JP2005084186A - Projection lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection lens reduced in the variation of a pupil position in the case of varying power. <P>SOLUTION: The projection lens incorporated in an enlargement projection device has an aperture diaphragm which does not have a refracting power for determining an aperture ratio. The aperture diaphragm is structured so as to move within an optical system in the direction of an optical axis independently of a lens and a lens group which have the other refracting powers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection lens used in a projection system such as a liquid crystal projector, which constitutes a projection apparatus that magnifies and projects illumination light onto a screen or the like.

  In recent years, liquid crystal projectors have come to be widely used in conferences and the like as devices that allow an image of a personal computer or the like to be enlarged and projected on a large screen. For the projection lens of such a liquid crystal projector, for example, the following is desired.

1) Realize a bright and compact projection system that can withstand use even in daylight 2) Infinite pupils on the liquid crystal display (reduction) side to ensure good pupil alignment with the illumination system It must be a compact telecentric optical system in the distance 3) Realize a compact high-magnification projection system that can be used in various installation and usage environments
Japanese Patent Laid-Open No. 10-161027

  However, in the conventional high-magnification projection system, an aperture stop that determines the aperture ratio of the projection system is included in the lens group having refractive power, and moves together with these lens groups at the time of zooming. The lens aperture ratio in this case depends on the zoom type, and when the projection system is used at the telephoto end, the amount of light on the screen is greatly reduced.

  In addition, since the aperture stop is included in a lens group having a refractive power and moves together with these lens groups at the time of zooming, the pupil position on the reduction side varies greatly from wide angle to telephoto end depending on the zoom type. There is also a problem.

  In Patent Document 1, an ideal lens is proposed as a projection lens for a liquid crystal projector in which the aperture ratio and the reduction-side pupil position do not change upon zooming from the wide angle to the telephoto end. Furthermore, the lens group behind the aperture stop must be fixed at the time of zooming, and the lens system becomes large, making it difficult to say a compact projection system.

  In addition, it is conceivable to adjust the aperture stop diameter at the time of zooming in order to reduce the aperture ratio change when zooming from the wide angle to the telephoto end, and to make it constant, but this also increases the size of the lens system. There was a problem.

  From another point of view, there were zoom lenses that adopted a multi-group zoom to reduce the zoom stroke of each group and reduce the variation in the pupil position on the reduction side from the wide angle to the telephoto end. However, there was a need to make the aperture ratio at the telephoto end as close as possible to the wide-angle end aperture ratio.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a projection lens having a small pupil position fluctuation upon zooming.

  In order to solve the above problems, the present invention is characterized by the following configuration.

  The projection lens included in the magnifying projection apparatus has an aperture stop for determining an aperture ratio having no refractive power, and the aperture stop has another optical refractive power in the optical axis direction inside the optical system. It is characterized by moving independently of the lens and the lens group.

  As described above, by independently moving the aperture stop having no refractive power within the optical system, various performances relating to the pupil can be controlled (brighter or darker) without breaking the optical specifications such as the zoom ratio and the lens size. It becomes possible.

  Further, the projection lens is a retrofocus type zoom lens, where the total lens length at the wide-angle end is L, and the distance from the most magnified lens surface vertex to the aperture stop is lw. It is characterized in that an aperture is arranged.

0.4 <lw / L <0.7 (1)
As for the projection lens, the retrofocus type lens is generally adopted because a color synthesis prism or the like enters between the lens and the projection element and requires a long back focus with respect to the focal length. At this time, it is preferable that the aperture stop is disposed near the center of the projection system that satisfies the conditional expression (1) as in the above conditional expression in consideration of the balance between the lens outer diameter size and aberration correction.

  The projection lens is a retrofocus type zoom lens, and the zoom lens has a zoom ratio of zr, and the enlargement-side pupil magnification during zooming is βp (= telephoto end pupil diameter / wide angle end pupil diameter). The aperture stop moves at the time of zooming so as to satisfy the equation.

0.7 <βp / zr <1.0 (2)
Conditional expression (2) represents the ratio of the enlargement-side pupil magnification to the zoom ratio. If the lower limit of conditional expression (2) is exceeded, the aperture ratio at the zooming telephoto end will be undesirably large. Conversely, if the upper limit is exceeded, the aperture ratio at the telephoto end becomes too small, and it becomes difficult to correct the aberration at the telephoto end.

  As described above, according to the present invention, it is possible to realize a compact retrofocus zoom lens having a small pupil position variation upon zooming from the wide angle to the telephoto end.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described in more detail based on examples.

(First embodiment)
A first numerical example of the present invention is listed in Table 1, and a cross-sectional view is shown in FIG. In the table, ri (i = 1 to 26) is a radius of curvature of the i th lens surface located from the screen side, and di (i = 1 to 26) is also between the i th and i + 1 th lens surfaces. , Ndi (i = 1 to 26) is the refractive index of the glass constituting the i-th lens with respect to the d-line, and Vdi (i = 1 to 26) is the Abbe number of the glass constituting the i-th lens. Respectively.

  GB represents a glass block such as a dichroic prism for color synthesis, ST represents a diaphragm surface, and LCD represents a liquid crystal display device.

  In the present embodiment, it is composed of six groups of negative positive positive negative positive in order from the object side.

  In zooming from the wide-angle end to the telephoto end, the first and sixth lens units are fixed and have a constant overall length, and the second to fifth lens units are independently moved to the enlargement side. Further, in order to ensure the illuminance on the screen, it is preferable to employ a multilayer coating on each lens surface.

  In this example, since a long back focus is required, a retro focus type is employed. Conventionally, the aperture disposed on the surface of the third lens group G8 lens R1 disposed in the middle of the optical system is reduced on the zooming side. It was moving from the enlargement side. For this reason, the paraxial pupil (reduction side) position at the wide-angle end moves inside the projection lens, and conversely at the telephoto end, the pupil moves toward the illumination system side, and the wide-angle end pupil position is near the allowable limit position. Also, the aperture ratio fluctuation due to zooming is F / 1.74-2.16, and the light output value at the telephoto end is about 85 compared with that at the wide-angle end when considered with a projection apparatus provided with a liquid crystal panel with a microlens array. %. Therefore, the aperture ratio determining means (aperture ST) having no refractive power according to the present invention is provided by shifting from the third lens group III to the enlargement side, and independently in the optical axis (enlargement side) direction upon zooming from the wide angle to the telephoto end. Has been moved to.

  As a result, first, the wide-angle-end reduction-side pupil position can be arranged farther away, and further, the magnification of the pupil relating to zooming can be increased by moving away from the second zoom lens unit during zooming. Since the aperture ratio can be made large, the aperture ratio at the telephoto end can be made smaller than that of the conventional zoom type, and the aperture ratio fluctuation during zooming can be reduced to 1.74 to 2.07, which is smaller than that of the conventional zoom type. The ratio can be suppressed to about 90%.

  Also, with regard to the telephoto end pupil position, it is also possible to suppress the reduction-side pupil position fluctuation at the time of zooming by setting the aperture moving speed to be smaller than that at the zooming time of the third lens group III. .

  FIGS. 4A and 4B show aberration diagrams at the wide-angle end and the telephoto end when the projection lens of the present embodiment is focused to 2.1 m by the first lens group I, respectively.

  Moreover, the calculated value by each conditional expression is as follows.

lw / L = 0.633 (3)
βp / zr = 0.839 (4)
(Second embodiment)
A second numerical example of the present invention is listed in Table 2, and a cross-sectional view is shown in FIG. In the table, ri (i = 1 to 26) is a radius of curvature of the i th lens surface located from the screen side, and di (i = 1 to 26) is also between the i th and i + 1 th lens surfaces. , Ndi (i = 1 to 26) is the refractive index of the glass constituting the i-th lens with respect to the d-line, and Vdi (i = 1 to 26) is the Abbe number of the glass constituting the i-th lens. Respectively.

  GB represents a glass block such as a dichroic prism for color synthesis, ST represents a diaphragm surface, and LCD represents a liquid crystal display device.

  In the present embodiment, it is composed of six groups of negative positive positive negative positive in order from the object side.

  In zooming from the wide-angle end to the telephoto end, the first and sixth lens units are fixed and have a constant overall length, and the second to fifth lens units are independently moved to the enlargement side. Further, in order to ensure the illuminance on the screen, it is preferable to employ a multilayer coating on each lens surface.

  In this example, the aperture stop on the R1 surface of the third lens group G7 is separated to the screen side as in the first embodiment and is moved independently of the other groups at the time of zooming.

  As a result, the wide-angle end enlargement-side pupil position can be increased, and good telecentric performance can be maintained.

  Since other points are the same as those of the first embodiment, detailed description thereof is omitted.

  FIGS. 5A and 5B show aberration diagrams at the wide-angle end and the telephoto end when the projection lens of the present embodiment is focused to 2.1 m by the first lens group I, respectively.

  Moreover, the calculated value by each conditional expression is as follows.

lw / L = 0.600 (5)
βp / zr = 0.831 (6)
(Third embodiment)
A third numerical example of the present invention is listed in Table 3, and a cross-sectional view is shown in FIG. In the table, ri (i = 1 to 24) is the radius of curvature of the i th lens surface located from the screen side, and di (i = 1 to 24) is the same between the i th and i + 1 th lens surfaces. , Ndi (i = 1 to 24) is the refractive index of the glass constituting the i-th lens with respect to the d-line, and Vdi (i = 1 to 24) is the Abbe number of the glass constituting the i-th lens. Respectively.

  GB represents a glass block such as a dichroic prism for color synthesis, ST represents a diaphragm surface, and LCD represents a liquid crystal display device.

  In the present embodiment, it is composed of six groups of negative positive positive negative positive in order from the object side.

  In zooming from the wide-angle end to the telephoto end, the first and sixth lens units are fixed and have a constant overall length, and the second to fifth lens units are independently moved to the enlargement side. Further, in order to ensure the illuminance on the screen, it is preferable to employ a multilayer coating on each lens surface.

  In this example, the aperture stop on the R1 surface of the third lens group G7 is separated to the screen side as in the first example, and the relative moving speed with respect to the second lens group II is further increased during zooming to increase the telephoto end aperture ratio. ing.

  As a result, first, the wide-angle end enlargement-side pupil position can be increased, and good telecentric performance can be maintained. Further, the amount of light is lost by increasing the aperture ratio at the telephoto end, but the projection lens size can be designed to be small.

  Since other points are the same as those of the first embodiment, detailed description thereof is omitted.

  FIGS. 6A and 6B show aberration diagrams at the wide-angle end and the telephoto end when the projection lens of the present embodiment is focused to 2.1 m by the first lens group I, respectively.

lw / L = 0.658 (7)
βp / zr = 0.803 (8)

Sectional drawing of the projection lens which is 1st Example of this invention Sectional drawing of the projection lens which is 2nd Example of this invention Sectional drawing of the projection lens which is 3rd Example of this invention FIG. 4A is an aberration diagram of the first example at the time of 2.1 m focusing, in which (a) shows longitudinal aberrations at the wide-angle end focal length, and (b) shows longitudinal aberrations at the telephoto end focal length, Indicates curvature of field and distortion. FIG. 5A is an aberration diagram of the second example at the time of 2.1 m focusing, where (a) shows longitudinal aberrations at the wide-angle end focal length, and (b) shows longitudinal aberrations at the telephoto end focal length, Indicates curvature of field and distortion. FIG. 4A is an aberration diagram of the third example at the time of 2.1 m focusing, in which (a) shows the longitudinal aberration at the focal length at the wide angle end, and (b) shows the longitudinal aberration at the focal length at the telephoto end, Indicates curvature of field and distortion.

Explanation of symbols

I First lens group
II Second lens group
III Third lens group
IV 4th lens group V 5th lens group
VI Sixth lens group LCD Liquid crystal display (image plane)
ST Aperture (aperture surface)
GB glass block (color synthesis prism)

Claims (3)

  The projection lens included in the magnifying projection apparatus has an aperture stop having no refractive power for determining the aperture ratio, and the aperture stop has other optical refractive power in the optical axis direction inside the optical system. A projection lens that moves independently of a lens and a lens group. The projection lens is a retrofocus type zoom lens, where L is the total lens length at the wide-angle end, and lw is the distance from the most magnified lens surface vertex to the aperture stop. Is a projection lens.
0.4 <lw / L <0.7 (1) The projection lens is a retrofocus type zoom lens, where the zoom ratio is zr, and the magnification side pupil magnification at the time of zooming is βp (= telephoto end pupil diameter / wide angle end pupil diameter), the following conditional expression: Wherein the aperture stop moves at the time of zooming.
0.7 <βp / zr <1.0 (2)

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