JP2547834B2 - Optical system with image deflection function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image pickup system having an image deflecting means, and in particular, a variable apex angle prism for varying a prism apex angle is provided in a lens system, and the variable apex angle is provided. 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 captured image is deflected by a prism and image blurring due to vibration or the like is corrected.

[Conventional technology]

When shooting from an on-going vehicle or the like, vibrations are transmitted to the shooting system and the shot image is blurred. Conventionally, there have been proposed various photographing systems having an image deflecting unit which corrects the image blur at this time by disposing a plane parallel plate or a variable apex angle prism in an optical system.

For example, Japanese Patent Publication No. Sho 56-21133 proposes an image pickup system in which image blurring is corrected by using a variable apex angle prism. In this publication, a liquid or a transparent elastic body is enclosed between two parallel plane glasses, and the blurring of the image is corrected by changing the angle formed by the two parallel plane plates.

In addition, the publication proposes a photographing system in which a plano-convex lens and a plano-concave lens having a curvature are slid between spherical surfaces to change the angle formed by the opposing planes to correct the blur of an image.

The conventional example disclosed in the publication has an advantage that the diameter of the variable vertical angle prism can be generally reduced because the variable vertical angle prism is provided in the lens system.

[Problems that the invention is trying to solve]

However, when the variable apex prism is provided inside the lens system as in the above-mentioned conventional example, there is a drawback that decentering distortion that occurs when the image is deflected, that is, when the apex is changed, becomes large. The description will be given below.

6 and 7 are views showing how decentering distortion occurs in the variable apex angle prism.

FIG. 6A shows a reference state in which the two surfaces of the variable apex angle prism are parallel to each other, and the rays 0, a and b are imaged at the screen center 0'and off-axis a ', b', respectively. The principal rays of the luminous flux are shown respectively. Figures 6 (B) and 7 show the variable apex angle prism
It shows the states of chief rays 0, a, and b when the apex angle of is attached. Letting the angle of view be θ, a ray incident on the variable apex angle prism having an apex angle of A as shown in FIG. 2 is θ ₁ = sin ⁻¹ (sin θ / N _P ) (1) θ ₂ = Θ ₁ + A (2) θ _P = sin ⁻¹ (N _P · sin θ ₂ ) −A (3) Refraction is performed and the angle formed with the optical axis is θp and the variable angle prism is emitted. . Where θ ₁ is the refraction angle on the first surface of the variable apex prism, θ ₂ is the incident angle on the second surface,
θ ₂ ′ is the exit angle, and θp is the angle formed by the exit ray with the optical axis. Note that N _P represents the refractive index of the prism. And the chief ray having an angle of θp with respect to the optical axis 0 is y ′ = f · tan θ
The image is formed at the image height represented by p.

Therefore, if the deflection angles δ (δ = θp−θ) of the chief rays on the second surface of the variable apex angle prism are all the same, the image is deflected on the image plane while maintaining the original shape. Actually, when the incident angle to the variable apex angle prism is different, the deflection angle of each principal ray is also different, and each point 0 ', a', on the image plane as shown in FIG.
b'behaves differently. To quantitatively show this, in the variable apex prism of FIG. 7, the ratio with respect to the change amount dθp of the exit angle when the apex angle changes from the reference state by a minute angle dA, that is, the sensitivity is set to the variable apex prism. When expressed as a function of the incident angle θ of Can be shown as This expression shows that the sensitivity dθ _P / dA increases with a positive value as the absolute value of the incident angle θ increases.

As shown in FIG. 7, since the axial ray 0 has a small incident angle on the prism surface, the deflection angle δ (δ = δ = δ) when the incident angle on the prism second surface, that is, the prism second surface changes to the angle A. θ
_P− θ) is proportional to the apex angle A, that is, δ≈ (N _P −
1) Indicated by A.

On the other hand, when the incident angle on the second surface is relatively large like the off-axis ray a, even if the apex angle A also changes by the angle A, the deflection angle is expressed by the above equation δ = (N _P −1) A. The absolute value is larger than the represented value.

For example, when the apex angle of the ray a becomes A in the direction of FIG. 7, the incident angle θ ₂ on the second surface of the variable apex prism changes to a direction larger than the reference state, and therefore the inclination angle θ _{P of the} emitted light Is θ
It becomes larger than + δ. Therefore, on the image plane, FIG.
As indicated by a _α ′ in FIG.

On the other hand, when the apex angle of the light beam of b becomes A, the incident angle θ ₂ of the variable apex angle prism on the second surface changes in a direction smaller in absolute value than in the reference state, so the inclination angle θ _{P of the} emitted light is an absolute value. At θ
It becomes smaller than + δ. Therefore, on the image plane, as shown by b _α ′ in FIG. 6 (B), the image is distorted in the over direction.

When there is such eccentric distortion, the image of the subject as shown in FIG. 8 (A) is distorted into the shape shown by the solid line in (B). The dotted line is an ideal image when there is no distortion.

Therefore, in the image stabilization optical system that corrects the image blur caused by camera shake by deflecting the image in the opposite direction with the variable apex angle prism,
When the eccentric distortion aberration as described above is present, the amount of movement differs between the point at the center of the screen and the point off-axis, so even if the image blur is corrected at the center of the screen, a flow of images will occur in the periphery. FIG. 8C shows the result of image blur correction of a subject as shown in FIG. 8A with an image stabilization optical system having eccentric distortion.

When the variable apex prism is provided inside the lens system, there is an advantage that the diameter of the variable apex prism can be reduced as described above. However, in a telephoto objective lens for which image stabilization is desired, the tilt angle of the principal ray of the off-axis light beam becomes large, and even if the same amount of deflection is obtained on the image plane, it is larger than when it is provided in front of the lens system. It is necessary to change the apex angle, and these two factors tend to cause more eccentric distortion aberration.

In view of this problem, it is an object of the present invention to provide an optical system having a high optical performance and, in particular, an image deflecting function with a good distortion, while reducing the size of the optical system.

[Means (and Action) for Solving Problems]

The present invention, in order from the object side, has a first fixed eccentricity.
An image deflecting unit having a lens group, a variable apex prism having a variable apex angle, and a second lens group fixed with respect to decentering, and deflecting an image by changing the apex angle of the variable apex prism. In the optical system provided, when the distortion aberration coefficients of the first lens group and the second lens group when the focal length of the entire system is normalized to 1 are V ₁ and V ₂ , respectively, V ₂ > 0 (4) −1.3 <V ₁ / V ₂ <−0.7 (5) By adopting an aberration correction method that satisfies the condition, a variable apex angle prism is provided inside the lens to decenter the eccentric distortion of the optical system for image deflection. The purpose is to correct aberrations to be small.

〔Example〕

Examples of the present invention will be described below. FIG. 5 is a diagram showing a schematic view of the optical system according to the present invention. I is the first lens group disposed in front of the variable apex angle prism P while I is causing the distortion to be over-prone, and II is disposed behind the variable apex angle prism P while keeping the distortion in the under tendency. It is a second lens group. F indicates a film surface. a shows the chief ray of the screen θ ₀ .

In the optical system shown in this embodiment, the first lens group I and the second lens group II each have a large distortion, but especially before the apex angle of the prism P is changed, that is, in the reference state. Shows that the over-distortion aberration generated by the first lens group is canceled by the under-distortion aberration generated by the second lens group, so that the entire photographing system (I, P, II) is shown in FIG. As shown in (), the aberration is satisfactorily corrected.

That is, in the reference state, the distortion aberrations generated by the first lens group I and the second lens group II are respectively Dis (θ ₀ ) _I , Dis
When (θ ₀ ) _II is set, the relationship Dis (θ ₀ ) _I ≈−Dis (θ ₀ ) _II is satisfied.

Next, FIG. 5 (B) shows a state in which the two lens groups I and II have been subjected to aberration correction in this way and then subjected to image deflection by changing the apex angle. The chief ray having the same angle of view θ ₀ as in the initial state naturally causes distortion aberration of the same value as in the initial state in the first lens group 1. Then, the principal ray a emitted from the first lens group I at an inclination angle of θ is deflected by Δ by the variable apex angle prism P having the apex angle of A, but as described above, The deflection amount is excessively large by deflecting more than the deflection amount δ≈ (N _P −1) A.

Therefore, the principal ray emitted from the variable apex angle prism P is (θ +
Δ) and the second lens group II with an inclination angle larger than the reference state by Δ
Will be incident on. At this time, the amount of distortion aberration at the tilt angle (θ + Δ) is larger in the under direction than the amount of distortion aberration at the tilt angle θ of the second lens group II, so that the principal ray deflected by the variable apex angle prism is Excessive deflection (that is, eccentric distortion of the variable apex prism) is corrected, and the difference between the deflection amount on the image plane and the deflection amount of the ray 0 incident on the optical axis can be corrected to be small. . That is, the eccentric distortion can be corrected to be small. The relation of the distortion aberration at this time can be expressed as Dis (θ ₀ ) ₁ + Dis (θ, A) _P ≈−Dis (θ + Δ) _II . Note that Dis (θ, A) _P is the distortion aberration that occurs in the variable apex angle prism having the apex angle of A, and Dis (θ +
Δ) _II represents the distortion of the second lens group of the light beam having the apex angle (θ + Δ).

Here, the necessary condition that the distortion aberration increases as the tilt angle of the off-axis light beam incident on the second lens group increases, V ₂ > 0 (where V ₂ is the third-order distortion aberration coefficient of the second lens group) 4) The expression (4) means that the distortion aberration is under.

Then, in order to satisfactorily correct the distortion aberration from the initial state to the state in which the image is deflected, when the third-order distortion aberration coefficient of the first lens group I is V ₁ , -1.3 <V ₁ / V ₂ <−0.7 (5) It is recommended to satisfy the conditional expression.

If the upper limit of conditional expression (5) is exceeded, the distortion aberration of the first lens group will become excessively excessive, and also distortion aberration that tends to be excessive in the initial state or during deflection will remain when viewed as the entire shooting system. Not preferable. On the other hand, when the value goes below the lower limit, the distortion aberration of the second lens group II becomes excessively under, and the distortion aberration which tends to be under at the time of reference or deflection remains in the entire photographing system, which is not preferable.

Next, theoretical support for the technology relating to the present invention will be described using decentering aberration theory. Although various attempts have been made to derive the relational expression between the eccentric aberration and the aberration coefficient, here, the format presented by Matsui at the 23rd Annual Meeting of the Applied Physics Society of Japan (1962) is used.
According to this, the aberration (ΔY ′) after decentering is represented by the sum of the aberration ΔY before decentering and the decentering aberration ΔY (ε) generated by decentering in the region of the third-order aberration as shown in equation (6). ε
Aberration ΔY (ε) newly generated by tilting
Is expressed as in equation (7).

Δ'Y = ΔY + ΔY (ε) (6) Regarding the inner eccentric distortion aberration (Vε1) and the eccentric distortion addition aberration (Vε2), the tilted surface is applied as a plane to the variable apex angle prism and expressed by the paraxial amount and the aberration coefficient of the second lens group (8). It is a formula and (9) Formula. In the meridional section, the normal line of the prism surface is inclined, and the decentering aberration and the eccentric addition aberration are summarized and expressed in the meridional section (10).

When the variable vertical angle prism is provided in the lens as in the present invention, the height _P of the paraxial chief ray of the variable vertical angle prism has a small value. And, among them, the dominant values are the two terms represented by the equation (11) in the parentheses of the equation (10). The first of equation (11)
Since the term has a positive value, the second term has a negative value, so that when V ₂ > 0, it contributes to the reduction of decentering distortion. If it is desired to correct the eccentric distortion aberration to almost zero, it may be generated so that the distortion aberration coefficient V ₂ of the second lens group satisfies the expression (12). Also in this case, the distortion aberration coefficient V ₁ of the first lens group must satisfy the expression (5) in order to correct the distortion aberration of the entire system in the reference state.

Therefore, when _P is the focal length of the entire system is normalized to 1 and the tilt angle when entering the lens system is −1, the tilt angle of the off-axis chief ray entering the variable apex angle prism is If a third-order distortion aberration coefficient of the second lens group is determined so as to satisfy the above condition, a better result can be obtained.

Furthermore, in the present embodiment, the first lens group and the second lens group are respectively separated by the largest air gap in the lens groups, and the first lens front group, the first lens rear group, the second lens front group, and the second lens front group. It is divided into 2 lens rear groups, and each focal length is
When f _I-1 and f _I-2 and f _II-1 and f _II-2 and the focal length of the entire system is f _T , 0.4 <f _I-1 / f _T <1.7 (14) 0.05 < If a focal length that satisfies the conditional expression of f _II-2 / f _T <0.7 (15) is adopted, a positive lens group of relatively strong power will be arranged at a position away from the variable apex angle prism. Not only distortion aberration related to the present invention but also other aberration correction can be performed without difficulty. In other words, if the focal length is shorter than the lower limits of conditional expressions (14) and (15), it is advantageous for correction of distortion aberration of each lens group, but much for correction of spherical aberration and astigmatism. The number of lenses will be required. On the other hand, the conditional expression (1
If the upper limits of 4) and (15) are exceeded, the size of the optical system and the prism itself will increase, which is not preferable.

Further, the principal point distance between the first lens front group and the first lens rear group is e _I , and the principal point distance between the second lens front group and the second lens rear group is e.
_{When II} , 0.1 <| f _I-2 | / f _T <0.7, f _I-2 <0 (16) 0.1 <| f _II-1 | / f _T <0.5, f _II-1 <0 (17 ) By adopting a power distribution that satisfies 0.25 <e _I / f _T <0.9 (18) 0.04 <e _II / f _T <0.3 (19), it is possible to obtain good optical performance with a smaller lens configuration. Can be issued. If the lower limit values of conditional expressions (16) and (17) are exceeded and the powers of the rear group of the first lens and the front group of the second lens become strong, it becomes difficult to correct spherical aberration and coma, and optical performance is maintained. If so, many lenses are required.
If the upper limit is exceeded, a large number of lenses will be required to generate the desired distortion. Also, conditional expression (18)
If the principal point relationship becomes longer than the upper limit of conditional expression (19), the total lens length becomes too large.

On the other hand, an effective means for correcting the distortion aberration of the second lens group to be under is a lens having a positive refractive power at a position closer to the image side than half of the total length of the second lens group and having a convex surface facing the object. Is to place. The radius of curvature R _X of the convex surface is preferably 0 <1 / R _X <6 / f _T (20). If the curvature exceeds the upper limit and becomes tight, it becomes difficult to correct astigmatism and coma.

By the way, in the formula (10) of the present invention, if the height of the off-axis chief ray in the variable apex angle prism becomes large in absolute value,
The astigmatism of the lens group and the contribution of Petzval's term increase. Since (3III ₂ + P ₂ ) has a positive value in the lens system which corrects the distortion aberration, which is an important aspect of the present invention, increasing the value of _{P with} a positive value is disadvantageous in correcting the eccentric distortion aberration.
_{Since P} is related to the distance l from the diaphragm to the variable apex prism, when the focal length of the entire system is normalized to 1, the variable apex prism of the variable apex is satisfied so that the condition of −0.4 <l <0.25 is satisfied. It is good to decide the position. If the variable apex angle prism is positioned on the front side of the optical system beyond the lower limit, the diameter of the variable apex angle prism becomes large and the meaning of incorporating it becomes small.

When the value exceeds the upper limit, a larger amount of distortion must be generated in the second lens group to correct decentering distortion, and a large number of lenses are needed.

FIG. 1 is an actual example of the present invention, which is used as a vibration-proof optical system. It is composed of a first lens group that is immobile with respect to eccentric drive from the object side, a variable apex angle prism, and a second lens group that is immobile with respect to eccentric drive, and is also shown by the output of a shake detector (not shown) such as an acceleration sensor. The image is deflected so as to reversely correct the image blur by changing the apex angle of the variable apex prism with an actuator. The variable apex angle prism is made by sandwiching transparent silicone rubber between two parallel plane plates.

In this embodiment, the third-order distortion aberration coefficient V ₁ of the first lens group I is −9.03, and the third-order distortion aberration coefficient of the second lens group II is
V ₂ has a value of 7.8, that is, the first lens group I causes distortion aberration in the over direction, and the second lens group II causes distortion in the under direction. It is corrected to a small value of 0.27% at 21.63 mm. Thus, the third-order distortion aberration V _{2 of} the second lens group II is V ₂
Since> 0, the eccentric distortion when the image is deflected by 1 mm by the variable apex angle prism is corrected to a small value of 0.017 mm at an image height of 18 mm. Here, the eccentric distortion aberration means the difference between the deflection amount of the principal ray of the off-axis light beam and the deflection amount of the principal ray of the light beam focused on the center. By the way, when the principle of the present invention is not introduced even with lenses having the same power arrangement, that is, when the variable apex angle prism is arranged at the most front, the center point is deflected by 1 mm and the image height is 18 m.
The point m is deflected 1.064 mm, so the eccentric distortion is 0.06
It is a big value of 4.

The first lens group I of the first embodiment is at D11 from the object side to the first positive lens front group II and the first negative lens rear group I-2, and the second lens group II is at D24 the object side. Is divided into a second negative lens front group II-1 and a second positive lens rear group II-2, and the distortions in the first lens group I and the second lens group II can easily satisfy the conditional expressions (4) and (5). The layout is set to satisfy the requirements.

In the present invention, as shown in FIG. 3, a plano-concave lens P ₁ and a plano-convex lens P _{2 in} which the facing spheres have substantially the same radius of curvature are relatively rotated along the spherical surface. The principles of the invention are also applicable to fusion for variable apex brisms.

Further, the present invention is not limited to the vibration isolation device, but can be applied to optical devices such as a sicht lens and an auto level.

In the present invention, the surfaces on both sides of the variable apex angle prism may be perfectly flat or may have a lens action on the prism itself, and at that time, a gentle curvature of 1.5f _T <| R | Is also good.

By the way, in the present invention, fixed means immovable with respect to eccentricity, and it may move along the optical axis for focusing or zooming.

An example is shown in FIG. The first lens group I comprises a focusing lens F that moves along the optical axis during focusing, a variator lens V and a compensator lens C that move along the optical axis during zooming. The second lens group II is composed of a relay lens R that performs an image forming action. The distortion of the first lens group I is kept over while the distortion of the second lens group II is kept under.

Next, numerical examples of the present invention will be shown. In the numerical example
Ri is the radius of curvature of the i-th lens surface in order from the object side, Di
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and the Abbe number of the glass of the i-th lens in order from the object side.

[Advantages of the Invention] In an image deflection optical system having a configuration in which a variable apex angle prism is built in a lens system, the diameter of the variable apex angle prism can be reduced, and thus the size of the deflection optical system including the surrounding mechanism can be reduced. Although there is an advantage that the driving force of the variable apex angle prism can be reduced, the decentration distortion aberration generated in such an image deflecting optical system can be corrected to be small according to the principle of the present invention. Therefore, when the image blur correction is performed, the flow of the peripheral image as shown in FIG. 7C is not generated, and when the image blur correction is performed, a high quality image is obtained over the entire screen.

The present invention can also be effectively applied to an optical system that deflects a beam using a variable apex angle prism.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of a numerical example according to the present invention, FIG. 2 (A) is an aberration diagram in its initial state, and FIG. 2 (B) is an aberration diagram when 1 mm image deflection is performed on the image plane. FIG. 3 is a sectional view of a lens according to a second embodiment of the present invention, FIG. 4 is a sectional view of a lens according to a third embodiment of the present invention, and FIG. , FIG. 6 and FIG. 7 are explanatory views of the principle of generation of decentering distortion, and FIG. 8 is a diagram illustrating the effect of decentering distortion on an image. I: first lens group, II: second lens group P: variable apex angle prism

Claims (5)

(57) [Claims] 1. A first fixed unit for eccentricity, in order from the object side.
An image deflection function is provided which has a lens group, a variable apex prism with a variable apex angle, and a second lens group that is fixed with respect to eccentricity, and which deflects an image by changing the apex angle of the variable apex angle prism. In the optical system provided, when the distortion aberration coefficients of the first lens group and the second lens group when the focal length of the entire system is normalized to 1 are V ₁ and V ₂ , respectively, V ₂ > 0 An optical system having an image deflection function, which satisfies the condition of −1.3 <V ₁ / V ₂ <−0.7. 2. A first lens front group, a first lens rear group, a second lens front group, and a second lens group, respectively, with a largest air gap in each of the first lens group and the second lens group. The focal length of each group is f _I-1 , f _I-2 , f _II-1 , f
_II-2 , and when the focal length of the entire system is f _T , it satisfies the conditional expression 0.4 <f _I-1 / f _T <1.7 0.05 <f _II-2 / f _T <0.7. An optical system having an image deflecting function according to claim 1. 3. A principal point interval between the first lens front group and the first lens rear group is e _I , and a principal point interval between the second lens front group and the second lens rear group is e _II . 0.1 <| f _I-2 | / f _T <0.7, f _I-2 <0 0.1 <| f _II-1 | / f _T <0.5, f _II-1 <0 0.25 <e _I / f _T < The optical system according to claim 2, wherein 0.9 0.04 <e _II / f _T <0.3 is satisfied. 4. The second lens group is the first lens group of the second lens group.
The image deflecting function according to claim 1, further comprising a lens having a positive refracting power and having a convex surface facing the object, which is located closer to the image side than 1/2 of the distance from the surface to the final surface. Optical system with. 5. A patent characterized in that when the focal length of the entire system is standardized to 1 and the distance from the diaphragm of the optical system to the variable apex angle prism is l, -0.4 <l <0.25 is satisfied. An optical system having an image deflecting function according to claim 1.