JP2012098463A - Projection zoom lens and image projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection zoom lens which secures a sufficient amount of light even in the peripheral portion of an image to be projected, and has a small light quantity loss.SOLUTION: In the projection zoom lens includes a first lens group to a six lens group which have a negative refractive power, a positive refractive power, a positive refractive power, a negative refractive power, a positive refractive power and a positive refractive power in order from a projected side, and in which when performing variable power between a wide angle end and a telephoto end, the first lens group and the six lens group are fixed, and the second lens group to the fifth lens group are moved, a value obtained by dividing the maximum light beam effective radius of the second lens group by the maximum light beam effective radius of the all lenses is 0.65 or more.

Description

  The present invention relates to a projection zoom lens and an image projection apparatus.

  A so-called projector or the like is known as an image projection apparatus, and an image formed by a personal computer or the like can be projected onto a screen. The projection lens of such an image projection apparatus needs a small F number in order to obtain a bright projection image. Further, in order to use a dichroic prism that synthesizes light beams emitted from a plurality of RGB liquid crystal panels for projecting a color image, a large back focus length is required. Further, a zoom function for adjusting the projected image size under a certain projection distance is also necessary.

  Therefore, a projection lens having a negative refractive power lens group disposed in the first lens group on the projection side and including a subsequent lens group is configured as a total of five or six lens systems. It was. Further, in order to make the total length constant at the time of zooming, the first group and the last group (the fifth group or the sixth group) are fixed, and an in-group lens having an appropriate refractive power is arranged between them, along the optical axis. A zoom configuration that moves is designed (see, for example, Patent Documents 1 to 5).

JP 2009-258185 A JP 2009-186026 A JP 2009-128684 A JP 2007-241184 A Japanese Patent Laying-Open No. 2005-084351

  In recent years, surface emitting light sources such as light emitting diodes have begun to be used in image projection apparatuses in place of high pressure mercury lamp light sources from the viewpoint of reducing power consumption and the regulation of harmful substances typified by mercury. In such a lens design of the image projection apparatus, it is important to efficiently guide the light emitted from the light source to a liquid crystal panel or the like, and to project to the screen while minimizing the loss of the projection optical system.

  In a surface emitting light source such as an LED, the Etendue becomes large, and in the design of a projection lens, it is necessary to reduce the F number so as to obtain a larger capture angle than the lamp light source, and to increase the light utilization efficiency as much as possible.

  On the other hand, as a design problem peculiar to the projection lens, it is necessary that the peripheral portion of the projected image be as uniform as possible. For this purpose, it is necessary to prevent as much light rays as possible from the center to the most peripheral part.

  As one embodiment of the present invention, the first to sixth lens groups having refractive powers of negative, positive, positive, negative, positive, and positive in order from the projection side are arranged between the wide-angle end and the telephoto end. Is a projection zoom lens in which the first lens unit and the sixth lens unit are fixed and the fifth lens unit moves from the second lens unit, and the maximum effective ray radius of the second lens unit is set to A projection zoom lens in which a value divided by the maximum effective ray radius is 0.65 or more is provided.

  As one embodiment of the present invention, a light source, a light modulation element that modulates the amount of light passing through the light source, and light modulated by the light modulation element are incident on a projection zoom lens. The first lens is composed of first to sixth lens groups whose refractive powers are negative, positive, positive, negative, positive and positive in order from the projection side, and the first lens at the time of zooming between the wide angle end and the telephoto end The zoom lens is a projection zoom lens in which the lens group and the sixth lens group are fixed and the fifth lens group moves from the second lens group, and is a value obtained by dividing the maximum ray effective radius of the second lens group by the maximum ray effective radius of all the lenses. An image projection apparatus having a value of 0.65 or more is provided.

  According to the present invention, it is possible to provide a projection zoom lens and an image projection apparatus that ensure a sufficient amount of light up to the peripheral portion of a projected image and reduce the loss of light amount.

It is a lens block diagram of the projection zoom lens which concerns on one Embodiment of this invention. It is a figure which shows the calculation result of the peripheral light quantity ratio at the time of changing the value of h2 / H in the lens of the projection zoom lens which concerns on one Embodiment of this invention. It is a figure which shows the graph which plotted the calculation result shown in FIG. It is a block diagram of the projection zoom lens which concerns on one Example of one Embodiment of this invention. It is an aberration diagram of a projection zoom lens according to an example of an embodiment of the present invention. It is a graph of the peripheral light quantity ratio of the projection zoom lens which concerns on one Example of one Embodiment of this invention. It is a block diagram of the projection zoom lens which concerns on one Example of one Embodiment of this invention. It is an aberration diagram of a projection zoom lens according to an example of an embodiment of the present invention. It is a graph of the peripheral light quantity ratio of the projection zoom lens which concerns on one Example of one Embodiment of this invention. It is an optical block diagram of the image projection apparatus which concerns on one Embodiment of this invention. It is an optical block diagram of the image projection apparatus which concerns on one Embodiment of this invention.

  Hereinafter, modes for carrying out the present invention will be described. Note that the present invention is not limited to the embodiments and examples described below. Various modifications can be made to the embodiments and examples described below.

(Embodiment 1)
FIG. 1 shows a lens configuration of a projection zoom lens according to an embodiment of the present invention. In FIG. 1, the upper part shows the lens arrangement at the wide-angle end, and the lower part shows the lens arrangement at the telephoto end. An intermediate arrow indicates the movement of the lens group during zooming.

  The projection zoom lens according to an embodiment of the present invention includes six lens groups. From the projection side (screen side) toward the display element side, the first lens group (1G), the second lens group (2G), the third lens group (3G), the fourth lens group (4G), and the fifth lens Assuming the group (5G) and the sixth lens group (6G), the refractive powers of the respective lens groups are negative, positive, positive, negative, positive, and positive in this order.

  By making the refractive power of the first lens group (1G) negative, it is possible to widen the angle when projecting an image. In the first lens group (1G), it is preferable to dispose a positive lens on the screen side. This is because at the place where the height of the off-axis chief ray is the highest, it is possible to effectively suppress distortion with this positive lens and the subsequent lens.

  By making the second lens group (2G) have an appropriate refractive power, it is possible to suppress a loss in the peripheral light amount. The second lens group (2G) is a lens group that mainly contributes to zooming, and can obtain an appropriate zoom ratio with little aberration fluctuation during zooming while obtaining a balance with the peripheral light amount. The second lens group (2G) includes at least a cemented lens including a lens having a positive refractive power and a lens having a negative refractive power, and the d-line refractive index of the material of the cemented lens (for example, glass) is 1.7 or more. By doing so, it is possible to suppress aberration fluctuations during zooming movement.

  If the focal length of the first lens group (G1) is f1, and the focal length of the second lens group (G2) is f2, the absolute value of f2 / f1 is 1.4 or more and 1.6 or less. Is preferred. If it is less than 1.4 or more than 1.6, the good relationship between the refractive powers of the first lens group (G1) and the second lens group (G2) will not be maintained, and the wide-angle zoom will not occur without insufficient peripheral light quantity. It becomes impossible to make it. That is, below 1.4, the refractive power of the second lens group (G2) becomes weak, and it becomes impossible to obtain a zoom ratio without a shortage of peripheral light quantity. On the other hand, if the value exceeds 1.6, the refractive power of the second lens group (G2) becomes strong, and if the zoom ratio is to be secured, the amount of peripheral light will be insufficient.

  The third lens group (3G) to the fifth lens group (5G) move along the optical axis in order to correct aberration variation and focal point variation during zooming. The first lens group (1G) moves along the optical axis for focus adjustment, but can be prevented from moving during zooming.

  The third lens group (3G) moves together with the aperture stop so as not to cause a shortage of peripheral light quantity even at the time of zooming. A large amount of peripheral light can be ensured even at the time of zooming by moving to the projection side as moving from the wide-angle end to the telephoto end. In order to allow the off-axis light beam emitted from the second lens group (2G) to reach the entire aperture stop without loss, it is preferable that the aperture stop is disposed on the most projection side in the third lens group (3G).

  The fourth lens group (4G) can correct off-axis aberrations by adopting a meniscus lens shape whose overall shape is concave on the display element side. Further, by using the fourth lens group (4G) as a cemented lens, the off-axis aberration of color can be corrected. Moreover, the Petzval sum of the entire projection zoom lens system can be reduced by setting the fourth lens group (4G) to an appropriate refractive power. Also, when the focal length of the fourth lens group (4G) is f4 and the focal length of the entire system at the wide angle end is Fw, the absolute value of f4 / Fw is less than 2.5 or more than 4.5. The Petzval sum canceling relationship with other lens units having positive refractive power cannot be maintained. Therefore, the absolute value of f4 / Fw is preferably 2.5 or more and 4.5 or less.

  The fifth lens group (5G) has at least two single lenses having positive refractive power. Thereby, in order to secure a peripheral light amount, the most off-axis light beam passing through the periphery of the fifth lens group (5G) can be gently refracted to suppress the aberration generated on the surface.

  The sixth lens group (6G) has a positive refractive power in order to make the center of the light beam on the display element side telecentric. Thus, by being telecentric, it is possible to obtain a uniform illuminance distribution in the screen regardless of the type of the display element, regardless of whether the display element is a liquid crystal panel or a micromirror array. By fixing the sixth lens group (6G) during zooming, telecentricity can be maintained even during zooming.

  In one embodiment of the present invention, it is possible to configure only a spherical lens without using an aspherical lens as a constituent lens. With this configuration, it is possible to obtain a projection zoom lens that is excellent in manufacturing and assembling and excellent in cost.

  The inventor of the present application sets the maximum ray effective radius of the second lens group (2G) as h2, and sets the maximum ray effective radius of all the lenses of the first lens group (1G) to the sixth lens group (6G) as H. In this case, it was found that the peripheral light amount ratio of the most off-axis image height can be controlled by the value of h2 / H.

  FIG. 2 shows a case where the value of h2 / H is changed to 0.69, 0.67, 0.65, 0.63, 0.61, 0.59, and 0.57 in the lens configuration at the wide angle end. The calculation result of the peripheral light quantity ratio of the off-axis image height from the center is shown. For each h2 / H value, the peripheral light amount ratio of the most off-axis image height is 80.2, 76.1, 71.4, 66.5, 61.5, 56 as shown in the bottom row. .5, 51.5.

  FIG. 3 is a graph in which the results shown in FIG. 2 are plotted with h2 / H on the x-axis and the peripheral light quantity ratio of the most off-axis image height on the y-axis. As shown in FIG. 3, h2 / H is 0.61 or more in order to set the peripheral light amount ratio of the most off-axis image height to 60% or more. In particular, in order to set the peripheral light amount ratio of the most off-axis image height to 70%, h2 / H is 0.65 or more.

Example 1
FIG. 4 is a lens configuration diagram of a projection zoom lens according to an example of an embodiment of the present invention. In FIG. 4, the upper part shows the lens arrangement at the wide-angle end, and the lower part shows the lens arrangement at the telephoto end. As in FIG. 1, the projection zoom lens is composed of six lens groups. From the projection side toward the display element side, the first lens group (1-G), the second lens group (2-G), the third lens group (3-G), and the fourth lens group (4-G) The fifth lens group (5-G), the sixth lens group (6-G), surface numbers are assigned in order from the lens surface on the projection side of the first lens group (1-G), and the distance between the lens surfaces is increased. Table 1 shows the radius of curvature of the lens surfaces, the distance between the lens surfaces, the d-line refractive index, and the Abbe number, where is the surface number i of the lens surface on the projection side. The surface number 32 is the surface number of the display element surface.

Table 2 shows the distance between the lens surfaces during zooming.

  In this embodiment, the focal length f, F number, and field angle ω are f = 24.0 mm to 29.0 mm, F = 1.59 to 1.97, and ω = 29.3 ° to 24.7 °. Become. Further, h2 / H is 0.69, the absolute value of f2 / f1 is 1.56, and the absolute value of f2 / Fw is 4.03.

  FIG. 5 shows aberration diagrams at the wide-angle end and the telephoto end. In the aberration diagram of astigmatism in FIG. 5, “(S)” is an abbreviation for Sagital, and “(T)” is an abbreviation for Tangential. FIG. 6 shows a graph of the peripheral light amount ratio with respect to the image height ratio. As shown in FIG. 6, a peripheral light amount ratio of 80% or more is secured even at the wide angle end.

(Example 2)
FIG. 7 is a lens configuration diagram of a projection zoom lens according to an example of an embodiment of the present invention. In FIG. 7, the upper part shows the lens arrangement at the wide-angle end, and the lower part shows the lens arrangement at the telephoto end. As in FIG. 1, the projection zoom lens is composed of six lens groups. From the projection side toward the display element side, the first lens group (1-G), the second lens group (2-G), the third lens group (3-G), and the fourth lens group (4-G) The fifth lens group (5-G) and the sixth lens group (6-G) are assigned surface numbers in order from the lens surface on the projection side of the first lens group (1-G). Table 3 shows the radius of curvature of the lens surface, the distance between the lens surfaces, the d-line refractive index, and the Abbe number, where Di is the surface number i of the lens surface on the projection side. As in FIG. 4, the surface number 35 is the surface number of the display element surface.

Table 2 shows the distance between the lens surfaces during zooming.

  In this embodiment, f = 24.0 mm to 29.0 mm, F = 1.60 to 1.90, and ω = 29.3 ° to 24.7 °. Further, h2 / H is 0.71, the absolute value of f2 / f1 is 1.45, and the absolute value of f2 / Fw is 2.89.

  FIG. 8 shows aberration diagrams at the wide-angle end and the telephoto end. In the aberration diagram of astigmatism in FIG. 8, “(S)” is an abbreviation for Sagital, and “(T)” is an abbreviation for Tangential. FIG. 9 shows a graph of the peripheral light amount ratio with respect to the image height ratio. As shown in FIG. 9, a peripheral light amount ratio of 90% or more is ensured even at the wide angle end.

(Embodiment 2)
FIG. 10 shows an optical configuration of an image projection apparatus using the projection optical system according to Embodiment 1 of the present invention.

  White light is sequentially incident on the two dichroic mirrors from the light source. As the light source, an LED, a laser light emitting element, an organic EL element, a phosphor, or the like can be used. Each dichroic mirror sequentially reflects light having a short wavelength. Thereby, the light corresponding to B of the RGB component is separated by the first dichroic mirror through which the light emitted from the light source passes, and the light corresponding to G and the remaining R are separated by the second dichroic mirror. Corresponding light is separated. Note that the order of B and R may be reversed.

  The light corresponding to B is further bent by 90 ° in the traveling direction by a mirror and is incident on a liquid crystal panel as a light modulation element. The light corresponding to G enters the liquid crystal panel. The light corresponding to R is further reflected by two mirrors and enters the liquid crystal panel.

  The amount of light passing through each pixel is controlled by modulation of the light incident on and emitted from each liquid crystal panel. Light emitted from the liquid crystal panel enters the dichroic prism and is synthesized. The synthesized light enters the projection optical system according to the first embodiment and is projected onto the screen.

(Embodiment 3)
FIG. 11 shows another optical configuration of the image projection apparatus using the projection optical system according to Embodiment 1 of the present invention.

  Light corresponding to R, G, and B is sequentially irradiated from a light source in a time division manner, and enters a DMD panel as a light modulation element via a lens or the like. Light whose light amount reflected and passed by each pixel by the DMD panel is controlled by modulation is incident on the projection optical system according to the first embodiment and projected onto the screen.

Claims (10)

The first lens is composed of first to sixth lens groups whose refractive powers are negative, positive, positive, negative, positive and positive in order from the projection side, and the first lens at the time of zooming between the wide angle end and the telephoto end A projection zoom lens in which the group and the sixth lens group are fixed and the fifth lens group moves from the second lens group;
A projection zoom lens having a value obtained by dividing the maximum effective ray radius of the second lens group by the maximum effective ray radius of all the lenses is 0.65 or more.   The projection zoom lens according to claim 1, wherein an absolute value of a value obtained by dividing the focal length of the second lens group by the focal length of the first lens group is 1.4 or more and 1.6 or less.   The projection zoom lens according to claim 1, wherein the second lens group includes a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power.   The projection zoom lens according to claim 3, wherein the cemented lens of the second lens group has a d-line refractive index of a constituent material of 1.7 or more.   The projection zoom lens according to claim 1, wherein the third lens group has an aperture stop.   The fourth lens group has a meniscus shape in which the overall shape is concave on the display element side, and the absolute value of the value obtained by dividing the focal length of the fourth lens group by the total focal length at the wide angle end is 2.5 or more. The projection zoom lens according to claim 1, wherein the projection zoom lens is 4.5 or less.   The projection zoom lens according to claim 1, wherein the fifth lens group includes two lenses having positive refractive power.   The projection zoom lens according to claim 1, wherein focus adjustment is possible by moving the first lens group along the optical axis. A light source;
A light modulation element for modulating the amount of light passing through the light emitted from the light source;
The image projection apparatus which has a projection zoom lens in any one of Claim 1 to 8 in which the light modulated by the said light modulation element injects.   The image projection apparatus according to claim 9, wherein the light source is an LED.