JPH0778579B2 - Photographic optical system with image deflection function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photographic optical system, and in particular, it is possible to obtain a stable image by deflecting an image. For example, an optical system suitable for a vibration isolation / optical system. Regarding

[Conventional technology]

There are many occasions when a still camera, a video camera, or a handheld camera is used to take a picture on a moving automobile or an airplane where there is a large amount of vibration, and in such a case, the image is likely to be blurred and the image quality is significantly deteriorated. This development becomes remarkable especially as the focal length of the taking lens increases. In recent years, as shooting lenses have become more compact and smaller and lighter, those that were always mounted on a tripod before shooting had more opportunities for handheld shooting because of their importance for maneuverability. Realization in the form is strongly desired.

On the other hand, Japanese Patent Application No. 60-187091 filed by the present applicant discloses a technique which discloses a specific driving mechanism for stabilizing an image by eccentricizing a part of a photographing lens in a direction perpendicular to an optical axis. . Also, Japanese Patent Application No. 61-282371 and Japanese Patent Application No. 61-262115.
The publication discloses a technique for correcting so-called decentering aberration that occurs when decentering.

[Object of the Invention]

The present invention relates to the improvement of the above-described photographic optical system, and particularly to correcting chromatic aberration that remarkably occurs when an image of a photographic system having a relatively long focal length is deflected.

Further, in the present invention, the fixed lens unit 1 which is immovable with respect to the movement in the direction orthogonal to the optical axis, and the correction lens for deflecting the image by eccentrically driving in the direction orthogonal to the optical axis, which is disposed on the image surface side thereof. In the optical system having the group 2, the correction lens group has at least one positive lens, the Abbe number of the positive lens is _P ν _d , the partial dispersion ratio is _P θ _{g, F} , (where
Assuming that the refractive indices for g-line, F-line, and C-line are n _g , n _F , and n _C , respectively, the partial dispersion ratio θ _{g, F} is It is expressed as ) _P ν _d > 75 ― (1) 0.525 < _P θ _{g, F} <0.545 ― (2) The conditional expression is satisfied.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are numerical examples 1 and 2 according to the present invention.
3 is a lens cross-sectional view of a photographic lens corresponding to FIG.

In the figure, 1 is a fixed lens group that is immovable with respect to the direction orthogonal to the optical axis, and 2 is a correction lens group that moves in the direction orthogonal to the optical axis and corrects image blur. The correction lens group 2 is driven by an actuator (not shown) as shown in Japanese Patent Application No. 60-187091. F is a lens group for focus, which is possible in the optical axis direction. In this embodiment,
Further, as shown in the above-mentioned Japanese Patent Application No. 61-282371, the correction lens unit 2 is arranged closer to the image side than the lens unit F for focus, and the decentering aberration caused by the change of the object distance is minimized. Is taking.

By the way, when a part of the lens group of a taking lens having a relatively long focal length such as a telephoto lens is decentered, a large amount of eccentric magnification chromatic aberration among aberrations caused by decentering, so-called eccentric aberration, and deterioration of image quality is caused. Invited. Therefore, even if the correction lens group 2 is aberration-corrected for two normal wavelengths of light without decentering, aberrations remain for other wavelengths, and residual aberrations occur when decentering occurs. The effect of is noticeable, and the image quality is deteriorated.

Therefore, in the present invention, by satisfying the conditional expressions (1) and (2), the residual aberration of the eccentric magnification chromatic aberration described above is favorably corrected over the entire visible wavelength range. Also, the responsiveness to the image blur is enhanced. That is, the correction lens group 2
By using an optical material having low dispersion and anomalous dispersion for the positive lens in the inside, the correction lens group 2 itself can be achromatized by the positive lens and the negative lens having weak refractive power, so that the lens thickness can be reduced. You can thin the thickness. Therefore, the weight of the positive lens can be reduced.

Then, by using a low-dispersion positive lens having an Abbe number larger than 75 shown in the conditional expression (1), the Abbe number is relatively large as a negative lens selected for correction of chromatic aberration, and for example, the content of lead oxide is small. It becomes easier to select the glass material.
If the content of lead oxide in the glass material is small, the specific gravity can be reduced, so that the correction lens group itself can be made lighter, and an optical system with good responsiveness can be achieved.

Further, when a glass material having a low lead oxide content is used for the negative lens, the secondary spectrum can be reduced as compared with the case where a glass material having a large amount of lead oxide is used. For example, fluorite is an optical material with a large Abbé number, which has an Abbé number of 95.15.

Next, the conditional expression (2) relates to the anomalous dispersion of the optical material used for the positive lens of the correction lens group. When the conditional expression (1) is satisfied and the partial dispersion ratio is smaller than the upper limit value, the partial dispersion ratio is large. It is possible to reduce the residual aberration of the eccentric magnification chromatic aberration, and to reduce the color blur when the eccentric drive is performed to correct the image blur. It can also be used to reduce the secondary spectrum of the entire system. Optical materials that exceed the lower limit are
It is difficult to obtain at this time.

By satisfying the above conditional expressions, the object of the present invention can be achieved. However, in order to perform better aberration correction, the correction lens group has at least one negative lens, and the correction lens group has at least one negative lens. When the number is _n ν _d and the partial dispersion ratio is _n θ _{g, F} , 45> _n ν _d … (3) −0.012 < _n θ _{g, F} −0.6438 + 0.001682 ・_n ν _d <−0.003…
It is preferable to satisfy the conditional expression (4).

In addition, if the expression of German optical glass manufacturer Schott is used for general glass, the relation between the partial dispersion θ _gF and the Abbé number νd is assumed to be on the straight line connecting the two glasses K7 and F2. The straight line is θ _{g, F} = 0.6438−0.0
01682 · νd The anomalous dispersion means that the anomalous dispersion largely deviates from this straight line, and the greater the deviation, the higher the anomalous dispersion.

Conditional expressions (3) and (4) are for correcting the chromatic aberration and further enhancing the effect described in the conditional expression (2) by using such an optical material for the negative lens of the correction lens group 2. . Conditional expression (3) is a condition for correcting the chromatic aberration of the correction lens, and if it deviates from the conditional expression, the amount of eccentric chromatic aberration is increased, which is not preferable. Conditional expression (4) represents the deviation of the partial dispersion ratio of the negative lens from the normal glass. If the upper limit is exceeded, further effects cannot be expected.
If the value exceeds the lower limit, it is difficult to manufacture glass.

Further, when the focal length of the positive lens is f _X and the focal length of the entire system is f _T , it is preferable to satisfy the conditional expression of 0.3f _T <f _X <0.7f _T (5).

Conditional expression (5) defines the focal length of the positive lens that satisfies conditional expressions (1) and (2). If the focal length is selected so as not to exceed the upper limit, conditional expression (1), The effect of the lens having the anomalous dispersion described in (2) can be sufficiently exerted. When the value goes below the lower limit, spherical aberration and coma are increased, and annular aberration is also increased, which is preferable. Based on conditional expression (2), the correction lens group further includes a second positive lens. has, when the Abbe's number of the positive lens of said 2 _n2 [nu _d, the partial dispersion ratio and _{n2 θ g, F, 0.003 <} n2 θ g, F -0.6438 + 0.001682 · n2 ν d <0.012 ...
It is preferable to satisfy the conditional expression (6).

Conditional expression (6) defines the condition of the optical material used for the other positive lens so as to further promote the effect described in conditional expression (2), and is defined by the lower limit of conditional expression (6). If the deviation of the dispersion ratio from the normal glass is large, a more sufficient effect can be obtained.

Those exceeding the upper limit are difficult in glass production.

In order to further promote the effect of anomalous dispersion, a positive lens is arranged on the most object side in the correction lens group in which the height h of paraxial on-axis rays is relatively high.

Next, numerical examples of the examples shown in FIGS. 1 and 3 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, and Ni and νi are i-th order from the object side, respectively.
The refractive index and the Abbe number of the glass of the th lens.

Table 1 shows the aberration coefficients of the numerical examples.

In this embodiment, specifically, the positive lens closest to the object side of the correction lens group is made of an optical material having an Abbe number of 81.6, a partial dispersion ratio θ _{g, and} a low dispersion and anomalous dispersion, and the eccentric magnification is The residual aberration of chromatic aberration is corrected to be small over the entire visible light range. Further, since the glass having a very low dispersion is used for the positive lens, the second negative lens can be made of a light glass material having an Abbé number of 34.7 and a small lead content, so that the correction lens becomes light and the drivability of the actuator is good. Also, since a negative lens can be selected to use a glass material having a relatively low refractive index,
The Betz-Bar sum of the correction lens can be reduced, and decentered field curvature and eccentric distortion can be reduced.

In Numerical Example 1, an optical material having anomalous dispersion with an Abbe number of 63.38, a partial dispersion ratio θ _{g, F} of 0.5439, and a deviation of θ _{g, F} from normal glass of 0.0067 for the positive lens closest to the image side of the correction lens. Is used to enhance the above effect.

In Example 2, similarly, an optical material having an Abbe number of 81.6 and a partial dispersion ratio θ _{g, F} of 0.537 is used for the positive lens closest to the object in the correction lens group, and the residual aberration of eccentric magnification chromatic aberration is distributed over the entire visible light range. Although corrected slightly, the anomalous dispersion of the Abe number 34.72, the partial dispersion ratio θ _{g, F} of 0.5821, and the deviation of the partial dispersion ratio θ _{g, F} from normal glass of −0.0033 is also applied to the second negative lens. The effect is enhanced by using the optical material.

[Effect] As described above, according to the present invention, the eccentric magnification chromatic aberration caused by the eccentricity can be corrected well over the entire wavelength range, the weight of the correction lens can be reduced, and a vibration-proof optical system with good response is achieved. To be done.

[Brief description of drawings]

1 and 3 are lens cross-sectional views of Numerical Examples 1 and 2 according to the present invention, and FIGS. 2 and 4 are aberration diagrams of Numerical Examples 1 and 2, respectively.
(A) is a diagram of various aberrations before decentering, (B) is a correction lens group of 2 m
It is a lateral-aberration figure at the time of making it eccentric. ΔM is a meridional image plane, ΔS is a sagittal image plane, d is a d-line, and g is a g-line.

Claims (4)

[Claims] 1. A fixed lens portion which is immovable with respect to a movement in a direction orthogonal to an optical axis, and a correction lens group which is disposed on the image surface side and deflects an image by eccentrically driving in a direction orthogonal to the optical axis. In the optical system including and, the correction lens group includes at least one positive lens and a negative lens, the Abbe number of the positive lens is _P ν _d , and the partial dispersion ratio is _P θ _{g, F} , ( However, if the refractive indices for g-line, F-line, and C-line are n _g , n _F , and n _C , the partial dispersion ratio θ _{g, F} is It is expressed as ), A photographing optical system with an image deflection function, which satisfies the conditional expression _P ν _d > 75 0.525 < _P θ _{g, F} <0.545. 2. When the Abbe number of the negative lens of the correction lens group is _n ν _d and the partial dispersion ratio is _n θ _{g, F} , 45> _n ν _d −0.012 < _n θ _{g, F} −0.6438 + 0 .001682 _n ν _d <−0.003 The photographic optical system with the image deflection function according to claim 1, characterized in that the conditional expression is satisfied. 3. When the focal length of the positive lens is f _X and the focal length of the entire system is f _T , the conditional expression of 0.3f _T <f _X <0.7f _T is satisfied. A photographing optical system having the image deflection function described in the first or second range. 4. The correction lens group further has a second positive lens, where 0.002 < _n2 , where the Abbe number of the second positive lens is _n2 ν _d and the partial dispersion ratio is _n2 θ _{g, F.} A photographing optical system having an image deflecting function according to claim 1, wherein the conditional expression θ _{g, F} −0.6438 + 0.001682 · n ₂ ν _d <0.012 is satisfied.