JP2010249877A - Variable power telephoto optical system and optical device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable power telephoto optical system which has a simply constituted variable-power driving mechanism, and the entire length of which is small, and capable of suppressing defocusing to the minimum even when varying the power under the temperature fluctuating environment, and to provide an optical device equipped with the variable power telephoto optical system. <P>SOLUTION: The variable power telephoto optical system includes a diffraction optical system G1 that includes a diffraction surface having a first optical axis; a reflection optical system G2, including a reflection surface having a second optical axis arranged in parallel to the first optical axis; a return mirror M1, arranged behind the diffraction optical system G1, for bending the first optical axis toward the second optical axis; an optical path switching mirror M2, arranged behind the reflection optical system G2, and on an intersection P between the bent optical axis and the other optical axis, capable of selectively obtaining a first state, where only the light coming from the diffraction optical system G1 is turned toward the rear optical path and a second state, where only the light coming from the reflection optical system G2 is turned to the rear optical path. Lenses constituting the diffraction optical system G1 and the reflection optical system G2 are constituted of glass materials, where the temperature dependence coefficient of the refractive index dn/dT is positive. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a variable magnification telephoto optical system and an optical apparatus including the same.

  In recent years, telephoto optical systems used for digital cameras, television cameras, and the like have been desired to have a simple zooming mechanism, a short overall length, and good imaging performance in a wide wavelength range.

  For example, by adopting a lens optical path switching method (see, for example, Patent Document 1) as a lens magnification changing method, the lens can be changed with a simple configuration in which one optical element constituting an optical system such as a mirror is moved. Since the magnification can be switched and it is not necessary to extend the optical system for zooming, the total length of the optical system can be shortened.

  However, if the technique of Patent Document 1 is applied as it is while increasing the focal length, the following problem has occurred. First, since a lens having a long focal length is used, there is a possibility that color blur due to chromatic aberration of the lens may appear in a captured image. Further, as the optical system becomes longer in focal length, the entire length of the optical system may become longer (even if the above zooming method is adopted).

  In order to deal with such problems, there is a method of using a reflection optical system. The reflective optical system has the advantages that, in principle, chromatic aberration does not occur, and a long focal length can be easily obtained while downsizing the entire optical system. However, it is difficult to increase the shooting angle of view, and since the light beam is used in a reciprocating manner, the light beam near the optical axis is vignetted and the substantial brightness of the entire optical system is lowered. is there.

  Therefore, it is conceivable to adopt a refractive optical system as the telephoto optical system and a reflective optical system as the supertelephoto optical system having a longer focal length while adopting the lens optical path switching method.

JP-A-4-3967

  In order to remove chromatic aberration that occurs in a wide wavelength range, the lens constituting the telephoto optical system as described above is made of a convex lens and a glass material having anomalous dispersion such as meteorite or ED (Extra-low Dispersion) glass. Often used. However, a glass material having anomalous dispersion often has a negative temperature dependency coefficient dn / dT of a refractive index, and its absolute value is larger than that of other general glass materials. Therefore, a convex lens using such a glass material has a function of greatly increasing the focal length when the temperature rises.

  In contrast, a general glass material having no anomalous dispersion often has a positive temperature dependence coefficient dn / dT of refractive index. However, since such a glass material is often used for a concave lens in the telephoto optical system as described above, it has a function of increasing the focal length of the telephoto optical system when the temperature rises as in the previous case.

  Therefore, in the conventional telephoto optical system, both the convex lens and the concave lens contribute to the increase of the focal length when the temperature fluctuates, resulting in a large focal length variation. For this reason, when switching between the super-telephoto of the reflection system and the telephoto of the refraction system, there is a possibility that a large defocus (focus shift) may occur.

  The present invention has been made in view of such problems. The drive mechanism for zooming is simple, the overall length of the optical system is short, and the defocus that occurs even when zooming is varied is minimized. An object of the present invention is to provide a variable magnification telephoto optical system and an optical apparatus including the same.

  In order to achieve such an object, according to a first aspect illustrating the present invention, a diffractive optical system including a diffractive surface having a first optical axis, and the first optical axis are arranged in parallel. A reflection optical system including a reflection surface having a second optical axis, and a diffractive optical system or a rear of the reflection optical system, and the first optical axis or the second optical axis is used as the other light. A reflecting member that bends toward the axis, and is disposed on the intersection of the bent optical axis and the other optical axis behind the diffractive optical system or the reflective optical system; An optical path conversion member capable of selectively taking a first state in which only light is directed toward the rear optical path and a second state in which only light from the reflection optical system is directed toward the rear optical path; In addition, the temperature dependence coefficient dn / dT of the refractive index is positive in the lenses constituting the reflective optical system. Zoom telephoto optical system which is characterized by using a glass material is provided.

  According to a second aspect illustrating the present invention, there is provided an optical apparatus comprising the variable magnification telephoto optical system according to the first aspect.

  According to the zoom-type telephoto optical system and the optical apparatus including the same according to the present invention, the drive mechanism for zooming is simple, the total length of the optical system is short, and defocusing that occurs even when zooming is performed during temperature fluctuations. It can be minimized.

It is a figure which shows schematically the structure of the variable magnification telephoto optical system which concerns on this embodiment. It is a figure which shows the shape of the diffractive optical element which comprises a diffractive optical system. It is a figure which shows the vertical spherical aberration and axial chromatic aberration of a diffractive optical system. It is a figure which shows roughly the structure of the telephoto optical system for a comparison. It is a figure which shows the vertical spherical aberration and axial chromatic aberration of the telephoto optical system for a comparison. It is a figure which shows the vertical spherical aberration and axial chromatic aberration of a reflective optical system. It is a figure which shows schematically the structure of an optical apparatus (camera) provided with the said variable magnification type telephoto optical system. It is a figure which shows schematically the other structure of the variable magnification telephoto optical system which concerns on this embodiment. It is the zoom schematic when using a diffractive optical system. It is the zoom schematic when using a reflective optical system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The optical path will be described with the optical axis as a representative. FIG. 1 is a diagram schematically showing a configuration of a variable magnification telephoto optical system according to the present embodiment. As shown in FIG. 1, the variable magnification telephoto optical system according to the present embodiment includes a diffractive optical system G1 that is a telephoto optical system having a different focal length, and a reflective optical system G2 that is a supertelephoto optical system. Are arranged in parallel so that their optical axes are substantially parallel, and the two optical paths are switched and used to perform zooming.

  A folding mirror M1 and an optical path switching mirror M2 are provided between the diffractive optical system G1 and the reflective optical system G2.

  The folding mirror M1 is disposed behind the diffractive optical system G1, and in order to bend the optical path A that has passed through the diffractive optical system G1 toward the optical axis of the reflective optical system G2, the reflecting surface is directed toward the reflective optical system G2. Is inclined.

  The optical path switching mirror M2 is disposed behind the reflective optical system G2, specifically, the optical path A ′ and the optical system G2 in order to match the optical path A ′ bent by the folding mirror M1 with the optical axis of the reflective optical system G2. On the intersection P with the optical path B that has passed, the reflecting surface is provided so as to face the reflecting surface of the folding mirror M1. The optical path switching mirror M2 is movable in the vertical direction along the optical path A ′ by the mirror driving device M2m, and is in a first state in which only the light from the diffractive optical system G1 is directed to the rear optical path (in FIG. 1). A position indicated by a solid line) and a second state (a position indicated by a dotted line in FIG. 1) in which only the light from the reflective optical system G2 is directed to the rear optical path can be taken selectively.

  Therefore, in the telephoto optical system according to the present embodiment, as shown by the solid line in FIG. 1, when the optical path switching mirror M2 is in the optical path of the reflective optical system G2, the imaging light beam obtained by the diffractive optical system G1 is folded back. Reflected by the mirror M1, passes through the optical path A ′, reflected by the optical path switching mirror M2, and forms an object image on an image plane I provided on the extension of the optical path B behind the mirror M2. At this time, the image obtained by the reflection optical system G2 is blocked by the optical path switching mirror M2, and cannot be guided to the image plane I.

  In addition, as shown by the dotted line in FIG. 1, when the mirror driving device M2m is driven to move the optical path switching mirror M2 and exit out of the optical path B of the reflective optical system G2, it passes through the reflective optical system G2. The light beam forms an object image on the image plane I as in the diffractive optical system G1. At this time, the image obtained by the diffractive optical system G1 is blocked by the optical path switching mirror M2, and cannot be guided to the image plane I.

  As described above, in this embodiment, zooming can be switched with a simple configuration in which the optical path switching mirror M2, which is one of the optical elements constituting the present optical system, is moved in the vertical direction along the optical path A ′. .

  The diffractive optical system G1 will be described. The diffractive optical system G1 according to this embodiment includes a diffractive optical element D1, a positive lens L1, a negative lens L2, a folding mirror M1, a correction lens L3, and an optical path switching mirror M2 arranged in order from the object side. It has a long focal length and a telephoto imaging function.

  The diffractive optical element D1 uses a parallel plate made of an ultraviolet curable resin as a substrate material, and a diffraction surface (corresponding to surface number 1 in Table 1 described later) is formed on the image side surface.

In general, the phase function φ of the diffractive optical element is expressed by the following equation (1), where r is the height from the optical axis, λ is the wavelength, and the coefficients are C _{2 to} C ₁₀ .

φ (r) = (2π / λ) · (C ₂ r ² + C ₄ r ⁴ + C ₆ r ⁶ + C ₈ r ⁸ + C ₁₀ r ¹⁰ ) (1)

In the present embodiment, since C _{4 to} C ₁₀ in the expression (1) are all 0, the following expression (2) is established when the focal length of the diffractive optical element D1 is f _D.

φ (r) = (2π / λ) · C 2 · r 2 = (2π / λ) · {-1 / (2f D)} · r 2 ... (2)

When the diffractive optical element D1 is in a state where the environmental temperature is 20 ° C., C ₂ = −1.2389 × 10 ⁻⁵ [mm ⁻¹ ], and therefore, f _D = 40356.8282 [mm] from Expression (2).

Subsequently, the shape of the diffractive optical element D1 is shown in FIG. In the diffractive optical element D1, the radius r _m of the m-th annular zone is set such that the wavelength λ _d of the d-line is 587.6 [nm] as a reference wavelength, and the focal length f _D of the diffractive optical element D1 is 40356.8282 [mm] (ambient temperature) (When 20 degrees), it is expressed by the following equation (3).

r _m = (2 m · λ _d · f _D ) ^(1/2) (3)

In the diffractive optical element D1, the height h of the serrated annular zone is expressed by the following equation (4) using the reference wavelength λ _d and the refractive index n of the substrate material of the diffractive optical element D1.

h = λ _d / (n−1) (4)

In this embodiment, when the reference wavelength λ _d is 587.6 [nm] and the refractive index n of the ultraviolet curable resin that is the substrate material of the diffractive optical element D1 is 1.500000, the height h of the serrated ring zone is 1.2 [μm].

  In the present embodiment, the positive lens L1, the negative lens L2, and the correction lens L3 are all made of a glass material having a positive temperature dependence coefficient dn / dT of the refractive index (see Table 3 described later).

  According to the above configuration, the diffractive optical system G1 uses normal optical glass that easily generates chromatic aberration in the positive lens L1, the negative lens L2, and the correction lens L3. However, due to the wavelength dispersion effect of the diffractive optical element D1, As shown in FIG. 3, axial chromatic aberration can be satisfactorily suppressed.

  Table 1 shows optical system data when the diffractive optical system G1 is in an ambient temperature state of 20 ° C., and Table 2 shows optical system data when it is in an environmental temperature state of 40 ° C. In Table 2, the changed numerical values are marked with an asterisk (*) as compared with the case where the environmental temperature in Table 1 is 20 ° C.

  In [Overall specifications] in the table, f represents the focal length of the entire system, F represents the F value, and ω represents the angle of view. In [Lens Data], the surface number is the order of the lens surfaces from the object side along the direction in which the light beam travels, r is the radius of curvature [unit mm] of each lens surface, and d is from The surface interval [unit mm], which is the distance on the optical axis to the optical surface (or image surface), nd indicates the refractive index and glass material name for the d-line (wavelength 587.6 nm). In addition, the description of the refractive index “1.000000” of air is omitted (the description of the table is the same for Table 4, Table 5, Table 7, and Table 8).

(Table 1)
When the diffractive optical system G1 is in an ambient temperature of 20 ° C. [Overall specifications]
f = 749.9981mm, F / 10, ω = 2.17 °
[Lens data]
Surface number r d nd (name of glass material)
1 (entrance pupil plane) ∞ 25.0000 Diffractive optical element D1
2 299.7409 14.0000 1.516330 (S-BSL7) L1
3 -216.6011 11.0000
4 -198.2239 8.0000 1.548141 (S-TIL1) L2
5 3633.9276 440.0000
6 51.4073 10.0000 1.516330 (S-BSL7) L3
7 46.3249 227.3592

(Table 2)
When the diffractive optical system G1 is at an ambient temperature of 40 ° C. [Overall specifications]
f = 749.9769 ^* mm, F / 10, ω = 2.17 °
[Lens data]
Surface number r d nd (name of glass material)
1 (surface entrance pupil) ∞ 24.9980 ^* diffractive optical element D1
2 299.7841 ^* 14.0020 ^* 1.516384 ^* (S-BSL7) L1
3 -216.6323 ^* 10.9986 ^*
4 -198.2580 ^* 8.0014 ^* 1.548177 ^* (S-TIL1) L2
5 3634.5526 ^* 439.9986 ^*
6 51.4147 ^* 10.0014 ^* 1.516384 ^* (S-BSL7) L3
7 46.3316 ^* 227.3555 ^*

  In calculating the optical system data in Tables 1 and 2, the data used (the linear expansion coefficient α of the lenses L1 to L3 and the temperature dependence coefficient dn / dt of the refractive index and the linear expansion coefficient α of the diffractive optical element D1) are used. Table 3 shows. Regarding the change in the air interval, the lens barrel is formed of an extremely low expansion member, and each of the diffractive optical element D1 and the lenses L1 to L3 has a side surface of the image side lens surface, a body surface, and a presser foot. The numerical value was calculated on the assumption that the lens barrel was adhered and held without a ring.

(Table 3)
Glass name Linear expansion coefficient [K ^-1 ] Temperature dependence coefficient dn / dT [K ^-1 ]
S-BSL7 7.2 × 10 ^-6 2.7 × 10 ^-6 L1, L3
S-TIL1 8.6 × 10 ^-6 1.8 × 10 ^-6 L2
UV curable resin 100 × 10 ^-6 − D1 (substrate material)

In calculating the optical system data in Tables 1 and 2, the change in the focal length of the diffractive optical element D1 due to the temperature change is defined as f _D ′, which is the focal length of the diffractive optical element D1 after the temperature change. When the focal length of the diffractive optical element D1 is f _D , the linear expansion coefficient of the material constituting the diffractive optical element D1 is α, and the temperature rise during temperature change is ΔT, the following equation (5) is derived.

f _D ′ = f _D (1 + 2 · α · ΔT) (5)

  When paraxial ray tracing is performed based on the optical system data in Tables 1 and 2, when the environmental temperature is changed from 20 ° C. to 40 ° C. in the diffractive optical system G1, the focal length of the diffractive optical system G1 is shortened by 0.0212 mm. Thus, it can be seen that the paraxial image plane position moves to the object side by 0.0036 mm. Therefore, it can be seen that the diffractive optical system G1 satisfactorily suppresses the occurrence of defocus due to temperature fluctuations.

  For comparison, a telephoto optical system G1 ′ configured using ED glass, in which the temperature dependence coefficient dn / dT of the refractive index is negative, is illustrated. As shown in FIG. 4, the telephoto optical system G1 ′ includes a positive lens La, a negative lens Lb, a positive lens Lc, and a correction lens Ld arranged in order from the object side. Each Lc was configured using an ED lens (S-FPL51) having a negative temperature dependence coefficient dn / dT of the refractive index. With this configuration, the telephoto optical system G1 ′ can suppress axial chromatic aberration as shown in FIG. 5 while having a telephoto imaging function with a long focal length.

  Table 4 shows optical system data when the comparative optical system G1 'is in an environmental temperature of 20 ° C, and Table 5 shows optical system data when the comparative optical system G1' is in an environmental temperature of 40 ° C. Indicates. In Table 5, the changed numerical values are marked with an asterisk (*) compared to the case where the environmental temperature in Table 2 is 20 ° C.

(Table 4)
When optical system G1 ′ including ED glass is in an ambient temperature of 20 ° C. [Overall specifications]
f = 750.0031 ^* mm, F / 10, ω = 2.17 °
[Lens data]
Surface number r d nd
1 (Pupil plane) 476.2539 14.0000 1.496999 (S-FPL51) La
2 -156.9465 7.0000
3 -145.6730 7.0000 1.516330 (S-BSL7) Lb
4 206.4596 5.0000
5 186.2614 12.0000 1.496999 (S-FPL51) Lc
6 -1135.6986 450.0000
7 61.3709 10.0000 1.516330 (S-BSL7) Ld
8 55.5313 233.6649

(Table 5)
When the optical system G1 ′ including ED glass is in an ambient temperature of 40 ° C. [Overall specifications]
f = 752.4021 ^* mm, F / 10, ω = 2.17 °
[Lens data]
Surface number r d nd
1 (entrance pupil plane) 476.3787 ^* 14.0037 ^* 1.496875 ^* (S-FPL51) La
2 -156.9876 ^* 6.9990 ^*
3 -145.6940 ^* 7.0010 ^* 1.516384 ^* (S-BSL7) Lb
4 206.4893 ^* 4.9969 ^*
5 186.3102 ^* 12.0031 ^* 1.496875 ^* (S-FPL51) Lc
6 -1135.9962 ^* 449.9986 ^*
7 61.3797 ^* 10.0014 ^* 1.516384 ^* (S-BSL7) Ld
8 55.5393 ^* 235.5788 ^*

  Table 6 shows data used in calculating the optical system data in Tables 4 and 5 (linear expansion coefficient α of lens La to Ld and temperature dependency coefficient dn / dt of refractive index). Regarding the change in the air interval, the lens barrel is made of an extremely low expansion member, and each of the lenses La to Ld has a lens mirror in a state where the side portion of the image side lens surface has no body surface and presser ring. The numerical value was calculated on the assumption that it was adhered and held on the cylinder.

(Table 6)
Glass name Linear expansion coefficient [K ^-1 ] Temperature dependence coefficient dn / dT [K ^-1 ]
^{S-FPL51 13.1 × 10 -6 -6.2} × 10 -6 La, Lc
S-BSL7 7.2 × 10 ^-6 2.7 × 10 ^-6 Lb, Ld

  When paraxial ray tracing is performed based on the optical system data in Tables 4 and 5, when the environmental temperature is changed from 20 ° C. to 40 ° C. in the comparative optical system G 1 ′, the focal length of the optical system G 1 ′ is 2 .3,990 mm, and the paraxial image plane position moves to the 1.9139 mm image side. Therefore, in the diffractive optical system G1 (see Tables 1 and 2) using a glass material in which the refractive index temperature dependency coefficient dn / dt is positive for the constituent lens, the refractive index temperature dependency coefficient dn / dt is negative for the constituent lens. Compared with the optical system G1 ′ using the glass material (see Tables 4 and 5), it can be clearly seen that the amount of defocus caused by temperature fluctuation is extremely small.

  Next, the reflection optical system G2 will be described. As shown in FIG. 1, the reflection optical system G2 includes a primary mirror M3, a secondary mirror M4, a correction lens L4, and a correction lens L5 arranged in the order of the optical paths, and has a very long focal length and a super telephoto connection. Has an image function. The primary mirror M3 and the secondary mirror M4 are extremely low expansion members, and the correction lenses L4 and L5 are glass materials (see Table 9) having a positive temperature dependence coefficient dn / dT of the refractive index, and the primary mirror M3 and the secondary mirror M4. The lens barrels that hold the correction lenses L8 and L9 are each composed of an extremely low expansion member.

  The total length of the reflective optical system G2 is 725 [mm] from the back surface of the secondary mirror M4 to the image plane, and is suppressed to 1/4 or less with respect to 3000 [mm] which is the focal length of the reflective optical system G2. The reflection optical system G2 is an optical system having a super-telephoto imaging function with a very long focal length as described above, but has a large amount of power for the primary mirror M3 and the secondary mirror M4 to collect the light beam. Therefore, as shown in FIG. 6, chromatic aberration hardly occurs in principle.

  In the reflection optical system G2 having such a configuration, optical system data when the ambient temperature is 20 ° C. is shown in Table 7, and optical system data when the ambient temperature is 40 ° C. is shown in Table 8. In Table 8, the changed numerical values are marked with an asterisk (*) compared to the case where the environmental temperature in Table 7 is 20 ° C. In the table, for the aspheric surface, the height in the direction perpendicular to the optical axis is y, and the distance along the optical axis from the tangential plane at the apex of the aspheric surface to the position on the aspheric surface at the height y (sag When the amount is z, the radius of curvature of the apex curvature reference sphere (paraxial radius of curvature) is r, and the cone coefficient is κ, the shape is expressed by the following equation (6).

z = cy ² / {1+ (1− (κ + 1) c ² y ² ) ^1/2 } (6)

(Table 7)
When the reflective optical system G2 is at an ambient temperature of 20 ° C. [Overall specifications]
f = 3000.5395mm, F / 10, ω = 0.54 °
[Lens data]
Surface number r d Cone coefficient κ nd (glass material name)
1 (entrance pupil plane) -1200.0000 -460.0000 -1.0535 (reflection) M3
2 -350.0000 478.0000 -2.7105 (Reflection) M4
3 192.4278 10.0000 (Spherical surface) 1.581439 (S-TIL25) L4
4 92.0105 2.0000 (spherical surface)
5 105.9285 10.0000 (Spherical surface) 1.882997 (S-LAH58) L5
6 161.4805 199.6938 (Spherical surface)

(Table 8)
When the reflective optical system G2 is at an ambient temperature of 40 ° C. [Overall specifications]
f = 3000.5006 * mm, F / 10, ω = 0.54 °
[Lens data]
Surface number r d Cone coefficient κ nd (glass material name)
1 (entrance pupil plane) -1200.0000 -460.0000 -1.0535 (reflection) M3
2 -350.0000 477.9985 * -2.7105 (Reflection) M4
3 192.4563 * 10.0015 * (Spherical surface) 1.581509 * (S-TIL25) L4
4 92.0241 * 1.9987 * (Spherical surface)
5 105.9425 * 10.0013 * (Spherical surface) 1.883095 * (S-LAH58) L5
6 161.5018 * 199.6913 * (Spherical surface)

  Table 9 shows data used for calculating the optical system data in Tables 7 and 8 (linear expansion coefficient α of lens L4, L5 and temperature dependence coefficient dn / dt of refractive index).

(Table 9)
Glass name Linear expansion coefficient [K ^-1 ] Temperature dependence coefficient dn / dT [K ^-1 ]
S-TIL25 7.4 × 10 ^-6 3.5 × 10 ^-6 L4
S-LAH58 6.6 × 10 ^-6 4.9 × 10 ^-6 L5

  When paraxial ray tracing is performed based on the optical system data in Tables 7 and 8, when the environmental temperature is changed from 20 ° C. to 40 ° C. in the reflective optical system G2, the focal length of the reflective optical system G2 is shortened by 0.0389 mm. Thus, it can be seen that the paraxial image plane position moves to the object side by 0.0025 mm. Therefore, it can be seen that the reflective optical system G2 satisfactorily suppresses the occurrence of defocus due to temperature fluctuations. The reflective optical system G2 (see Tables 7 and 8) is a comparative telephoto optical system G1 ′ (Tables 4 and 5) using a glass material having a negative temperature dependence coefficient dn / dt of the refractive index as a constituent lens. Compared with the reference), it can be seen that the amount of defocus caused by temperature fluctuation is extremely small. In addition, the reflection optical system G2 and the diffractive optical system G1 have substantially the same defocus amount generated when the temperature fluctuates, and even if the optical systems G1 and G2 are switched when the temperature fluctuates, the defocus does not become a problem. it is conceivable that.

  FIG. 7 shows a configuration of a camera CAM as an example of an optical apparatus including the telephoto optical system according to the present embodiment, that is, the diffractive optical system G1 and the reflective optical system G2. The camera CAM drives the mirror driving device M2m to move the switching mirror M2 along the optical path A ′, and the light from the subject (not shown) is condensed by the selected diffractive optical system G1 or the reflective optical system G2. Then, an image is formed on an image pickup device (for example, a CCD or a CMOS) arranged on the image plane I.

  In FIG. 8, the configurations of the diffractive optical system G1 and the reflective optical system G2 are the same as those described above, but the image plane I is an intermediate image plane I ′, and a focusing lens is located behind the intermediate image plane I ′. An example in which a group G3, a variator lens group G4, and a compensator lens group G5 are arranged is shown.

  The focusing lens group G3, variator lens group G4, and compensator lens group G5 constitute a relay system having a zoom function, and the magnification is 0.5 to 2 times. Therefore, in this embodiment, the optical system composed of the diffractive optical system G1 and the lens groups G3, G4, and G5 and the optical system composed of the reflective optical system G2 and the lens groups G3, G4, and G5 each have a zoom ratio of 4 times. The zoom lens that has it will be constructed. Further, since the focal lengths of the diffractive optical system G1 and the reflective optical system G2 are four times different, the focal length can be reduced from 375 mm by combining the zoom of the relay system and the switching of the diffractive optical system G1 and the reflective optical system G2. This also constitutes a variable magnification telephoto optical system that can change 16 times up to 6000 [mm].

  The focusing group G3 is a lens group used for focusing during close-up shooting and is not used for zooming. During zooming, the variator lens group G4 and the compensator lens group G5 are moved along the optical axis as shown in FIGS.

  In this embodiment, the optical axis of the diffractive optical system G1 is made to coincide with the optical axis of the reflective optical system G2 by the folding mirror M1 and the optical path switching mirror M2, so that an intermediate image plane is obtained as shown in FIG. The lens groups G3, G4, G5 behind I ′ can be shared. Therefore, the mechanism becomes simple and the cost of the entire apparatus can be suppressed. The total length of the optical system (that is, from the back surface of the secondary mirror M4 of the reflective optical system G2 to the image plane I) is 2285 mm, which is suppressed to less than half of the maximum focal length of 6000 mm. Further, as described above, the amount of defocus that occurs when the temperature fluctuates is extremely small in both the diffractive optical system G1 and the reflective optical system G2, so that even if the diffractive optical system G1 and the reflective optical system G2 are switched during temperature fluctuation, the defocus amount is reduced. The amount of focus generation is extremely small.

  As described above, according to the zoom-type telephoto optical system and the optical apparatus including the same according to the present embodiment, the drive mechanism for zooming is simple, the total length of the optical system is short, and zooming is performed when temperature changes. However, it is possible to minimize the defocus that occurs.

  In addition, in order to make this invention intelligible, although demonstrated with the component requirement of embodiment, it cannot be overemphasized that this invention is not limited to this.

G1 Diffractive optical system G2 Reflective optical system G3 Focusing lens group G4 Variator lens group G5 Compensator lens group M1 Folding mirror (reflective member)
M2 Optical path switching mirror (optical path conversion member)
M3 primary mirror M4 secondary mirror CAM camera (optical device)
D1 Diffractive optical element L1-L3 Constituent lens of diffractive optical system L4, L5 Lens constituting reflective optical system La-Lb Lens constituting optical system for comparison I Image plane I ′ Intermediate imaging plane

Claims (5)

A diffractive optical system including a diffractive surface having a first optical axis;
A reflective optical system including a reflective surface having a second optical axis arranged in parallel with the first optical axis;
A reflective member disposed behind the diffractive optical system or the reflective optical system and configured to bend the first optical axis or the second optical axis toward the other optical axis;
The first optical system is disposed behind the diffractive optical system or the reflective optical system and on the intersection of the bent optical axis and the other optical axis, and directs only the light from the diffractive optical system to the rear optical path. And an optical path conversion member capable of selectively taking the second state in which only the light from the reflective optical system is directed to the rear optical path,
A variable magnification telephoto optical system, wherein a glass material having a positive temperature dependence coefficient dn / dT of a refractive index is used for the lenses constituting the diffractive optical system and the reflective optical system.   2. The variable magnification telephoto optical system according to claim 1, wherein the diffractive optical system includes at least one positive lens and at least one negative lens.   The zoom lens system according to claim 1 or 2, further comprising a variator lens and a compensator lens on the image side of the optical path conversion member.   The zoom lens system according to any one of claims 1 to 3, further comprising a focusing lens.   An optical apparatus comprising the variable magnification telephoto optical system according to any one of claims 1 to 4.

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