JP2754547B2 - Imaging system having image deflection means - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing system having an image deflecting means, and more particularly, to a variable vertex angle prism for changing a prism vertex angle in a lens system, and the variable vertex angle. The present invention relates to a photographing system having image deflecting means suitable for a photographic camera, a video camera, or the like, in which a photographed image is deflected by a prism to correct image blur due to vibration or the like. (Prior Art) When an image is taken from a vehicle or the like in progress, vibrations are transmitted to a photographing system, and the photographed image is blurred. Conventionally, various imaging systems having image deflection means for correcting image blurring at this time by disposing a parallel plane plate or a variable apex prism in an optical system have been proposed. For example, Japanese Patent Publication No. 56-21133 proposes a photographing system in which image blur is corrected using a variable apex angle prism. In this publication, a liquid or a transparent elastic body is sealed between two parallel flat glass plates, and the angle between the two parallel flat plates is made variable to correct image blur. In addition, the publication proposes an imaging system in which the angle between the opposing planes is made variable by sliding a plano-convex lens and a plano-concave lens having a curvature between spherical surfaces to correct image blurring. Generally, when a variable apex angle prism is arranged in front of or in a lens system to correct image blur, if the apex angle of the variable apex angle prism has a certain angle, the chromatic dispersion of the prism causes the image to be distorted. The eccentric magnification chromatic aberration occurs along with the deflection. This effect is shown in FIG. P is a variable apex angle prism. When the apex angle is changed as shown in FIG. 10 (A), the g-line is deflected more than the d-line. Therefore,
As shown in FIG. 10 (B), when the variable apex angle is attached to the master lens M to deflect the image, chromatic aberration of eccentric magnification occurs. The eccentric magnification chromatic aberration is generated in substantially the same amount and in the same direction over the entire screen from the center to the periphery of the screen, which causes a decrease in contrast and color bleeding. As described above, the eccentric magnification chromatic aberration is also generated at the center of the screen of the main subject unlike the normal chromatic aberration of magnification, and is a major cause of image quality deterioration. In contrast, U.S. Pat. No. 3,514,192 and Japanese Patent Publication No. 57-7116
In the publication, two variable apex prisms having different dispersions are used,
There has been proposed an imaging system in which eccentric magnification chromatic aberration is reduced by driving while maintaining a constant angle ratio so as to satisfy the achromatic condition. However, this method requires two variable apex angle prisms, increases the thickness of the deflecting element, and tends to have a relatively complicated structure for driving the two prisms while maintaining a constant apex angle ratio. Was. In Japanese Patent Application Laid-Open No. 61-223819, a cemented lens having a refractive power almost equal to zero is provided at the rear of the imaging system separately from the variable apex angle prism, and the optical axis is synchronized with the movement of the variable apex angle prism. An imaging system has been proposed in which eccentric magnification chromatic aberration is corrected by a variable apex angle prism system by eccentric driving in the vertical direction. In this method, two optical elements located at remote locations must be driven in precise synchronization, and the control structure is complicated,
There have been problems such as an increase in the size of the apparatus, an increase in the number of members to be moved in the optical system, and the influence of the inclination of the cemented lens. In addition, Japanese Patent Publication No. Sho 56-40805 proposes a photographing system that corrects image blur by forming a prism with a substantially variable apex angle using a rotating sliding method of a plano-convex lens and a plano-concave lens. doing. However, although this method can reduce the occurrence of eccentric magnification chromatic aberration, the variable apex angle prism tends to be relatively large. (Problems to be Solved by the Invention) According to the present invention, a variable apex angle prism having a variable apex angle is arranged in a lens system, and is arranged on the object side with respect to the variable apex angle prism when correcting blurring of a photographed image. By appropriately setting the lens configuration of the first lens group and the second lens group disposed on the image side and the configuration of the variable apex angle prism, it is possible to satisfactorily correct the optical performance of the entire screen, particularly the fluctuation of the chromatic aberration of magnification. It is an object of the present invention to provide a photographing system having an image deflecting unit capable of correcting a blur of a photographed image. (Means for Solving the Problem) A fixed first lens group, a variable apex prism with a variable apex angle, and a fixed second lens group in that order from the object side, and the apex angle of the variable apex prism In a photographing system having an image deflecting means for deflecting a photographed image by changing the distance, a diaphragm is arranged in the vicinity of the variable apex angle prism, and when the focal length of the entire system is normalized to 1, The magnification chromatic aberration coefficients of the first lens group and the second lens group are T ₁ and T ₂ , respectively.
Each N _P refractive index with respect to the reference wavelength and the second wavelength of the variable apex angle prism, and _{N P 'δNP = | N P} -N P | time was _{-0.012 <T 2 - (δNP)} / (N P - 1) <0.012 ... (1) Satisfying the following conditions. (Embodiment) FIGS. 1, 2 and 3 show numerical embodiments 1, 2, and 3 of the present invention.
It is a lens sectional view of. In the figure, I is a fixed first lens group, and P is a variable apex angle prism with a variable apex angle, which constitutes a part of the image deflecting means. II is a fixed second lens group. In this embodiment, the blur of the photographed image is corrected by changing the prism apex angle of the variable apex angle prism P.
In the embodiment shown in FIGS. 1 and 2, transparent silicon rubber is sealed between two glass plates to form a variable apex prism, and the apex angle is changed by driving the apex angle with an actuator to correct image blur. doing. In this embodiment, the light beam emitted from the first lens group is substantially afocal. When the axial light beam of the light beam incident on the variable apex angle prism is close to an afocal, that of the axial paraxial ray when the focal length of the whole system is f _T inclination alpha is approximately | alpha
If it is small enough to satisfy the condition of | <0.3 <f _T , the occurrence of eccentric coma, eccentric astigmatism, and eccentric field curvature in the variable apex angle prism is smaller than in the case where the afocal light beam is not used. If the spherical aberration, coma and astigmatism of the sub-system of the lens group are corrected to be small, the occurrence of eccentric coma, eccentric astigmatism and eccentric field curvature can be reduced in principle, and the configuration of the second lens group The number of lenses can be reduced. Further, when the variable apex angle prism is formed by enclosing transparent silicon rubber between two glass plates as in this embodiment, there is a feature that a variable apex angle prism having a small thickness can be achieved. In the embodiment shown in FIG. 3, a variable apex angle prism is formed by a plano-convex lens and a plano-concave lens whose opposing lens surfaces have the same radius of curvature, and the angle between the opposing planes is formed by sliding the opposing lens surfaces together. It is variable and the apex angle is substantially changed. In the present invention, by setting the lens configurations of the first lens unit and the second lens unit and the configuration of the variable apex angle prism as described above in the above-described configuration, shooting is performed while maintaining the optical performance of the entire screen in a good condition. Image blur is corrected. FIG. 7 is an explanatory view of an eccentric aberration coefficient when any one lens surface ν in the lens system is decentered by an angle εv, and FIG. 8 does not change the apex angle of the variable apex prism in the imaging system according to the present invention. FIG. 9 is an explanatory diagram in the case where the apex angle of the variable apex angle prism is changed. FIG. 8 shows the optical paths of the on-axis light beam and the off-axis light beam at two wavelengths, the d-line as the reference wavelength and the g-line as the second wavelength. FIG. 9 shows a state in which the optical path of the axial luminous flux at two wavelengths, d-line and g-line, is deflected by ΔY when the apex angle of the variable apex angle prism is changed by ε. First, the eccentric aberration in the present embodiment will be described with reference to FIG. For decentering aberration when the ν lens surface of the lens system as shown in FIG. 7 ν is inclined angle epsilon _v "Setting tertiary decentering aberrations and tolerances, 1975, lens design seminars, chapter 7; Ozeki" It is described in. An eccentric lateral chromatic aberration according to which △ (△ Y) is _{△ (△ Y) = cosφ V} · V · ε V · f T / α K ' Can be expressed as Here, the aberration coefficient and the paraxial amount are values when the focal length of the entire system is normalized to 1, f _T is the focal length of the entire system, and _V is the eccentric magnification chromatic aberration when the ν lens surface ν is inclined. It is a coefficient. Next, this equation is applied to a variable apex angle prism, modified and arranged. When the prism surface is represented by a suffix P and the fixed lens group after the variable apex prism, that is, the second lens group is represented by a suffix 2, Δ (△ Y) = − cos φ _P · ε _P · f _T · ｛(N _P −1) _{) (P L 2 -h P T} 2) + h P (δN P)} /
α _K ′. Where N _P is variable apex angle reference wavelength for the prism, for example, the refractive index of the d-line, (.delta.N _P) is reference wavelength d line when the second wavelength of the variable apex angle prism, for example, the refractive index of the g-line and an N2 Is the difference | N _P −N 2 | For eccentric lateral chromatic aberration is not generated △ (△ Y) because there must be _{≒ 0 (N P -1) (} P -L P T 2) + h P (δN P) ≒ 0 proviso second lens What is necessary is that the group coefficients L ₂ and T ₂ are satisfied.
In this equation, both the axial chromatic aberration and the chromatic aberration of magnification of the second lens group are related. However, when a variable apex angle prism is provided inside the lens as in the present invention, it can be regarded as near the stop. In many cases, _P becomes a small value in this case, and the chromatic aberration of magnification of the second lens group becomes dominant in correcting the eccentric chromatic aberration. Therefore, in general, the chromatic aberration of the second lens group should be corrected so as to satisfy the condition of T ₂ ≒ (δN _P ) / (N _P −1). Since the right side of this equation is a positive value, if the chromatic aberration of magnification of the second lens group is corrected so as to generate a large under value, the occurrence of eccentric chromatic aberration can be reduced. Actually, if the coefficient T ₂ satisfies the condition of −0.012 <T ₂ − (δN _P ) / (N _P −1) <0.012 (1) as described above, the chromatic aberration of eccentric magnification is obtained. Can be reduced to such an extent as not to affect the occurrence. If the lower limit value of conditional expression (1) is exceeded, the correction of the eccentric magnification chromatic aberration is insufficient. If the upper limit value is exceeded, the eccentric magnification chromatic aberration is excessively corrected. Occur. Furthermore, in order to correct the lateral chromatic aberration in the reference state,
If T ₁ is the chromatic aberration of magnification of the first lens group, It is better to satisfy the conditional expression (1). This means that the chromatic aberration of magnification of the first lens group is generated in a direction opposite to that of the second lens group, and is corrected with good balance. If the lower limit of conditional expression (2) is exceeded, lateral chromatic aberration will remain in the over direction in the reference condition, and if the upper limit value of conditional expression (2) is not satisfied, lateral chromatic aberration will remain in the under direction in the reference condition,
The chromatic aberration of magnification in the reference state is large, and satisfactory image quality cannot be obtained. According to the above formula, according to Matsui's “Lens Design Method” ('81 Kyoritsu Shuppan), the magnification chromatic aberration coefficient T _i of each lens surface is obtained by normalizing the focal length of the entire system to 1. However, And the chromatic aberration of magnification △ (△ y) of the entire system is Can be represented by Next, the magnification chromatic aberration coefficient by the variable apex angle prism will be described with reference to FIGS. In the variable apex angle prism with the wedge angle ε, the chromatic aberration of magnification due to the variable apex angle prism (this is also the eccentric magnification chromatic aberration) △ (△ Y) because the ray of the g-line is refracted more than the d-line. _P is _{△ (△ Y) P α tan} (△ ω) △ ω ≒ -ε · (N P -1) (N P is the refractive index of the prism) in the over direction in proportion to the deflection angle of the variable apex angle prism Occur. On the other hand, chromatic aberration of magnification is proportional to the angle of view. In an eccentric state in which the apex angle is changed, the angle of view when the light ray enters the second lens group corresponds to the deflection angle of the light ray passing through the variable apex angle prism. When the magnification chromatic aberration in the second lens group is corrected so as to generate, at this time magnification chromatic aberration △ (△ Y) ₂ generated in the second lens group to the magnification chromatic aberration coefficient of the second lens group and T _2, △ (△ Y) ₂ ∝−T ₂ tan (△ ω) and a value proportional to the angle of view are generated. In the present embodiment, the magnification chromatic aberration coefficient T ₂ of the second lens group is selected to be a positive value, that is, the magnification chromatic aberration is corrected so as to generate under chromatic aberration in the second lens group. And the eccentric magnification chromatic aberration is corrected in a well-balanced manner in the entire system. On the same side of the deflection direction as the principal ray of the off-axis light, the angle of incidence on the second lens group is greater in the decentered state than in the reference state, and the under magnification chromatic aberration generated in the second lens group is increased. This corrects over-magnification chromatic aberration generated by the variable apex angle prism. In this embodiment, the first lens group corrects chromatic aberration such that chromatic aberration of magnification occurs excessively, and the second lens group corrects chromatic aberration such that chromatic aberration of magnification largely occurs under. The chromatic aberration of magnification is corrected in a well-balanced manner. In a photographing system in which a variable apex angle prism is provided between two fixed lens groups as in this embodiment, the deflection ΔY of the image on the image plane by the variable apex angle prism is such that the image of the first lens group has a variable apex angle. It generated upon relayed imaging magnification beta ₂ by the second lens group and thereafter is deflected by △ Y ₁ by a prism. That is, ΔY ₁ = S · tan ｛(N _P −1) · ε _P ｝ Δ = Y = (・ Y ₁ ) · β ₂ = S · β ₂ · tan ｛N _P -1) · ε _P ｝ . Here, S is the distance from the variable apex angle prism to the image plane of the first lens group. Similarly, deflection of the image of the second wavelength △ Y ′
_{Is, △ Y '= S'β 2'} · tan {(N P '-1) · ε P} now decentering lateral chromatic aberration △ (△ Y) = △ Y'- △ Y
Is 0 (S′β ₂ ′ / (S · β ₂ ) = tan ｛(N _P −1) · ε _P ｝ / tan ｛(N _P −1)
ε _P ｝ ≒ (N _P −1) / (N _P ′ −1). When the chromatic aberration of the first lens group is small 'so _{≒ S, β 2' S /} β 2 ≒ can be approximated by _{(N P -1) / (N} P '-1). From imaging magnification of each wavelength of the second lens group which may be designed so as to be inversely proportional to the (N _P -1) of each wavelength of the variable apex angle prism. In the present embodiment, when the first lens unit is not afocal, that is, when the focal lengths of the entire system of the first lens unit are f ₁ and f, respectively, | f ₁ | <20 f, the imaging magnifications β ₂ and β ₂ 'But Is set so as to satisfy the condition (1), whereby the occurrence of the eccentric magnification chromatic aberration is reduced to such an extent that the influence is not exerted. When the value exceeds the upper limit of conditional expression (3), the correction of the eccentric magnification chromatic aberration becomes insufficient. When the value exceeds the lower limit, the eccentric magnification chromatic aberration is overcorrected. Not so good. When the light beam emitted from the first lens group is afocal, particularly when | f ₁ |> 20f, the focal length of the second lens group is set to f.
_{If it is 2} , it is expressed as ΔY = f ₂ · tan ・ (N _P -1) · ε _P ｝. Similarly, with the second wavelength △ Y is expressed _{as' = f 2 '· tan {} (N P' -1) · ε P}. Eccentric magnification chromatic aberration △ (ΔY)
= △ Y'- △ Y becomes 0 when f ₂ // f ₂ = tan ｛(N _P -1) ・ ε _P ) / tan ｛(N _P −１-1) ・ ε
_P} ≒ becomes _{(N P -1) / (N} P '-1). The focal length of each wavelength of the second lens group, may be set to be inversely proportional to (N _P -1) of each wavelength of the variable apex angle prism. This also means that the chromatic aberration of magnification is generated under the second lens group and the chromatic aberration of eccentricity of magnification generated by the variable apex angle prism is corrected. In the present embodiment, the focal length f ₂ of the reference wavelength of the second lens group and the focal length f ₂ ′ of the second wavelength are Is set so as to satisfy the following conditional expression, and the occurrence of eccentric magnification chromatic aberration is reduced to such an extent as not to be affected. When the value exceeds the upper limit of conditional expression (4), the correction of the eccentric magnification chromatic aberration is insufficient. When the value exceeds the lower limit, the eccentric magnification chromatic aberration is overcorrected. Not good because it occurs. In this embodiment, when the photographing system is a photographic lens, it is preferable to take d-line as the reference wavelength and select g-line as the second wavelength, but it is also possible to select light having a wavelength longer than d-line as the second wavelength. good. In other optical instruments, the reference wavelength is the dominant wavelength in the optical instrument, and the second wavelength is preferably the light of the shortest wavelength used. In the present embodiment, the first and second lens groups are fixed with respect to eccentric driving, but the lens groups include a lens group that moves in the optical axis direction, such as a focus lens group and a variable power lens group. May be. In this embodiment, in order to perform better correction of the chromatic aberration of magnification, it is preferable that the chromatic aberration of magnification is generated in the under direction by the second lens group. For this purpose, the second lens group is configured as follows. Is good. That is, the second lens group is divided into two lens groups of a 2A lens group and a 2B lens group from the object side with the largest air gap in the lens group as a boundary, and each lens constituting the second B lens group is divided into two. The refractive power is φ2Bi, the Abbe number of the material is ν2Bi, the equivalent Abbe number is V2B, In this case, the following condition is satisfied: V2B <40. If the equivalent Abbe number V2B increases as a result of deviating from the conditional expression (5), the refracting power of the second B lens unit must be increased. As a result, a large amount of coma and astigmatism is generated, which is good. Absent. In each of the above embodiments, the surfaces on both sides of the variable apex angle prism are not necessarily flat, but may have a gentle curvature. The photographing system according to the present embodiment can be applied to optical devices such as a shift lens and an automatic level. Next, numerical examples of the present invention will be described. In numerical examples
Ri is the radius of curvature of the i-th lens surface in order from the object side,
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side. 12A and 12B show various aberration diagrams when the variable apex angle prism of Numerical Example 1 is disposed on the object side of the first lens unit (FIG. 11) for comparison. . (Effects of the Invention) According to the present invention, by configuring each lens group and the variable apex angle prism as described above, the eccentricity which is a problem when the variable apex angle prism method is used without providing a special mechanism. It has an image deflecting means capable of correcting the occurrence of chromatic aberration of magnification to a small extent, obtaining a high-quality image with less color blur and high contrast when driven eccentrically, and also correcting the chromatic aberration of magnification in the reference state to be small. A photography system can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are lens cross-sectional views of Numerical Examples 1, 2, and 3 of the present invention, and FIGS. 4, 5, and 6 are numerical implementations of the present invention, respectively. For example,
FIGS. 1, 2, and 3 are diagrams illustrating various aberrations, FIG. 7 is a diagram illustrating an eccentric aberration coefficient according to the present invention, and FIGS. Fig. 10 (A), (B)
FIG. 11 is an explanatory view of a conventional variable apex prism, and FIGS. 11 and 12 are a lens cross-sectional view and an aberration diagram when the variable apex prism is disposed on the object side of the first lens group in Numerical Embodiment 1. In the aberration diagrams, (A) is an object distance of 15 m, and (B) is a lateral aberration when the image is deflected by ΔY = 1 mm. In the figure, I is a first lens group, II is a second lens group, P is a variable apex prism, ΔM is a meridional image plane, and ΔS is a sagittal image plane.

Claims (1)

(57) [Claims] A fixed first lens group, a variable apex angle prism having a variable apex angle, and a fixed second lens group in order from the object side;
In a photographing system having an image deflecting unit that deflects a photographed image by changing the apex angle of the variable apex angle prism, an aperture is arranged near the variable apex angle prism, and the first lens group The chromatic aberration of magnification of the first lens group and the second lens group when the chromatic aberration of magnification of the second lens group is overcorrected and the chromatic aberration of magnification of the second lens group is undercorrected and the focal length of the entire system is normalized to 1 Coefficient
T _1, T _2, wherein the variable angle prism reference wavelength and each N _P refractive index for the second wavelength, 'and _{δNP = | N P -N P'} | N P and the time -0.012 <T ₂ - ( _{δNP) / (N P -1)} <0.012 An imaging system having image deflecting means, characterized by satisfying the following conditions. 2. When the focal length f ₁ of the first lens group is | f ₁ | ≦ 20f, and the imaging magnifications of the second lens group with respect to the reference wavelength and the second wavelength are β ₂ and β ₂ ′, respectively. 2. A photographing system having image deflecting means according to claim 1, wherein the following conditions are satisfied. 3. When the focal length f ₁ of the first lens group is | f ₁ |> 20f, and when the focal lengths of the second lens group for the reference wavelength and the second wavelength are f ₂ and f ₂ ′, respectively. 2. A photographing system having image deflecting means according to claim 1, wherein the following conditions are satisfied. 4. The second lens group is divided into two lens groups, a 2A lens group and a 2B lens group, from the object side with the largest spatial interval in the lens groups as a boundary, and the refraction of each lens constituting the 2B lens group The force is φ2Bi, the Abbe number of the material is ν2Bi, and the equivalent Abbe number is V2B. 4. A photographing system having image deflecting means according to claim 2 or 3, wherein the following condition is satisfied: V2B <40.