JP2002131641A - Zoom lens and projecting device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens and a projecting optical system using the same capable of projecting picture information displayed by a liquid crystal display element on a screen surface while maintaining high optical performance. SOLUTION: A variable power optical system is provided with a 1st lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, a fifth lens group and a sixth lens group having positive refractive power in order from a first conjugate point side at a longer distance; and three or more lens groups out of the second to the fifth lens groups are moved in the case of varying power from a focal distance at a wide-angle end to a focal distance at a telephoto end and the first lens group and the sixth lens group are fixed in the midst of varying power. In the optical system, one or more lens groups out of a plurality of lens groups are provided with one or more diffraction type optical elements rotationally symmetric with respect to an optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens and a projection apparatus using the same, and is suitable for a projection apparatus for enlarging and projecting an image of a display body on a screen at a fixed finite distance. Especially, a simple configuration suitable for performing high-definition image projection on a screen via a single projection lens after using a plurality of liquid crystals or the like for each color light for a display body and color-combining each color light. And a small zoom lens having telecentric performance and a projection apparatus using the same.

[0002]

2. Description of the Related Art A negative lead type zoom lens, which is preceded by a lens group having a negative refractive power, has features such as a relatively wide angle of view and a capability of maintaining a performance at a close shooting distance. However, on the other hand, it has disadvantages such as an increase in the amount of movement for zooming, difficulty in achieving high zooming, and large fluctuations in chromatic aberration of magnification.

[0003] A zoom lens which has improved these drawbacks and has achieved miniaturization and high zoom ratio of the whole lens system is disclosed in, for example, JP-B-49-23912, JP-A-53-34539, and JP-A-57-34539. 163213, JP-A-58-4
No. 113, JP-A-63-241511, and JP-A-2-201310.

In each of these publications, a zoom lens is composed of four lens groups as a whole in order from the object side, having negative, positive, negative, and positive refractive power, and a predetermined lens group is appropriately moved. Let me change the magnification.

However, these zoom lenses have a finite exit pupil position, cannot be said to have a sufficiently long back focus, and have not been able to completely correct lateral chromatic aberration.

As a zoom lens for liquid crystal projection, the present applicant has disclosed in Japanese Patent Application No. 9-272245.
A four-group type telecentric zoom lens comprising four lens groups having negative, positive, positive, and positive refractive powers has been proposed. Here, the function of each lens group is such that the first to third lens groups have a large conjugate (object) with respect to zooming from the wide-angle end to the telephoto end.
Side and the fourth lens group move to a small conjugate (image plane) side, and proposes a telecentric zoom lens that satisfactorily corrects distortion and chromatic aberration corresponding to an XGA panel.

Further, the applicant of the present invention has disclosed Japanese Patent Application Laid-Open No. 11-190821.
In the publication, the first negative refractive power in order from the conjugate point side with the longest distance
A second group having a positive refractive power, a third group having a negative refractive power, a fourth group having a positive refractive power, and a fifth group having a positive refractive power. Is moved to the long conjugate point side to perform zooming from the wide angle end to the telephoto end, and a zoom lens in which the short conjugate point side is substantially telecentric has been proposed.

[0008]

When a display image is enlarged and projected on a screen by an optical system, in particular, a liquid crystal display is used for each of a plurality of color lights, and each color light is synthesized and projected by one projection lens. In this case, it is necessary to satisfy the following conditions.

(A-1) The pupil (exit pupil) on the panel side is far away in order to eliminate the influence of the light distribution characteristics of the liquid crystal or the angle dependence of the color combining dichroic mirror when combining a plurality of color lights. What is called a telecentric optical system.

(A-2) A long back focus is required in order to secure a space for the color combining element interposed between the display body and the projection lens.

(A-3) Normally, in order to project a display image upward on a screen, the display body is used with its center position shifted with respect to the optical axis of the projection lens. Indicates that the effective area to be used is not
Since it is deviated upward and the diameter of the front lens becomes large, improvement means is required.

(A-4) Since a plurality of color lights are combined, it is necessary to minimize the chromatic aberration of magnification generated in the lens as much as possible.

(A-5) With respect to the projected image, it is necessary to sufficiently correct the distortion so that the contour is not distorted and unsightly. In particular, a sharp change in distortion at the peripheral portion and the intermediate portion significantly reduces image quality, which is not desirable.

A projection lens for a liquid crystal projector meeting the above requirements is disclosed in, for example, Japanese Patent Laid-Open No. 10-186.
235 and Japanese Patent Application Laid-Open No. 10-268193. The projection lenses disclosed in these publications are:
The first lens unit and the fifth lens unit include five lens units in which lens units having negative, positive, positive, negative, and positive optical refractive powers are arranged in order from the enlargement side, and when zooming from the wide-angle end to the telephoto end. Is fixed, and all the second to fourth lens groups inside the lens system are moved to the enlargement side.

Since the first lens unit disposed on the most enlarged side and the fifth lens unit disposed on the most reduced side are fixed during zooming, the total length is kept constant during zooming. In addition, these optical systems constitute a telecentric zoom lens having a back focal length of a certain length, and having reduced distortion and chromatic aberration of magnification.

However, in recent years, the miniaturization of the main body of the liquid crystal projector, the miniaturization of the liquid crystal panel, and the higher definition have been further advanced, and the requirements for the projection lens are further miniaturization, higher resolution, and lower magnification chromatic aberration. If it is attempted to obtain the same resolution as the conventional one in a state where the liquid crystal panel is downsized, the aperture ratio of the liquid crystal display device is reduced, and the ratio between the illuminated area and the size of the light emitting light source (= the size of the illuminated area / the size of the light source) (Size) becomes smaller, the illumination efficiency generally lowers, and the brightness becomes lower than before, even though the device can be downsized.

In order to ensure a practically satisfactory screen illuminance even in a place with normal brightness, an open F-number at the wide-angle end of the projection lens is
It is desirable to set around 2.0.

However, when the F-number is around 2.0 or brighter, it becomes difficult to correct aberrations, especially spherical aberration, and the optical performance may be degraded. To solve this problem, it is possible to perform aberration correction satisfactorily by increasing the number of components of the lens system. However, this increases the size of the optical system and lowers its commercial value.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a zoom lens suitable for a projector which is bright, miniaturized, and has a high zoom ratio, and which satisfactorily corrects chromatic aberration of magnification, and a projection apparatus using the same.

In addition, the present invention comprises six lens groups as a whole, adopts a negative lead type as a lens type, and appropriately configures each lens group, thereby reducing the size of the entire lens system while changing the lens system. It is an object of the present invention to provide a zoom lens suitable for a liquid crystal projector having good optical performance over the entire screen while maintaining good telecentric conditions over the entire magnification range, and a projection device using the same.

[0021]

According to a first aspect of the present invention, there is provided a zoom lens having a first lens unit having a negative refractive power and a second lens having a positive refractive power in order from the first conjugate point having a longer distance. Group, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power,
A fifth lens group, a sixth lens group having a positive refractive power, and when changing the focal length from the wide-angle end to the telephoto end, three of the second to fifth lens groups are used. By moving the above lens groups, the first lens group and the sixth lens group are one of the plurality of lens groups in a variable power optical system fixed during variable power.
The above lens group is characterized by having one or more diffraction type optical elements rotationally symmetric with respect to the optical axis.

According to a second aspect of the present invention, when the refractive power of the second lens group is φ2 and the refractive power at the wide-angle end of the entire system is φw, 0 <φ2 / φw <1.5. Is satisfied.

According to a third aspect of the present invention, in the second aspect of the present invention, the first lens group has a positive lens having a convex surface having a stronger refractive power on the object side than on the image side, closest to the object side. I have.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the first lens group has the Abbe number of the lens having the smallest Abbe number among the positive lenses disposed in the lens group, ν1p, When the Abbe number of the lens having the largest Abbe number among the negative lenses arranged in the group is ν1n, ν1n−ν1p> 10 is satisfied.

According to a fifth aspect of the present invention, in the fourth aspect, the combined refractive power of the second lens unit and the third lens unit at the wide angle end is φ23 w, and the refractive power of the entire system at the wide angle end is φw.
Where 0 <φ23w / φw <1.5 is satisfied.

According to a sixth aspect of the present invention, when the refractive power of the fourth lens group is φ4w and the refractive power of the entire system at the wide-angle end is φw, 0 <| φ4w / φw | <1 .5.

According to a seventh aspect of the present invention, in the sixth aspect, the second lens group includes one or more positive lenses and one or more negative lenses, and the second lens group has the largest Abbe number among the positive lenses. When the Abbe number of the positive lens is ν2p, and the Abbe number of the negative lens having the smallest Abbe number among the negative lenses is ν2n, ν2p−ν2n> 10 is satisfied.

An eighth aspect of the present invention is characterized in that, in the seventh aspect of the present invention, the second group or the third group has a stop.

According to a ninth aspect of the present invention, when the refractive power of the sixth lens group is φ6w and the refractive power of the entire system at the wide-angle end is φw, 0 <φ6w / φw <1.5. Is satisfied.

According to a tenth aspect of the present invention, in any one of the first to ninth aspects, the focal length of the entire system at the wide-angle end is f.
w, during zooming, when the shortest exit pupil length in absolute value from the final lens surface is tk, | tk | / fw> 1.5 is satisfied.

According to an eleventh aspect of the present invention, in any one of the first to tenth aspects, the back focus is bf,
When the focal length at the wide-angle end of the entire system is fw, 0.9 <bf / fw is satisfied.

According to a twelfth aspect of the present invention, in any one of the first to eleventh aspects, when the material of any positive lens constituting the sixth lens group is ν6p, ν6p> 30 is satisfied. It is characterized by satisfaction.

According to a thirteenth aspect of the present invention, in the first aspect of the invention, the sixth lens group includes one positive lens, and the Abbe number of the material of the positive lens is ν6
When p, ν6p> 35 is satisfied.

According to a fourteenth aspect of the present invention, in any one of the first to thirteenth aspects, the focal length of the entire system at the wide-angle end is fw, the focal length of the entire system at the telephoto end is ft, and the i-th lens unit is Assuming that the focal length is fi, 1.1 <| f1 / f2 | <2.3.

[0035]

(Equation 3)

Is satisfied.

According to a fifteenth aspect of the present invention, when the focal length of the first lens unit is f1 and the focal length at the wide-angle end of the entire system is fw, 1 <| It is characterized by satisfying f1 | / fw <2.5.

According to a sixteenth aspect of the present invention, in any one of the first to fifteenth aspects, the lateral magnifications of the second lens unit at the wide-angle end and the telephoto end are β2w and β2t, respectively, The focal lengths at the ends are respectively fw and ft, the change β2t / β2w of the lateral magnification β2 of the second lens group is Z2, and the change ft / fw of the focal length of the entire system is Z, and the second lens group and the fifth lens group Assuming that the moving amounts at full magnification are M2 and M5, respectively, 0.8 <Z2 / Z <1.11.0 <| M2 / M5 | <11.00.4 <M2 / (ft− fw) <1.3.

According to a seventeenth aspect, in the invention according to any one of the first to sixteenth aspects, when the focal length of the i-th lens unit is fi, 0.01 <| f2 / f5 | <0.9. It is characterized by satisfaction.

The invention of claim 18 is the invention according to any one of claims 1 to 17, wherein the back focus is bf,
When the focal length of the i-th lens unit is fi, 0.3 <bf / f6 <2.5 0.9 <| f1 | / bf <1.6 is satisfied.

According to a nineteenth aspect of the present invention, when the focal length of the sixth lens group is f6 and the focal length at the wide-angle end of the entire system is fw, 0.5 <F6 / fw <3.5.

According to a twentieth aspect of the present invention, in any one of the first to nineteenth aspects, the focal length of the i-th lens unit is fi, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and f.
t

[0043]

(Equation 4)

Is satisfied.

A projection apparatus according to a twenty-first aspect is characterized in that an original projection image is projected on a screen surface by using the zoom lens according to any one of the first to twentieth aspects.

[0046]

FIG. 1, FIG. 2 and FIG. 3 are sectional views of a lens according to a first embodiment of the present invention, and a wide-angle end at an object distance of 2.5 m when the numerical value of the first embodiment is expressed in mm. FIG. 7 is an aberration diagram at a telephoto end.

FIGS. 4, 5 and 6 show a second embodiment of the present invention.
FIG. 7 is a lens cross-sectional view of the optical system, and aberration diagrams at the wide-angle end and the telephoto end when the object distance is 2.5 m when the numerical values of the numerical examples are expressed in mm.

FIGS. 7, 8 and 9 show a third embodiment of the present invention.
FIG. 7 is a lens cross-sectional view of the optical system, and aberration diagrams at the wide-angle end and the telephoto end when the object distance is 2.5 m when the numerical values of the numerical examples are expressed in mm.

In the sectional view of the lens, PL is a zoom lens. L1 is a first group (first lens group) having a negative refractive power, L2 is a second group (second lens group) having a positive refractive power, L
Reference numeral 3 denotes a third group (third lens group) having a weak positive refractive power, L4 denotes a fourth group (fourth lens group) having a negative refractive power, L5 denotes a fifth group (fifth lens group), and L6 denotes a positive lens. The sixth group (sixth lens group) having the refractive power of (a). SP denotes an aperture, which is included in the second or third lens group, and moves with zooming.

S is a screen surface (projection surface) corresponding to the object side. The LCD is an original image (projected surface) such as a liquid crystal panel (liquid crystal display element) and is arranged on the image plane IP. The screen surface S and the original image LCD are in a conjugate relationship. Generally, the screen surface S is located at the longer conjugate point (first conjugate point), and the original image LCD is located at the shorter conjugate point (second conjugate point). Point).

GB is a color combining prism or a polarizing filter,
And a glass block such as a color filter.

The zoom lens PL is mounted on the main body of the liquid crystal video projector via a connecting member (not shown). The liquid crystal display element LCD side after the glass block GB is included in the projector main body.

The zoom lens PL of the present embodiment comprises a substantially telecentric lens system for projecting an image (LCD) on the display surface onto the screen (S) in an enlarged manner.

In the present embodiment, focusing is performed by moving the first lens unit on the optical axis. Focusing may be performed by moving the first and second units at the same time, or by moving the third, fifth, and entire units. Alternatively, the display may be performed by moving the display panel.

The projection apparatus of the present invention projects the original image of the LCD onto the screen using the zoom lens PL.

(Note that the following description is developed as a reduction system opposite to the usage as a projector. However, since light rays are reversible optically, only the evaluation place is different. The zoom lens of the present invention moves at least three groups when transitioning from the focal length at the wide-angle end to the focal length at the telephoto end, and the first lens group and the sixth lens group are fixed during zooming. is there. Further, at least one lens group is provided with at least one diffraction-type optical element rotationally symmetric with respect to the optical axis.

Further, by making at least three lens groups movable among the lens groups constituting the zoom lens of the present invention, the size of the entire optical system can be maintained equal to or smaller than that of the conventional optical system. , The optical performance at the time of brightening the F-number is prevented, and various aberrations, particularly spherical aberrations, are satisfactorily corrected.

Also, at the time of zooming, the first lens unit and the sixth lens unit are fixed, so that there is little change in the weight balance, and the working unit is not exposed, so that it is unlikely to break down. It has an advantageous effect on the surface.

It is to be noted that an aspherical surface may be introduced into the optical system for compactness and high performance. As the aspherical surface, a glass mold type, a replica aspherical type, a ground aspherical lens, or the like can be considered. If an aspherical surface is to be applied to a sensitive surface, a plastic aspherical lens may be used.

The positive lens disposed closest to the object and having a strong convex surface on the object side satisfactorily corrects spherical aberration and distortion.

In the present invention, in order to achieve effective zooming while reducing the size with a simple lens configuration, reduce the amount of movement of the zooming group, and further reduce the occurrence and fluctuation of chromatic aberration, When the focal length at the telephoto end is longer than the focal length at the wide-angle end, the distance between the third lens group and the fourth lens group increases, and the distance between the fifth lens and the sixth lens group increases. It is good to move the group.

Here, the second lens group is a main variable power lens group. The second lens group is changed in magnification by moving, and the fourth lens group is moved in accordance with the zooming. Compensate for fluctuations.

Further, the second lens group, the fourth lens group, and the fifth lens group are moved toward the screen at a different speed during zooming, and the fluctuation of the image forming position at which the third lens group is moved by zooming is corrected. You may move it.

In zooming, the third lens unit may be fixed, and the magnification may be changed only by the second, fourth, and fifth lens units.

The second lens unit, which is the main zooming unit, includes at least one positive lens and one negative lens.
It is preferable that the lens group includes at least one positive lens and the fourth lens group includes at least one negative lens to achieve a simple configuration.

The sixth lens group is closest to the panel as the display body, and realizes a telecentric system by giving a relatively strong positive refractive power. Further, it is desirable that the fifth lens group is constituted by one positive lens having a convex surface directed to the screen side so as to achieve both correction of off-axis field curvature and simplification of the constitution.

By moving the second lens group and the fifth lens group in the same direction to change the magnification, it is possible to achieve a zoom lens with a high zoom ratio while reducing the moving amount and moving space of each group. As a result, the overall length is reduced, the overall length does not fluctuate due to zooming, and the distance from the entrance pupil position to the front lens is shortened, so that the diameter of the front lens determined by the off-axis oblique light beam can be reduced.

The first lens group has a negative refractive power,
A long back focus is secured for the space of the color combining element. In particular, in order to lengthen the back focus, it is preferable to dispose a negative meniscus lens having a convex surface on the screen side in the first lens group.

Further, by appropriately arranging the refractive powers of the respective groups and fixing the first lens group during zooming, fluctuations in the position of the off-axis oblique light beam are reduced, the structure is simplified, and the lens has a uniform length. A system can be achieved.

In order to reduce distortion at the wide-angle end, it is also desirable to dispose a convex lens closest to the object side of the first lens unit and to perform distortion correction at the position passing the most off-axis light beam. In particular, this convex lens is preferably a positive lens having a convex surface on the screen side.

It is also desirable to arrange an aspherical surface in the optical system to correct spherical aberration and distortion.

The zoom lens according to the first embodiment shown in FIG. 1 has, in order from the object side (screen side), six groups of negative, positive, positive, negative, positive, and positive, and performs zooming (variation) from the wide-angle end to the telephoto end. Magnification), the first lens group and the sixth lens group are fixed and the total length is fixed, and the second lens group, the third lens group, the fourth lens group,
The fifth lens group moves independently to the screen side S. At this time, the magnification of the second lens group and the fourth lens group is increased, and the magnification of the third lens group and the fifth lens group is reduced throughout the zoom range. The sixth lens group is provided with a diffractive optical element, and mainly corrects lateral chromatic aberration.

In this embodiment, focusing is performed by the first lens group.

The second lens unit is a main zooming unit, and is given a large power (refractive power). Therefore, it is preferable to use a glass material having a high refractive index for the convex lens (positive lens) because the Petzval sum can be reduced. Further, it is preferable that fluctuation of spherical aberration due to zooming can be reduced.

In this embodiment, the distortion generated in the first lens group is corrected by the second lens group. The aperture is disposed on the object side of the third lens unit, and moves together with the third lens unit during zooming, thereby suppressing fluctuations in off-axis aberrations during zooming.

The fourth lens group has a negative power and plays a role of correcting the movement of the focus plane (image plane fluctuation) due to zooming.

The fifth lens group has a negative lens having a positive power and a strong negative refractive power on the object side as compared with the image plane side on the most screen side. The Petzval sum is efficiently reduced by the negative lens. Furthermore, the position of the rear principal point is controlled to ensure good telecentricity, and a required length of back focus is obtained.

The object of the present invention can be achieved even if the fifth lens unit has a negative power, provided that conditional expression (17) described later is satisfied.

The diffractive optical element surface used in the present invention is represented by the following equation.

As the phase φ (h)

(Equation 7) Here, λ: wavelength Ci: coefficient representing the phase h: height from the optical axis It can be understood from the above equation (a) that the phase can be adjusted by the distance h from the optical axis. The greater the lens diameter, the greater the effect of higher order coefficients.

The diffractive optical element is formed by a groove having a considerably narrow width (a groove having a width on the order of several microns or submicrons). In order to prevent dust from adhering to the surface of the diffractive optical element. The diffractive optical element is preferably provided on a surface other than the surface closest to the object.

As described above, the diffractive optical elements arranged in the sixth lens group reduce the chromatic aberration of magnification occurring in each lens group, and also reduce the fluctuation of the chromatic aberration of magnification due to the movement of the second lens group due to zooming. .

The diffractive optical element used in the present invention may be manufactured by a lithographic technique, which is a technique for manufacturing a holographic optical element (HOE), or by using binary optics, which is an optical element manufactured in a binary manner. good. In this case, in order to further increase the diffraction efficiency, a saw-like shape called a kinoform may be used.

Further, it may be formed and manufactured by a mold prepared by these methods.

Although these diffractive optical elements are provided on an optical surface, their bases may be spherical, planar or aspherical.

Further, a film of plastic or the like may be attached to those optical surfaces as the diffractive optical surface (a so-called replica aspherical surface).

The zoom lens shown in FIG. 2 has, in order from the object side (screen side), six groups of negative, positive, positive, negative, positive, and positive. The zooming from the wide-angle end to the telephoto end makes the first lens group. And the sixth lens group are fixed and the total length is constant, and the second lens group, the third lens group, the fourth lens group, and the fifth lens group move independently to the screen side S. At this time, the magnification of the second lens group and the fourth lens group is increased, and the magnification of the third lens group and the fifth lens group is reduced throughout the zoom range. A diffractive optical element is arranged in the second lens group to correct lateral chromatic aberration.

In this embodiment, focusing is performed by the first lens group.

The second lens group is a main zooming group, and has a large power. Therefore, it is preferable to use a glass material having a high refractive index for the convex lens because the Petzval sum can be reduced. It is also desirable to reduce fluctuations in spherical aberration due to zooming. In the present embodiment, the distortion generated in the first lens group is corrected by the second lens group. The aperture is disposed on the object side of the third lens unit, and moves together with the third lens unit during zooming, thereby suppressing fluctuations in off-axis aberrations during zooming. The fourth lens group
It has a negative power and plays a role in correcting the movement of the focal plane due to zooming. The fifth lens group includes a negative lens having a positive power and a strong negative refractive power on the object side as compared with the image plane side on the most screen side. The Petzval sum is efficiently reduced by the negative lens. Furthermore, the position of the rear principal point is controlled to ensure good telecentricity, and a necessary back focus is obtained.

The surface of the diffractive optical element is represented by the above equation (a).

As described above, the chromatic aberration of magnification occurring in each group is suppressed by the diffractive optical elements arranged in the second group, and the fluctuation due to zooming of the chromatic aberration of magnification due to the movement of the second group is also suppressed. .

As the diffractive optical element of this embodiment, the same one as described in the first embodiment can be applied.

The zoom lens shown in FIG. 3 has, in order from the object side (screen side), six groups of negative, positive, positive, negative, positive, and positive. The zooming from the wide-angle end to the telephoto end makes the first lens group. And the sixth lens group are fixed and the total length is constant, and the second lens group, the third lens group, the fourth lens group, and the fifth lens group move independently to the screen side. At this time, the magnification of the second lens group and the fourth lens group is increased, and the magnification of the third lens group and the fifth lens group is reduced throughout the zoom range. A diffractive optical element is arranged in the fifth lens group to correct lateral chromatic aberration.

In this embodiment, focusing is performed by the first lens group.

The second lens group is a main zooming group, and has a large power. Therefore, it is preferable to use a glass material having a high refractive index for the convex lens because the Petzval sum can be reduced. It is also desirable to reduce fluctuations in spherical aberration due to zooming. In the present embodiment, the distortion generated in the first lens group is corrected by the second lens group. The aperture is disposed on the object side of the third lens unit, and moves together with the third lens unit during zooming, thereby suppressing fluctuations in off-axis aberrations during zooming. The fourth lens group
It has a negative power and plays a role in correcting the movement of the focal plane due to zooming. The fifth lens group includes a negative lens having a positive power and having a strong negative refractive power on the object side as compared with the image plane side on the screen side. The Petzval sum is efficiently reduced by the negative lens.
Furthermore, the position of the rear principal point is controlled to ensure good telecentricity, and a necessary back focus is obtained.

The surface of the diffractive optical element is represented by the above-mentioned formula (a).

As described above, the diffractive optical elements arranged in the fifth lens unit reduce the chromatic aberration of magnification occurring in each lens unit and also reduce the fluctuation of the chromatic aberration of magnification due to the movement of the second lens unit due to zooming. Configuration.

As the diffractive optical element of this embodiment described so far, the same one as described in the first embodiment can be applied.

In the present invention, in order to obtain a high optical performance over the entire screen with a small aberration variation over the entire zoom range while further securing a predetermined zoom ratio, one of the following conditions is required.
It is better to satisfy at least one. When two or more conditions are satisfied, any combination may be used.

(A-1) The refractive power of the second lens group is φ
2. When the refractive power at the wide-angle end of the entire system is φw, the following condition is satisfied: 0 <φ2 / φw <1.5 (1)

The expression (1) defines the power of the second lens group that most contributes to zooming. If the lower limit of conditional expression (2) is exceeded, the overall length of the lens becomes longer, making it impossible to reduce the size. When the value exceeds the upper limit of the conditional expression (1), a configuration advantageous for miniaturization is obtained. However, aberration fluctuation at the time of zooming becomes large, which is not desirable.

(A-2) The first lens group has a positive lens closest to the object side and having a convex surface having a stronger refractive power on the object side than on the image plane side.

(A-3) In the first lens group, the Abbe number of the lens having the smallest Abbe number among the positive lenses disposed in the lens group is ν1p, and the negative lens disposed in the lens group. When the Abbe number of the lens having the largest Abbe number among them is ν1n, ν1n−ν1p> 10 (2) is satisfied.

Equation (2) is a conditional equation for suppressing chromatic aberration generated in the first lens group having the highest off-axis ray height in the optical system. In this case, it is preferable that the pupil (aperture) of this lens system is located near the second lens group or the third lens group. Specifically, the most screen side surface or the most panel side surface of the second lens group, Alternatively, it is preferable to make the second lens group or the third lens group have the same position as the surface closest to the screen or the surface closest to the panel of the third lens group. There may be. By doing so, the position through which off-axis light passes in the first lens group is not so far from the optical axis, which is also effective in generating chromatic aberration of magnification. Further, the effective diameter of the first lens group can be reduced, and a compact and simple zoom lens can be achieved.

(A-4) When the combined refractive power of the second lens unit and the third lens unit at the wide-angle end is φ23 w and the refractive power of the entire system at the wide-angle end is φw, 0 <φ23w / φw <1.5 ... (3) must be satisfied.

The equation (3) defines the magnification of the zooming group at the wide-angle end. If the lower limit of conditional expression (3) is exceeded, the overall length of the lens becomes longer, making it impossible to reduce the size. If the upper limit of conditional expression (3) is exceeded, a configuration advantageous for miniaturization will be obtained, but aberration fluctuation during zooming will be large, which is not desirable.

(A-5) The refractive power of the fourth lens group is φ
4w, when the refractive power of the entire system at the wide-angle end is φw, the following condition is satisfied: 0 <| φ4w / φw | <1.5 (4)

Formula (4) defines the magnification of the image plane position correction (compensator) group at the wide-angle end. If the lower limit of conditional expression (4) is exceeded, the refractive power of the fourth lens unit becomes weak, the Petzval sum increases in the positive direction with the third order aberration coefficient, and the field curvature becomes undesirably large. Further, it is difficult to obtain a desired back focus, which is not desirable. Further, a fourth correction for correcting the image plane position at the time of zooming is performed.
The amount of movement of the lens group increases, and aberration fluctuations that occur during zooming become large, which is not desirable. If the upper limit of conditional expression (4) is exceeded, the refracting power of the fourth lens unit will become strong, and the back focus will be unnecessarily long, making compactness difficult, which is not desirable.

(A-6) The second lens group is composed of one or more positive lenses and one or more negative lenses, and the Abbe number of the positive lens having the largest Abbe number among the positive lenses is ν2p When the Abbe number of the negative lens having the smallest Abbe number among the negative lenses is ν2n, ν2p−ν2n> 10 (5) is satisfied.

The expression (5) not only suppresses the chromatic aberration generated in the second lens group which is the main variable power system, but also works in the direction of canceling the chromatic aberration of magnification generated in the remaining first lens group which cannot be corrected.

(A-7) The second lens group or the third lens group has a stop.

It is preferable that the pupil (aperture) of the lens system is located near the second lens group or the third lens group. Specifically, the most screen side surface or the most panel side surface of the second lens group, Alternatively, it is preferable to make the second lens group or the third lens group have the same position as the surface closest to the screen or the surface closest to the panel of the third lens group. There may be.
By doing so, the position through which off-axis light passes in the first lens group and the second lens group is not so far away from the optical axis, which is effective in generating chromatic aberration of magnification. Further, the effective diameter of the first lens group can be reduced, and a compact and simple zoom lens can be achieved.

It is preferable that the stop moves independently of the lens unit during zooming. According to this, it is possible to satisfactorily suppress aberration fluctuations due to zooming. Further, the diaphragm may be moved integrally with the second lens group or the third lens group. According to this, a simple lens barrel configuration can be obtained.

(A-8) The refractive power of the sixth lens group is φ
Assuming that 6w and the refractive power of the entire system at the wide-angle end is φw, the following condition is satisfied: 0 <φ6w / φw <1.5 (6)

Formula (6) defines the refractive power of the sixth lens group. By arranging the sixth lens group in the vicinity of the image plane, the combined refractive power from the first lens group to the fifth lens group is reduced, which is advantageous for widening the angle and increasing the aperture.

If the lower limit of conditional expression (6) is exceeded, the refracting power of the sixth lens unit will become so strong that distortion and introverted coma flare will increase, which is not desirable. If the upper limit of conditional expression (6) is exceeded, the refractive power of the sixth lens unit will be weak, and the effect of weakening the combined refractive power from the first lens unit to the fifth lens unit will be reduced, resulting in a wide angle and a large aperture. It is not desirable because it has an adverse effect on the formation.

(A-9) The focal length of the entire system at the wide-angle end is represented by f
w, during zooming, when the shortest exit pupil length in absolute value from the last lens surface is tk, | tk | / fw> 1.5 (7) is satisfied.

The pupil (exit pupil) on the panel side is far away in order to eliminate the influence of the light distribution characteristics of the liquid crystal as the display panel or the angle dependence of the color combining dichroic mirror film when combining a plurality of color lights. A so-called telecentric optical system is effective for a lens as efficient illumination means. In particular, the pupil (exit pupil) of the lens on the display panel side (reduction side) needs to be far away. Specifically, in order to eliminate the angle dependency, it is preferable that the zoom lens of the present invention satisfies the conditional expression (7).

At this time, it is preferable that the pupil (aperture) of this lens system is located near the second lens group or the third lens group, and more specifically, the surface of the second lens group closest to the screen,
Alternatively, it is preferable that the second lens group or the third lens group be constituted by a plurality of lenses, which are the same as the most panel side surface, the most screen side surface of the third lens group, or the most panel side surface. Sometimes it may be inside the lens group.

When used as a projection lens for a color liquid crystal projection TV, a long back focus is necessary because a dichroic mirror and the like must be arranged on the image plane side. In addition, in order to enable projection at an extremely short projection distance, it is preferable to increase the refractive power of the entire projection lens system. In order to achieve both of these conditions, it is preferable to satisfy conditional expression (7).

(A-10) Assuming that the back focus is bf and the focal length at the wide-angle end of the entire system is fw, 0.9 <bf / fw (8) is satisfied.

When the zoom lens of the present invention is used as a projection lens for a color liquid crystal projection TV,
A long back focus is necessary because a dichroic mirror and the like need to be arranged on the image plane side. In the present invention, the refractive power of the entire projection lens system is increased in order to achieve a very short projection distance. Conditional expression (8) is for achieving both of these conditions.

(A-11) When the Abbe number of the material of any positive lens constituting the sixth lens group is ν6p, ν6p> 30 (9) is satisfied.

In the sixth lens group which is closest to the display panel and whose off-axis light beam passes the outside of the lens other than the first lens group, it is not good that the telecentric relationship is broken by the wavelength. To this end, assuming that the Abbe number of the material of any positive lens forming the sixth lens group is ν6p, at least one of the positive lenses forming the sixth lens group preferably satisfies the conditional expression (9). .

(A-12) The sixth lens group is composed of one positive lens, and the Abbe number of the material of the positive lens is ν6p
Ν6p> 35 (10)

The technical meaning of conditional expression (10) is the same as that of conditional expression (9).

(A-13) The focal length of the entire system at the wide-angle end is represented by f
w, when the focal length of the entire system at the telephoto end is ft, and the focal length of the i-th lens unit is fi, 1.1 <| f1 / f2 | <2.3 (11)

[0128]

(Equation 5)

It is preferable to satisfy the following conditional expression.

The above equation appropriately defines the relationship between the second lens unit and the first lens unit, which are the main zooming units.

If the value falls outside the lower limit of the expression (11), the front lens diameter determined by the first lens unit becomes large, and the distortion at the wide-angle end becomes large, which is not appropriate. If the upper limit is deviated, it is necessary to increase the amount of movement of the second lens group in order to obtain a desired zoom ratio.

Equation (12) is to make the power of the main zooming unit appropriate. If the power exceeds the lower limit, the image plane becomes overcorrected, which is not appropriate. In addition, if the upper limit is exceeded, the second
It is necessary to increase the amount of movement of the lens group, and the entire system is increased in size, which is not appropriate.

(A-14) The focal length of the first lens group is f
1. When the focal length at the wide-angle end of the entire system is fw, the following condition is satisfied: 1 <| f1 | / fw <2.5 (13)

The conditional expression (13) is mainly for favorably correcting distortion. When the value exceeds the upper limit of the expression (13), the distortion at the wide-angle end exceeds the lower limit, and the distortion at the telephoto end cannot be properly corrected. (A-15) The lateral magnifications of the second lens group at the wide-angle end and the telephoto end are respectively β2w and β2t, the focal lengths of the whole system at the wide-angle end and the telephoto end are respectively fw and ft, and the lateral magnification β2 of the second lens group. The change β2t / β2w of Z is Z2, the change ft / fw of the focal length of the entire system is Z, and the second lens group and the fifth
When the amounts of movement of the lens unit at all magnifications are M2 and M5, respectively, 0.8 <Z2 / Z <1.1 (14) 1.0 <| M2 / M5 | <11 ... (15) 0.4 <M2 / (ft−fw) <1.3 (16)

Equation (14) appropriately defines the ratio of zooming between the second lens unit and the fourth lens unit, which are zooming units.
The third lens group is preferably in this range in order to reduce the magnification upon zooming. Outside of this range, a lens system having a desired zoom ratio becomes large.

The expressions (15) and (16) make the length of the entire lens and the amount of movement of each zooming unit appropriate. Especially the second
Since the power of the fifth lens group is apt to be weaker between the lens group and the fifth lens group, this range is preferable in order to appropriately share the magnification. In particular, the movement amount of the second lens group is the fifth.
More preferably, the movement amount of the lens group is exceeded.

(A-16) The focal length of the i-th lens group is f
When i, 0.01 <| f2 / f5 | <0.9 (17) is satisfied.

Equation (17) is an equation for appropriately setting the Petzval sum while appropriately arranging the power and zooming of the main zooming group.

(A-17) When the back focus is bf and the focal length of the i-th lens unit is fi, 0.3 <bf / f6 <2.5 (18) 0.9 <| f1 | / Bf <1.6 (19).

The conditional expressions (18) and (19) are for appropriately setting the exit pupil and distortion of the entire system. The back focus bf is a distance from the sixth lens group to the display, and is an air-equivalent length excluding a dichroic prism and the like.

Equation (18) is for making the entire system appropriately telecentric. This is a condition for allowing a light beam emitted perpendicularly from the display panel to enter the fifth lens group and be refracted efficiently to reach the pupil (diaphragm), and to make the effective diameter near the front lens (first lens group) appropriate. . Exceeding the upper limit increases the size,
If the lower limit is exceeded, distortion occurs.

Equation (19) is also a condition for making the exit pupil longer and making it telecentric while appropriately taking distortion.
If the value exceeds the upper limit, the diameter of the first lens unit becomes large, and if the value exceeds the lower limit, the distortion particularly at the wide-angle end increases, which is not appropriate.

(A-18) The focal length of the sixth lens group is f
6. When the focal length at the wide-angle end of the entire system is fw, the following condition is satisfied: 0.5 <f6 / fw <3.5 (20)

Conditional expression (20) is for optimizing the distance from the lens to the panel while making the telecentric system optimal. If the lower limit of the conditional expression (20) is exceeded, the optimum telecentricity cannot be satisfied.

(A-19) The focal length of the ith lens group is represented by f
i, the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and ft, respectively.
And when

[0146]

(Equation 6)

Is satisfied.

These conditional expressions mainly make the power arrangement of each lens group appropriate and the amount of movement of each lens group appropriately.
This is to reduce the size of the entire optical system.

The expression (21) is for sufficiently suppressing the distortion in the first lens unit and ensuring a sufficient back focus. If the value exceeds the upper limit, the amount of movement for focusing increases, the overall length increases, and the back focus becomes short, which is not preferable. Conversely, if the lower limit is exceeded, the amount of movement for focusing is reduced, but it is not preferable because it becomes difficult to correct distortion and the Petzval sum becomes large negatively and the image surface falls.

Equation (22) allows the third lens group fixed during zooming to appropriately contribute to zooming with respect to the fourth lens group.
This is a condition for the lens group to be able to play with a simple fixed structure.

Formula (23) shows an appropriate power arrangement of the lens group that contributes to zooming. If each of the upper limits is exceeded, the amount of movement for obtaining a desired zoom ratio becomes large, and the entire lens system becomes large, which is not appropriate. If the lower limit value is exceeded, the amount of movement of each lens unit becomes small, but the fluctuation of aberrations due to zooming, especially the fluctuation of curvature of field increases, which is not appropriate.

Equation (24) is a condition necessary for making the exit pupil longer and telecentric together with equation (18). If the lower limit value is exceeded, distortion will occur in the fifth lens unit even if it is telecentric, which is not appropriate. If the ratio exceeds the upper limit, the size of the entire system becomes large, which is not suitable.

FIG. 10 is a schematic view of a principal part when the zoom lens of the present invention is applied to a color liquid crystal projector using three dichroic mirrors and a dichroic prism as projection lenses.

In FIG. 10, light emitted from a light source 201 using a metal halide lamp is converted into red light (about 600 nm to about 700 nm) by a red reflecting dichroic mirror 202.
nm light) and transmits other light. The reflected red light is redirected by the reflection mirror 203 and enters the red liquid crystal light valve 206. The light transmitted through the red reflecting dichroic mirror 202 is converted into green light (about 500 nm to about 60 nm) by the blue transmitting dichroic mirror 204.
0 nm) is reflected and blue light (about 400 nm to about 5 nm) is reflected.
00 nm light) is transmitted. Dichroic mirror 2
The green light reflected at 04 is a liquid crystal light valve 205 for green.
Then, the transmitted blue light enters the blue liquid crystal light valve 207, respectively. A polarizer 221 and an analyzer 222 are attached to each liquid crystal light valve, whereby light is modulated for each color to form an image.

The blue light modulated by the blue liquid crystal light valve 207 is reflected by the reflection mirror 208, enters the blue transmission dichroic prism 227, passes through, and is enlarged and projected by the projection lens 211. Green liquid crystal light valve 2
The green light that has been light-modulated by the light 05 is incident on and reflected by the red-transmitting dichroic mirror 209, and is enlarged and projected by the projection lens 211. The red light that is modulated by the liquid crystal light valve 206 for red transmits a red dichroic mirror 209.
And is transmitted therethrough, and is enlarged and projected by the projection lens 211.

Examples of the present invention will be described below.

In the numerical examples, Ri is the radius of curvature of the i-th surface in order from the screen side, Di is the i-th optical member and the air gap in order from the screen side, and Ni and νi are the i-th optical members in order from the screen side. Are the refractive index and Abbe number of the material of the optical member.

In the numerical examples, the last two surfaces indicate glass blocks such as a color separation prism and a filter.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0160]

[Outside 1]

[0161]

[Outside 2]

[0162]

[Outside 3]

[0163]

[Table 1]

[0164]

According to the present invention, it is possible to achieve a zoom lens suitable for a projector aiming for brightness, miniaturization, and high zoom ratio, and further favorably correcting magnification chromatic aberration, and a projection apparatus using the same. it can.

In addition, according to the present invention, the entire lens system can be reduced in size by adopting a negative lead type lens as a whole, including six lens groups, and appropriately configuring each lens group. In addition, a zoom lens suitable for a liquid crystal projector and a projection apparatus using the same, which maintain good telecentric conditions over the entire zoom range and have good optical performance over the entire screen, can be achieved.

[Brief description of the drawings]

FIG. 1 is an optical sectional view of a numerical example 1 of the present invention.

FIG. 2 is an optical cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is an optical sectional view of a numerical example 3 of the present invention.

FIG. 4 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the wide-angle end when numerical values of Numerical Example 1 of the present invention are displayed in units of mm.

FIG. 5 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the telephoto end when the numerical value of Numerical Example 1 of the present invention is displayed in units of mm.

FIG. 6 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the wide-angle end when numerical values of Numerical Example 2 of the present invention are displayed in units of mm.

FIG. 7 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the telephoto end when the numerical value of Numerical Example 2 of the present invention is displayed in units of mm.

FIG. 8 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the wide-angle end when a numerical value of Numerical Example 3 of the present invention is displayed in units of mm.

FIG. 9 is an aberration diagram at the time of focusing on an object distance of 2.5 m at the telephoto end when a numerical value of Numerical Example 3 of the present invention is displayed in units of mm.

FIG. 10 is a schematic diagram of a main part of the projection device of the present invention.

[Explanation of symbols]

 L1 First group L2 Second group L3 Third group L4 Fourth group L5 Fifth group L6 Sixth group GB Glass block IP Image plane (LCD) ΔM Meridional image plane ΔS Sagittal image plane SP Aperture

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/1335 G02F 1/1335 G03B 21/00 G03B 21/00 E 21/14 21/14 Z F term ( (Reference) 2H049 AA12 AA16 AA26 AA34 AA51 AA55 2H087 KA06 MA12 NA02 NA14 PA11 PA19 PB13 QA02 QA07 QA12 QA14 QA22 QA26 QA34 QA41 QA45 RA02 RA42 RA46 SA57 SA63 SA64 SA65 SA66 SA71 SA72 SB00 SB04 2SA14 SB12 SB12 SB14 MA07

Claims (21)

[Claims] A first lens group having a negative refractive power, a second lens group having a positive refractive power, and a second lens group having a positive refractive power.
A third lens group having a positive refractive power, a fourth lens group having a negative refractive power, a fifth lens group, and a sixth lens group having a positive refractive power;
When zooming from the focal length at the wide-angle end to the focal length at the telephoto end, three or more of the second to fifth lens units are moved, and the first and sixth lens units are moved. In a variable power optical system fixed during variable power, at least one of the plurality of lens groups has a diffraction optical element rotationally symmetric with respect to one or more optical axes. A zoom lens characterized by the following. 2. The optical system according to claim 1, wherein 0 <φ2 / φw <1.5 is satisfied, where φ2 is the refractive power of the second lens group and φw is the refractive power of the entire system at the wide-angle end. Zoom lens. 3. The zoom lens according to claim 2, wherein said first lens group has a positive lens having a convex surface having a stronger refractive power on the object side than on the image side, closest to the object side. 4. The first lens group has the Abbe number of a lens having the smallest Abbe number among the positive lenses arranged in the lens group as v1p, and the first lens group has the smallest Abbe number among the negative lenses arranged in the lens group. 4. The zoom lens according to claim 3, wherein, when the Abbe number of the lens having a large Abbe number is ν1n, ν1n−ν1p> 10 is satisfied. 5. Assuming that the combined refractive power of the second lens unit and the third lens unit at the wide-angle end is φ23w and the refractive power of the entire system at the wide-angle end is φw, 0 <φ23w / φw <1.5 is satisfied. 5. The zoom lens according to claim 4, wherein: 6. When the refractive power of the fourth lens group is φ4w and the refractive power of the entire system at the wide-angle end is φw, the following condition is satisfied: 0 <| φ4w / φw | <1.5. Item 5. The zoom lens according to item 5. 7. The second lens group includes one or more positive lenses and one or more negative lenses, and the positive lens having the largest Abbe number among the positive lenses is represented by ν2p,
7. The zoom lens according to claim 6, wherein when the Abbe number of the negative lens having the smallest Abbe number among the negative lenses is ν2n, ν2p−ν2n> 10 is satisfied. 8. The zoom lens according to claim 7, wherein said second group or said third group has a stop. 9. The optical system according to claim 8, wherein 0 <φ6w / φw <1.5, where φ6w is the refractive power of the sixth lens group and φw is the refractive power of the entire system at the wide-angle end. Zoom lens. 10. The focal length at the wide-angle end of the entire system is fw, and during zooming, the shortest exit pupil length in absolute value from the final lens surface is tk.
The zoom lens according to any one of claims 1 to 9, wherein: | tk | / fw> 1.5 is satisfied. 11. The lens system according to claim 1, wherein 0.9 <bf / fw is satisfied, where bf is the back focus and fo is the focal length at the wide-angle end of the entire system. Zoom lens. 12. The optical system according to claim 1, wherein when an Abbe number of a material of an arbitrary positive lens included in said sixth lens group is ν6p, ν6p> 30 is satisfied. Zoom lens. 13. The sixth lens group according to claim 1, wherein the sixth lens group comprises one positive lens, and when the Abbe number of the material of the positive lens is ν6p, ν6p> 35 is satisfied. Or the zoom lens of item 1. 14. The focal length of the entire system at the wide-angle end is fw, the focal length of the entire system at the telephoto end is ft, and the focal length of the i-th lens unit is f.
where i is 1.1 <| f1 / f2 | <2.3 14. The zoom lens according to claim 1, wherein the following is satisfied. 15. When the focal length of the first lens group is f1, and the focal length of the entire system at the wide-angle end is fw, 1 <| f1 | / fw <2.5 is satisfied. 15. The zoom lens according to any one of 1 to 14. 16. The lateral magnifications of the second lens group at the wide-angle end and the telephoto end are respectively β2w and β2t, the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fw and ft, and the lateral magnification β2 of the second lens group. Is the change β2t / β2w of Z2, and the change ft of the focal length of the entire system
/ Fw is Z, and the moving amounts of the second lens unit and the fifth lens unit at full magnification are M2 and M5, respectively. 0.8 <Z2 / Z <1.11.0 <| M2 The zoom lens according to any one of claims 1 to 15, wherein the following condition is satisfied: / M5 | <11.0 0.4 <M2 / (ft-fw) <1.3. 17. The lens system according to claim 1, wherein 0.01 <| f2 / f5 | <0.9, where fi is the focal length of the i-th lens unit. Zoom lens. 18. When the back focus is bf and the focal length of the i-th lens unit is fi, 0.3 <bf / f6 <2.50.9 <| f1 | / bf <1.6 is satisfied. The zoom lens according to any one of claims 1 to 17, wherein: 19. When the focal length of the sixth lens group is f6 and the focal length at the wide-angle end of the entire system is fw, the following condition is satisfied: 0.5 <f6 / fw <3.5. 19. The zoom lens according to any one of 1 to 18. 20. When the focal length of the i-th lens unit is fi and the focal lengths at the wide-angle end and the telephoto end of the entire system are fw and ft, respectively: 20. The zoom lens according to claim 1, wherein the following condition is satisfied. 21. A projection apparatus, wherein an original projection image is projected on a screen surface using the zoom lens according to any one of claims 1 to 20.