JPH0760224B2 - Shooting optical system for image stabilization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to image stabilization (or image stabilization) for correcting image blur that often occurs during photography by decentering a part of the optical system in parallel. The present invention relates to a suitable photographing optical system.

[Prior art]

In normal shooting, the exposure time is long, so that a good image cannot be obtained due to camera shake or image blurring when shooting on a moving car, ship, or helicopter. Especially in a telephoto lens, the image blur is remarkable. Therefore, a vibration-proof optical system is indispensable for a camera.

There have been several proposals that use a rhythm with a variable apex angle as an optical system to prevent image blur, but with this method, a larger drive system that changes the apex angle and a new photographic lens are used. I had to add this variable apex angle prism.

On the other hand, as shown in Fig. 11, a lens group that has a converging function.
A proposal has been made to form an afocal optical system by 1a and a lens group 1b having a diverging action, and then to construct a movable lens group 2 movable in a direction perpendicular to the optical axis to perform image stabilization.
No. 47012 publication.

According to this application, when the camera vibrates due to some influence and the image shifts, the shift amount at the image point is calculated by the acceleration sensor 4 and the moving lens 2 is moved in a direction to cancel the shift amount. It can be moved to keep the image stationary. Three
Is an actuator such as a voice coil or a stack of piezo elements.

However, in this application, aberrations caused by decentering, that is, decentering aberrations are not considered.

In addition, the embodiment constitutes an afocal optical system, and the ratio of the amount of movement of the image to the amount of movement of the moving lens, that is, the sensitivity l is limited to "1".

[Problems to be solved by the invention]

An object of the present invention is to provide a photographic optical system that reduces decentering aberration caused by decentering.

In the present invention, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group are provided, and the second lens group is arranged with respect to the optical axis. In a photographing optical system that decenters an image by eccentricity, the second lens group includes at least one positive lens,
With at least one negative lens, the focal length of the entire system is f, and the focal length of the second lens group is f _II , the conditional expression of −1.65 <f _II /f<−0.1 is satisfied. There is.

〔Example〕

 Examples of the present invention will be described below.

First, in general, when some lens groups are decentered with respect to the optical axis, the aberration amount of the entire optical system is ΔY, and the decentering amount E with respect to the optical axis is
And decentering aberration caused by decentering the moving lens group is ΔY (E), ΔY = [abnormality in reference state] + ΔY (E)

Further, even in the reference state, there are spherical aberration, coma aberration, astigmatism, field curvature, distortion aberration, etc.
The following is also present in (E).

IIE, IIIE, PE, VE1, and VE2 are the first-order eccentric coma, the first-order eccentric astigmatism, the eccentric field curvature aberration, and the first-order eccentric distortion, respectively.
Next eccentric distortion aberration, eccentric distortion aberration coefficient of eccentric distortion aberration, By R. and W. Azimuth. E is the amount of parallel eccentricity.

In other words, in an optical system that prevents image blur by decentering a part of the lens group of the photographing optical system, in order to maintain good optical performance, it is preferable to maintain spherical aberration, coma aberration, Five aberrations, point aberration, field curvature, and distortion, and aberrations caused by decentering, that is, decentering coma aberration, decentering astigmatism, decentering field curvature, and decentering distortion must be suppressed. .

Therefore, in the present invention, in order to reduce the above-mentioned aberrations, decentering aberrations, etc. in the reference state, the first lens group 1 has a positive refractive power, and the second lens group decenters in the direction perpendicular to the optical axis to correct image blur. 2 has a negative refracting power, and the third lens group 3 has a positive refracting power to reduce decentration aberrations in a balanced manner. Further, when the second lens group is equipped with at least one positive lens and at least one negative lens, and the focal length of the entire system is f and the focal length of the second lens group is f _II. , −1.65 <f _II /f<−0.1 (1) The conditional expression is satisfied.

Conditional expression (1) relates to the ratio of the focal length of the second lens, which is also the correction lens, to the focal length of the entire system, and is the ratio of the amount of movement of the image to the amount of movement of the lens, so-called sensitivity l, and good optical This is for maintaining appropriate physical performance.

When the value goes below the lower limit, the sensitivity decreases, and it is necessary to increase the amount of movement of the second lens group, which increases the size of the driving mechanism. Further, the moving lens has to be moved relatively large, so that many decentration aberrations occur.

If the upper limit is exceeded, the focal length f _II of the second lens group becomes negative and small, and it becomes difficult to correct aberrations in the reference state and when decentering, so a large amount of decentration aberration occurs with a slight amount of decentration. .

By satisfying the above conditional expressions, it is possible to properly maintain the aberration while appropriately maintaining the sensitivity which is also the object of the present invention, but satisfy the following conditional expressions in order to maintain further optical performance. Good thing.

That is, when the focal length of the third lens group is f _III , the conditional expression is 0.15 <f _III / f <3 (2).

Conditional expression (2) relates to the power arrangement of the third lens group, and when it is below the lower limit, f _III becomes small and the refractive power of the third lens group becomes strong, so that aberration in the reference state becomes difficult. come. If the upper limit is exceeded, the refractive power will be too weak, and it will be difficult for the third lens group to cancel decentration aberrations that occur in the second lens group.

Next, it is more preferable to configure the second lens group as follows while satisfying the following conditional expression (1) or (2).

That is, when the curvature of the lens surface closest to the object in the second lens group is R _II1 , by satisfying the condition R _II1 /f>−0.2,0.1<R _II1 / f (3) is there.

Conditional expression (3) relates to the first surface of the second lens group, and if R _II1 /f<−0.2, the first surface becomes a strong concave surface, and coma aberration occurs in the reference state and when decentered. Becomes large and correction becomes difficult. On the other hand, if R _II1 /f<0.15, the first surface becomes a strong convex surface, and spherical aberration in the reference state becomes excessive.

When a positive and negative cemented lens is provided in the second lens group to reduce aberrations such as spherical aberration, when the radius of curvature of the cemented surface of this cemented lens is R _IIc , | R _IIc / f |> 0.05 (4) It is advisable to satisfy the conditional expression.

Conditional expression (4) relates to the radius of curvature of the cemented lens, and if the value goes below the lower limit, the curvature becomes tight and a large amount of high-order decentering aberration occurs.

On the other hand, when the second lens group does not include a cemented lens and has an air lens, the radius of curvature on the object side and the image surface side of the air lens that minimizes the thickness of the air lens are R _IIa and R _IIb , respectively.
Then, it is preferable to satisfy the conditional expression | R _IIa / R _IIb | <1.8 (5).

Conditional expression (5) is the ratio of the radius of curvature of the air lens with the smallest thickness of the second lens group, and if the upper limit is exceeded, the curvature of R _IIb on the image side and the lens surface becomes considerably tighter. ,
It becomes difficult to correct eccentric coma and eccentric astigmatism.

Next, in order to obtain better aberrations while satisfying the conditional expressions (1) and (2), the third lens group may be composed of at least a positive lens and a negative lens, and may be structured as follows.

That is, when the most object side lens surface and the most image side lens surface of the third lens group are R _III1 and R _IIIK , respectively, the conditional expression | R _III1 / R _IIIK | <2.0 (6) To be satisfied.

The conditional expression (6) is a ratio between the first surface and the final surface of the third lens group, and the astigmatism in the standard state and the
This is an expression for maintaining good eccentric astigmatism. If the upper limit is exceeded, decentering astigmatism will become noticeably large.

Next, when the third lens group includes only the air lens, that is, when the third lens group does not have a cemented surface, the focal length of the air lens that minimizes the thickness of the air lens is f _AIR , and 0.05 <| f _AIR /f|<1.8 (7) It is recommended to satisfy the conditional expression.

Conditional expression (7) relates to the focal length (refractive power) of the air lens. When the value goes below the lower limit, the focal length of the air lens becomes smaller, and accordingly the curvature becomes tighter, and higher-order aberrations in the reference state remain. Will end up. On the contrary, when the value exceeds the upper limit, the curvature becomes gentle, and it becomes difficult to cancel the decentering coma aberration generated in the moving lens unit.

Next, numerical examples of the present invention will be shown. Ri in the numerical examples
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 νi
Are the refractive index and the Abbe number of the glass of the i-th lens in order from the object side.

Table 1 shows the numerical values related to the above-mentioned conditional expressions.

As described above, according to the present invention, decentering aberration As described above, according to the present invention, it is possible to provide an optical system in which eccentric aberration is satisfactorily corrected, and the decentering sensitivity is set to an appropriate value to effectively stabilize an image. You can

[Brief description of drawings]

FIG. 1 is a sectional view of an optical system showing a conventional example, and FIGS. 2 to 6 are numerical examples 1 to 5 relating to the present invention, respectively.
FIGS. 7 (A), 8 (A), 9 (A), 10 (A), and 11 (A) are numerical examples 1 to 5, respectively. FIG. 8 is a longitudinal aberration diagram and a lateral aberration diagram when the second lens group II is not decentered (reference state). FIGS. 7 (B), 8 (B), 9 (B), 10 (B) and 11 (B) show the optical axes of the second lens groups of Numerical Examples 1 to 5, respectively. FIG. 6 is a lateral aberration diagram when decentered by 1 mm. I ... 1st lens group II ... 2nd lens group (correction lens group) III ... 3rd lens group

Claims (6)

[Claims] 1. A first lens group having a positive refracting power, a second lens group having a negative refracting power, and a third lens group in order from the object side, and the second lens group with respect to the optical axis. In a photographic optical system that displaces an image by decentering, the second lens group has at least one positive lens and at least one negative lens, and has a focal length f of the entire system,
When the focal length of the second lens group and the f _II, the photographing optical system for image stabilization, characterized by satisfying -1.65 <f _II /f<-0.1 conditional expression. When a wherein a focal length of the third lens group and the _{f III, 0.15 <f III /} f <3 following condition stable image of satisfaction to be Claims paragraph 1, wherein the formula Photographic optical system for commercialization. 3. When the radius of curvature of the lens surface closest to the object in the second lens group is R _II1 , the conditional expression of R _II1 /f<−0.2,0.1<R _II1 / f is satisfied. A photographic optical system for stabilizing an image according to claim 1 or 2. 4. When the second lens group does not include a cemented surface and has only an air lens, the radius of curvature on the object side and the image surface side of the air lens that minimizes the thickness of the air lens are R _IIa , R
_IIb , the photographic optical system for stabilizing an image according to claim 1 or 2, characterized in that the conditional expression | R _IIa / R _IIb | <1.8 is satisfied. 5. When the most object side lens surface and the most image side lens surface of the third lens group are R _III1 and R _IIIK , respectively, | R _III1 / R _IIIK | <2.0 is satisfied. An image pickup optical system for stabilizing an image according to claim 2. 6. When the third lens group does not include a cemented lens and includes only an air lens, and the focal length of the air lens that minimizes the thickness of the air lens is f _AIR , 0.05 <| f _AIR / f A photographing optical system for image stabilization according to claim 5, characterized in that the conditional expression | <1.8 is satisfied.