JP6815375B2 - Variable magnification optical system and imaging device - Google Patents

Description

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

Conventionally, a variable magnification optical system including a catadioptric system has been proposed. For example, the following Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 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 U.S. Pat. No. 4,971,428 Chinese Patent Application Publication No. 106772963

In recent years, the demand for surveillance cameras used for distant surveillance at ports and / or airports has increased, and along with this, the demand for telephoto and super-telephoto variable magnification optical systems has increased. In this type of variable magnification optical system, the optical element arranged near the object side tends to have a large diameter and the weight balance tends to be poor. Therefore, it is required to reduce the load on the object side portion. It is also required to have an inexpensive configuration, a high magnification ratio, and high performance.

However, the variable magnification optical system described in Patent Document 1 requires a large-diameter aspherical optical element and is expensive. The variable magnification optical system described in Patent Document 2 has a low magnification ratio and requires a large-diameter aspherical optical element, which is expensive. The variable magnification optical system described in Patent Document 3 is expensive because a lens having a large diameter is often used on the object side and the effective diameter of a lens group that moves at the time of magnification change is large. Further, in the variable magnification optical system described in Patent Document 3, a heavy object is located at the tip end portion on the object side. The variable magnification optical system described in Patent Document 4 is also expensive because it frequently uses a lens having a large diameter on the object side, and a heavy object is located at the tip portion on the object side.

In view of the above circumstances, the present invention is a variable magnification optical system which can reduce the load on the portion on the object side, can be constructed at low cost, and has good optical performance while achieving a high magnification ratio. An object of the present invention is to provide an image pickup apparatus provided with the variable magnification optical system.

In order to solve the above problems, the variable magnification optical system of the present invention includes two reflecting mirrors in which each reflecting surfaces are arranged to face each other in order from the object side, and is fixed to the image plane at the time of scaling. It consists of an optical system and a second optical system including a plurality of lens groups that move at the time of magnification change. The two reflectors are optical elements having power located on the object side most on the optical path and are on the object side. A first reflector having a reflecting surface with a concave surface facing the object and reflecting light rays from the object toward the object side, and a reflecting surface having a reflecting surface with a convex surface facing the image side to image the reflected light from the first reflecting mirror. It consists of a second reflecting mirror that reflects to the side, and the second optical system is continuous from the object side in order and always moves to the object side when scaling from the wide-angle end to the telescopic end and has a positive refractive force. The second reflecting mirror and the first lens group include a first lens group and a second lens group having a positive refractive force that moves in the optical axis direction in a trajectory different from that of the first lens group at the time of magnification change. An intermediate image is formed between them, and the intermediate image is reimaged via the second optical system.

In the variable magnification 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 which is composed of two or less lenses and is in close contact with the intermediate image.

In the variable magnification optical system of the present invention, the first optical system is arranged in the optical path from the first reflector to the second reflector and in the optical path from the second reflector to the position of the intermediate image. Moreover, it is preferable to include a correction lens group composed of two or less lenses having an optical axis common to the first reflector and the second reflector.

In the variable magnification optical system of the present invention, it is preferable that the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror have a spherical shape.

In the variable magnification optical system of the present invention, the first optical system consists of a field lens group having a positive refractive force, which is a lens component closest to an intermediate image and is composed of two or less lenses, and a first reflecting mirror. Two lenses that are arranged in the optical path to the second reflector and in the optical path from the second reflector to the position of the intermediate image, and have the same optical axis as the first reflector and the second reflector. The only optical elements having power included in the first optical system, including the correction lens group consisting of the following lenses, are the first reflector, the second reflector, the field lens group, and the correction lens group. Is preferable.

In the variable magnification optical system of the present invention, the lens on the image side of the first lens group and the lens on the object side of the second lens group both have a positive refractive power and have convex surfaces facing each other. Is preferable.

In the variable magnification optical system of the present invention, it is preferable that the lens on the most object side of the first lens group has a negative refractive power and has a concave surface facing the object side.

In the variable magnification optical system of the present invention, the second optical system includes at least one lens group on the image side of the second lens group, and the lens group on the image side of the second optical system has a positive refractive power. Is preferable.

In the variable magnification optical system of the present invention, it is preferable that the lens group on the image side of the second optical system is a single single lens.

In the variable magnification optical system of the present invention, the radius of curvature of the reflecting surface of the first reflecting mirror is rM1.
When the radius of curvature of the reflecting surface of the second reflecting mirror is rM2, the following conditional expression (13) is preferably satisfied, and the following conditional expression (13-1) is more preferable.
1 <rM1 / rM2 <2.5 (13)
1.2 <rM1 / rM2 <2.2 (13-1)

In the variable magnification optical system of the present invention, the first optical system is arranged in the optical path from the first reflector to the second reflector and in the optical path from the second reflector to the position of the intermediate image. In addition, a correction lens group consisting of two or less lenses having an optical axis common to the first reflector and the second reflector is included, and the radius of curvature of the reflecting surface of the first reflector is rM1, and the correction lens group. When the focal length of the lens is fC, it is preferable that the following conditional expression (14) is satisfied, and it is more preferable that the following conditional expression (14-1) is satisfied.
0.07 <rM1 / fC <0.5 (14)
0.1 <rM1 / fC <0.45 (14-1)

In the variable magnification optical system of the present invention, when the lateral magnification of the second optical system at the telephoto end when the object is in focus at infinity is βrT and the magnification ratio of the variable magnification optical system is MAG, the following conditional equation (15) Is more preferable, and the following conditional formula (15-1) is more preferable.
-0.45 <βrT / MAG <-0.25 (15)
-0.4 <βrT / MAG <-0.28 (15-1)

In the variable magnification optical system of the present invention, the first optical system includes a field lens group having a positive refractive power, which is a lens component that consists of two or less lenses and is in close contact with the intermediate image, and is the focal length of the field lens group. When the distance is fFd and the distance on the optical axis from the intermediate image when focusing on an infinity object to the lens surface on the most object side of the second lens group at the wide-angle end is LA, the following conditional expression (16) is satisfied. It is more preferable that the following conditional formula (16-1) is satisfied.
0.4 <fFd / LA <1 (16)
0.5 <fFd / LA <0.8 (16-1)

In the variable magnification optical system of the present invention, when the focal length of the first lens group is fG1 and the focal length of the second lens group is fG2, it is preferable that the following conditional expression (17) is satisfied, and the following conditional expression (17) is satisfied. It is more preferable to satisfy 17-1).
1.5 <fG1 / fG2 <4 (17)
1.7 <fG1 / fG2 <3.8 (17-1)

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

In addition to the components listed above, "consisting of" and "consisting of" in the present specification refer to lenses having substantially no refractive power, and lenses such as diaphragms, filters, and cover glasses. It is intended that optical elements other than the above, as well as mechanical parts such as a lens flange, a lens barrel, an image sensor, and an image stabilization mechanism, and the like may be included.

In addition, in this specification, "the group having a positive refractive power" means that the group as a whole has a positive refractive power. Similarly, the "group having a negative refractive power" means that the group as a whole has a negative refractive power. "Lens with positive refractive power", "positive lens", and "positive lens" are synonymous. "Lens with negative refractive power", "negative lens", and "negative lens" are synonymous. The "lens group" is not limited to a configuration consisting of a plurality of lenses, and may be a configuration consisting of only one lens. "Single lens" means a single lens that is not joined. However, a composite aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally formed and function as one aspherical lens as a whole) is a bonded lens. Is not considered and is treated as a single lens. The "lens component" is a lens having only two air contact surfaces on the optical axis, one on the object side and the other on the image side, and one lens component is one single lens or one set of junction lenses. Means. "Having power" means that the reciprocal of the focal length is not zero. Unless otherwise specified, the sign of the refractive power, the surface shape, and the radius of curvature of the surface for the optical element including the aspherical surface shall be considered in the paraxial region. As the sign of the radius of curvature, the sign of the radius of curvature of the surface having the convex surface facing the object side is positive, and the sign of the radius of curvature of the surface having the convex surface facing the image side is negative. The "focal length" used in the conditional expression is the paraxial focal length. The values of the conditional expressions other than the conditional expression relating to the partial dispersion ratio are the values when the d line is used as a reference in the state of focusing on the infinity object.

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

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 certain lens is θCt = (NC-Nt) when the refractive indexes of the lens with respect to the t line, the F line, and the C line are Nt, NF, and NC, respectively. ) / (NF-NC).

According to the present invention, a variable magnification optical system that can reduce the load on the portion on the object side, can be constructed at low cost, and has good optical performance while achieving a high magnification ratio, and this variation. An imaging device including a magnification optical system can be provided.

It is sectional drawing which shows the structure and the optical path at the wide-angle end and the telephoto end of the variable magnification optical system (the variable magnification optical system of Example 1 of this invention) which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 2 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 3 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 4 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 5 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 6 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 7 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 8 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 9 of this invention. It is sectional drawing which shows the structure and an optical path at a wide-angle end and a telephoto end of the variable magnification optical system of Example 10 of this invention. It is each aberration diagram of the variable magnification optical system of Example 1 of this invention. It is each aberration diagram of the variable magnification optical system of Example 2 of this invention. It is each aberration diagram of the variable magnification optical system of Example 3 of this invention. It is each aberration diagram of the variable magnification optical system of Example 4 of this invention. It is each aberration diagram of the variable magnification optical system of Example 5 of this invention. It is each aberration diagram of the variable magnification optical system of Example 6 of this invention. It is each aberration diagram of the variable magnification optical system of Example 7 of this invention. It is each aberration diagram of the variable magnification optical system of Example 8 of this invention. It is each aberration diagram of the variable magnification optical system of Example 9 of this invention. It is each aberration diagram of the variable magnification optical system of Example 10 of this invention. It is a schematic block diagram of the image pickup apparatus which concerns on one Embodiment of this 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 and a cross-sectional view of an optical path according to an embodiment of the present invention. In FIG. 1, the upper row labeled "WIDE" shows the wide-angle end state, and the lower row labeled "TELE" shows the telephoto end state. The example shown in FIG. 1 corresponds to the variable magnification optical system of Example 1 described later. In FIG. 1, the left side of the paper surface is the object side and the right side of the paper surface is the image side, showing a state in which the object is in focus at infinity.

The variable magnification optical system of the present embodiment includes a first optical system U1 and a second optical system U2 in this order from the object side to the image side. The first optical system U1 is fixed to the image plane Sim at the time of scaling. The second optical system U2 includes a plurality of lens groups that move at the time of magnification change.

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 total length can be shortened by folding back the optical path. The two reflectors are composed of a first reflector and a second reflector. The first mirror M1 of the present embodiment corresponds to the first reflector, and the second mirror M2 corresponds to the second reflector.

The first mirror M1 is an optical element having power located closest to the object side on the optical path. If the refraction optical system is arranged in the optical path on the object side of the first mirror M1, the refraction optical system requires a large aperture and is therefore expensive. Further, if the refraction optical system is arranged in the optical path on the object side of the first mirror M1, the center of gravity of the variable magnification optical system is biased toward the tip portion and the weight balance becomes poor, which is not preferable. Further, since the reflective optical element does not transmit light, it has an advantage that the degree of freedom in material selection is higher than that of the transmissive optical element.

The first mirror M1 has a reflecting surface having a concave surface facing the object side, and is configured to reflect light rays from the object toward the object side. The second mirror M2 has a reflecting surface having a convex surface facing the image side, and is configured to reflect the reflected light from the first mirror M1 toward the image side. With such a configuration, the total 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 reflective surface of the first mirror M1 and the reflective surface of the second mirror M2 are preferably spherical. In this case, it can be manufactured at low cost, and deterioration of the image due to eccentricity and / or tilting can be reduced.

The second optical system U2 is a first lens group G1 which is continuous from the object side in order and always moves to the object side when the magnification is changed from the wide-angle end to the telephoto end and has a positive refractive power, and a first lens group G1 when the magnification is changed. It includes a second lens group G2 having a positive refractive power that moves in the optical axis direction with a trajectory different from that of the lens group G1. That is, the first lens group G1 is arranged on the most object side of the second optical system U2, and the second lens group G2 is arranged 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 powers in the second optical system U2, which is a variable magnification optical system, spherical aberration on the wide-angle side is generated at the time of magnification change, although the configuration is simple. It is possible to suppress fluctuations in spherical aberration, fluctuations in astigmatism during scaling, and fluctuations in distortion during scaling, facilitating high magnification ratios. In addition, the effective diameter of the lens group that moves at the time of variable magnification can be reduced.

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 reimaged 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 variable magnification optical system as the reimaging optical system, it is possible to reduce the diameter of the lens group that moves during the magnification change, and it is possible to realize weight reduction and speeding up of the magnification change operation.

The first optical system U1 may be configured to include a field lens group Gfd which is a lens component closest to the intermediate image. The "intermediate image" of "closest to the intermediate image" here is an intermediate image when the object is in focus at infinity. Further, "the field lens group Gfd closest to the intermediate image" includes the 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 composed of two or less lenses and having a positive refractive power. By arranging the positive refractive power in the vicinity of the intermediate image, light rays with a peripheral angle of view can intersect the optical axis Z inside the variable magnification optical system, so that the increase in the effective diameter of the variable magnification optical system is suppressed. can do. As an example, the field lens group Gfd in the example of FIG. 1 is composed of a set of bonded lenses formed by joining a negative lens Lf1 and a positive lens Lf2 in order from the object side, and the lens Lf1 has a concave surface on the object side. The lens Lf2 has a convex surface facing the image side, and the joint surface between the lens Lf1 and the lens Lf2 has a convex surface facing the object side.

Further, the first optical system U1 may be configured to include a correction lens group Gc having an aberration correction action. 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 using two or less, the load on the object-side portion of the variable magnification optical system can be suppressed to a small value, and the strength required for the gantry for installing the variable magnification optical system can be reduced. In order to reduce the number of optical elements used and improve the manufacturability, it is preferable that the correction lens group Gc is composed of one lens. The correction lens group Gc in the example of FIG. 1 comprises only one lens Lc1. As an example, the lens Lc1 in FIG. 1 is a meniscus lens with a convex surface facing the object side. The correction lens group Gc may be configured to be composed of two lenses, and in such a case, astigmatism can be satisfactorily corrected. For example, the correction lens group Gc can be configured to consist of two meniscus-shaped single lenses having a convex surface facing the object side.

It is preferable that the correction lens group Gc is 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 rays are corrected lens group Gc twice, when the light reflected by the first mirror M1 is directed to the second mirror M2 and when the light reflected by the second mirror M2 is directed to the position P of the intermediate image. It is preferable that it is configured to pass through. By arranging the correction lens group Gc in the optical path in which the light beam reciprocates in this way, it becomes easy to satisfactorily correct spherical aberration even if the number of optical elements such as lenses and mirrors is reduced, and further, optics. Even when the number of elements is reduced and neither the first mirror M1 nor the second mirror M2 uses an aspherical surface, it becomes easy to satisfactorily correct spherical aberration.

It is preferable that the optical elements having power included in the first optical system U1 are 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 the first mirror M1, the second mirror M2, the field lens group Gfd, and the correction lens group Gc as the 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 that does not consider the optical path, the second mirror M2 is located 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 located closer to the image side than the correction lens group Gc. The field lens group Gfd is arranged 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 near 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 passes through the correction lens group Gc. Then, it is reflected by the second mirror M2 and heads toward the image side, passes through the correction lens group Gc again, then passes through the field lens group Gfd, and is incident on the second optical system U2.

In the second optical system U2 of the example of FIG. 1, the first lens group G1, the second lens group G2, the third lens group G3, and the second lens group G1 are sequentially arranged from the object side to the image side along the optical axis Z. It consists of four lens groups G4. In the example of FIG. 1, the first lens group G1 is composed of three lenses of lenses L11 to L13, the second lens group G2 is composed of one lens of lens L21, and the third lens group G3 is composed of lenses L31 to L31. It is composed of four lenses of the lens L34, and the fourth lens group G4 is composed of one lens of the lens L41. 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 magnification change, the first lens group G1, the second lens group G2, and the third lens group G3 move while changing the distance between the adjacent lens groups in the optical axis direction. The fourth lens group G4 is fixed to the image plane Sim. That is, at the time of scaling, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction on different trajectories. In FIG. 1, 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 when scaling from the wide-angle end to the telephoto end. The movement locus 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 at the time of magnification change, such as the fourth lens group G4, the movement locus is indicated by a linear arrow in the vertical direction.

The lens on the most object side of 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 off-axis luminous flux with respect to the optical axis Z can be reduced, and the fluctuation of the effective diameter of the lenses included in the first lens group G1 and the second lens group G2 at the time of scaling can be reduced. Can be made smaller.

It is preferable that the lens on the most image side of the first lens group G1 and the lens on the most object side of the second lens group G2 both have a positive refractive power and have convex surfaces facing each other. In this case, fluctuations in spherical aberration during scaling can be suppressed.

It is preferable that the second optical system U2 includes at least one lens group on the image side of the second lens group G2, and the lens group on the most image side of the second optical system U2 has a positive refractive power. In this case, it is advantageous to correct the chromatic aberration of magnification. The lens group on the most image side of the second optical system U2 may be configured to be one single lens, and in this case, the amount of movement of the first lens group G1 and the second lens group G2 may be increased. It can be secured, and it is advantageous to realize a high magnification ratio while suppressing fluctuations in various aberrations.

For example, as in the example shown in FIG. 1, the second optical system U2 has a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in order from the object side. It consists of a third lens group G3 having a refractive power of 1 and a fourth lens group G4 having a positive refractive power, and at the time of magnification change, the first lens group G1, the second lens group G2, and the third lens group G3. The fourth lens group G4 can be configured to be fixed to the image plane Sim by moving in the optical axis direction with different trajectories. In this case, the fluctuation of astigmatism at the time of scaling can be suppressed.

Alternatively, as in Example 7 described later, the second optical system U2 has a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in this order from the object side. The first lens group G1 and the second lens group G2 move in the optical axis direction in different trajectories at the time of scaling, and the third lens group G3 is an image. It may be configured to be fixed to the surface Sim. In this case, since all the lens groups constituting the second optical system U2 have a positive refractive power, an image due to eccentricity and / or tilting between the lens groups is suppressed while suppressing fluctuations in spherical aberration during scaling. It is possible to suppress the deterioration of.

Alternatively, as in Example 9 described later, in the second optical system U2, the first lens group G1 having a positive refractive power and the second lens group G2 having a positive refractive power are positive in order from the object side. It is composed of a third lens group G3 having an optical power of, and at the time of magnification change, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction in different trajectories. It may be configured as. In this case, all the lens groups constituting the second optical system U2 have a positive refractive power, and the degree of freedom of the paraxial solution is increased. Therefore, the fluctuation and variation of the spherical aberration at the time of scaling are increased. It is possible to suppress the deterioration of the image due to the eccentricity and / or tilt of the lens groups while suppressing the fluctuation of the astigmatism at the time of magnification.

Alternatively, as in Example 10 described later, the second optical system U2 is composed of a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in this order from the object side. At the time of scaling, the first lens group G1 and the second lens group G2 may be configured to move in the optical axis direction on different trajectories. In this case, the configuration becomes simple and the scaling mechanism can be simplified.

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

Next, the configuration relating to the conditional expression of the variable magnification optical system of the present embodiment will be described. The average value of the partial dispersion ratio between the g-line and F-line of all positive lenses in the second optical system U2 is θgFp, and the partial dispersion ratio between the g-line and F-line of all negative lenses in the second optical system U2. When the average value of is θgFn, it is preferable that the following conditional expression (1) is satisfied. By satisfying the conditional expression (1), it is possible to suppress the occurrence of secondary axial chromatic aberration and secondary chromatic aberration of magnification in the visible light region. If the configuration satisfies the following conditional expression (1-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (1-2), the characteristics are even better. 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 the d-line reference Abbe numbers of all the positive lenses in the second optical system U2 is νdp, and 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 to satisfy the following conditional expression (2). By keeping the condition below the lower limit of the conditional expression (2), it becomes easy to correct the axial chromatic aberration. The occurrence of secondary chromatic aberration can be suppressed by not exceeding the upper limit of the conditional expression (2). If the configuration satisfies the following conditional expression (2-1), better characteristics can be obtained.
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 of is θCtn, it is preferable that the following conditional expression (3) is satisfied. By satisfying the conditional expression (3), it is possible to suppress the occurrence of secondary chromatic aberration in the wavelength range from red to infrared. If the configuration satisfies the following conditional expression (3-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (3-2), even better characteristics can be obtained. 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 sure that the value does not fall below the lower limit of the conditional expression (4), 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 not exceeding the upper limit of the conditional expression (4), it becomes easy to correct the secondary chromatic aberration in the wavelength range from red to infrared. If the configuration satisfies the following conditional expression (4-1), better characteristics can be obtained.
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 making sure that the value does not fall below the lower limit of the conditional expression (5), it becomes easy to correct the secondary chromatic aberration in the wavelength range from red to infrared. By not exceeding the upper limit of the conditional expression (5), 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. If the configuration satisfies the following conditional expression (5-1), better characteristics can be obtained.
0.75 <θCtp <0.9 (5)
0.78 <θCtp <0.85 (5-1)

When the average value of the Abbe numbers with respect to the d-line 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 sure that the value does not fall below the lower limit of the 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 it becomes easy to correct the secondary chromatic aberration in the visible light region. By not exceeding the upper limit of the conditional expression (6), 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. If the configuration satisfies the following conditional expression (6-1), better characteristics can be obtained.
50 <νdn <65 (6)
52 <νdn <60 (6-1)

When the average value of the refractive indexes of all the negative lenses in the second optical system U2 with respect to the d line is Ndn, it is preferable that the following conditional expression (7) is satisfied. By making sure that the value does not fall below the lower limit of the conditional expression (7), it is possible to suppress the occurrence of higher-order spherical aberration, and it becomes easier to select a material having a small Abbe number, which is advantageous for correcting primary chromatic aberration. .. By not exceeding the upper limit of the conditional expression (7), the absolute value of the Petzval sum can be suppressed to a small value, and the curvature of field can be satisfactorily corrected. If the configuration satisfies the following conditional expression (7-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (7-2), even better characteristics can be obtained. 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 sure that the value does not fall below the lower limit of the 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 the primary chromatic aberration. By not exceeding the upper limit of the conditional expression (8), it becomes easy to correct the secondary chromatic aberration in the visible light region. If the configuration satisfies the following conditional expression (8-1), better characteristics can be obtained.
0.53 <θgFn <0.58 (8)
0.535 <θgFn <0.565 (8-1)

When the average value of the partial dispersion ratio 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 making sure that the value does not fall below the lower limit of the conditional expression (9), it becomes easy to correct the secondary chromatic aberration in the visible light region. By not exceeding the upper limit of the conditional expression (9), 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. If the configuration satisfies the following conditional expression (9-1), better characteristics can be obtained.
0.5 <θgFp <0.65 (9)
0.52 <θgFp <0.6 (9-1)

When the average value of the Abbe numbers with respect to the d-line 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 the condition not less than the lower limit of the 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 not exceeding the upper limit of the 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 it becomes easy to correct the secondary chromatic aberration in the visible light region. If the configuration satisfies the following conditional expression (10-1), better characteristics can be obtained.
70 <νdp <100 (10)
72 <νdp <90 (10-1)

When the average value of the refractive indexes 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 sure that the value does not fall below the lower limit of the conditional expression (11), the absolute value of the Petzval sum can be suppressed to a small value while suppressing the occurrence of spherical aberration, and the curvature of field can be satisfactorily corrected. By not exceeding the upper limit of the conditional expression (11), it becomes easy to select a material having a large Abbe number, which is advantageous for correcting the primary chromatic aberration. If the configuration satisfies the following conditional expression (11-1), better characteristics can be obtained.
1.43 <Npd <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 sure that the ratio does not fall below the lower limit of the conditional expression (12), a high magnification ratio can be realized even if the amount of movement of the first lens group G1 at the time of scaling is reduced. By not exceeding the upper limit of the conditional expression (12), fluctuations in spherical aberration during scaling can be suppressed. If the configuration satisfies the following conditional expression (12-1), better characteristics can be obtained.
0.2 <fU2 / fG1 <0.45 (12)
0.22 <fU2 / fG1 <0.4 (12-1)

When the radius of curvature of the reflecting surface of the first mirror is rM1 and the radius of curvature of the reflecting surface of the second mirror is rM2, it is preferable that the following conditional expression (13) is satisfied. It is advantageous to shorten the total length by not falling below the lower limit of the conditional expression (13). The occurrence of astigmatism can be suppressed by not exceeding the upper limit of the conditional expression (13). If the configuration satisfies the following conditional expression (13-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (13-2), even better characteristics can be obtained. 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 value does not fall below the lower limit of the conditional expression (14), it is advantageous for correcting spherical aberration. By not exceeding the upper limit of the conditional expression (14), axial chromatic aberration can be suppressed, and the occurrence of a difference in spherical aberration depending on the wavelength can be suppressed. If the configuration satisfies the following conditional expression (14-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (14-2), even better characteristics can be obtained. 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 when the object is in focus at infinity is βrT and the magnification ratio of the variable magnification optical system is MAG, it is preferable to satisfy the following conditional expression (15). By making sure that the value does not fall below the lower limit of the conditional expression (15), fluctuations in spherical aberration during scaling can be suppressed. By not exceeding the upper limit of the conditional expression (15), a high magnification ratio can be realized even if the amount of movement of the lens group that moves at the time of scaling is reduced. If the configuration satisfies the following conditional expression (15-1), better characteristics can be obtained.
-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 when focusing on an infinity object to the lens surface of the second lens group G2 on the most object side at the wide-angle end is LA, the following It is preferable that the conditional expression (16) is satisfied. By satisfying the conditional expression (16), the off-axis light beam can be intersected with the optical axis Z at an appropriate position, which is advantageous for reducing the diameter of the lens group that moves at the time of scaling. If the configuration satisfies the following conditional expression (16-1), better characteristics can be obtained, and if the configuration satisfies the following conditional expression (16-2), even better characteristics can be obtained. 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 the conditional equation (17), the refractive power can be appropriately distributed to the first lens group G1 and the second lens group G2, and thus the fluctuation of the spherical aberration at the time of magnification change can be suppressed. Further, the effective diameters of the first lens group G1 and the second lens group G2 can be reduced. If the configuration satisfies the following conditional expression (17-1), better characteristics can be obtained.
1.5 <fG1 / fG2 <4 (17)
1.7 <fG1 / fG2 <3.8 (17-1)

Although not shown in FIG. 1, various parallel plate-shaped filters and / or cover glasses are arranged between the lens on the most image side and the image plane Sim, and / or between the optical elements and the optical elements. You may. The change in aberration due to the placement of various filters and / or cover glass can be corrected to the extent that it does not pose a practical problem by changing a small number of design parameters.

Any combination of the above-mentioned preferable configurations and possible configurations is possible, and it is preferable that they are appropriately selectively adopted according to the required specifications. According to the present embodiment, the load on the part on the object side can be reduced, the configuration can be performed at low cost, and a variable magnification optical system having good optical performance while achieving a high magnification ratio is realized. It is possible. The term "high scaling ratio" as used herein means that the scaling 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 the optical path of the variable magnification optical system of the first embodiment are shown in FIG. 1, and the configuration and the method of drawing the same are as described above. The variable magnification optical system of the first embodiment includes a first optical system U1 and a second optical system U2 in this order from the object side to the image side. The first optical system U1 is fixed to the image plane Sim at the time of scaling. The second optical system U2 includes a plurality of lens groups that move at the time of magnification change. 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 of the 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. An intermediate image is formed near the object side of the field lens group Gfd in the state of being in focus on the infinity object. 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. The light beam from the object passes 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 enters the second optical system U2. The second optical system U2 includes 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 in order from the object side. , A fourth lens group G4 having a positive refractive power. At the time of scaling, the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction on different trajectories, and the fourth lens group G4 is fixed with respect to the image plane Sim. ing. The first lens group G1 is composed of three lenses, a lens L11 to a lens L13. The second lens group G2 is composed of one lens of the lens L21. The third lens group G3 is composed of four lenses, a lens L31 to a lens L34. The fourth lens group G4 is composed of one lens of the lens L41. The third lens group G3 has a bonded lens in which a positive lens and a negative lens are joined. 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 variable surface spacing, and Table 3 shows the aspherical coefficient. Tables 1 and 2 are data in a state of being in focus on an infinity object. Table 1 shows the components along the optical path. In Table 1, the surface number column indicates the surface number when the surface closest to the object on the optical path is the first surface and the number is increased one by one toward the image side along the optical path. The column shows the radius of curvature of each surface, and the column d shows the surface distance 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 name of the manufacturing company is shown roughly. For example, "OHARA" refers to OHARA Corporation. The Nd column of 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 based on the d-line, and the θgF column shows the g-line of each component. The partial dispersion ratio between the F lines is shown, and the partial dispersion ratio between the C line and the t line of each component is shown in the column of θCt.

In Table 1, the sign of the radius of curvature of the surface having the convex surface facing the object side is positive, and the sign of the radius of curvature of the surface having the convex surface facing the image side is negative. In the surface number column of Table 1, in addition to each surface number, enter "(reflective surface)" on the surface corresponding to the reflective surface, and enter "(intermediate image)" on the surface corresponding to the intermediate image. Fill in and write "(image plane)" on the plane corresponding to the image plane Sim. Further, in Table 1, the variable surface spacing is entered in the column d with the plane number on the object side of the spacing in "D".

In Table 2, the absolute value, F number, maximum image height, and maximum half angle of view of the entire system are shown in "| Focal length |", "FNo.", "Image height", and "Half angle of view", respectively. It is shown in the line written as. Table 2 shows the values of each variable surface spacing. 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 the columns labeled W, M1, M2, and T, respectively.

In Table 1, the surface numbers of the aspherical surface are marked with *, and the numerical value of the radius of curvature of the paraxial axis is described in the column of the radius of curvature of the aspherical surface. In Table 3, the surface numbers of the aspherical surface are shown, and the numerical values of the aspherical surface coefficients for each aspherical surface are shown in the columns of K and Am (m = 4, 6, 8, 10). The numerical value “E ± n” (n: integer) of the aspherical coefficient in Table 3 means “× 10 ^{± n} ”. K and Am are aspherical coefficients in the aspherical expression represented by the following equation.
Zd = C × h ² / {1 + (1- (1 + K) × C ² × h ² ) ^1/2 } + ΣAm × h ^m
However,
Zd: Aspherical depth (length of a perpendicular line drawn from a point on the aspherical surface at height h to a plane perpendicular to the optical axis where the aspherical apex touches)
h: Height (distance from the optical axis to the lens surface)
C: The reciprocal of the radius of curvature of the paraxial K, Am: the aspherical coefficient, and the aspherical Σ means the sum with respect 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 other suitable optical systems can be used even if they are proportionally expanded or contracted. Units can also be used. In addition, in each table shown below, numerical values rounded to a predetermined digit are listed.

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

Unless otherwise specified, the symbols, meanings, description methods, and illustration methods of the data related to the above-mentioned Example 1 are the same in the following Examples, and thus duplicate description will be omitted below.

[Example 2]
FIG. 2 shows a cross-sectional view and an optical path of the variable magnification optical system of the second embodiment. 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 variable surface spacing, and FIG. 12 shows each aberration diagram.

[Example 3]
A cross-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 of lenses Lc1 to Lc2, and the third lens group G3 is composed of three lenses of lenses L31 to L33. Unlike the first embodiment, other points have the same configuration as the outline of the variable magnification optical system of the first embodiment. Table 6 shows the basic lens data of the variable magnification optical system of Example 3, Table 7 shows the specifications and the variable surface spacing, and FIG. 13 shows each aberration diagram.

[Example 4]
A cross-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 is composed of two lenses, the lens Lc1 and the lens Lc2, and the other points are the outline of the variable magnification optical system of the first embodiment. It has a similar configuration. Table 8 shows the basic lens data of the variable magnification optical system of Example 4, Table 9 shows the specifications and the variable surface spacing, and FIG. 14 shows each aberration diagram.

[Example 5]
FIG. 5 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 5. The variable magnification optical system of the fifth embodiment is different from the first embodiment in that the correction lens group Gc is composed of two lenses, the lens Lc1 and the lens Lc2, and the other points are the outline of the variable magnification optical system of the first embodiment. It has a similar configuration. The basic lens data of the variable magnification optical system of Example 5 is shown in Table 10, the specifications and variable surface spacing are shown in Table 11, and each aberration diagram is shown in FIG.

[Example 6]
FIG. 6 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 6. 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, the lens Lc1 and the lens Lc2, and the other points are the outline of the variable magnification optical system of the first embodiment. It has a similar configuration. The basic lens data of the variable magnification optical system of Example 6 is shown in Table 12, the specifications and variable surface spacing are shown in Table 13, and each aberration diagram is shown in FIG.

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

The basic lens data of the variable magnification optical system of Example 7 is shown in Table 14, the specifications and variable surface spacing are shown in Table 15, and each aberration diagram is shown in FIG.

[Example 8]
FIG. 8 shows a cross-sectional view and an optical path of the variable magnification optical system of Example 8. The variable magnification optical system of Example 8 has the same configuration as the outline of the variable magnification optical system of Example 7. The basic lens data of the variable magnification optical system of Example 8 is shown in Table 16, the specifications and variable surface spacing are shown in Table 17, and each aberration diagram is shown in FIG.

[Example 9]
A cross-sectional view and an optical path of the variable magnification optical system of Example 9 are shown in FIG. In the variable magnification optical system of Example 9, the point that the first lens group G1, the second lens group G2, and the third lens group G3 move in the optical axis direction on different trajectories at the time of magnification change is that in Example 7. However, other points have the same configuration as 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 variable surface spacing, and FIG. 19 shows each aberration diagram.

[Example 10]
A cross-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 the tenth embodiment has a configuration of the second optical system U2 different from that of the seventh embodiment, and the first optical system U1 has the same configuration as the outline of the variable magnification optical system of the seventh embodiment. The second optical system U2 of the tenth embodiment is composed of a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power in this order from the object side. The lens group G1 and the second lens group G2 move in the optical axis direction on different trajectories. The first lens group G1 is composed of 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 bonded lenses in which a positive lens and a negative lens are joined. Table 20 shows the basic lens data of the variable magnification optical system of Example 10, Table 21 shows the specifications and the variable surface spacing, Table 22 shows the aspherical coefficient, and FIG. 20 shows each aberration diagram.

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

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

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

The image pickup apparatus 10 includes a variable magnification optical system 1, a filter 4 arranged on the image side of the variable magnification optical system 1, an image pickup element 5 for capturing an image of a subject imaged by the variable magnification optical system 1, and an image pickup system. A signal processing unit 6 for arithmetically processing an output signal from the element 5 and a scaling control unit 7 for performing scaling of the scaling optical system 1 are provided. Note that 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 electric signal. The image pickup surface of the image pickup device 5 is arranged so as to coincide with the image plane of the variable magnification optical system 1. As the image sensor 5, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) or the like can be used. Although only one image sensor 5 is shown in FIG. 21, the image sensor of the present invention is not limited to this, and may be a so-called three-plate image sensor having three image sensors.

Although the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, the interplanar 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.

1 Variable magnification optical system 4 Filter 5 Imaging element 6 Signal processing unit 7 Variable magnification control unit 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 Movement trajectory of the first lens group trG2 Second lens Group movement trajectory trG3 Movement trajectory of the third lens group trG4 Movement trajectory of the fourth lens group 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 with each reflecting surface facing each other and fixed to the image plane at the time of scaling, and a second optical system including a plurality of lens groups moving at the time of scaling. Consists of an optical system
The two reflectors
A first reflector which is an optical element having power located on the object side most on the optical path, has a reflecting surface having a concave surface facing the object side, and reflects light rays from the object toward the object side.
It consists of a second reflector that has a reflecting surface with a convex surface facing the image side and reflects the reflected light from the first reflecting mirror toward the image side.
The second optical system is continuous in order from the object side.
The first lens group that always moves to the object side and has a positive refractive power when scaling from the wide-angle end to the telephoto end,
It includes a second lens group having a positive refractive power that moves in the optical axis direction with a trajectory different from that of the first lens group at the time of scaling.
A variable magnification optical system in which an intermediate image is formed between the second reflecting mirror and the first lens group, and the intermediate image is reimaged via the second optical system. The variable magnification optical system 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 is composed of two or less lenses. The first optical system is
It is arranged in the optical path from the first reflector to the second reflector and in the optical path from the second reflector to the position of the intermediate image, and the first reflector and the second reflector. The variable magnification optical system according to claim 1 or 2, which includes a correction lens group including two or less lenses having an optical axis common to that of the retroreflector. The variable magnification optical system according to any one of claims 1 to 3, wherein the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror have a spherical shape. The first optical system is
A group of field lenses consisting of two or less lenses and having a positive refractive power, which is a lens component closest to the intermediate image,
It is arranged in the optical path from the first reflector to the second reflector and in the optical path from the second reflector to the position of the intermediate image, and the first reflector and the second reflector. Including a correction lens group consisting of two or less lenses having a common optical axis with the retroreflector of
Any of claims 1 to 4, wherein the optical element having power included in the first optical system is only the first reflector, the second reflector, the field lens group, and the correction lens group. The variable magnification optical system according to item 1. Any of claims 1 to 5, wherein the lens on the most image side of the first lens group and the lens on the most object side of the second lens group both have a positive refractive power and have convex surfaces facing each other. The variable magnification optical system according to item 1. The variable magnification optical system according to any one of claims 1 to 6, wherein the lens on the most object side of the first lens group has a negative refractive power and has a concave surface facing the object side. The second optical system includes at least one lens group on the image side of the second lens group.
The variable magnification optical system according to any one of claims 1 to 7, wherein the lens group on the most image side of the second optical system has a positive refractive power. The variable magnification optical system according to claim 8, wherein the lens group on the most image side of the second optical system is a single single lens. The radius of curvature of the reflecting surface of the first reflecting mirror is rM1,
When the radius of curvature of the reflecting surface of the second reflecting mirror is rM2,
1 <rM1 / rM2 <2.5 (13)
The variable magnification optical system according to any one of claims 1 to 9, which satisfies the conditional expression (13) represented by. The first optical system is
It is arranged in the optical path from the first reflector to the second reflector and in the optical path from the second reflector to the position of the intermediate image, and the first reflector and the second reflector. Includes a correction lens group consisting of two or less lenses that share the same optical axis as the retroreflector of
The radius of curvature of the reflecting surface of the first reflecting mirror is rM1,
When the focal length of the correction lens group is fC,
0.07 <rM1 / fC <0.5 (14)
The variable magnification optical system according to any one of claims 1 to 10, which satisfies the conditional expression (14) represented by. The lateral magnification of the second optical system at the telephoto end when the object is in focus at infinity is βrT,
When the magnification ratio of the variable magnification optical system is MAG,
-0.45 <βrT / MAG <-0.25 (15)
The variable magnification optical system according to any one of claims 1 to 11, which satisfies the conditional expression (15) represented by. The first optical system includes a field lens group consisting of two or less lenses and having a positive refractive power, which is a lens component closest to the intermediate image.
The focal length of the field lens group is fFd,
When the distance on the optical axis from the intermediate image when focusing on an infinity object to the lens surface on the most object side of the second lens group at the wide-angle end is set to LA.
0.4 <fFd / LA <1 (16)
The variable magnification optical system according to any one of claims 1 to 12, which satisfies the conditional expression (16) represented by. The focal length of the first lens group is fG1,
When the focal length of the second lens group is fG2,
1.5 <fG1 / fG2 <4 (17)
The variable magnification optical system according to any one of claims 1 to 13, which satisfies the conditional expression (17) represented by. 1.2 <rM1 / rM2 <2.2 (13-1)
The variable magnification optical system according to claim 10, which satisfies the conditional expression (13-1) represented by. 0.1 <rM1 / fC <0.45 (14-1)
The variable magnification optical system according to claim 11, which satisfies the conditional expression (14-1) represented by. -0.4 <βrT / MAG <-0.28 (15-1)
The variable magnification optical system according to claim 12, which satisfies the conditional expression (15-1) represented by. 0.5 <fFd / LA <0.8 (16-1)
The variable magnification optical system according to claim 13, which satisfies the conditional expression (16-1) represented by. 1.7 <fG1 / fG2 <3.8 (17-1)
The variable magnification optical system according to claim 14, which satisfies the conditional expression (17-1) represented by. An imaging device including the variable magnification optical system according to any one of claims 1 to 19.