 -30.168 0 2.78649E-02 -3.89274E-03 -3.12008E-05 4.63052E-05
4 2.188 0 5.22849E-04 -6.91877E-04 1.51793E-03 -4.32471E-04
14 -16.622 0 -1.47489E-02 5.53106E-02 -2.17956E-02 3.97374E-03

Total focal length (front): 0.596mm
F number: 5.6
Half field angle Front object side: 70 °
Near side object side (minimum field angle to maximum field angle): 85 to 125 °
Image height: 1.35mm
Total lens length: 12.91mm
Back focus: 0mm

Next, data relating to the conditional expression in the optical system of the present embodiment will be shown.
R _{21 1} / f _{F 21} : 7.735
f _{S Mid} : 0.798
f _{S Max} : 1.961
1 / f _{S twenty one Mid} : -0.646
1 / f _{S twenty one Max} : -0.194

  FIG. 18 is a cross-sectional view taken along the optical axis, showing the configuration and optical path of the optical system according to the present example. FIG. 19 is a cross-sectional view taken along the optical axis, showing the surfaces of the optical system shown in FIG.

  20A and 20B are aberration curve diagrams in the case where a light ray traveling from the object side in front of the optical system illustrated in FIGS. 18 and 19 to the imaging surface is traced, in which FIG. The coma relating to the sagittal surface, (c) shows astigmatism. Each figure shows aberrations in the case of half angles of view of 63 °, 50 °, 40 °, 30 °, and 0 ° in order from the top. FIG. 21 is an aberration curve diagram in the case where a light ray traveling from the object side on the substantially lateral side of the optical system shown in FIGS. 18 and 19 to the imaging surface is traced, (a) is a coma aberration related to the meridional surface, (b) ) Shows coma with respect to the sagittal surface, and (c) shows astigmatism. Each figure shows the aberrations in the case of the half field angles of 125 °, 116 °, 106 °, 95 °, and 85 ° in order from the top.

First, the configuration of the optical system of the present embodiment will be described with reference to FIGS. The optical system of the present embodiment includes, on the optical axis LC of light from the front object side, in order from the front object side, a first lens group G ₁ having a negative refractive power, a second lens group G ₂ , An aperture stop S and a third lens group G ₃ having a positive refractive power are disposed.

The first lens group G ₁ includes, in order from the front object side, a lens L ₁₁ that is a plano-concave lens with a concave surface facing the image side.

The second lens group G ₂ includes, in order from the front object side, a lens L ₂₁ that is a catadioptric lens and a lens L ₂₂ that is a negative meniscus lens having a convex surface facing the image side.

The third lens group G ₃ includes, in order from the front object side, a lens L ₃₁ that is a biconvex lens, a cemented lens, a lens L ₃₄ that is a biconvex lens with an aspheric surface on the image side, and a lens that is a flat lens. L ₃₅ . The cemented lens includes, in order from the front object side, a lens L _{32 that} is a biconvex lens and a lens L ₃₃ that is a biconcave lens.

  The shape of these lenses is a shape in the vicinity of the optical axis of light from the front object side.

  In addition, since the optical path of the optical system of the present embodiment and the shape of the catadioptric lens are substantially the same as those of the optical systems of Embodiments 1 to 3, their descriptions are omitted.

  Next, the configuration and numerical data of the lenses constituting the optical system according to the present example are shown.

Numerical data 4
Unit mm
Surface data Surface number Curvature radius Surface spacing Refractive index Abbe number s r d nd νd
Object ∞ 8.836
1 ∞ 0.7 1.8830 40.8
2 1.611 0.7
3 (Aspherical surface) -50.750 0.85 1.5163 64.1
4 (Aspherical) 2.179 1.396
5 2.700 2.700
6 -0.828 0.4 1.5163 64.1
7 -1.161 0.1
8 (Aperture stop) ∞ 0.863
9 21.240 1.35 1.8040 46.6
10 -2.513 0.285
11 7.223 1.5 1.7292 54.7
12 -3.444 0.4 1.9229 18.9
13 7.489 0.1
14 3.922 1 1.5163 64.1
15 (Aspherical surface) -3.548 0.75
16 ∞ 2 1.5163 64.1
17 ∞ 0
Image plane ∞ 0
The radius of curvature according to the surface number 5 is the radius of curvature of the third surface of the lens L ₂₁ that is a catadioptric lens, that is, a cylindrical surface centered on the optical axis. The interval is the distance from the optical axis to the surface with surface number 5.

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
s r k A ₄ A ₆ A ₈ A ₁₀
3 -50.750 0 2.66474E-02 -3.53765E-03 2.86303E-04 -4.91689E-06
4 2.179 0 5.85590E-02 -4.50177E-02 1.08714E-02 -8.24111E-04
15 -3.548 0 -4.87606E-02 1.36108E-01 -8.85664E-02 2.36820E-02

Total focal length (front): 0.614 mm
F number: 5.6
Half field angle Front object side: 70 °
Near side object side (minimum field angle to maximum field angle): 80 to 125 °
Image height: 1.35mm
Total lens length: 12.39mm
Back focus: 0mm

Next, data relating to the conditional expression in the optical system of the present embodiment will be shown.
R _{21 1} / f _{F 21} : 12.659
f _{S Mid} : 0.697
f _{S Max} : 1.414
1 / f _{S twenty one Mid} : -0.137
1 / f _{S twenty one Max} : 0.824

  Further, the lenses constituting the lens group of the optical system of the present invention are not limited to the shapes and the number of sheets shown in the above embodiments, and various optical systems including catadioptric lenses are also included.

  Although not arranged in the above embodiment, a low-pass filter with an IR cut coat, a CCD cover glass, or the like may be arranged between the optical system and the image sensor.

  In the above embodiments, the optical system is configured by three lens groups. However, the optical system of the present invention is not limited to these examples, and two lens groups or four or more lens groups are used. You may comprise by a lens group.

G ₁ 1st lens group G ₂ 2nd lens group G ₃ 3rd lens group LC Optical axis L Light entering the _F catadioptric lens from the front object side Entering the L _S catadioptric lens from the substantially object side Light L _Sc catadioptric lens principal ray of light incident from substantially side object side L _Sp catadioptric lens near ray L ₁₁ , L ₂₁ , parallel to principal ray of light incident from substantially side object side L ₂₂ , L ₃₁ , L ₃₂ , L ₃₃ , L ₃₄ , L ₃₅ lens L ₂₁ a, RLa first surface L ₂₁ a ₁ , RLa ₁ first transmitting surface L ₂₁ a ₂ , RLa ₂ first reflecting surface L ₂₁ b, RLb second surface L ₂₁ b ₁ , RLb ₁ second transmission surface L ₂₁ b ₂ , RLb ₂ second reflection surface L ₂₁ c, RLc third surface RL catadioptric lens r catadioptric member ra first reflector member rb Second reflecting member ra ₁ , rb ₁ transmitting surface ra ₂ , rb ₂ reflecting surface S Aperture stop

Claims (6)

An optical system for observing a front object and a substantially lateral object,
A first lens group having a negative refractive power, a second lens group including a catadioptric lens, an aperture stop, and a third lens group having a positive refractive power are arranged in order from the front object side. ,
The catadioptric lens is formed on the entire surface between the first surface formed on the front object side, the second surface formed on the image side, and the first surface and the second surface. Having a third side,
The first surface has a first transmission surface formed around the optical axis and a first reflection surface facing the image side and formed around the first transmission surface, The surface shape in the vicinity of the optical axis is a concave shape on the object side around the optical axis , and the surface shape in the vicinity of the first reflecting surface is an aspheric surface convex on the object side ,
The second surface is formed around the optical axis, and has a concave second transmission surface on the image surface side and a second surface formed toward the front object side and around the second transmission surface. Two reflective surfaces,
The optical system, wherein the third surface is a transmission surface. After light from the front object side is incident on the first transmission surface, it is emitted from the second transmission surface to the image side,
Light from the substantially object side is incident on the third surface, is then sequentially reflected by the second reflecting surface and the first reflecting surface, and is emitted from the second transmitting surface to the image side. The optical system according to claim 1. The optical system according to claim 1, wherein the following conditional expression is satisfied.
2 <R 2 — ₁₁ / f F — ₂₁ <30
Where f F — ₂₁ is the focal length of the catadioptric lens with respect to a paraxial ray of light from the front object side, and R 2 — ₁₁ is the paraxial radius of curvature of the first surface of the catadioptric lens. . The optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
1 / f _{S_21_Mid} <1 / f _{S_21_MAX}
However, f _{S — 21_Mid} is the focal length of the catadioptric lens with respect to the light from which the principal ray passes the intermediate angle of view among the light from the substantially lateral object side, and f _{S — 21_MAX} is from the approximately lateral object side. Is the focal length of the catadioptric lens with respect to the light whose principal ray passes the maximum angle of view. The optical system according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
f _{S — 21 — Mid} <0
However, f _{S — 21 — Mid} is a focal length of the catadioptric lens with respect to light from which the principal ray passes through an intermediate field angle among light from the substantially lateral object side. The optical system according to any one of claims 1 to 5, wherein the following conditional expression is satisfied.
f _{S_Mid} <f _{S_MAX}
However, f _{S_Mid} is the focal length of the optical system with respect to the light from which the principal ray passes the intermediate field angle among the light from the substantially lateral object side, and f _{S_MAX} is the distance from the approximately lateral object side. This is the focal length of the optical system with respect to the light whose principal ray passes through the maximum angle of view.

Images