JP2019148791A - Zoom optical system and image capturing device - Google Patents

Abstract

A variable power optical system having a high zoom ratio and high performance, and an imaging apparatus equipped with this variable power optical system are provided. Kind Code: A1 A variable magnification optical system includes, in order from an object side, a first optical system U1 that is fixed during magnification, and a second optical system U2 that includes a plurality of lens groups that move during magnification. The first optical system U1 includes a first mirror M1 and a second mirror M2 whose reflecting surfaces are arranged to face each other. The first mirror M1 has a reflecting surface with a concave surface facing the object side. The second mirror M2 has a reflecting surface with a convex surface facing the image side. An intermediate image is formed between the second mirror M2 and the second optical system U2. A predetermined conditional expression regarding the partial dispersion ratio of the lenses included in the second optical system U2 is satisfied. [Selection drawing] Fig. 1

Description

  The present invention relates to a variable magnification optical system and an imaging apparatus.

  Conventionally, a variable magnification optical system including a catadioptric optical system has been proposed. For example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 described below describe a variable magnification optical system including two mirrors and a plurality of lenses.

JP-A-11-202208 U.S. Pat. No. 4,235,508 US Pat. No. 4,971,428 Chinese Patent Application No. 106729633

  In recent years, there has been an increasing demand for surveillance cameras used for remote surveillance in harbors and / or airports, and there has been an increasing demand for telephoto and super telephoto variable magnification optical systems that can be used for such surveillance cameras. . Such a variable magnification optical system is required to have a good imaging performance with a small variation in spherical aberration, astigmatism, distortion, and chromatic aberration at the time of zooming while having a high zoom ratio. Yes.

  However, the variable power optical system described in Patent Document 1 has large fluctuations in astigmatism and distortion during zooming. The zoom optical system described in Patent Document 2 has a low zoom ratio. The variable magnification optical system described in Patent Document 3 has a large distortion. In the variable magnification optical system described in Patent Document 4, spherical aberration is not corrected well.

  In view of the above circumstances, the present invention provides a variable power optical system that has good optical performance while achieving a high zoom ratio with a small variation in various aberrations at the time of zooming, and an image pickup provided with the variable power optical system. An object is to provide an apparatus.

In order to solve the above-described problem, a variable magnification optical system according to the present invention includes, in order from the object side, two reflecting mirrors whose reflecting surfaces are arranged to face each other. The second optical system includes an optical system and at least two positive lenses and at least one negative lens. The two reflecting mirrors have a reflecting surface with a concave surface facing the object side and are separated from the object. A first reflecting mirror that reflects light rays toward the object side, and a second reflecting mirror that has a reflecting surface with a convex surface facing the image side and reflects reflected light from the first reflecting mirror toward the image side, The second optical system includes a first lens group that continuously moves from the object side to the object side at the time of zooming from the wide-angle end to the telephoto end, and has a positive refractive power. And a second lens group having a positive refractive power that moves in the optical axis direction along a different locus, and the second reflecting mirror and the first lens group The intermediate image is formed again through the second optical system, and the average value of the partial dispersion ratios between the g-line and the F-line of all the positive lenses in the second optical system is θgFp. When the average value of the partial dispersion ratios between the g-line and the F-line of all negative lenses in the two optical systems is θgFn, the following conditional expression (1) is satisfied.
−0.04 <θgFp−θgFn <0.1 (1)

In the variable magnification optical system of the present invention, it is preferable that the following conditional expression (1-1) is satisfied.
−0.02 <θgFp−θgFn <0.06 (1-1)

In the variable magnification optical system of the present invention, the average value of the d-line reference Abbe numbers of all positive lenses in the second optical system is νdp, and the d-line reference Abbe numbers of all negative lenses in the second optical system. When the average value of νdn is νdn, it is preferable to satisfy the following conditional expression (2), and it is more preferable to satisfy the following conditional expression (2-1).
10 <νdp−νdn <40 (2)
14 <νdp−νdn <35 (2-1)

In the variable magnification optical system of the present invention, the average value of the partial dispersion ratio between the C line and the t line of all the positive lenses in the second optical system is θCtp, and the C line of all the negative lenses in the second optical system. When the average value of the partial dispersion ratio between the t-line is θCtn, it is preferable to satisfy the following conditional expression (3), and it is more preferable to satisfy the following conditional expression (3-1).
−0.1 <θCtp−θCtn <0.1 (3)
−0.07 <θCtp−θCtn <0.05 (3-1)

  In the zoom optical system of the present invention, it is preferable that the first optical system includes a field lens group having a positive refractive power, which is a lens component that is composed of two or less lenses and is closest to the intermediate image.

  In the variable magnification optical system of the present invention, it is preferable that the first reflecting mirror is an optical element having power located closest to the object side on the optical path.

  In the zoom optical system of the present invention, the first optical system is disposed in the optical path from the first reflecting mirror to the second reflecting mirror and in the optical path from the second reflecting mirror to the position of the intermediate image, In addition, it is preferable to include a correction lens group including two or less lenses having a common optical axis with the first reflecting mirror and the second reflecting mirror.

In the variable magnification optical system of the present invention, when the average value of the partial dispersion ratio between the C line and the t line of all the negative lenses in the second optical system is θCtn, the following conditional expression (4) is satisfied. Is preferable, and it is more preferable that the following conditional expression (4-1) is satisfied.
0.75 <θCtn <0.9 (4)
0.77 <θCtn <0.85 (4-1)

In the variable magnification optical system of the present invention, when the average value of partial dispersion ratios between the C line and the t line of all the positive lenses in the second optical system is θCtp, the following conditional expression (5) is satisfied. Is preferable, and it is more preferable that the following conditional expression (5-1) is satisfied.
0.75 <θCtp <0.9 (5)
0.78 <θCtp <0.85 (5-1)

In the variable magnification optical system of the present invention, it is preferable that the following conditional expression (6) is satisfied, where νdn is an average value of d-line reference Abbe numbers of all negative lenses in the second optical system.
50 <νdn <65 (6)

In the variable power optical system of the present invention, it is preferable that the following conditional expression (7) is satisfied, where Ndn is the average value of the refractive indices of all negative lenses in the second optical system for the d-line.
1.5 <Ndn <1.75 (7)

In the variable magnification optical system of the present invention, when the average value of the partial dispersion ratios between the g-line and the F-line of all the negative lenses in the second optical system is θgFn, the following conditional expression (8) is satisfied. Is preferred.
0.53 <θgFn <0.58 (8)

In the variable magnification optical system of the present invention, when the average value of partial dispersion ratios between the g-line and the F-line of all the positive lenses in the second optical system is θgFp, the following conditional expression (9) is satisfied. Is preferred.
0.5 <θgFp <0.65 (9)

In the variable magnification optical system of the present invention, it is preferable that the following conditional expression (10) is satisfied, where νdp is an average value of d-line reference Abbe numbers of all positive lenses in the second optical system.
70 <νdp <100 (10)

In the variable magnification optical system of the present invention, it is preferable that the following conditional expression (11) is satisfied, where Ndp is the average value of the refractive indices of all positive lenses in the second optical system with respect to the d-line.
1.43 <Ndp <1.75 (11)

  The imaging apparatus of the present invention includes the variable magnification optical system of the present invention.

  In addition, “consisting of” and “consisting of” in the present specification are lenses having substantially no refractive power, and lenses such as a diaphragm, a filter, and a cover glass, in addition to the constituent elements listed. It is intended that an optical element other than the above and a mechanical part such as a lens flange, a lens barrel, an imaging device, and a camera shake correction mechanism may be included.

  In this specification, “having positive refractive power to group” means that the entire group has positive refractive power. Similarly, “having negative refractive power to group” means that the entire group has negative refractive power. “Lens having positive refractive power”, “positive lens”, and “positive lens” are synonymous. “Lens having negative refractive power”, “negative lens”, and “negative lens” are synonymous. The “lens group” is not limited to a configuration including a plurality of lenses, and may be configured to include only one lens. “Single lens” means a single lens that is not cemented. However, a composite aspheric lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally formed and functions as one aspherical lens as a whole) is a cemented lens. Is treated as a single lens. The “lens component” is a lens in which the air contact surface on the optical axis is only two of the object side surface and the image side surface, and one lens component is one single lens or one set of cemented lenses. Means. “Having power” means that the reciprocal of the focal length is not zero. Unless otherwise specified, the sign of refractive power, the surface shape, and the curvature radius of the surface regarding an optical element including an aspheric surface are considered in the paraxial region. As for the sign of the curvature radius, the sign of the curvature radius of the surface having the convex surface facing the object side is positive, and the sign of the curvature radius of the surface having the convex surface facing the image side is negative. The “focal length” used in the conditional expression is a paraxial focal length. The value of the conditional expression other than the conditional expression related to the partial dispersion ratio is a value when the d-line is used as a reference in a state in which the object is focused on infinity.

  “D line”, “C line”, “F line”, “g line”, and “t line” described in this specification are bright lines. In this specification, the wavelength of d-line is 587.56 nm (nanometer), the wavelength of C-line is 656.27 nm (nanometer), the wavelength of F-line is 486.13 nm (nanometer), and the wavelength of g-line is The wavelength of 435.84 nm (nanometer) and the t-line wavelength are treated as 1013.98 nm (nanometer).

  The partial dispersion ratio θgF between the g-line and the F-line of a lens is θgF = (Ng−NF) when the refractive indexes of the lens with respect to the g-line, F-line, and C-line are Ng, NF, and NC, respectively. ) / (NF-NC). The partial dispersion ratio θCt between the C line and the t line of a lens is θCt = (NC−Nt, where Nt, NF, and NC are the refractive indexes of the lens with respect to the t line, the F line, and the C line, respectively. ) / (NF-NC).

  According to the present invention, there are provided a variable magnification optical system having good optical performance while achieving a high variable magnification ratio with a small variation in various aberrations at the time of variable magnification, and an imaging apparatus equipped with this variable magnification optical system. can do.

It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system which concerns on one Embodiment of this invention (variable magnification optical system of Example 1 of this invention). It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 2 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 3 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 4 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 5 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 6 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 7 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 8 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 9 of this invention. It is sectional drawing which shows the structure and optical path in the wide-angle end and telephoto end of the variable magnification optical system of Example 10 of this invention. FIG. 6 is an aberration diagram of the variable magnification optical system according to Example 1 of the present invention. It is each aberration figure of the variable magnification optical system of Example 2 of this invention. It is each aberration figure of the variable magnification optical system of Example 3 of this invention. It is each aberration figure of the variable magnification optical system of Example 4 of this invention. It is each aberration figure of the variable magnification optical system of Example 5 of this invention. It is each aberration figure of the variable magnification optical system of Example 6 of this invention. It is each aberration figure of the variable magnification optical system of Example 7 of this invention. It is each aberration figure of the variable magnification optical system of Example 8 of this invention. It is each aberration figure of the variable magnification optical system of Example 9 of this invention. It is each aberration figure of the variable magnification optical system of Example 10 of this invention. 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a configuration of a variable magnification optical system according to an embodiment of the present invention and a sectional view of an optical path. In FIG. 1, the wide-angle end state is shown in the upper stage labeled “WIDE”, and the telephoto end state is shown in the lower stage labeled “TELE”. The example shown in FIG. 1 corresponds to a variable magnification optical system of Example 1 described later. In FIG. 1, the left side of the drawing is the object side, and the right side of the drawing is the image side, showing a state where the object is focused on an object at infinity.

  The variable magnification optical system of the present embodiment includes a first optical system U1 and a second optical system U2 in order from the object side to the image side. The first optical system U1 is fixed with respect to the image plane Sim at the time of zooming. The second optical system U2 includes at least two positive lenses and at least one negative lens.

  The first optical system U1 includes two reflecting mirrors in which the reflecting surfaces are arranged to face each other. According to this configuration, the entire length can be shortened by folding the optical path. The two reflecting mirrors include a first reflecting mirror and a second reflecting mirror. The first mirror M1 of the present embodiment corresponds to the first reflecting mirror, and the second mirror M2 corresponds to the second reflecting mirror.

  The first mirror M1 is preferably an optical element having power that is located closest to the object side on the optical path. If a refractive optical system is disposed in the optical path closer to the object side than the first mirror M1, the refractive optical system requires a large aperture and thus becomes expensive. If the refractive optical system is disposed in the optical path closer to the object than the first mirror M1, the center of gravity of the variable magnification optical system is biased toward the tip and the weight balance is deteriorated. Furthermore, since the reflective optical element does not transmit light, there is an advantage that the degree of freedom in selecting a material is higher than that of the transmissive optical element.

  The first mirror M1 has a reflecting surface with a concave surface facing the object side, and is configured to reflect light rays from the object to the object side. The second mirror M2 has a reflecting surface with a convex surface facing the image side, and is configured to reflect the reflected light from the first mirror M1 to the image side. With such a configuration, the overall length can be shortened without causing chromatic aberration, and the optical system is suitable for a super telephoto system. As an example, FIG. 1 shows an example in which the first mirror M1 and the second mirror M2 are configured to have a common optical axis Z.

  The reflecting surface of the first mirror M1 and the reflecting surface of the second mirror M2 are preferably spherical. In this case, it can be manufactured at low cost, and image deterioration due to eccentricity and / or tilting can be reduced.

  The second optical system U2 includes a first lens group G1 that continuously moves from the object side to the object side at the time of zooming from the wide-angle end to the telephoto end, and has a positive refractive power. And a second lens group G2 having a positive refractive power that moves in the optical axis direction along a different locus from the lens group G1. That is, the first lens group G1 is disposed closest to the object side of the second optical system U2, and the second lens group G2 is disposed adjacent to the first lens group G1 on the image side of the first lens group G1. By continuously arranging a plurality of lens groups having positive refractive power in the second optical system U2 which is a variable magnification optical system, it is possible to generate spherical aberration on the wide angle side, Variation in spherical aberration, variation in astigmatism during zooming, and variation in distortion during zooming can be suppressed, and a high zoom ratio is facilitated. Further, it is possible to reduce the effective diameter of the lens group that moves during zooming.

  An intermediate image is formed between the second mirror M2 and the first lens group G1. FIG. 1 shows the position P of the intermediate image on the optical axis. The intermediate image is re-imaged on the image plane Sim via the second optical system U2. That is, the second optical system U2 functions as a relay optical system. By using the re-magnification optical system as the re-imaging optical system, the diameter of the lens group that moves during zooming can be reduced, and the weight reduction and the speeding up of the zooming operation can be realized.

  The first optical system U1 may include a field lens group Gfd that is a lens component closest to the intermediate image. Here, the “intermediate image” of “closest to the intermediate image” is an intermediate image when focused on an object at infinity. The “field lens group Gfd closest to the intermediate image” includes a case where the position P of the intermediate image is located inside the field lens group Gfd. The field lens group Gfd is preferably a lens group including two or less lenses and having a positive refractive power. By arranging positive refractive power in the vicinity of the intermediate image, it is possible to cross the optical axis Z inside the variable magnification optical system, and to prevent the increase in the effective diameter of the variable magnification optical system. can do. The field lens group Gfd in the example of FIG. 1 includes, as an example, a pair of cemented lenses configured by cementing a negative lens Lf1 and a positive lens Lf2 in order from the object side. The lens Lf1 has a concave surface on the object side. The lens Lf2 has a convex surface facing the image side, and the cemented surface between the lens Lf1 and the lens Lf2 has the convex surface facing the object side.

  The first optical system U1 may be configured to include a correction lens group Gc having an aberration correction function. The correction lens group Gc is preferably composed of two or less lenses having an optical axis Z common to the first mirror M1 and the second mirror M2. By setting the number to two or less, the load on the object side portion of the variable magnification optical system can be kept small, and the strength required of the mount for installing the variable magnification optical system can be reduced. In order to increase the manufacturability by reducing the number of optical elements to be used, the correction lens group Gc is preferably composed of a single lens. The correction lens group Gc in the example of FIG. 1 includes only one lens Lc1. As an example, the lens Lc1 in FIG. 1 is a meniscus lens having a convex surface directed toward the object side. The correction lens group Gc may be configured to include two lenses. In such a case, astigmatism can be corrected well. For example, the correction lens group Gc can be configured to include two meniscus single lenses having a convex surface facing the object side.

  The correction lens group Gc is preferably arranged both in the optical path from the first mirror M1 to the second mirror M2 and in the optical path from the second mirror M2 to the position P of the intermediate image. That is, the light beam is reflected twice in the correction lens group Gc when the light reflected by the first mirror M1 goes to the second mirror M2 and when the light reflected by the second mirror M2 goes to the position P of the intermediate image. It is preferable that it is comprised so that it may pass. In this way, by arranging the correction lens group Gc in the optical path along which the light beam reciprocates, it becomes easy to satisfactorily correct the spherical aberration even if the number of optical elements such as lenses and mirrors is reduced. Even when the number of elements is reduced and an aspheric surface is not used for both the first mirror M1 and the second mirror M2, it is easy to satisfactorily correct spherical aberration.

  The optical elements having power included in the first optical system U1 are preferably only the first mirror M1, the second mirror M2, the field lens group Gfd, and the correction lens group Gc. By reducing the number of optical elements, it is possible to suppress a decrease in the transmittance of the entire first optical system U1.

  In the example of FIG. 1, the first optical system U1 has only a first mirror M1, a second mirror M2, a field lens group Gfd, and a correction lens group Gc as optical elements having power. In the example of FIG. 1, all the optical elements included in the first optical system U1 have a common optical axis Z. As an arrangement not considering the optical path, the second mirror M2 is positioned closest to the object side, the correction lens group Gc is arranged near the image side of the second mirror M2, and the first mirror M1 is closer to the image side than the correction lens group Gc. The field lens group Gfd is disposed in the vicinity of the first mirror M1. In the example of FIG. 1, the first mirror M1 has a ring shape with a hollow center. The intermediate image is located in the vicinity of the object side of the field lens group Gfd.

  In the example of FIG. 1, the light beam incident on the first optical system U1 along the optical path from the object side to the image side is first reflected by the first mirror M1 toward the object side and transmitted through the correction lens group Gc. Then, the light is reflected by the second mirror M2, travels toward the image side, passes through the correction lens group Gc again, then passes through the field lens group Gfd, and enters the second optical system U2.

  The second optical system U2 in the example of FIG. 1 includes, in order from the object side to the image side along the optical axis Z, the first lens group G1, the second lens group G2, the third lens group G3, 4 lens group G4. In the example of FIG. 1, the first lens group G1 is composed of three lenses L11 to L13, the second lens group G2 is composed of one lens L21, and the third lens group G3 is composed of lenses L31 to L31. The fourth lens group G4 includes one lens L41. The fourth lens group G4 includes four lenses L34. However, the configuration shown in FIG. 1 is an example, and the number of lens groups constituting the second optical system U2 and the number of lenses constituting each lens group are different from those in the example of FIG. It is also possible to construct a system.

  In the example of FIG. 1, at the time of zooming, the first lens group G1, the second lens group G2, and the third lens group G3 move while changing the distance in the optical axis direction between adjacent lens groups, The fourth lens group G4 is fixed with respect to the image plane Sim. That is, at the time of zooming, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction along different paths. In FIG. 1, when zooming from the wide-angle end to the telephoto end, the movement locus trG1 of the first lens group G1, the movement locus trG2 of the second lens group G2, the movement locus trG3 of the third lens group G3, and the fourth lens. The movement trajectory trG4 of the group G4 is schematically indicated by an arrow between the wide-angle end state and the telephoto end state. For a lens group that does not move during zooming, such as the fourth lens group G4, the movement trajectory is indicated by a vertical straight arrow.

  The lens closest to the object side in the first lens group preferably has a negative refractive power and has a concave surface facing the object side. In this case, the angle of the principal ray of the off-axis light beam with respect to the optical axis Z can be reduced, and the variation in effective diameter at the time of zooming of the lenses included in the first lens group G1 and the second lens group G2 can be reduced. Can be small.

  It is preferable that the most image side lens of the first lens group G1 and the most object side lens of the second lens group G2 have positive refracting power and have convex surfaces facing each other. In this case, it is possible to suppress the variation of spherical aberration during zooming.

  The second optical system U2 preferably includes at least one lens group closer to the image side than the second lens group G2, and the most image side lens group of the second optical system U2 preferably has a positive refractive power. This is advantageous for correcting the lateral chromatic aberration. The lens group closest to the image side of the second optical system U2 may be configured as a single lens. In such a case, the movement amounts of the first lens group G1 and the second lens group G2 are set as follows. This is advantageous for realizing a high zoom ratio while suppressing fluctuations in various aberrations.

  For example, as in the example shown in FIG. 1, the second optical system U2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a negative And a fourth lens group G4 having a positive refractive power, and at the time of zooming, the first lens group G1, the second lens group G2, and the third lens group G3. Can move in the optical axis direction along different trajectories, and the fourth lens group G4 can be configured to be fixed with respect to the image plane Sim. In such a case, fluctuations in astigmatism during zooming can be suppressed.

  Alternatively, as in Example 7 described later, the second optical system U2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a positive The first lens group G1 and the second lens group G2 move in the optical axis direction along different paths during zooming, and the third lens group G3 is an image. You may comprise so that it may be fixed with respect to surface Sim. In such a case, all the lens groups constituting the second optical system U2 have positive refractive power, so that an image caused by decentering and / or tilting of the lens groups is suppressed while suppressing fluctuation of spherical aberration during zooming. Can be prevented from worsening.

  Alternatively, as in Example 9 described later, the second optical system U2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a positive The first lens group G1, the second lens group G2, and the third lens group G3 move in the direction of the optical axis along different paths at the time of zooming. You may comprise. In this case, all the lens units constituting the second optical system U2 have a positive refractive power, and the degree of freedom of the paraxial solution is increased. While suppressing fluctuations in astigmatism at the time of doubling, image deterioration due to decentering and / or tilting of the lens groups can be suppressed.

  Alternatively, as in Example 10 described later, the second optical system U2 includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. In zooming, the first lens group G1 and the second lens group G2 may move in the optical axis direction along different paths. In such a case, the structure becomes simple and the zooming mechanism can be simplified.

  As for focusing, for example, focusing can be performed by changing the distance between the first mirror M1 and the second mirror M2. In that case, by focusing only by moving only the first mirror M1 in the optical axis direction with respect to the image plane Sim, by moving only the second mirror M2 in the optical axis direction with respect to the image plane Sim. It is preferable to adopt one of a method for performing focusing and a method for performing focusing by moving the second mirror M2 and the correction lens group Gc integrally in the optical axis direction. Alternatively, focusing may be performed by moving a part of the second optical system U2 in the optical axis direction.

Next, the configuration related to the conditional expression of the variable magnification optical system of the present embodiment will be described. The average value of partial dispersion ratios between g-line and F-line of all positive lenses in the second optical system U2 is θgFp, and the partial dispersion ratio between g-line and F-line of all negative lenses in the second optical system U2 Is an average value of θgFn, the zoom optical system of the present embodiment satisfies the following conditional expression (1). By satisfying conditional expression (1), it is possible to suppress the occurrence of secondary axial chromatic aberration and secondary lateral chromatic aberration in the visible light range. In addition, if it is set as the structure which satisfies the following conditional expression (1-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (1-2), still more favorable characteristics and can do.
−0.04 <θgFp−θgFn <0.1 (1)
−0.02 <θgFp−θgFn <0.06 (1-1)
−0.015 <θgFp−θgFn <0 (1-2)

When the average value of d-line reference Abbe numbers of all positive lenses in the second optical system U2 is νdp, and the average value of d-line reference Abbe numbers of all negative lenses in the second optical system U2 is νdn It is preferable that the following conditional expression (2) is satisfied. The axial chromatic aberration can be easily corrected by avoiding the lower limit of conditional expression (2) from being reached. By avoiding exceeding the upper limit of conditional expression (2), occurrence of secondary chromatic aberration can be suppressed. In addition, if it is set as the structure which satisfies the following conditional expression (2-1), it can be set as a more favorable characteristic.
10 <νdp−νdn <40 (2)
14 <νdp−νdn <35 (2-1)

The average value of the partial dispersion ratio between the C line and the t line of all the positive lenses in the second optical system U2 is θCtp, and the partial dispersion ratio between the C line and the t line of all the negative lenses in the second optical system U2 When the average value is θCtn, it is preferable that the following conditional expression (3) is satisfied. By satisfying conditional expression (3), it is possible to suppress the occurrence of secondary chromatic aberration in the wavelength range from red to infrared. In addition, if it is set as the structure which satisfies the following conditional expression (3-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (3-2), still more favorable characteristics and can do.
−0.1 <θCtp−θCtn <0.1 (3)
−0.07 <θCtp−θCtn <0.05 (3-1)
−0.06 <θCtp−θCtn <0.015 (3-2)

When the average value of the partial dispersion ratio between the C line and the t line of all the negative lenses in the second optical system U2 is θCtn, it is preferable that the following conditional expression (4) is satisfied. By making it not below the lower limit of conditional expression (4), it becomes easy to ensure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct primary chromatic aberration. By avoiding the upper limit of conditional expression (4) from being exceeded, correction of secondary chromatic aberration in the wavelength region from red to infrared becomes easy. In addition, if it is set as the structure which satisfies the following conditional expression (4-1), it can be set as a more favorable characteristic.
0.75 <θCtn <0.9 (4)
0.77 <θCtn <0.85 (4-1)

When the average value of the partial dispersion ratio between the C line and the t line of all the positive lenses in the second optical system U2 is θCtp, it is preferable that the following conditional expression (5) is satisfied. By avoiding the lower limit of conditional expression (5) from being reached, correction of secondary chromatic aberration in the wavelength range from red to infrared becomes easy. By making sure that the upper limit of conditional expression (5) is not exceeded, it becomes easy to ensure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct primary chromatic aberration. In addition, if it is set as the structure which satisfies the following conditional expression (5-1), it can be set as a more favorable characteristic.
0.75 <θCtp <0.9 (5)
0.78 <θCtp <0.85 (5-1)

When the average value of the d-line reference Abbe numbers of all the negative lenses in the second optical system U2 is νdn, it is preferable that the following conditional expression (6) is satisfied. By making it not below the lower limit of conditional expression (6), it becomes easy to select a material having a small partial dispersion ratio between the g-line and the F-line, and correction of secondary chromatic aberration in the visible light region becomes easy. By avoiding exceeding the upper limit of conditional expression (6), it becomes easy to ensure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. In addition, if it is set as the structure which satisfies the following conditional expression (6-1), it can be set as a more favorable characteristic.
50 <νdn <65 (6)
52 <νdn <60 (6-1)

When the average value of the refractive index with respect to the d-line of all the negative lenses in the second optical system U2 is Ndn, it is preferable that the following conditional expression (7) is satisfied. By making it not below the lower limit of conditional expression (7), it is possible to suppress the occurrence of high-order spherical aberration and to easily select a material with a small Abbe number, which is advantageous for correcting primary chromatic aberration. . By making the value not to exceed the upper limit of conditional expression (7), the absolute value of the Petzval sum can be kept small, and the field curvature can be corrected well. In addition, if it is set as the structure which satisfies the following conditional expression (7-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (7-2), still more favorable characteristics and can do.
1.5 <Ndn <1.75 (7)
1.55 <Ndn <1.7 (7-1)
1.57 <Ndn <1.65 (7-2)

When the average value of the partial dispersion ratio between the g-line and the F-line of all the negative lenses in the second optical system U2 is θgFn, it is preferable that the following conditional expression (8) is satisfied. By making it not to be below the lower limit of conditional expression (8), it becomes easy to secure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct primary chromatic aberration. By avoiding the upper limit of conditional expression (8) from being exceeded, correction of secondary chromatic aberration in the visible light region is facilitated. In addition, if it is set as the structure which satisfies the following conditional expression (8-1), it can be set as a more favorable characteristic.
0.53 <θgFn <0.58 (8)
0.535 <θgFn <0.565 (8-1)

When the average value of the partial dispersion ratios between the g-line and the F-line of all the positive lenses in the second optical system U2 is θgFp, it is preferable that the following conditional expression (9) is satisfied. By avoiding the lower limit of conditional expression (9) from being reached, correction of secondary chromatic aberration in the visible light region is facilitated. By making sure that the upper limit of conditional expression (9) is not exceeded, it becomes easy to ensure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct primary chromatic aberration. In addition, if it is set as the structure which satisfies the following conditional expression (9-1), it can be set as a more favorable characteristic.
0.5 <θgFp <0.65 (9)
0.52 <θgFp <0.6 (9-1)

When the average value of d-line reference Abbe numbers of all the positive lenses in the second optical system U2 is νdp, it is preferable that the following conditional expression (10) is satisfied. By making it not to be below the lower limit of conditional expression (10), it becomes easy to secure the Abbe number difference between the negative lens and the positive lens, and it becomes easy to correct the primary chromatic aberration. By making it not exceed the upper limit of conditional expression (10), it becomes easy to select a material having a large partial dispersion ratio between the g-line and the F-line, and correction of secondary chromatic aberration in the visible light region becomes easy. In addition, if it is set as the structure which satisfies the following conditional expression (10-1), it can be set as a more favorable characteristic.
70 <νdp <100 (10)
72 <νdp <90 (10-1)

When the average value of the refractive indices of all the positive lenses in the second optical system U2 with respect to the d-line is Ndp, it is preferable that the following conditional expression (11) is satisfied. By making it not below the lower limit of conditional expression (11), the absolute value of the Petzval sum can be reduced while suppressing the occurrence of spherical aberration, and the field curvature can be corrected well. By avoiding the upper limit of conditional expression (11) from being exceeded, it becomes easier to select a material having a large Abbe number, which is advantageous for correcting primary chromatic aberration. In addition, if it is set as the structure which satisfies the following conditional expression (11-1), it can be set as a more favorable characteristic.
1.43 <Ndp <1.75 (11)
1.44 <Ndp <1.55 (11-1)

When the focal length of the second optical system U2 at the telephoto end is fU2 and the focal length of the first lens group G1 is fG1, it is preferable that the following conditional expression (12) is satisfied. By making it not below the lower limit of conditional expression (12), a high zoom ratio can be realized even if the amount of movement of the first lens group G1 during zooming is reduced. By avoiding the upper limit of conditional expression (12) from being exceeded, fluctuations in spherical aberration during zooming can be suppressed. In addition, if it is set as the structure which satisfies the following conditional expression (12-1), it can be set as a more favorable characteristic.
0.2 <fU2 / fG1 <0.45 (12)
0.22 <fU2 / fG1 <0.4 (12-1)

When the radius of curvature of the reflective surface of the first mirror is rM1 and the radius of curvature of the reflective surface of the second mirror is rM2, it is preferable that the following conditional expression (13) is satisfied. By making it not to be below the lower limit of conditional expression (13), it is advantageous for shortening the total length. The occurrence of astigmatism can be suppressed by preventing the conditional expression (13) from exceeding the upper limit. In addition, if it is set as the structure which satisfies the following conditional expression (13-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (13-2), still more favorable characteristics and can do.
1 <rM1 / rM2 <2.5 (13)
1.2 <rM1 / rM2 <2.2 (13-1)
1.6 <rM1 / rM2 <2.1 (13-2)

When the radius of curvature of the reflecting surface of the first mirror is rM1 and the focal length of the correction lens group Gc is fC, it is preferable that the following conditional expression (14) is satisfied. By making sure that the lower limit of conditional expression (14) is not exceeded, it is advantageous for correcting spherical aberration. By avoiding the upper limit of conditional expression (14) from being exceeded, axial chromatic aberration can be suppressed, and the occurrence of a difference in spherical aberration due to wavelength can be suppressed. In addition, if it is set as the structure which satisfies the following conditional expression (14-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (14-2), still more favorable characteristics and can do.
0.07 <rM1 / fC <0.5 (14)
0.1 <rM1 / fC <0.45 (14-1)
0.2 <rM1 / fC <0.4 (14-2)

When the lateral magnification of the second optical system U2 at the telephoto end at the time of focusing on an object at infinity is βrT and the zoom ratio of the zoom optical system is MAG, it is preferable that the following conditional expression (15) is satisfied. By preventing the conditional expression (15) from being below the lower limit, it is possible to suppress the variation in spherical aberration during zooming. By avoiding exceeding the upper limit of conditional expression (15), a high zoom ratio can be realized even if the amount of movement of the lens group that moves during zooming is reduced. In addition, if it is set as the structure which satisfies the following conditional expression (15-1), it can be set as a more favorable characteristic.
−0.45 <βrT / MAG <−0.25 (15)
−0.4 <βrT / MAG <−0.28 (15-1)

When the focal length of the field lens group Gfd is fFd and the distance on the optical axis from the intermediate image at the time of focusing on an object at infinity to the lens surface closest to the object side of the second lens group G2 at the wide angle end is LA, It is preferable to satisfy conditional expression (16). By satisfying conditional expression (16), the off-axis light beam can intersect the optical axis Z at an appropriate position, which is advantageous for reducing the diameter of the lens unit that moves during zooming. In addition, if it is set as the structure which satisfies the following conditional expression (16-1), it can be set as a more favorable characteristic, and if it is set as the structure which satisfies the following conditional expression (16-2), still more favorable characteristics and can do.
0.4 <fFd / LA <1 (16)
0.5 <fFd / LA <0.8 (16-1)
0.55 <fFd / LA <0.75 (16-2)

When the focal length of the first lens group G1 is fG1, and the focal length of the second lens group G2 is fG2, it is preferable that the following conditional expression (17) is satisfied. By satisfying conditional expression (17), it is possible to appropriately distribute the refractive power to the first lens group G1 and the second lens group G2, thereby suppressing the variation of spherical aberration during zooming. In addition, the effective diameters of the first lens group G1 and the second lens group G2 can be reduced. In addition, if it is set as the structure which satisfies the following conditional expression (17-1), it can be set as a more favorable characteristic.
1.5 <fG1 / fG2 <4 (17)
1.7 <fG1 / fG2 <3.8 (17-1)

  Although not shown in FIG. 1, various parallel plate filters and / or cover glasses are arranged between the lens closest to the image side and the image plane Sim and / or between the optical element and the optical element. May be. The change in aberration due to the arrangement of various filters and / or cover glasses can be corrected to an extent that does not cause a practical problem by changing a small number of design parameters.

  The preferred configurations and possible configurations described above can be arbitrarily combined, and are preferably selectively adopted as appropriate according to the required specifications. According to the present embodiment, it is possible to realize a variable magnification optical system having good optical performance while achieving a high zoom ratio with small fluctuations in various aberrations during zooming. Here, the “high zoom ratio” means that the zoom ratio is 4 times or more.

Next, numerical examples of the variable magnification optical system of the present invention will be described.
[Example 1]
The cross-sectional view and optical path of the variable magnification optical system of Example 1 are shown in FIG. 1, and the configuration and method of illustration are as described above. The variable magnification optical system of Example 1 includes a first optical system U1 and a second optical system U2 in order from the object side to the image side. The first optical system U1 is fixed with respect to the image plane Sim at the time of zooming. The second optical system U2 includes a plurality of lens groups that move during zooming. The first optical system U1 includes a ring-shaped first mirror M1, a second mirror M2, a correction lens group Gc, and a field lens group Gfd. The correction lens group Gc is composed of one lens Lc1. The field lens group Gfd is composed of two lenses, a lens Lf1 and a lens Lf2, in order from the object side. All the optical elements included in the first optical system U1 have a common optical axis Z. In a state where an object at infinity is focused, an intermediate image is formed in the vicinity of the object side of the field lens group Gfd. The first mirror M1 is an optical element having power located closest to the object side on the optical path, and also has a function as a diaphragm surface. Light rays from the object pass through the first mirror M1, the correction lens group Gc, the second mirror M2, the correction lens group Gc, and the field lens group Gfd in this order, and then enter the second optical system U2. The second optical system U2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power. And a fourth lens group G4 having a positive refractive power. At the time of zooming, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction along different paths, and the fourth lens group G4 is fixed with respect to the image plane Sim. ing. The first lens group G1 includes three lenses, a lens L11 to a lens L13. The second lens group G2 includes one lens L21. The third lens group G3 includes four lenses, a lens L31 to a lens L34. The fourth lens group G4 is composed of one lens L41. The third lens group G3 has a cemented lens in which a positive lens and a negative lens are cemented. The above is the outline of the variable magnification optical system of Example 1.

  Table 1 shows the basic lens data of the variable magnification optical system of Example 1, Table 2 shows the specifications and the variable surface interval, and Table 3 shows the aspheric coefficient. Tables 1 and 2 are data in a state of focusing on an object at infinity. Table 1 shows components along the optical path. In Table 1, the surface number column indicates the surface number when the surface closest to the object side on the optical path is the first surface, and the number is increased by one as it goes to the image side along the optical path. The column shows the radius of curvature of each surface, and the column d shows the surface spacing on the optical axis between each surface and the surface adjacent to the image side on the optical path. In the material column, the material name of each component and the name of the manufacturer of the material are shown with an underscore. The manufacturer name is shown schematically. For example, “OHARA” is OHARA Inc. The Nd column in Table 1 shows the refractive index of each component with respect to the d-line, the νd column shows the Abbe number of each component d-line reference, and the θgF column shows the g-line of each component. The partial dispersion ratio between the F lines is shown, and the θCt column shows the partial dispersion ratio between the C line and the t line of each component.

  In Table 1, the sign of the curvature radius of the surface with the convex surface facing the object side is positive, and the sign of the curvature radius of the surface with the convex surface facing the image side is negative. In the surface number column of Table 1, in addition to each surface number, “(reflective surface)” is written in the surface corresponding to the reflective surface, and “(intermediate image)” is written in the surface corresponding to the intermediate image. In this case, “(image plane)” is written on the surface corresponding to the image plane Sim. Further, in Table 1, the variable surface interval is indicated in the column “d” by adding the surface number on the object side of the interval to “D”.

  Table 2 shows the absolute value of the focal length of the entire system, the F number, the maximum image height, and the maximum half angle of view, respectively, “| focal length |”, “FNo.”, “Image height”, “half angle of view”. Is shown on the line. Table 2 shows the value of each variable surface interval. The values shown in Table 2 are values based on the d-line. In Table 2, the values of the wide-angle end state, the first intermediate focal length state, the second intermediate focal length state, and the telephoto end state are shown in columns labeled W, M1, M2, and T, respectively.

In Table 1, the surface number of the aspheric surface is marked with *, and the numerical value of the paraxial curvature radius is described in the column of curvature radius of the aspheric surface. In Table 3, the surface number of the aspheric surface is shown, and the values of the aspheric coefficient for each aspheric surface are shown in the columns of K and Am (m = 4, 6, 8, 10). The numerical value “E ± n” (n: integer) of the aspheric coefficient in Table 3 means “× 10 ^{± n} ”. K and Am are aspheric coefficients in the aspheric expression represented by the following expression.
^{Zd = C × h 2 / {} 1+ (1- (1 + K) × C 2 × h 2) 1/2} + ΣAm × h m
However,
Zd: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface of height h to a plane perpendicular to the optical axis where the aspherical vertex contacts)
h: Height (distance from the optical axis to the lens surface)
C: Reciprocal K of paraxial radius of curvature, Am: aspherical coefficient, and Σ in the aspherical expression means a total sum related to m.

  In the data in each table, degrees are used as the unit of angle, and mm (millimeter) is used as the unit of length, but the optical system can be used even when proportionally enlarged or reduced, so that other appropriate values can be used. Units can also be used. In the following tables, numerical values rounded by a predetermined digit are described.

  FIG. 11 shows aberration diagrams in a state in which the infinitely far object of the zoom optical system of Example 1 is focused. In FIG. 11, spherical aberration, astigmatism, distortion, and lateral chromatic aberration are shown in order from the left. In FIG. 11, an aberration diagram at the wide-angle end is shown in the upper stage labeled WIDE, and an aberration diagram at the telephoto end is shown in the lower stage labeled TELE. In the spherical aberration diagram, aberrations at a wavelength of 1970.1 nm, C-line, d-line, F-line, and g-line are indicated by a long broken line, an alternate long and short dash line, a solid line, a short dashed line, and a two-dot chain line, respectively. In the astigmatism diagram, the aberration at the d-line in the sagittal direction is indicated by a solid line, and the aberration at the d-line in the tangential direction is indicated by a short broken line. In the distortion diagram, the aberration at the d-line is shown by a solid line. In the chromatic aberration diagram of magnification, aberrations at a wavelength of 1970.1 nm and g line are indicated by a long broken line and a two-dot chain line, respectively. FNo. Means F number, and IH in other aberration diagrams means image height. Since the first mirror M1 has a ring shape, data near 0 on the vertical axis of the spherical aberration diagram of FIG. 11 is shown as reference data.

  Since the symbols, meanings, description methods, and illustration methods of each data related to the first embodiment are the same in the following embodiments unless otherwise specified, the duplicate description will be omitted below.

[Example 2]
A sectional view and an optical path of the variable magnification optical system of Example 2 are shown in FIG. The variable magnification optical system of Example 2 has the same configuration as the outline of the variable magnification optical system of Example 1. Table 4 shows the basic lens data of the variable magnification optical system of Example 2, Table 5 shows the specifications and the distance between the variable surfaces, and FIG. 12 shows aberration diagrams.

[Example 3]
A sectional view and an optical path of the variable magnification optical system of Example 3 are shown in FIG. In the variable magnification optical system of Example 3, the correction lens group Gc is composed of two lenses L1 to Lc2, and the third lens group G3 is composed of three lenses L31 to L33. Unlike Example 1, the other points have the same configuration as the outline of the variable magnification optical system of Example 1. Table 6 shows the basic lens data of the variable magnification optical system of Example 3, Table 7 shows the specifications and the distance between the variable surfaces, and FIG. 13 shows aberration diagrams.

[Example 4]
A sectional view and an optical path of the variable magnification optical system of Example 4 are shown in FIG. The variable magnification optical system of the fourth embodiment is different from the first embodiment in that the correction lens group Gc includes two lenses Lc1 to Lc2, and the other points are the same as the outline of the variable magnification optical system of the first embodiment. It has the same configuration. Table 8 shows the basic lens data of the variable magnification optical system of Example 4, Table 9 shows the specifications and the distance between the variable surfaces, and FIG. 14 shows aberration diagrams.

[Example 5]
A sectional view and an optical path of the variable magnification optical system of Example 5 are shown in FIG. The variable magnification optical system of the fifth embodiment is different from the first embodiment in that the correction lens group Gc includes two lenses Lc1 to Lc2, and the other points are the same as the outline of the variable magnification optical system of the first embodiment. It has the same configuration. Table 10 shows the basic lens data of the variable magnification optical system of Example 5, Table 11 shows the specifications and the distance between the variable surfaces, and FIG. 15 shows aberration diagrams.

[Example 6]
A sectional view and an optical path of the variable magnification optical system of Example 6 are shown in FIG. The variable magnification optical system of the sixth embodiment is different from the first embodiment in that the correction lens group Gc is composed of two lenses Lc1 to Lc2, and the other points are the same as the outline of the variable magnification optical system of the first embodiment. It has the same configuration. The basic lens data of the variable magnification optical system of Example 6 is shown in Table 12, the specifications and the variable surface interval are shown in Table 13, and each aberration diagram is shown in FIG.

[Example 7]
A sectional view and an optical path of the variable magnification optical system of Example 7 are shown in FIG. The variable magnification optical system of the seventh embodiment is different from the first embodiment in that the correction lens group Gc is composed of two lenses Lc1 to Lc2, and the configuration of the second optical system U2, and the first optical system U1 is different from the first embodiment. Except for the correction lens group Gc, the zoom lens system has the same configuration as the outline of the variable magnification optical system of Example 1. The second optical system U2 of Example 7 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens having a positive refractive power. It consists of a lens group G3. At the time of zooming, the first lens group G1 and the second lens group G2 move in the optical axis direction along different paths, and the third lens group G3 is fixed with respect to the image plane Sim. The first lens group G1 includes three lenses, a lens L11 to a lens L13. The second lens group G2 includes five lenses, a lens L21 to a lens L25. The third lens group G3 includes one lens L31. The second lens group G2 has a cemented lens in which a positive lens and a negative lens are cemented. The above is the outline of the variable magnification optical system of Example 7.

  Table 14 shows the basic lens data of the variable magnification optical system of Example 7, Table 15 shows the specifications and the distance between the variable surfaces, and FIG. 17 shows aberration diagrams.

[Example 8]
A sectional view and an optical path of the variable magnification optical system of Example 8 are shown in FIG. The variable magnification optical system of Example 8 has the same configuration as the outline of the variable magnification optical system of Example 7. Table 16 shows the basic lens data of the variable magnification optical system of Example 8, Table 17 shows the specifications and the distance between the variable surfaces, and FIG. 18 shows aberration diagrams.

[Example 9]
FIG. 9 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 9. In the variable power optical system of Example 9, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction along different trajectories at the time of zooming. Unlike the above, the configuration is the same as that of the outline of the variable magnification optical system of Example 7. Table 18 shows the basic lens data of the variable magnification optical system of Example 9, Table 19 shows the specifications and the distance between the variable surfaces, and FIG. 19 shows aberration diagrams.

[Example 10]
A sectional view and an optical path of the variable magnification optical system of Example 9 are shown in FIG. The variable magnification optical system of Example 10 is different from Example 7 in the configuration of the second optical system U2, and the first optical system U1 has the same configuration as the outline of the variable magnification optical system of Example 7. The second optical system U2 of Example 10 includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power. The lens group G1 and the second lens group G2 move in the optical axis direction along different paths. The first lens group G1 includes three lenses, a lens L11 to a lens L13. The second lens group G2 is composed of seven lenses L21 to L27. The second lens group G2 has two sets of cemented lenses in which a positive lens and a negative lens are cemented. The basic lens data of the variable magnification optical system of Example 10 is shown in Table 20, the specifications and the variable surface interval are shown in Table 21, the aspheric coefficient is shown in Table 22, and the aberration diagrams are shown in FIG.

Table 23 shows corresponding values of conditional expressions (1) to (17) of the variable magnification optical systems of Examples 1 to 10. Corresponding values other than the partial dispersion ratio in Table 23 are values on the d-line basis.

  As can be seen from the above data, the variable magnification optical systems of Examples 1 to 10 have small variations in various aberrations at the time of variable magnification, and a high variable magnification ratio is achieved with a variable magnification ratio of 4.9 times or more. The load on the side portion can be reduced, and it can be configured at low cost. Various aberrations are well corrected in a wide range from the visible light region to the infrared light region, and high optical performance is realized.

  Next, an imaging apparatus according to an embodiment of the present invention will be described. FIG. 21 shows a schematic configuration diagram of an imaging apparatus 10 using the variable magnification optical system 1 according to the embodiment of the present invention as an example of the imaging apparatus of the embodiment of the present invention. Examples of the imaging device 10 include a surveillance camera, a video camera, and an electronic still camera.

  The imaging apparatus 10 includes a variable magnification optical system 1, a filter 4 disposed on the image side of the variable magnification optical system 1, an imaging element 5 that captures an image of a subject formed by the variable magnification optical system 1, and imaging A signal processing unit 6 that performs arithmetic processing on an output signal from the element 5 and a zooming control unit 7 that performs zooming of the zooming optical system 1 are provided. FIG. 21 schematically shows the first optical system U1 and the second optical system U2 included in the variable magnification optical system 1. The image sensor 5 captures an image of a subject formed by the variable magnification optical system 1 and converts it into an electrical signal. The image pickup surface of the image pickup device 5 is disposed so as to coincide with the image plane of the variable magnification optical system 1. As the imaging device 5, for example, a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) can be used. Although only one image sensor 5 is shown in FIG. 21, the image pickup apparatus of the present invention is not limited to this, and may be a so-called three-plate type image pickup apparatus having three image pickup elements.

  While the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the radius of curvature, the surface spacing, the refractive index, the Abbe number, the aspherical coefficient, and the like of each optical element are not limited to the values shown in the above numerical examples, and may take other values.

DESCRIPTION OF SYMBOLS 1 Variable magnification optical system 4 Filter 5 Image pick-up element 6 Signal processing part 7 Variable magnification control part 10 Imaging device G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group Gc Correction lens group Gfd Field lens group L11 to L13, L21 to L27, L31 to L34, L41, Lc1, Lc2, Lf1, Lf2 Lens M1 First mirror M2 Second mirror P Intermediate image position Sim Image plane trG1 First lens group movement locus trG2 Second lens Group movement locus trG3 Third lens group movement locus trG4 Fourth lens group movement locus U1 First optical system U2 Second optical system Z Optical axis

Claims (20)

In order from the object side, a first optical system including two reflecting mirrors whose reflecting surfaces are arranged to face each other and fixed to the image plane at the time of zooming, at least two positive lenses and at least one negative lens And a second optical system including
The two reflectors are
A first reflecting mirror having a reflecting surface with a concave surface facing the object side and reflecting light rays from the object to the object side;
A second reflecting mirror having a reflecting surface with a convex surface facing the image side and reflecting the reflected light from the first reflecting mirror to the image side;
The second optical system is continuously in order from the most object side,
A first lens group that always moves toward the object side and has positive refractive power when zooming from the wide-angle end to the telephoto end;
A second lens group having a positive refractive power that moves in the optical axis direction along a locus different from that of the first lens group at the time of zooming,
An intermediate image is formed between the second reflecting mirror and the first lens group, and the intermediate image is re-imaged through the second optical system,
An average value of partial dispersion ratios between g-line and F-line of all positive lenses in the second optical system is θgFp,
When the average value of the partial dispersion ratio between the g-line and the F-line of all the negative lenses in the second optical system is θgFn,
−0.04 <θgFp−θgFn <0.1 (1)
A variable magnification optical system that satisfies the conditional expression (1) expressed by: The average value of the d-line reference Abbe numbers of all positive lenses in the second optical system is νdp,
When the average value of the Abbe numbers based on the d-line of all the negative lenses in the second optical system is νdn,
10 <νdp−νdn <40 (2)
The zoom optical system according to claim 1, wherein a conditional expression (2) expressed by the following is satisfied. An average value of partial dispersion ratios between C-line and t-line of all positive lenses in the second optical system is θCtp,
When the average value of the partial dispersion ratio between the C line and the t line of all the negative lenses in the second optical system is θCtn,
−0.1 <θCtp−θCtn <0.1 (3)
The zoom optical system according to claim 1 or 2, wherein a conditional expression (3) represented by:   4. The variable according to claim 1, wherein the first optical system includes a field lens group having a positive refractive power, which is a lens component closest to the intermediate image and includes two or less lenses. 5. Double optical system.   5. The variable magnification optical system according to claim 1, wherein the first reflecting mirror is an optical element having a power located closest to the object side on the optical path. The first optical system includes:
The first reflecting mirror and the second reflecting mirror are disposed in an optical path from the first reflecting mirror to the second reflecting mirror and in an optical path from the second reflecting mirror to the position of the intermediate image. 6. The variable magnification optical system according to claim 1, further comprising a correction lens group including two or less lenses having a common optical axis with the reflecting mirror. When the average value of the partial dispersion ratio between the C line and the t line of all the negative lenses in the second optical system is θCtn,
0.75 <θCtn <0.9 (4)
The zoom optical system according to any one of claims 1 to 6, wherein a conditional expression (4) represented by: When the average value of the partial dispersion ratio between the C line and the t line of all the positive lenses in the second optical system is θCtp,
0.75 <θCtp <0.9 (5)
The zoom optical system according to any one of claims 1 to 7, wherein a conditional expression (5) represented by: When the average value of the Abbe numbers based on the d-line of all the negative lenses in the second optical system is νdn,
50 <νdn <65 (6)
The zoom optical system according to any one of claims 1 to 8, which satisfies a conditional expression (6) expressed by: When the average value of the refractive index for the d-line of all negative lenses in the second optical system is Ndn,
1.5 <Ndn <1.75 (7)
The zoom optical system according to any one of claims 1 to 9, wherein a conditional expression (7) expressed by: 0.53 <θgFn <0.58 (8)
The variable power optical system according to claim 1, wherein a conditional expression (8) represented by: 0.5 <θgFp <0.65 (9)
The zoom optical system according to any one of claims 1 to 11, which satisfies a conditional expression (9) expressed by: When the average value of the d-line reference Abbe numbers of all positive lenses in the second optical system is νdp,
70 <νdp <100 (10)
The zoom optical system according to any one of claims 1 to 12, which satisfies a conditional expression (10) expressed by: When the average value of the refractive index for the d-line of all the positive lenses in the second optical system is Ndp,
1.43 <Ndp <1.75 (11)
The zoom optical system according to any one of claims 1 to 13, which satisfies a conditional expression (11) expressed by: −0.02 <θgFp−θgFn <0.06 (1-1)
The variable power optical system according to claim 1, wherein a conditional expression (1-1) represented by: 14 <νdp−νdn <35 (2-1)
The zoom optical system according to claim 2, wherein a conditional expression (2-1) represented by: −0.07 <θCtp−θCtn <0.05 (3-1)
The zoom optical system according to claim 3, wherein a conditional expression (3-1) represented by: 0.77 <θCtn <0.85 (4-1)
The variable power optical system according to claim 7, wherein a conditional expression (4-1) represented by: 0.78 <θCtp <0.85 (5-1)
The zoom optical system according to claim 8, which satisfies a conditional expression (5-1) represented by: An imaging apparatus comprising the variable magnification optical system according to any one of claims 1 to 19.