JP2000147373A - Photographing optical system and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a retrofocus photographing lens that transverse chromatic aberration is specially excellently corrected though the viewing angle thereof is wide by providing at least one surface of a photographing optical system with a rotation-symmetric diffraction optical surface with respect to an optical axis. SOLUTION: A first lens group L1 whose refractive power is negative, a (2a)th lens group L2a whose refractive power is positive and a (2b)th lens group L2b whose refractive power is positive are arranged in turn from an object side. Then, a second lens group L2 whose refractive power is positive is constituted of the groups L2a and L2b. Besides, a diaphragm SP is arranged at a conjugate side being shorter than the group L1 whose refractive power is negative and the diffraction optical surface is arranged at the conjugate side being shorter than the diaphragm SP. When height in a vertical direction to the optical axis is defined as (h), the diffracting degree of diffracted light is defined as (m), design wavelength is defined as λ, the phase shape of a diffraction optical element is defined as 4(h and m) and the phase coefficient of (n) order in the case that it is expressed by an expression is defined as Cn, the expression of ψ [(h) and (m)] =(2π/mλ0)(C2h2+C4h4+C6h6...)C2<0 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silver halide photographic camera,
More specifically, the present invention relates to a retro-focus type photographing optical system and a camera having a long back focus and a good imaging performance by combining a refractive optical element and a diffractive optical element. It is about.

[0002]

2. Description of the Related Art Negative first
A retrofocus type optical system having a lens group and a positive second lens group is widely used for a wide-angle lens particularly for a single-lens reflex camera because it is advantageous for reducing the front lens diameter and increasing the back focus. Japanese Patent Laid-Open No. 6-3242
No. 62 discloses this.

On the other hand, there is a method using a diffractive optical element in addition to a method of correcting aberration of a photographing lens, particularly, a correction of chromatic aberration using a plurality of lenses (refractive optical elements) made of materials having different dispersions. A photographic lens in which various aberrations including chromatic aberration have been corrected by using a diffractive optical element is disclosed in, for example, JP-A-6-32.
No. 4262 proposes this.

[0004]

Generally, in order to secure a wide angle of view and a long back focus, a so-called front lens group having a strong negative refractive power and a rear lens group having a positive refractive power have been described. It is desirable to configure the lens system so as to be a reverse telephoto type (retro focus type).

However, in general, a retrofocus type photographing lens has a problem in that an off-axis ray passes through a position relatively far from the optical axis in the first lens unit having a negative refractive power.
Negative chromatic aberration of magnification is likely to occur.

As a technique for correcting the chromatic aberration of magnification, a convex lens (positive lens) using high dispersion glass is arranged inside or near the first lens unit having a negative refractive power. However, if it is attempted to completely correct the chromatic aberration of magnification with only this convex lens, the chromatic aberration of magnification will be overcorrected (distortion of positive color) in a portion where the image height is high. To take
The lateral chromatic aberration has to remain, such as under at the intermediate image height and over at the maximum image height.

Further, as a technique for reducing the burden of correcting the chromatic aberration of magnification of the convex lens and reducing the chromatic distortion,
In an optical system on the image side of the stop in the second lens group having a positive refractive power, low dispersion glass is used as a material of the convex lens, and a cemented lens is disposed. However, the second lens group having a positive refractive power has a smaller correction effect of chromatic aberration of magnification since the position where an off-axis ray passes is closer to the optical axis than the first lens group having a negative refractive power, and has a sufficient correction. Can not. Further, since the low-dispersion glass has a low refractive index, it is necessary to increase the number of lenses in order to secure the refractive power of the second lens group having a positive refractive power to some extent. Since the unit must be composed of at least two lenses (a positive lens and a negative lens), the size of the optical system has been increased.

It is an object of the present invention to provide a retrofocus type photographing lens and a camera which is a wide-angle lens and in which chromatic aberration of magnification is particularly well corrected.

[0009]

According to the present invention, there is provided a photographing optical system comprising:
(1-1) In order from the long conjugate side, in an imaging optical system having a first lens group having a negative refractive power and a second lens group having a positive refractive power, the imaging optical system has at least one surface with respect to the optical axis. And a rotationally symmetric diffractive optical surface.

(1-2) In a photographing optical system having a first lens unit having a negative refractive power and a second lens unit having a positive refractive power in order from the long conjugate side, the photographing optical system diffracts at least one surface. It is characterized by having an optical surface.

In particular, in the configuration (1-1) or (1-2), (1-2)
-1) a stop is provided on a conjugate side shorter than the first lens unit having the negative refractive power, and the diffractive optical surface is disposed on a conjugate side shorter than the stop; h: perpendicular to the optical axis Height in direction m: diffraction order of diffracted light λ: design wavelength, phase shape of the diffractive optical element is 4 (h, m), and C _n is an n-order phase coefficient when represented by the following polynomial. Then, ψ (h, m) = (2π / mλ ₀ ) (C ₂ h ² + C ₄ h ⁴
+ C ₆ h ⁶ ...) C ₂ <0 must be satisfied.

(1-2-2) An aperture is provided on a conjugate side shorter than the first lens unit having the negative refractive power, and the diffractive optical surface is disposed on a conjugate side longer than the aperture. : Height in the direction perpendicular to the optical axis, m: diffraction order of diffracted light, λ: design wavelength, phase shape of the diffractive optical element is 4 (h, m), and C _n is represented by the following polynomial. When an nth-order phase coefficient is set, 次 (h, m) = (2π / mλ ₀ ) (C ₂ h ² + C ₄ h ⁴⁾
+ C ₆ h ⁶ ...) C ₂ > 0 must be satisfied.

(1-2-3) The second lens group has two lens groups, a second lens group having a positive refractive power and a second lens group having a positive refractive power. The focus on the object is moved toward the object while reducing the distance between the two.

(1-2-4) The second lens group is moved to the object side to focus from an object at infinity to an object at a short distance.

(1-2-5) The second lens group is characterized by having a flare cut stop.

The camera according to the present invention comprises (2-1) configuration (1-1) or
(1-2) It has a photographing optical diameter.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a paraxial refractive power arrangement for explaining an optical action of a photographing optical system (photographing lens) of the present invention.

According to the present invention, in a retrofocus type imaging optical system having a first lens unit having a negative refractive power and a second lens unit having a positive refractive power in order from the long conjugate side, light is applied to at least one lens surface. A diffraction optical surface (also referred to as a diffractive surface or a diffractive optical element) having a rotationally symmetric shape with respect to the axis is provided.

Hereinafter, the optical action of the present invention will be described with reference to FIG.

FIGS. 1A and 1B are schematic diagrams of paraxial arrangements for explaining the optical action of the present invention. FIG.
1A shows a case where the diffraction surface A is arranged on the object side from the stop SP, and FIG. 1B shows a case where the diffraction surface A is arranged on the image side of the stop SP. M is an optical system (photographing optical system)
(Here, for the sake of simplicity, the problem is considered as a thin single lens), A is a diffractive surface, P is a paraxial on-axis ray, and Q is a pupil paraxial ray. IP is an image plane.

With respect to the above-described optical arrangement, the equation of the aberration coefficient (T) of the magnification color is obtained as follows.

[0022]

(Equation 1) Becomes Where φ _{M is} the refractive power of the refractive optical part forming the optical system φ _{A is} the refractive power of the diffracted light of the design order of the diffractive surface ν _{M is} the refractive power of the refractive optical part (the thin single lens) of the optical system Ν _A : converted Abbe number of the diffractive surface (equivalent to -3.45) h _M : height of a paraxial axial ray incident on the refractive optical system part constituting the optical system h _A : incident on the diffractive surface Height of paraxial ray

[0023]

(Equation 2) It is.

As described above, in the case of a photographing lens having a wide angle of view, generally, negative chromatic aberration of magnification tends to remain. In this case, since the magnification chromatic aberration coefficient is positive, in the equation, the magnification color aberration coefficient of the refractive optical system portion of the first term is:

[0025]

(Equation 3) Becomes Therefore, in order to reduce the aberration coefficient of the magnification color of the entire system, the aberration coefficient of the magnification color of the diffraction surface in the second term may be set to a negative value. That is,

[0026]

(Equation 4) It is.

Here, as shown in FIG. 1A, when the diffraction surface A is arranged on the object side with respect to the stop SP,

[0028]

(Equation 5) Therefore, the refractive power of the diffraction surface A may be set to φ _A <0. Conversely, as shown in FIG. 1B, when the diffraction surface A is disposed closer to the image than the stop SP,

[0029]

(Equation 6) Therefore, the refractive power of the diffraction surface may be set to φ _A > 0.

The refractive power φ of the diffraction surface is determined by the phase shape of the diffraction surface ψ
Is given by the following polynomial: ψ (h, m) = (2π / mλ ₀ ) (C ₂ h ² + C ₄ h ⁴ + C ₆ h ⁶ ) where h: with respect to the optical axis Vertical height m: diffraction order of diffracted light λ ₀ : design wavelength Ci: phase coefficient (i = 1, 2, 3,...).

For an arbitrary wavelength λ and an arbitrary diffraction order m, using the phase coefficient C ₂ , the following is obtained: φ (λ, m) = − 2C ₂ · mλ / λ ₀ . When the diffractive portion is disposed closer to the object side than the stop as in (A), m> 0, λ> 0, λ ₀ >
0, φ _A <0, and the phase coefficient C ₂ > 0. Conversely, as shown in FIG. 1B, when the diffractive portion is located closer to the image than the stop, the phase coefficient is C ₂ <0.

Further, a case in which axial chromatic aberration is considered will be described. An optical system described so far, when sets a axial chromatic aberration coefficient (L), the case of ^{_{L = h M 2 · φ M}} / ν M + h A 2 · φ A / ν A ... wide angle of view of the imaging lens, Since the focal length is relatively short, negative axial chromatic aberration generally tends to remain. In this case, since the axial chromatic aberration coefficient is positive, the equation shows that the axial aberration coefficient of the first-order refractive optical system portion is h _M ² · φ _M / ν _M > 0.

Therefore, in order to reduce the axial chromatic aberration coefficient of the whole system, the axial chromatic aberration coefficient of the diffraction surface in the second term may be set to a negative value. That is, h _A ² · φ _A / ν _A <0. Here, since h _A > 0 and ν _A <0, the refractive power of the diffraction surface may be φ _A > 0.

The phase coefficient C ₁ of the diffractive surface satisfies the following equation: C ₂ <0

Therefore, in order to correct the lateral chromatic aberration and the axial chromatic aberration with the same diffraction surface, it is sufficient to dispose the diffraction surface on the image side of the stop and set the phase coefficient C ₂ <0, thereby obtaining a better result. Image performance is obtained.

If the distortion of the positive color is extremely large in the entire optical system, the height in the direction perpendicular to the optical axis at the periphery of the diffraction surface is Hh, and the intermediate portion of the diffraction surface (the center portion and the peripheral portion). Between)
When the height in the direction perpendicular to the optical axis of the optical axis is represented by Hm, the phase shape で given by the equation is, as shown in FIG. Hh, m) <ψ (Hm, m) Conversely, as shown in FIG. 1B, when the diffraction portion is arranged on the image side of the stop, ψ (Hh, m)> ψ (Hm, m) It is sufficient to set a higher-order phase coefficient such that The taking optical system of the present invention appropriately configures each element by utilizing the above optical properties.

Next, a specific lens configuration will be described.

FIGS. 2 and 3 are a sectional view and an aberration diagram, respectively, of a numerical example 1 of the present invention. 4 and 5 are a sectional view and an aberration diagram, respectively, of a numerical example 2 of the present invention. 6 and 7 are a sectional view and an aberration diagram, respectively, of a numerical example 3 of the present invention. 8 and 9 are a sectional view and an aberration diagram, respectively, of a numerical example 4 of the present invention. FIGS. 10 and 11 are a sectional view and an aberration diagram, respectively, of a numerical example 5 of the present invention. 12 and 13 are a sectional view and an aberration diagram, respectively, of a numerical example 6 of the present invention. FIG.
FIG. 15 is a sectional view and an aberration diagram of a numerical example 7 of the present invention. 16 and 17 are a sectional view and an aberration diagram, respectively, of a numerical example 8 of the present invention. FIGS. 18 and 19 are a sectional view and an aberration diagram, respectively, of a numerical example 9 of the present invention. 20 and 21 are a sectional view and an aberration diagram, respectively, of a numerical example 10 of the present invention. In the figure, (A) shows a lens cross-sectional view and an aberration diagram when an object at infinity is in focus, and (B) shows a close-range object (-250 for Numerical Examples 1, 2, 5, 6, 7, and 8; Example 3
4, 9 and 10 show a lens cross-sectional view and an aberration diagram at the time of focusing (−300).

In the present embodiment, a camera is constructed by attaching or detachably attaching the photographing optical system shown in these numerical examples to a camera body (not shown).

Next, numerical examples in each figure will be described in order.

FIG. 2 shows the first negative refractive power in order from the object side.
A lens unit L1, a second-a lens unit L2a having a positive refractive power, and a second-b lens unit L2b having a positive refractive power are arranged. The second-a lens unit L2a and the second-b lens unit L2b constitute a second unit L2 having a positive refractive power. FS is a flare cutter (flare stop), SP is a stop, and IP is an image plane.
Focusing from an infinite object to a close object is the first
The lens unit L1 is fixed, and the second-a lens unit L2a and the second
Floating is performed by moving each of the b lens units L2b to the object side while reducing the distance between them. At this time, the stop SP moves integrally with the second-b lens group.

The first group has two meniscus-shaped negative lenses G1 and G2 whose convex surfaces face the object side, and a positive lens G3 whose both lens surfaces are convex. The second lens subunit includes a cemented lens of a positive lens G4 and a negative lens G5, a positive lens G6 having both lens surfaces convex, and a negative lens G7 having a concave surface facing the image surface side. The second lens subunit has a cemented lens composed of a negative lens G8 and a positive lens G9 with the concave surface facing the object side, and two positive lenses G10 and G11 with the convex surfaces facing the image surface side. A diffractive optical element is provided on the object side lens surface of the final lens G11.

FIG. 4 shows the first negative refractive power in order from the object side.
A lens unit L1, a second-a lens unit L2a having a positive refractive power, and a second-b lens unit L2b having a positive refractive power are arranged. The second-a lens unit L2a and the second-b lens unit L2b constitute a second unit L2 having a positive refractive power. FS is a flare cutter (flare stop), SP is a stop, and IP is an image plane.
Focusing from an infinite object to a close object is the first
The lens unit L1 is fixed, and the second-a lens unit L2a and the second
Floating is performed by moving each of the b lens units L2b to the object side while reducing the distance between them. At this time, the stop SP moves integrally with the second-b lens group.

The lens arrangement is different from that of the numerical example 1 in FIG. 2 in that the second lens subunit L2b has a negative lens G8 having a concave surface facing the object side, and two positive lenses G9 and G having a convex surface facing the image plane.
10 is different from that of the first embodiment, and the other configurations are the same. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G9.

6 and 8, a first lens unit L1 having a negative refractive power and a second lens unit L2 having a positive refractive power are arranged in this order from the object side. FS is a flare cutter, SP is an aperture,
IP is an image plane. Focusing from an object at infinity to an object at a short distance is performed by moving the first lens unit L1 and the second lens unit L2 integrally to the object side.

In Numerical Embodiment 3 shown in FIG. 6, the first lens unit comprises a negative meniscus lens G1 having a convex surface facing the object side, and the second lens unit comprises a positive lens G2 having both convex lens surfaces and both lens surfaces being convex. It comprises a concave negative lens G3 and two positive lenses G4, G5. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G4.

In Numerical Example 4 shown in FIG. 8, the first group is composed of a meniscus negative lens G1 with the convex surface facing the object side, and the second group is a cemented lens of a positive lens G2 and a negative lens G3.
Both lens surfaces are composed of a concave negative lens G4, a laminated lens of a negative lens G5 and a positive lens G6, and a positive lens G7. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G6.

In FIGS. 10, 12, 14, and 16, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power are arranged in this order from the object side. SP is an aperture and IP is an image plane. Focusing from an object at infinity to an object at a short distance is performed by fixing the first lens group and moving the second lens group to the object side.

In the numerical example 5 of FIG. 10, the first lens unit is a positive lens G1, and a meniscus-shaped negative lens G with a convex surface facing the object side.
2. It is composed of a positive lens G3. A meniscus negative lens G4 having the second group convex toward the object side, three positive lenses G5, G6, and G7, and a negative lens G having both lens surfaces concave.
8, and two positive lenses G9 and G10. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G9.

In Numerical Example 6 shown in FIG. 12, the first lens unit has a negative meniscus lens G1 having a convex surface facing the object side, a positive meniscus lens G2 having a convex surface facing the object side, and a convex surface facing the object side. It is composed of two meniscus negative lenses G3 and G4, and a cemented lens of a negative lens G5 and a positive lens G6. The second group is composed of a cemented lens of a positive lens G7 and a negative lens G8, a negative lens G9, a positive lens G10 and a negative lens G.
11 bonded lenses, negative lens G12 and positive lens G1
3 and a positive lens G14. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G13.

In the numerical embodiment 7 shown in FIG. 14, two negative meniscus lenses G1 and G having the first lens unit with the convex surface facing the object side are used.
2. It is composed of a positive lens G3. A meniscus-shaped negative lens G4 and a positive lens G with the second group having a convex surface facing the object side
5, a positive lens G6, a laminated lens of a negative lens G7 and a positive lens G8, a laminated lens of a negative lens G9 and a positive lens G10, and a positive lens G11. Positive lens G
A diffractive optical element is provided on the lens surface on the image plane side of No. 10.

In Numerical Embodiment 8 shown in FIG. 16, the first lens unit comprises a negative meniscus lens G1 having a convex surface facing the object side, and a positive lens G2 having both lens surfaces convex. A meniscus negative lens G3 having the second group convex toward the object side, a negative lens G4 having both concave lens surfaces, a positive lens G5 having both convex lens surfaces, a negative lens G6, a lens G7 for forming an aspheric surface, It comprises a cemented lens of a positive lens G8 and a negative lens G9, a positive lens G10, and a positive lens G11. Positive lens G
A diffractive optical element is provided on the lens surface on the image plane side of No. 10.

18 and 20 show, in order from the object side, a first lens unit L1 having a negative refractive power and a second a lens unit L having a positive refractive power.
2a, a second lens unit L2b having a positive refractive power is disposed. The second-a lens unit L2a and the second-b lens unit L2b constitute a second unit L2 having a positive refractive power. SP is an aperture and IP is an image plane. Focusing from an object at infinity to an object at a short distance is performed by moving the first lens group toward the object side while keeping the distance between the second lens group and the second lens group small. At this time, the aperture SP is 2b
It is moving together with the lens group.

In the ninth embodiment shown in FIG. 18, the first lens unit has two meniscus-shaped negative lenses G1 and G with the convex surface facing the object side.
2. Both lens surfaces are composed of a positive lens G3 having a convex surface. The second group is composed of a positive lens G4 having both convex lens surfaces, a negative meniscus lens G5 having a convex surface facing the object side, a laminated lens of the positive lens G6 and the negative lens G7, and a laminated lens of the negative lens G8 and the positive lens G9. Lens, two positive lenses G1
0 and G11. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G10.

In numerical embodiment 10 shown in FIG. 20, two meniscus negative lenses G1 and G with the first lens unit having the convex surface facing the object side are used.
2. Both lens surfaces are composed of a positive lens G3 having a convex surface. The second group includes a positive lens G4 having both convex lens surfaces, a meniscus-shaped negative lens G5 having a convex surface facing the object side, a laminated lens of a positive lens G6 and a negative lens G7, and a negative lens G8 having a concave surface facing the object side. And two positive lenses G9 and G10. A diffractive optical element is provided on the lens surface on the image plane side of the positive lens G9.

In each embodiment of the present invention, the case where one diffraction surface having a positive refractive power is provided is shown.
More than one may be added, thereby obtaining better optical performance. The diffractive surface is formed on one surface based on a spherical lens, but may be formed on an aspheric lens or a parallel plate glass (a parallel plate glass having no diffractive surface is a filter), or may be formed on both surfaces. Furthermore, it may be applied to the cemented surface of the cemented lens, and the material of the base is not particularly limited to glass as long as it allows light to pass through.

The diffraction grating shape 101 of the diffractive optical element in the above embodiment has a kinoform shape shown in FIG. FIG. 23 shows the wavelength dependence of the first-order diffraction efficiency of the diffractive optical element shown in FIG. The actual configuration of the diffraction grating is such that an ultraviolet curable resin is applied to the surface of the base material 102, and the first-order diffraction efficiency is 100 nm at a wavelength of 530 nm.
% Of the lattice 103 having a lattice thickness d.
As is clear from FIG. 23, the diffraction efficiency at the design order decreases as the distance from the optimized wavelength of 530 nm increases, while the 0th-order and second-order diffracted lights near the design order increase. This increase in diffracted light other than the design order causes a flare, which leads to a reduction in the resolution of the optical system. FIG. 24 shows the MTF characteristics with respect to the spatial frequency when the above-described embodiment is created with the lattice shape of FIG. From this figure, it can be seen that the MTF in the low frequency region is lower than a desired value. Therefore, FIG.
The diffraction grating of the laminated type shown in (1) is the grating shape of the diffractive optical element in the embodiment of the present invention. FIG. 26 shows the wavelength dependence of the first-order diffraction efficiency of the diffractive optical element having this configuration. As a specific configuration, an ultraviolet curable resin (nd = 1.49
9, νd = 54) to form a first diffraction grating 104,
A second diffraction grating 105 made of another ultraviolet curable resin (nd = 1.598, vd = 28) is formed thereon. With this combination of materials, the grating thickness d1 of the first diffraction grating portion is d
1 = 13.8 μm, the grating thickness d2 of the second diffraction grating portion is d = 10.
5 μm. As can be seen from FIG. 26, by using a diffraction grating having a laminated structure, the diffraction efficiency of the design order has a high diffraction efficiency of 95% or more over the entire used wavelength range. FIG. 27 shows MTF characteristics with respect to the spatial frequency in this case. By using a diffraction grating having a laminated structure, low frequency M
TF is improved and desired MTF characteristics are obtained. As described above, by using a diffraction grating having a laminated structure as the diffractive optical element of the embodiment of the present invention, the optical performance is further improved.

The material of the above-mentioned diffractive optical element having a laminated structure is not limited to an ultraviolet-curable resin, but other plastic materials or the like can be used. It may be formed on a substrate. Further, it is not necessary that the grating thicknesses be different, and depending on the combination of materials, the two grating thicknesses can be made equal as shown in FIG. In this case, since the grating shape is not formed on the surface of the diffractive optical element, it is excellent in dust resistance, the workability of assembling the diffractive optical element is improved, and a more inexpensive optical system can be provided.

Hereinafter, numerical examples of the present invention will be described. However,
In each embodiment, ri is the radius of curvature of the i-th surface counted from the object side, di is the axial top surface interval of the i-th reference state counted from the object side, and ni and νi are counted from the object side. The refractive index and the Abbe number of the ith lens with respect to the d-line are shown. f indicates the focal length, Fno indicates the F number, and 2ω indicates the angle of view.

Further, k, A, B, C, D, E, F,...
Is the aspherical coefficient, and the shape of the aspherical surface is defined as X, the distance in the optical axis direction between the intersection of the lens surface and the optical axis and the aspherical surface is defined as X, and the optical axis in the perpendicular direction to the optical axis. When the distance of the spherical surface is Y

[0061]

(Equation 7) It is assumed that the following expression is used.

The phase shape 回 折 of the diffraction surface in each embodiment is
It is represented by the following equation.

Ψ (h, m) = (2π / mλ ₀ ) (C ₂ h
A ^{_{2 + C 4 h 4 + C}} 6 h 6 ...) Here, h: height of a direction perpendicular to the optical axis m: diffraction order of the diffracted light lambda _0: design wavelength Ci: phase coefficients (i = 1, 2, 3 …)

In each embodiment, the diffraction order m of the diffracted light is 1, and the design wavelength λ ₀ is the d-line wavelength (587.56 n
m).

[0065]

[Outside 1]

[0066]

[Outside 2]

[0067]

[Outside 3]

[0068]

[Outside 4]

[0069]

[Outside 5]

[0070]

[Outside 6]

[0071]

[Outside 7]

[0072]

[Outside 8]

[0073]

[Outside 9]

[0074]

[Outside 10]

[0075]

As described above, according to the present invention,
It is possible to achieve a retrofocus type photographing lens and camera in which chromatic aberrations, particularly chromatic aberrations such as chromatic aberration of magnification, are well corrected while having a wide angle of view.

[Brief description of the drawings]

FIG. 1 is a layout diagram of paraxial refractive power for explaining the optical action of a photographing optical system according to the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 3 is an aberration diagram of a numerical example 1 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 5 is an aberration diagram of a numerical example 2 of the present invention.

FIG. 6 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 7 is an aberration diagram of a numerical example 3 of the present invention.

FIG. 8 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 9 is an aberration diagram of a numerical example 4 of the present invention.

FIG. 10 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 11 is an aberration diagram of a numerical example 5 of the present invention.

FIG. 12 is a sectional view of a lens according to a sixth numerical example of the present invention;

FIG. 13 is an aberrational diagram of Numerical Example 6 of the present invention.

FIG. 14 is a sectional view of a lens according to a numerical example 7 of the present invention.

FIG. 15 is an aberration diagram of a numerical example 7 of the present invention.

FIG. 16 is a sectional view of a lens according to a numerical example 8 of the present invention.

FIG. 17 is an aberration diagram of a numerical example 8 of the present invention.

FIG. 18 is a sectional view of a lens according to a ninth embodiment of the present invention.

FIG. 19 is an aberration diagram of a numerical example 9 of the present invention.

FIG. 20 is a sectional view of a lens according to a numerical example 10 of the present invention.

FIG. 21 is an aberration diagram of a numerical example 10 of the present invention.

FIG. 22 is an explanatory view of a diffractive optical element according to the present invention.

FIG. 23 is an explanatory diagram of the wavelength dependence of the diffractive optical element according to the present invention.

FIG. 24 is an MTF characteristic diagram of the diffractive optical element according to the present invention.

FIG. 25 is an explanatory view of a diffractive optical element according to the present invention.

FIG. 26 is an explanatory diagram of the wavelength dependence of the diffractive optical element according to the present invention.

FIG. 27 is an MTF characteristic diagram of the diffractive optical element according to the present invention.

FIG. 28 is an explanatory view of a diffractive optical element according to the present invention.

[Explanation of Symbols] L1 First lens unit L2a Second lens unit L2b Second lens unit L2 Second lens unit SP aperture FS flare cut aperture IP image plane d d line g g line C C line ΔM Meridional image plane with respect to d line Sagittal image plane

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H087 KA02 KA03 LA03 MA04 MA08 MA09 NA14 PA05 PA09 PA10 PA16 PA17 PA18 PA19 PB05 PB07 PB10 PB11 PB14 QA02 QA07 QA12 QA17 QA21 QA22 QA25 QA26 QA32 QA11 QA11 RAA RA32 RA46 UA01 9A001 GG11

Claims (8)

[Claims] 1. A first lens having a negative refractive power in order from a long conjugate side.
An imaging optical system having a lens group and a second lens group having a positive refractive power, wherein the imaging optical system has at least one surface having a diffraction optical surface rotationally symmetrical with respect to the optical axis. system. 2. A negative refractive power of a first conjugate in order from a long conjugate side.
An imaging optical system having a lens group and a second lens group having a positive refractive power, wherein the imaging optical system has at least one diffractive optical surface. 3. A stop on a conjugate side shorter than the first lens unit having the negative refractive power, wherein the diffractive optical surface is disposed on a conjugate side shorter than the stop. H: With respect to the optical axis M: the diffraction order of the diffracted light, λ: the design wavelength, the phase shape of the diffractive optical element is 4 (h, m), and the nth-order phase coefficient when C _n is represented by the following polynomial: 、 (H, m) = (2π / mλ ₀ ) (C ₂ h ² + C ₄ h ⁴
+ C ₆ h ⁶ ... C ₂ <0, wherein the imaging optical system according to claim 1 or 2 is satisfied. 4. A stop on a conjugate side shorter than the first lens unit having the negative refractive power, wherein the diffractive optical surface is disposed on a conjugate side longer than the stop. H: With respect to the optical axis M: the diffraction order of the diffracted light, λ: the design wavelength, the phase shape of the diffractive optical element is 4 (h, m), and the nth-order phase coefficient when C _n is represented by the following polynomial: 、 (H, m) = (2π / mλ ₀ ) (C ₂ h ² + C ₄ h ⁴
+ C ₆ h ⁶ ... The imaging optical system according to claim 1, wherein C ₂ > 0 is satisfied. 5. The second lens unit has a second lens unit having a positive refractive power.
It has two lens groups, a lens group and a 2b lens group having a positive refractive power, and focuses from an object at infinity to an object at a short distance by moving the object to the object side while reducing the distance between the two. 5. The photographing optical system according to claim 1, 2, 3, or 4, wherein 6. The imaging optical system according to claim 1, wherein the second lens group is moved to the object side to focus from an object at infinity to an object at a short distance. 7. The photographic optical system according to claim 1, wherein said second lens group has a flare cut stop. 8. A camera comprising the photographing optical system according to claim 1.