JPH02168223A - Optical system having image deflecting function - Google Patents

Abstract

PURPOSE:To correct small an eccentric distortion generated in an image deflection optical system by constituting the optical system so that distortion coefficients of a first lens group and a second lens group at the time when a focal distance of the whole system is normalized to '1' satisfy specific conditions. CONSTITUTION:The system is provided with a first lens group I which is fixed with regard to eccentricity, a variable apex angle prism 4 whose apex angle is variable, and a second lens group II which is fixed with regard to eccentricity, and provided with an image deflecting means for varying an apex angle of a variable apex angle prism P so that an image is deflected. In this state, when distortion coefficients of a first lens group I and a second lens group II at the time when a focal distance of the whole system is normalized to '1' are denoted as V1 and V2, respectively, such an aberration system as satisfies conditions of an expression I is taken. In such a way, an eccentric distortion of the optical system which is provided with the variable apex angle prism P on the inside of the lens and executes an image deflection can be corrected small.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a photographing system having an image deflecting means, and in particular, a variable apex prism having a variable apex angle is provided in a lens system, and the variable apex angle is The present invention relates to a photographing system having an image deflecting means suitable for a photographic camera, a video camera, etc., in which a photographed image is deflected by a prism to correct image blur caused by vibration or the like.

[Conventional technology] When photographing from above a moving vehicle, vibrations are transmitted to the photographing system.
A number of photographic systems have been proposed in the past that have image deflection means that compensate for the blurring of images by arranging parallel plane plates or variable apex angle prisms in the optical system. ing.

For example, Japanese Patent Publication No. 56-21133 proposes an imaging system that uses a variable apex angle prism to correct image blur. In this publication, a liquid or a transparent elastic body is sealed between two parallel plane glasses, and the angle formed by the two plane parallel plates is made variable to correct image blur.

In addition, the same publication proposes an imaging system in which image blur is corrected by varying the angle formed by opposing planes by sliding a plano-convex lens and a plano-concave lens having curvature between spherical surfaces.

In the conventional example disclosed in this publication, since the variable apex angle prism is provided in the lens system, there is an advantage that the diameter of the variable apex angle prism can generally be made small.

[Problem to be solved by the invention] However, if a variable apex angle prism is provided inside the lens system as in the conventional example described above, eccentric distortion occurs when the image is deflected, that is, when the apex angle is changed. It has the disadvantage that it is thick (this will be explained below).

FIGS. 6 and 7 are diagrams showing how eccentric distortion aberration occurs in a variable apex angle prism.

FIG. 6(A) shows a reference state in which the two surfaces of the variable apex angle prism are parallel, and the ray 0. a and b respectively indicate the chief rays of the light beams that form images at the screen center 0' and off-axis a/ and bl. 6(B) and 7 show the chief ray 0.0 when the variable apex angle prism has an apex angle of A. a,
This shows the state of b. The angle of view is θ, and a light ray that enters at an angle θ into a variable apex prism whose second surface is tilted A and has an apex angle of A is expressed as θ1 = sin” (sin θ/N
P) (1) θ2=θ, +A
(2) θp = Sjn-' (N p
'Sjnθ2) A As expressed by the equation (3), the beam is refracted and exits the variable apex prism at an angle of θp with the optical axis. Here, θ1 is the refraction angle at the first surface of the variable apex prism, θ2 is the incident angle at the second surface, θ2 is the exit angle, and θp is the angle that the exit light ray makes with the optical axis. Furthermore, N
P indicates the refractive index of the prism. And θ with respect to the optical axis O
The chief ray with angle p is y = f - tan /l?
The image will be formed at an image height represented by p.

Therefore, if the deflection angles δ (δ = θp - θ) of the principal rays on the second surface of the variable apex prism are all the same, the image will be deflected while maintaining its original shape on the image plane. However, in reality, when the angle of incidence on the variable apex prism differs, the deflection angle of each principal ray also differs, and as shown in FIG. 6(B), each point o/ on the image plane,
a/ and bl behave differently. To show this quantitatively, in the variable apex angle prism shown in Fig. 7, the ratio of the change in the exit angle fidθp when the apex angle changes by a small angle dA from the reference state, that is, the sensitivity to the variable apex angle prism, is When expressed as a function of the incident angle θ, it can be shown as follows. This equation shows that the absolute value of the incident angle θ is large (indeed, the sensitivity dθP/dA becomes large with a positive value).

As shown in FIG. 7, since the angle of incidence of the axial ray O on the prism surface is small, the deflection angle δ (δ=θ2
-θ) is proportional to the apex angle A, that is, δ# (NP-
1) Indicated by A.

On the other hand, when the angle of incidence on the second surface is relatively large, such as an off-axis ray a, even if the apex angle A changes by the same angle A, the deflection angle is expressed by the old formula δ = (N, -1)A. takes a value that is larger in absolute value than the value given.

For example, when the apex angle of ray a becomes A in the direction shown in Fig. 7, the incident angle θ2 on the second surface of the variable apex prism changes to be larger than the reference state, so the inclination angle θ2 of the emitted light becomes θ+
becomes larger than δ. Therefore, on the image plane, it is distorted in the over direction as shown by ad in FIG. 6(B).

On the other hand, when the apex angle of the ray of light becomes A, the angle of incidence θ2 on the second surface of the variable apex prism changes to be smaller in absolute value than the reference state, so the inclination angle θ1 of the emitted light is θ1 in absolute value. It becomes smaller than 10δ. Therefore, on the image plane, b in Fig. 6(B)
As shown in 7I, distortion occurs in one direction.

When eccentric distortion aberration exists in this way, the image of the object shown in FIG. 8(A) is distorted into the shape shown by the solid line in FIG. 8(B).

Note that the dotted line is an ideal image without distortion.

Therefore, in an anti-vibration optical system that corrects image blur caused by camera shake by deflecting the image in the opposite direction using a variable apex prism, if there is eccentric distortion as described above, the center point of the screen and the axis Since the amount of movement differs at the outer points, even if image blur is corrected at the center of the screen, image drift will occur at the periphery. FIG. 8(C) shows the result of image pre-correction of an object like that in FIG. 8(A) using an anti-vibration optical system with eccentric distortion aberration.

The configuration in which the variable apex angle prism is provided inside the lens system has the advantage that the diameter of the variable apex prism can be reduced as described above. However, in a telephoto objective lens where image stabilization is desired, the angle of inclination of the principal ray of the off-axis beam becomes large, and in order to obtain the same amount of deflection on the image plane, the angle of inclination of the principal ray of the off-axis beam becomes larger than when it is installed in front of the lens system. The need to change the apex angle tends to cause larger eccentric distortion due to these two factors.

SUMMARY OF THE INVENTION In view of this problem, it is an object of the present invention to provide an optical system that has high optical performance, particularly an image deflection function with good distortion aberration, while reducing the size of the optical system.

[Means for solving the problem (and operation)] The present invention provides, in order from the object side, a first lens group that is fixed with respect to eccentricity;
It had a variable apex angle prism with a variable apex angle, a second lens group whose eccentricity was fixed, and an image deflecting means configured to deflect an image by changing the apex angle of the variable apex prism. In the optical system, when the focal length of the entire system is normalized to 1 and the distortion aberration coefficients of the first lens group and the second lens group are respectively V and V2, v2>0 (4) 1 By adopting an aberration correction method that satisfies the following conditions: .3<V, /V2<-0,7 (5), a variable apex prism can be installed inside the lens to reduce eccentric distortion of the optical system that deflects the image. The purpose is to reduce (correct) aberrations.

〔Example〕

The present invention will be explained in detail below. FIG. 5 is a diagram showing a schematic diagram of an optical system according to the present invention. ■ The variable apex prism P tends to cause excessive distortion, while the variable apex prism P
The first lens group is placed in front of the variable apex prism P, and the second lens group is placed behind the variable apex angle prism P. F indicates the film surface.

a is the angle of view θ. shows the chief ray of

In the optical system shown in this example, the first lens group (■) and the second lens group (■) each have large distortion, but especially before the apex angle of the prism P is changed, that is, in the reference state. The over distortion generated by the first lens group is canceled out by the under distortion generated by the second lens group, and the entire imaging system (I, P,
n), the aberrations are well corrected as shown in FIG. 5(A).

That is, the distortion generated by the first lens group I and the second lens group ① in the reference state are respectively Dis (θo)InDi
When s (θo)n, the following relationship is satisfied: Dis (θo)1 = -Dis (θo)a.

Now, next are the two lens groups 1. FIG. 5(B) shows a state in which the aberrations of II are corrected in this way and the apex angle is changed to perform image deflection. The angle of view θ is the same as the initial state. Naturally, the chief ray causes distortion in the first lens group (2) with exactly the same value as in the initial state.

The principal ray a exiting the first lens group I at an inclination angle of θ is deflected by Δ by the variable apex angle prism P with an apex angle of A, but as mentioned earlier, the rays near the optical axis Deflection amount δ#
(NP-1) It is deflected more than A, and the amount of deflection is excessive.

Therefore, the chief ray exiting the variable apex angle prism P is (θ + Δ
) and enters the second lens group (2) at an inclination angle that is Δ larger than the reference state. At this time, the inclination angle θ of the second lens group ■
The amount of distortion when the tilt angle is (θ + Δ) is thicker in one direction than the amount of distortion when the angle of inclination is (θ + Δ). The difference between the amount of deflection on the image plane and the amount of deflection of the ray O incident on the optical axis can be reduced (corrected. In other words, the eccentric distortion aberration can be reduced). The relationship of distortion aberration at this time is Dis(θo)t+Dis(θ*A)P#Di
It can be expressed as s(θ+Δ)■. Furthermore, Dis (θ
, A) P represents the distortion caused by the variable apex angle prism having the apex angle of A, and Dis (θ+Δ)n represents the distortion of the second lens group of the ray with the inclination angle (θ+Δ).

Here, the necessary condition that the distortion increases as the inclination angle of the off-axis beam incident on the second lens group increases is the second
When the third-order distortion aberration coefficient of the lens group is V2, v 2>o (4) is satisfied. Note that this equation (4) means that the distortion is under.

In order to properly correct distortion aberration throughout the entire process from the initial state to the state where the image is deflected, the first
When the third-order distortion aberration coefficient of lens group (2) is V, it is preferable to satisfy the following conditional expressions: 1.3<V, /V2<-0,7 (5).

If the upper limit of conditional expression (5) is exceeded, the distortion of the first lens group becomes excessively excessive, and when the photographing system as a whole is viewed, distortion that tends to be excessive remains in the initial state or during deflection. Undesirable. On the other hand, if the lower limit is exceeded, the distortion of the second lens group H will be excessively under-distorted, and the distortion aberration that tends to be under-exposed will remain in the photographing system as a whole, which is not desirable.

Next, the theoretical basis of the technology related to the present invention will be explained using decentering aberration theory. Various attempts have been made to derive the relational expression between decentering aberration and aberration coefficient, but here we will use the format presented by Matsugen at the 23rd Annual Conference of the Japan Society of Applied Physics (1962). According to this, the aberration after eccentricity (ΔY') in the third-order aberration region is expressed as the sum of the aberration before eccentricity ΔY and the eccentric aberration ΔY(ε) caused by eccentricity, as shown in equation (6), and when a certain surface Aberration ΔY (
ε) is expressed as in equation (7).

Δ′Y field ΔY+ΔY(ε) −(1−Np) (h p DI 2−h P v2
)(Vg2) = (1--) a P + (1-
N,) h,p2p +3 (I Np) h,v2(t-N,) hp(
3m 2 +P2) 1 Eccentric distortion aberration (V e l
) and eccentric distortion aberration (Vε2), applied to the variable apex angle prism with the inclined surface as a flat surface, and expressed by the paraxial amount and the aberration coefficient of the second lens group, are expressed by equations (8) and (9). be.

If the normal line of the prism surface is tilted in the meridional cross section, then the eccentric aberration and the decentered additional aberration are collectively expressed in the meridional cross section by the equation (lO).

When a variable apex angle prism is provided in a lens as in the present invention, the height hP of the paraxial chief ray of the variable apex angle prism becomes a small value. Among them, the dominant value is the two terms shown in equation (11) in the parentheses of equation (10). Since the first term of equation (11) takes a positive value, the second term takes a negative value, so V2
>O, this will contribute to reducing eccentric distortion aberration. If it is desired to correct decentering distortion to almost zero, it is sufficient to generate the distortion aberration coefficient v2 of the second lens group so as to satisfy equation (12). In this case as well, the distortion aberration coefficient vI of the first lens group must satisfy equation (5) in order to correct the distortion aberration of the entire system in its reference state.

Therefore, when IP is normalized to the focal length of the entire system as 1, and the inclination angle when it enters the lens system is (the inclination angle of the off-axis principal ray entering the variable apex prism when 1 = -1), Even better results can be obtained if the third-order distortion coefficient of the second lens group is determined so as to satisfy the following.

Furthermore, in this embodiment, the first lens group and the second lens group are separated by a large air gap and have a large air gap, respectively, to form a first lens front group, a first lens rear group, and a second lens front group.
The second lens is divided into the rear group, and the focal length of each lens is set to fK in order.
-+ and fs-2 and f+ and fn-2, and when the focal length of the entire system is f□, 0.4< f X-t/f
, <1.7 (14)0.05<f n
-z/f T <0.7 If we adopt a focal length that satisfies the conditional expression (15), a positive lens group with relatively strong power will be placed at a position away from the variable apex prism. , it is possible to easily correct not only the distortion aberration related to the present invention but also other aberrations. In other words, if the focal length exceeds the lower limit of conditional expressions (14) and (15) and the focal length is short, even if it is advantageous for correcting distortion of each lens group, it will be difficult to correct spherical aberration and astigmatism. On the other hand, conditional expression (14).

Exceeding the upper limit of (15) is not preferable because the optical system and the prism themselves become larger.

Furthermore, the distance between the principal points of the first lens front group and the first lens rear group is e! , the distance between the principal points of the second lens front group and the second lens rear group is e
When a, 0.1<l fl-21/fT<0.7. f
I-2<O(16)0.1<l fn-+ l/f
T<0.5. f a-+<O(17)0.25
<e! / f r < 0.9 (
18) By adopting a power arrangement that satisfies 0.04<e a/fT <o, 3 (19), good optical performance can be achieved with a smaller lens configuration. If the lower limits of conditional expressions (16) and (17) are exceeded and the powers of the first lens rear group and the second lens front group become strong, it becomes difficult to correct spherical aberration and coma aberration, so it is necessary to maintain optical performance. This requires many lenses.

If the upper limit is exceeded, a large number of lenses will be required to generate the desired distortion. Also, conditional expression (18
) and the interval between principal points is long (
In this case, the total length of the lens becomes too large.

On the other hand, an effective means of under-correcting the distortion aberration of the second lens group is to use a lens that has positive refractive power at a position closer to the image side than 1/2 of the total length of the second lens group and has a convex surface facing the object. It is to place. And the radius of curvature RX of the convex surface is 0 < l / Rx < 6 / f T
(20) is desirable. If the curvature becomes steeper than the upper limit, it becomes difficult to correct astigmatism and coma.

By the way, in equation (10) of the present invention, if the height of the off-axis principal ray in the variable apex angle prism increases in absolute value, the second
The contributions of the astigmatism and Petzval terms of the lens group increase. In a lens system that corrects distortion aberration like the present invention, (3<2>+P2) takes a positive value, and therefore, it is disadvantageous for eccentric distortion aberration correction to have a large positive value.

5. is related to the distance l from the aperture to the variable apex prism, so when the focal length of the entire system is normalized to 1, -
It is preferable to determine the position of the variable apex angle prism so as to satisfy the following condition: 0.4<1<0.25. If the variable apex angle prism is located in front of the optical system beyond the lower limit, the diameter of the variable apex prism becomes large, and there is little point in incorporating it.

If the upper limit is exceeded, larger distortion must be generated in the second lens group in order to correct decentering distortion, and a large number of lenses are required.

FIG. 1 shows an embodiment of the present invention, which is used as an anti-vibration optical system. From the object side, it consists of a first lens group that does not move with respect to eccentric drive, a variable apex angle prism, and a second lens group that does not move with respect to eccentric drive. The apex angle of the variable apex prism is changed using an actuator to deflect the image so as to reversely correct image blur. The variable apex angle prism is made of transparent silicone rubber sandwiched between two parallel flat plates.

In this example, the third-order distortion aberration coefficient V of the first lens group I has a value of -9.03, and the third-order distortion aberration coefficient v2 of the second lens group II has a value of 7.8, that is, , first lens group I
Distortion is generated in one over direction in the second lens group (2), and in one under direction in the second lens group (2), and the distortion in the entire system is as small as 0.27% at an image height of 21.63 mm. It has been corrected. In this way, 3 of the second lens group H
The next distortion aberration v2 is v2>0, so when the image is deflected by 1 mm with the variable apex angle prism, the eccentric distortion aberration is the image height 1
8 mm is corrected to a small value of 0.017 mm.

Here, decentering distortion means the difference between the amount of deflection of the principal ray of the off-axis beam and the amount of deflection of the principal ray of the beam focused on the center. By the way, even if the lens has the same power arrangement, if the principle of the present invention is not introduced, that is, when the variable apex prism is placed at the frontmost position, the center point is deflected by 1 mm, and the image height is 18 mm.
The point is deflected by 1.064 mm, and therefore the eccentric distortion aberration has a large value of 0.064.

The first lens group (2) of the first embodiment includes the first positive lens front group 1-1. The first negative lens rear group 1-2 and the second lens group (2) are divided from the object side by D24 into a second negative lens front group n-1 and a second positive lens rear group 11-2,
Distortion aberration between the first lens group I and the second lens group ■ is expressed by the conditional expression (
The power arrangement is such that 4) and (5) can be easily satisfied.

In addition, in the present invention, as shown in FIG. 3, a plano-concave lens P whose spherical surfaces facing each other have a radius of curvature of -1 and a plano-convex lens P2 are rotated relative to each other along the spherical surfaces. The principles of the present invention can also be effectively applied to variable apex angle prisms.

Furthermore, the present invention is not limited to image stabilization devices, but can also be applied to optical devices such as shift lenses and autolevels.

In the present invention, the surfaces on both sides of the variable apex angle prism do not have to be completely flat, but the prism itself may have a lens function, and in that case, it has a gentle curvature of 1.5 f Also good.

Incidentally, in the present invention, fixed means immobile with respect to eccentricity, and may be moved along the optical axis for focusing or zooming.

An example is shown in FIG. The first lens group I is composed of a focusing lens F which moves along the optical axis during focusing, a variator lens V and a compensator lens C which move along the optical axis during zooming. The second lens group ■ is a relay lens R that performs an imaging function.
Consists of.

The distortion aberration of the first lens group 1 is maintained to be excessive, while the distortion aberration of the second lens group (2) is maintained to be under.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Table 1 Numerical example 1 F=300 FNO=1:2.8 2W=4.12゜ 1 = 1.43387 2 = 1.49700 3 = 1.77250 4 = 1.56873 N 5 = 1.80518 N 6=1.56873 N 7 = 1.56732 N 8 = 1.8740O N 9 = 1.49700 1=95.1 2=81.6 3=49.6 4=63.2 ν　5=25.4 ν　6=　63.2 ν　7=42.8 ν　8=35.3 ν　9=　81.6 N12=1.51633 N13 = 1.4970O N14=1.69895 N15=1.7620O N16=1.8061O N17=1.85026 C12=64.1 ν13=81.6 C14=30.1 ν15=40.1 C16=40.9 ν17 = 32.3 It is located at 2.5 from the 19th surface of the second diaphragm toward the image side.

〔Effect of the invention〕

An image deflection optical system that has a variable apex angle prism built into the lens system can reduce the diameter of the variable apex prism (this makes it possible to reduce the size of the deflection optical system, including the surrounding mechanisms). Although there is an advantage in that the driving force of the prism can be reduced, the principle of the present invention also makes it possible to correct decentering distortion generated in such an image deflection optical system to a small value.Therefore, when image pre-correction is performed, ), and a high-quality image can be obtained over the entire screen when image pre-correction is performed.

Further, the present invention can be effectively applied to an optical system that uses a variable apex angle prism to deflect a beam.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a lens in a numerical example related to the present invention, Figure 2 (A) is an aberration diagram in its initial state, and Figure 2 (B) is when the image is deflected by 1 mm on the image plane. Aberration diagram, 3rd
The figure is a cross-sectional view of a lens according to a second embodiment of the present invention;
The figure is a sectional view of a lens of a third embodiment of the present invention, and a fifth embodiment of the present invention.
The figure is a schematic diagram showing the principle of optical action related to the present invention.
Figure 7 and Figure 7 are explanatory diagrams of the principle of generation of eccentric distortion aberration, and Figure 8.
The figure is a diagram illustrating the influence of eccentric distortion aberration on an image. ! ...First lens group ■...Second lens group P
...Variable vertex angle prism JjJII brother astigmatism 1 All songs A and chromatic aberration ■ n Engineering P ■

Claims (1)

[Scope of Claims] (1) In order from the object side, there is a first lens group whose eccentricity is fixed, a variable apex angle prism whose apex angle is variable, and a second lens group whose apex angle is fixed, the variable apex angle being fixed. In an optical system with an image deflection function that deflects an image by changing the apex angle of the prism, the focal length of the entire system is set to 1.
When the distortion aberration coefficients of the first lens group and the second lens group when normalized are V_1 and V_2, respectively, V_2
An optical system having an image deflection function characterized by satisfying the following condition: >0 -1.3<V_1/V_2<-0.7. (2) The first lens group, the first rear lens group, the second front lens group, and the second rear lens group in order, separated by the 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, 0.4<f_ I ____1/f_T<1.7 0.05<f_II_-_2/f_T<0 An optical system having an image deflection function according to claim 1, wherein the optical system satisfies the conditional expression .7. (3) When 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_II, then 0 .1<|f_
I ＿−＿2｜/f_T<0.7, f_ I ＿−＿2＜0
0.1<|f_II_−_1|/f_T<0.5, f_I
The optical system according to claim 2, characterized in that it satisfies the following: I_-_1<00.25<e_I/f_T<0.9 0.04<e_II/f_T<0.3. (4) The second lens group has a lens having positive refractive power and having a convex surface facing the object, located closer to the image side than 1/2 of the distance from the first surface to the final surface of the second lens group. An optical system having an image deflection function according to claim 1. (5) When the focal length of the entire system is standardized to 1 and the distance from the aperture of the optical system to the variable apex prism is l, it is characterized by satisfying -0.4<l<0.25. An optical system having an image deflection function according to claim 1.