JPH1144836A - Rear focus type zoom lens including transmitted light quantity adjusting means and image pickup device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of ghost or flare caused by reflected light from the surface of an image pickup element by providing a transmitted light quantity adjusting means consisting of a material element in an optical path where luminous flux is converged or diverged all over the variable power range. SOLUTION: This zoom lens is constituted of a 1st group L1 having positive refractive power, a 2nd group L2 having negative refractive power, a 3rd group L3 having the positive refractive power and a 4th group L4 having the positive refractive power. An aperture diaphragm SP is arranged in front of the 3rd group L3. In the zoom lens, the transmitted light quantity adjusting means EC consisting of the material element whose light incident surface and light emitting surface are parallel planes such as a liquid crystal element or an electrochromic element is arranged in the optical path between the 3rd group L3 and the 4th group L4 where the luminous flux is converged or diverged all over the variable power range. Thus, reflected light from the surface of the image pickup element is prevented from forming an image on the surface of the image pickup element when it is reflected on the light incident surface or the light emitting surface of the material element and returned to the surface of the image pickup element, so that the occurrence of the flare or the ghost is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens including a transmitted light amount adjusting means and an image pickup apparatus using the same, and more particularly to a transmitted light amount adjusting means formed of a physical element such as a liquid crystal element or an electrochromic element. It is suitable for an image pickup apparatus such as a photographic camera, a video camera, and a broadcast camera in which the amount of transmitted light is appropriately adjusted.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. Emphasis is placed on simplification.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens which performs focusing by moving a lens group other than the first group on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which moves and focuses the first lens group, so that the entire lens system can be easily miniaturized, and close-up photography can be performed. In particular, extremely close-up photography is facilitated, and the relatively small and lightweight lens group is moved, so that the driving force of the lens group is small and quick focusing can be performed.

As such a rear focus type zoom lens, Japanese Patent Laid-Open Publication No. 3-15813 discloses a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, in order from the object side.
The zoom lens has four lens groups, a third group having a positive refractive power and a fourth group having a positive refractive power, and performs zooming by changing the distance between the second group and the third group. A zoom lens that focuses by moving some lens groups is disclosed.

In Japanese Patent Application Laid-Open Nos. 61-296317 and 61-296318, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a positive refractive power are sequentially arranged from the object side. The zoom lens has four lens groups, a third group of power and a fourth group of positive refractive power, and performs zooming by changing the distance between the second and third groups. And an aperture stop is arranged between
A zoom lens that performs focus by moving a group is disclosed.

On the other hand, a photographing lens provided with a physical element such as a liquid crystal element or an electrochromic element in an optical path is mounted on a camera body, and the amount of light passing through the photographing lens and reaching the image pickup element is adjusted by the physical element. Various imaging devices have been proposed.

FIG. 14 is a cross-sectional view including the optical axis of a photographing optical system of a camera in which a physical element such as a liquid crystal element is used as a light amount adjusting means in a photographing optical system, and FIG. 15 photographs an EC element (electrochromic element). FIG. 2 is a cross-sectional configuration diagram including an optical axis of a photographing optical system of a camera used as a transmitted light amount adjusting unit in the optical system.

In FIG. 14 and FIG.
Is a lens constituting the photographing optical system, 107 is an optical axis of the photographing optical system, 108 is an imaging surface (imaging element surface), and 109 in FIG.
Is a physical element such as a liquid crystal whose opening area or density can be adjusted, and is electrically connected to a control circuit on the camera body side by an electric signal line (not shown).

Reference numeral 110 in FIG. 15 denotes an EC element whose opening area or density can be adjusted, and is electrically connected to a control circuit on the camera body (not shown) by an electric signal line (not shown).
The control circuit electrically controls the aperture area or the light transmittance of the physical element 109 and the EC element 110 so that a predetermined amount of light is incident on the imaging surface 108.

[0011]

Generally, when a rear focus system is adopted in a zoom lens, the whole lens system can be reduced in size, quick focus can be achieved, and further, advantages such as easy close-up photographing can be obtained.

On the other hand, however, aberration fluctuation at the time of focusing becomes large, and it becomes very difficult to obtain high optical performance over the entire object distance from an object at infinity to an object at a short distance.

Particularly, in a zoom lens having a large aperture ratio and a high zoom ratio, it is very difficult to obtain high optical performance over the entire zoom range and over the entire object distance while simplifying the mechanism.

For example, in the above-mentioned Japanese Patent Application Laid-Open No. 3-15813, the size of the entire lens system is reduced by using a rear focus system. However, the diaphragm is driven to move the diaphragm integrally with the third lens unit. Since the IG meter to be controlled was also moved with the magnification change, the mechanism tended to be complicated.

On the other hand, the surface of a cover glass or the surface of an image pickup device of a CCD or the like, which is currently often used as an image pickup device of a video camera, generally has a high reflectivity. The light is reflected by a lens surface, a lens barrel, or the like, re-enters the image sensor, and causes so-called ghost or flare.

In most cases, an imaging lens of a video camera is provided with an ND filter or the like in the vicinity of an aperture to reduce the amount of light together with the aperture for a high brightness subject. However, in order to dispose the ND filter and the like, a predetermined air gap is required, and there is a problem that the entire length of the lens is correspondingly increased.

The present invention employs a rear focus system which is advantageous for downsizing the lens system, and provides a transmitted light amount adjusting means comprising a physical element in an optical path in which a light beam converges or diverges over the entire zoom range. This prevents ghosts and flares from occurring due to reflected light from the image sensor surface, and extends over the entire zoom range from the wide-angle end to the telephoto end.
It is also an object of the present invention to provide a rear focus type zoom lens including a short transmission length adjusting means having a short overall lens length having good optical performance over an entire object distance from an object at infinity to a very close object and an imaging apparatus using the same. I do.

[0018]

The rear focus type zoom lens including the transmitted light amount adjusting means according to the present invention comprises: (1-1) a first lens unit having a positive refractive power and a negative lens having a negative refractive power in order from the object side. The zoom lens has four lens groups, a second group, a third group having a positive refractive power, and a fourth group having a positive refractive power. The second group is moved toward the image plane to change from the wide-angle end to the telephoto end. A zoom lens that performs magnification and corrects the image plane variation due to zooming by moving part or all of the fourth group, and moves part or all of the fourth group to perform focusing. Providing a transmitted light amount adjusting means using a physical element in an optical path between the third group and the fourth group;
It is characterized in that the amount of transmitted light is adjusted.

The rear focus type zoom lens including the transmitted light amount adjusting means and the imaging apparatus using the same according to the present invention include: (2-1) a rear focus type zoom lens including the transmitted light amount adjusting means of the constitution (1-1). The lens is detachably attached to the camera body.

[0020]

FIG. 1 is a sectional view of an essential part of a first embodiment of an image pickup apparatus using a rear focus type zoom lens including a transmitted light amount adjusting means according to the present invention, and FIGS. FIG. 9 is an aberration diagram at a zoom position at a wide-angle end, a middle position, and a telephoto end in the first embodiment.

FIG. 5 is a sectional view of a principal part of a second embodiment of an image pickup apparatus using a rear focus type zoom lens including a transmitted light amount adjusting means of the present invention, and FIGS.
7 is an aberration diagram at a zoom position at a wide-angle end, a middle position, and a telephoto end.

FIG. 9 is a sectional view of a principal part of a third embodiment of an image pickup apparatus using a rear focus type zoom lens including a transmitted light amount adjusting means according to the present invention, and FIGS. 10, 11, and 12 show a wide angle view of the third embodiment. FIG. 9 is an aberration diagram at a zoom position at an end, a middle, and a telephoto end.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, and L4 is a fourth group having a positive refractive power. . SP denotes an aperture stop, which is arranged in front of the third lens unit L3. GB is a glass block such as a low-pass filter, a face plate, and a color filter. IP is an image plane on which an image sensor such as a CCD is arranged.

EC is a transmitted light amount adjusting means, which is composed of a physical element whose light incident surface and light exit surface such as a liquid crystal element and an electrochromic element are parallel planes, and in which the light flux converges or diverges over the entire zoom range. It is arranged in the optical path of the third and fourth groups.

Thus, when the reflected light from the image pickup device surface is reflected on the light incident surface or light exit surface of the physical element and returns to the image pickup device surface, an image is not formed on the image surface device surface so that flare or ghost is generated. Has been prevented.

The physical element EC may be arranged, for example, before or after the stop as long as the light beam converges or diverges over the entire zoom range, that is, in an optical path that is not parallel.

The physical element as the transmitted light amount adjusting means in the present embodiment is driven and controlled based on a signal from a control circuit provided in the zoom lens main body or the camera main body to change its density, thereby providing a high-luminance subject. When photographing the image, the amount of light passing through the zoom lens and entering the image sensor is adjusted.

In the present embodiment, the physical element EC is disposed in the optical path where the air gap is already secured, and the space is effectively used.

Each element of the first lens unit L1 to the fourth lens unit L4 constitutes one element of a zoom lens (zoom lens unit) ZL. Glass block GB and image sensor are camera body C
It is stored in B. The zoom lens unit ZL is detachably attached to the camera body CB via a mount member (not shown).

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation due to zooming is partly or entirely included in the fourth lens unit. In the present embodiment, all of them are corrected while moving along a convex locus toward the object side.

Also, a rear focus system is employed in which a part or the whole (all in the present embodiment) of the fourth group is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third units are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane fluctuation caused by zooming, and the fourth lens unit is moved to perform focusing. In particular, curve 4 in FIG.
When zooming from the wide-angle end to the telephoto end, as shown in FIGS.
Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as shown by a straight line 4c in FIG.

The video camera (image pickup apparatus) of the present invention comprises at least the zoom lens, glass block GB, image pickup device, image pickup signal processing circuit, control circuit for driving the physical element, and the like.

In this embodiment, as described above, the transmission light amount adjusting means EC is provided between the third group and the fourth group in the rear focus type zoom lens composed of four lens groups having a predetermined refractive power. Appropriately controls the amount of light passing through the luminous object, and effectively prevents the reflected light from the image sensor IP from being reflected by the transmitted light amount adjusting means and returning to the image sensor surface to cause flare or ghost. , High optical performance.

The features of another lens configuration of the rear focus type zoom lens including the transmitted light amount adjusting means of the present invention will be described.

[A1] The focal lengths of the entire system at the wide-angle end and the telephoto end are fW and fT, respectively, and the combined focal lengths of the first to third groups at the wide-angle end and the telephoto end are fMW and fMW, respectively.
fMT,

[0038]

(Equation 2) In this case, the following condition is satisfied: 0.1 <fM / fAM <0.9 (1)

This conditional expression (1) means the degree of convergence of the light beam from the third lens unit. Generally, the most stable aberration correction method is to make the light beam diverged by the zoom unit substantially afocal in the third lens unit. However, FIG.
As a result, as shown in FIG. 3, the bundle of rays coming out of the third group becomes almost parallel rays, and the reflected light from the imaging element surface IP is reflected by this physical element surface EC and re-enters the imaging element surface. Ghosts and flares will occur. This condition (1) effectively prevents this.

Furthermore, in the present embodiment, the total length of the lens can be further shortened by making the light beam emitted from the third lens unit a convergent light beam.

If the lower limit value of conditional expression (1) is exceeded, the light beam becomes almost parallel light, and the reflected light from the image pickup device is effectively removed from being reflected by the physical element surface EC and becoming a ghost or a flare. It becomes difficult to do. Conversely, if the value exceeds the upper limit, the degree of convergence increases and the effect of reducing the size of the lens system increases, but aberration fluctuation due to zooming and focusing increases, making it difficult to perform satisfactory aberration correction over the entire zoom range.

In the present invention, if the upper limit value and the lower limit value of conditional expression (12) are set to 0.16 <fM / fAM <0.6） (1a), flare and ghost can be further stabilized. In addition, it is easy to achieve both aberration correction and shortening of the overall length of the lens.

[A2] The focal length of the second lens unit is f2, and the F-number and the focal length of the entire system at the wide-angle end are FNW and fN, respectively.
W, the focal length of the whole system at the telephoto end is fT,

[0044]

(Equation 3) 0.4 <| f2 | × FNW / fM <0.7 (2)

This conditional expression (2) is equivalent to the focal length f2 of the second lens unit.
And is greatly related to the F-number FNW at the wide-angle end. The second lens unit mainly moves on the optical axis during zooming because of its zooming function. For this reason, the aberration fluctuation that occurs must be corrected well. In particular, coma greatly fluctuates. Conditional expression (2) is for correcting this satisfactorily.

When the value exceeds the lower limit of conditional expression (2), F at the wide-angle end
If the number FNW is brightened or the focal length of the second lens unit is shortened, a high-order coma flare is largely generated and correction becomes difficult. Conversely, if the focal length of the second lens unit is unnecessarily increased beyond the upper limit or the F-number FNW at the wide-angle end is darkened, the optical performance increases, but the overall length of the lens increases.
Miniaturization becomes difficult. Desirably, the range of conditional expression (2) should be suppressed to the range of 0.45 to 0.65.

[A3] One of the aims of the present invention is to achieve a high zoom ratio. It is desirable that the chromatic aberration generated with zooming be canceled in the first and second units. However, the manner of occurrence of chromatic aberration of magnification accompanying zooming differs greatly between the first and second groups, and tends to be overcorrected at the wide-angle end. Therefore, the chromatic aberration of magnification of the fourth group is insufficiently corrected, thereby maintaining the balance of chromatic aberration as a whole.

In this case, the chromatic aberration on the axis can be corrected without greatly disturbing the balance when the zoom ratio is small. Therefore, it is possible to use the third lens unit as a single positive lens. However, when aiming at high zooming and a large aperture as in the present invention, the axial chromatic aberration is insufficiently corrected as a whole and high performance is maintained. Becomes difficult.

Therefore, in the present invention, the third lens unit has an appropriate refractive power N
(1.55 <N) and a positive lens having an Abbe number νd (νd <65) and a meniscus-shaped negative lens having a strong concave surface facing the object side or the image plane side are formed alone or joined together. ,
By employing one aspherical surface for the third lens unit, chromatic aberration is optimally corrected over the entire zoom range. Further, spherical aberration having a high-order flare component is suppressed to a small value.

As described above, according to the present invention, the zoom ratio is 10 to 16 and the F-number at the wide-angle end is 1.
A high zoom ratio and a large aperture of about 8, and high optical performance is maintained.

[A4] Basically, in the lens configuration of each group, if the lens is cemented, the eccentricity in the group can be effectively suppressed and the product performance can be stabilized. The degree of freedom is reduced by one, and it is difficult to achieve sufficient initial performance while satisfying the specifications of a large aperture and a small zoom.

Therefore, in Numerical Embodiment 1 of the present invention, the third lens unit is composed of a cemented lens in which a positive lens and a meniscus-shaped negative lens having a concave surface facing the object side are joined, and the strongest positive lens in the third lens unit. By applying an aspherical surface on the convex surface of the refractive power of which the positive refractive power becomes weaker toward the periphery of the lens, the higher order flare component of the spherical aberration is corrected and the eccentricity within the group is effectively suppressed. We have achieved a larger aperture with a more accurate zoom lens.

In the second and third numerical embodiments, the fourth lens unit has a cemented lens in which a positive lens and a negative lens are bonded to each other, so that the eccentricity in the lens group can be effectively suppressed as in the third lens unit. , Achieving a more accurate zoom lens.

In Numerical Embodiment 1, a convex surface having the strongest positive refractive power in the fourth lens unit is formed of an aspherical surface having a shape such that the positive refractive power becomes weaker toward the periphery of the lens. By correcting the flare component and astigmatism, a large-diameter, ultra-high-magnification zoom lens with high accuracy has been achieved.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the ith lens surface in order from the object side, Di is the ith lens thickness and air spacing in order from the object side, and Ni and νi are the ith lens in order from the object side. Are the refractive index and Abbe number of the glass. The aspherical shape has a radius of curvature R at the center of the lens surface, the optical axis direction (the traveling direction of light) is the X axis, the direction perpendicular to the optical axis is the Y axis,
When B, C, D and E are each aspheric coefficients

[0056]

(Equation 4) This is represented by “E-0X” means “× 10 ^−X ”. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

The two lens surfaces closest to the image plane in Numerical Examples 1 to 3 represent glass blocks such as a color separation prism, an optical filter, and a face plate.

[0058]

[Outside 1]

[0059]

[Outside 2]

[0060]

[Outside 3]

[0061]

[Table 1]

[0062]

According to the present invention, as described above, the luminous flux converges or diverges over the entire zoom range while adopting the rear focus method which is advantageous for downsizing the lens system by setting each element. In the optical path, a transmitted light amount adjusting means made of a physical element is provided to prevent ghost and flare from being generated by reflected light from the imaging element surface, and to cover the entire zoom range from the wide-angle end to the telephoto end. Over the entire object distance from infinite objects to super close objects,
It is possible to achieve a rear focus type zoom lens including a transmitted light amount adjusting means having a short overall length of a lens having excellent optical performance, and an imaging apparatus using the same.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a first embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention.

FIG. 2 is an aberration diagram of a first embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention at a wide angle end.

FIG. 3 is an intermediate aberration diagram of Embodiment 1 of the imaging apparatus using the rear focus type zoom lens including the transmitted light amount adjusting means of the present invention.

FIG. 4 is an aberration diagram at a telephoto end of an image pickup apparatus using a rear focus zoom lens including a transmitted light amount adjusting unit according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view of a main part of an image pickup apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to a second embodiment of the present invention;

FIG. 6 is an aberration diagram at a wide-angle end of an image pickup apparatus using a rear focus zoom lens including a transmitted light amount adjusting unit according to a second embodiment of the present invention.

FIG. 7 is an intermediate aberration diagram of Embodiment 2 of the imaging apparatus using the rear focus type zoom lens including the transmitted light amount adjusting means of the present invention.

FIG. 8 is an aberration diagram at a telephoto end of an image pickup apparatus using a rear focus zoom lens including a transmitted light amount adjusting unit according to a second embodiment of the present invention.

FIG. 9 is a sectional view of a principal part of a third embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention;

FIG. 10 is a third embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention.
At the wide-angle end

FIG. 11 is a third embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention.
Middle aberration diagram

FIG. 12 is a third embodiment of an imaging apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit according to the present invention.
At the telephoto end

FIG. 13 is an explanatory diagram of an optical path of an image pickup apparatus using a rear focus type zoom lens including a transmitted light amount adjusting unit of the present invention.

FIG. 14 is an explanatory diagram of a zoom lens having a conventional transmitted light amount adjusting unit.

FIG. 15 is an explanatory diagram of a zoom lens having a conventional transmitted light amount adjusting unit.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group SP Aperture IP Image plane d d-line g g-line S Sagittal image plane M Meridional image plane GB Glass block

Claims (9)

[Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. The second lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation caused by zooming is corrected by moving part or all of the fourth lens unit. A zoom lens for focusing by moving a part or all of the fourth group, and
A rear focus type zoom lens including a transmitted light amount adjusting unit, wherein a transmitted light amount adjusting unit using a physical element is provided in an optical path with the group to adjust the transmitted light amount. 2. A light beam emitted from the third group is a convergent light or a divergent light over the entire zoom range, and a light incident surface and a light exit surface of the physical element are formed of parallel planes. A rear focus type zoom lens including the transmitted light amount adjusting means according to claim 1. 3. The physical element adjusts the amount of transmitted light by making its density variable.
Rear focus zoom lens including transmission light amount adjusting means. 4. A rear focus type zoom lens according to claim 1, wherein said physical property element is an all solid state electrochromic element. 5. The focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fW and fT, and the combined focal lengths of the first to third groups at the wide-angle end and the telephoto end are respectively fMW and fMT.
And Wherein the condition 0.1 <fM / fAM <0.9 is satisfied.
Or a rear focus type zoom lens including the transmitted light amount adjusting means. 6. A transmission light amount adjusting means, wherein a rear focus type zoom lens including the transmission light amount adjusting means according to claim 1 is detachably mounted on a camera body. An imaging device using a rear focus type zoom lens. 7. An imaging apparatus using a rear focus type zoom lens including a transmission light amount adjusting means according to claim 6, wherein the physical element is driven and controlled by a control circuit provided on the camera body side. . 8. An imaging apparatus using a rear focus type zoom lens including a transmission light amount adjusting means according to claim 6, wherein the physical element is drive-controlled by a control circuit provided on the zoom lens side. . 9. The rear focus type zoom lens according to claim 8, wherein the control circuit drives and controls the physical element based on a signal from the camera body. The imaging device used.