JP2013120365A - Projection optical system and image projection device - Google Patents

Abstract

The present invention provides a new and improved projection optical system and image projection apparatus which can realize aberration correction and performance fluctuation suppression due to temperature environment simultaneously using a plastic lens.
A projection optical system 100a reflects a first optical system I that is a refractive optical system that transmits light incident from an image display element side and light incident from the first optical system side by a reflecting surface. A second optical system II that is a reflective optical system, and the first optical system includes a first group including at least one aspheric plastic lens, and is disposed closer to the reflective optical system than the first group. A second group including at least two aspheric plastic lenses, and a lens thickness at the maximum light ray height and a lens thickness on the optical axis of the two aspheric plastic lenses included in the second group, Satisfies the predetermined conditional expression.
[Selection] Figure 1

Description

  The present invention relates to a projection optical system and an image projection apparatus, and more particularly to a projection optical system and an image projection apparatus having an ultrashort focal point capable of projecting a large screen at a short projection distance.

  In recent years, a market demand for a short focus projection optical system capable of projecting a large screen with a short projection distance is increasing. Such a short focus projection optical system may have a short distance between the projection surface and the projection optical system even when a large screen is projected. For this reason, for example, when a short-focus projection optical system is used in a front projection type image projection apparatus, there is little projection light hitting a person standing near the projection surface. Therefore, there is an advantage that the dazzle felt by a person near the projection surface is small. Further, when a short-focus projection optical system is used in a rear projection type image projection apparatus, there is an advantage that the size of the apparatus can be reduced.

  In order to realize a short-focus projection optical system, an aspherical lens and a free-form surface lens are used for aberration correction, but at this time, by using a plastic lens, it is easy to manufacture and low cost. There is an advantage (for example, Patent Document 1).

JP 2011-150030 A

  However, plastic lenses have a large variation in characteristics due to temperature changes. For this reason, the optical system is sensitive to temperature change, and focus fluctuation has been a problem in terms of practicality.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is a novel and capable of simultaneously realizing aberration correction and performance fluctuation suppression due to temperature environment using a plastic lens. An object of the present invention is to provide an improved projection optical system and image projection apparatus.

In order to solve the above-described problem, according to an aspect of the present invention, a first optical system that is a refractive optical system that transmits light incident from the image display element side and a first reflecting optical system from the first optical system side by a reflecting surface. A second optical system that is a reflective optical system that reflects incident light, wherein the first optical system includes a first group including at least one aspheric plastic lens, and the reflection from the first group. A second group including at least two aspheric plastic lenses disposed on the optical system side, and a lens thickness e_21a at the maximum ray height of the first aspheric plastic lens included in the second group, And the lens thickness t_21a on the optical axis of the first aspheric plastic lens is
1.4 <(e_21a) / (t_21a) <1.9
Meet the requirements of
The second aspheric plastic lens included in the second group and disposed closer to the reflective optical system than the first aspheric plastic lens has a lens thickness e_22a at the maximum light ray height, and the second The lens thickness t_22a on the optical axis of the aspheric plastic lens is
2.5 <(e_22a) / (t_22a) <2.8
A projection optical system characterized by satisfying the following conditions is provided.

  Since the off-axis ray height is high in the second group, the first aspherical plastic lens and the second plastic lens included in the second group can mainly correct off-axis aberrations. However, plastic lenses are sensitive to temperature changes and are subject to performance fluctuations. For this reason, image plane fluctuations may occur when the temperature changes. However, according to the above-described configuration, even if the performance of the aspheric plastic lens fluctuates due to a temperature rise, the two aspheric plastic lenses included in the second group can change the image plane due to a temperature change to other factors. It can be offset with the optical member.

In addition, the focal length f_1a of the aspheric plastic lens included in the first group is given by f_1 as the focal length of the first group.
(F_1a) / (f_1)> 7.0
You may meet the conditions.

  An intermediate image may be formed between the first optical system and the second optical system.

  The reflective surface of the second optical system may have a concave shape.

  The first group may have a diaphragm.

  The first optical system may be a coaxial optical system.

In order to solve the above problems, according to another aspect of the present invention, a first optical system that is a refractive optical system that transmits light incident from the image display element side, and the first optical system by a reflecting surface. A second optical system that is a reflection optical system that reflects light incident from the system side, and the first optical system includes a first group including at least one aspheric plastic lens, and the first group. And a second group that is disposed on the reflective optical system side and includes at least two aspheric plastic lenses,
The lens thickness e_21a at the light ray maximum height of the first aspheric plastic lens included in the second group, and the lens thickness t_21a on the optical axis of the first aspheric plastic lens are:
1.4 <(e_21a) / (t_21a) <1.9
Meet the requirements of
The second aspheric plastic lens included in the second group and disposed closer to the reflective optical system than the first aspheric plastic lens has a lens thickness e_22a at the maximum light ray height, and the second The lens thickness t_22a on the optical axis of the aspheric plastic lens is
2.5 <(e_22a) / (t_22a) <2.8
An image projection apparatus provided with a projection optical system, characterized by satisfying the above condition.

  As described above, according to the present invention, in a projection optical system using a plastic lens, a new and improved projection optical system and image projection capable of simultaneously realizing aberration correction and performance fluctuation suppression due to a temperature environment. An apparatus can be provided.

It is explanatory drawing for demonstrating the outline | summary of the projection optical system which concerns on the 1st Embodiment of this invention. It is a block diagram of the projection optical system which concerns on the same embodiment. It is a MTF (Modulation Transfer Function) figure which shows the performance before the temperature change of the projection optical system which concerns on the same embodiment. It is a lattice figure which shows the screen distortion before the temperature change of the projection optical system which concerns on the same embodiment. It is a MTF figure which shows the performance at the time of the temperature change of the projection optical system which concerns on the same embodiment. It is a lattice figure which shows the screen distortion at the time of the temperature change of the projection optical system concerning the embodiment. It is explanatory drawing for demonstrating the outline | summary of the projection optical system which concerns on the 2nd Embodiment of this invention. It is a block diagram of the projection optical system which concerns on the same embodiment. It is a MTF figure which shows the performance before the temperature change of the projection optical system which concerns on the same embodiment. It is a lattice figure which shows the screen distortion before the temperature change of the projection optical system which concerns on the same embodiment. It is a MTF figure which shows the performance at the time of the temperature change of the projection optical system which concerns on the same embodiment. It is a lattice figure which shows the screen distortion at the time of the temperature change of the projection optical system concerning the embodiment. It is explanatory drawing which shows the structure of the 3 plate-type liquid crystal projector using the projection optical system which concerns on one Embodiment of this invention. It is explanatory drawing which shows the structure of the single plate type | mold DLP (Digital Light Processing) projector using the projection optical system which concerns on one Embodiment of this invention. It is a side view showing the composition of the front projection type image projection device using the projection optical system concerning one embodiment of the present invention. It is a top view of the front projection type image projector of FIG. It is a side view which shows the structure of the rear projection type image projection apparatus using the projection optical system which concerns on one Embodiment of this invention. It is a top view of the rear projection type image projector of FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Overview>
In recent years, market demands for short-focus projection optical systems have increased. In order to realize a short-focus projection optical system, a large aspheric lens is used to correct various aberrations. When a plastic lens is used for this aspheric lens, the performance varies greatly with temperature changes. In practice, performance fluctuations due to temperature changes are undesirable. Therefore, the present invention proposes an optical form and arrangement of a plastic lens capable of suppressing performance fluctuation due to temperature change.

  The projection optical system according to an embodiment of the present invention is a second optical system which is a first optical system composed of a refractive optical system in order from the image display element side and a reflective optical system composed of a single reflecting surface having a concave reflecting surface shape. System. An intermediate image is formed between the first optical system and the second optical system, and the second optical system can reflect the intermediate image and project it on an enlarged scale.

  The first optical system further includes a first group I on the image display element side and a second group II disposed on the second optical system side from the first group I. The first group I has at least one aspheric plastic lens. The second group II has at least two aspheric plastic lenses.

  At this time, the aspheric plastic lens in the first lens group I mainly has an effect of correcting axial aberration. In addition, when the aspheric plastic lens in the first lens group I satisfies the condition expressed by the following formula (1), it is possible to achieve an effect of canceling the focus fluctuation due to the temperature change with other optical members.

(F_1a) / (f_1)> 7.0 Formula (1)
Here, f_1a is the focal length of the aspheric plastic lens in the first lens group I. F_1 is the focal length of the first lens unit I.

  At this time, the aspheric plastic lens in the second lens group II mainly has an effect of correcting off-axis aberrations such as field curvature aberration and screen distortion. Further, when the aspheric plastic lens in the second lens group II satisfies the following conditions, it is possible to obtain an effect of canceling the image plane variation due to the temperature change with other optical members.

1.4 <(e_21a) / (t_21a) <1.9 Expression (2)
2.5 <(e_22a) / (t_22a) <2.8 (3)
Here, e — 21a is the lens thickness at the maximum light ray height of the aspheric plastic lens arranged closest to the image display element among the second group of aspheric plastic lenses. T_21a is the lens thickness on the optical axis of the aspheric plastic lens arranged closest to the image display element among the second group of aspheric plastic lenses. Further, e_22a is the lens thickness at the maximum light ray height of the aspheric plastic lens disposed next to the image display element side in the second group of aspheric plastic lenses. T_22a is the lens thickness on the optical axis of the aspheric plastic lens.

  Hereinafter, the first embodiment and the second embodiment of the projection optical system having such a configuration will be described in detail using configuration examples and numerical examples. Further, application examples of the projection optical system according to these embodiments to an image projection apparatus will be exemplified.

<2. First Embodiment>
Here, the projection optical system according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram for explaining the outline of the projection optical system according to the first embodiment of the present invention. FIG. 2 is a configuration diagram of the projection optical system according to the embodiment. FIG. 3 is an MTF (Modulation Transfer Function) diagram showing the performance of the projection optical system according to the embodiment before the temperature change. FIG. 4 is a lattice diagram showing screen distortion before temperature change of the projection optical system according to the embodiment. FIG. 5 is an MTF diagram showing the performance of the projection optical system according to the embodiment when the temperature changes. FIG. 6 is a lattice diagram showing screen distortion at the time of temperature change of the projection optical system according to the embodiment.

(Constitution)
First, referring to FIG. 1, a projection optical system 100a according to a first embodiment of the present invention is shown. The projection optical system 100a includes a first optical system I that is a refractive optical system and a second optical system II that is a reflective optical system. Light incident on the first optical system I from the image display element is transmitted through the first optical system I and then reflected by the second optical system II. An intermediate image is formed between the first optical system I and the second optical system II. The light reflected by the second optical system II is magnified and travels to the screen.

  Next, a detailed lens configuration of the projection optical system 100a will be described with reference to FIG. The first optical system I includes a first group I-i (L01 to L09) on the side close to the image display element, and a second group I- disposed on the second optical system II side with respect to the first group I-i. ii (L10 to L14). The first group Ii includes one aspheric plastic lens L07. The first group I-i has a stop D.

  The second group I-ii that transmits the light incident from the first group I-i to the second optical system II side includes two aspheric plastic lenses (L12 and L14). The two aspherical plastic lenses L12 and L14 are odd-numbered aspherical surfaces particularly for correcting screen distortion.

  Further, the reflecting surface RS1 of the second optical system has a concave shape and is formed of an odd-order aspheric surface. All optical members are coaxial optical systems in which the optical axes coincide. If the projection distance is 390 mm and the screen is 90 inches and 16: 9 screen, the slow ratio is 0.2 or less. Therefore, the projection optical system 100a is an ultrashort focus projection optical system. Here, the slow ratio is a numerical value obtained by dividing the projection distance by the horizontal size of the projection screen.

(Numerical example)
Table 1 below shows numerical data of the projection optical system 100a according to the embodiment. This numerical data includes a radius of curvature, a surface interval, a d-line refractive index, and an Abbe number with respect to the surface number and the lens number. The lens numbers shown here correspond to the symbols in FIG.

  Next, an aspheric lens surface or reflection surface included in the first group I-i is expressed by the following mathematical formula (4). By substituting the values in Tables 2 and 3 into this aspherical expression, the shape of the lens surface or reflecting surface is expressed. In Table 2, surface numbers 16, 27, and 28 are described, and in Table 3, surface numbers 31 to 33 are described.

・・・数式（４）

... Formula (4)

Here, the function and characteristics of the projection optical system 100a having the above-described configuration will be further examined. The aspherical plastic lens L07 of the first group Ii has the effect of correcting the aberration and canceling the focus fluctuation at the time of temperature change. In general, the refractive index temperature change of a plastic material has a sign opposite to that of a glass material with respect to the refractive index temperature change (dn / dt) and fluctuates several tens of times. Further, the linear expansion coefficient of the plastic material is about 10 times larger than the linear expansion coefficient (α) of the glass material. For example, the refractive index temperature change and the linear expansion coefficient of plastic used for the general glass BK7 and the aspheric plastic lens L07 according to the present embodiment are as follows.
Refractive index temperature change (dn / dt) General glass BK7: + 2.7E-6
L07 plastic: -100E-6
Linear expansion coefficient (α) General glass BK7: + 7.6E-6
L07 plastic: + 60E-6

When the aspheric plastic lens L07 in the first group Ii has a positive refractive power as in the example of the present embodiment, the direction of change of the refractive power with respect to the temperature change is the normal positive power. The opposite effect of a glass lens with a refractive power of. In addition, since plastic has a large coefficient of linear expansion, if the refractive power of plastic is strong, deformation with respect to temperature changes increases and aberration performance changes greatly. The first optical system I of this embodiment has a positive refractive power. The first group Ii of the first optical system I also has a positive refractive power as a whole. For this reason, the glass lens occupying most of the first lens group I-i changes in a direction in which its refractive power increases as a whole due to a temperature change, and the focus changes in one direction. Therefore, the refractive power of the aspheric plastic lens L07 is designed so as to give an appropriate refractive power in consideration of thermal deformation due to linear expansion. As a result, it is possible to cancel out the focus fluctuation due to the temperature, and to realize a projection optical system with small aberration fluctuation by suppressing the surface deformation due to the temperature. Therefore, it is preferable that the refractive power of the aspheric lens is given by the ratio of the refractive power of the entire first lens unit, that is, the focal length. With respect to the aspheric plastic lens L07 of the present embodiment, the value of Equation (1) is calculated as follows.
(F_1a) / (f_1) = 7.76 Formula (1)

  If the value of the numerical formula (1) is 7.0 or less, the refractive power of the aspherical lens with respect to the first group becomes relatively strong, and the focus variation cannot be compensated with other optical members for correction. Therefore, it is desirable that the value of the mathematical formula (1) is configured to be larger than 7.0.

  The two aspherical plastic lenses L12 and L14 included in the second lens group I-ii correct aberrations and cancel out-axis aberrations at the time of temperature change, in other words, screen distortion and image plane fluctuation. Has the effect of In the case of a projection optical system in which the short focus, that is, the wide angle is further advanced as in the present embodiment, the difficulty of correcting screen distortion and field curvature aberration increases. For this reason, in the first optical system I, it is conceivable to effectively correct this screen distortion and aberration in the second group I-ii in which the height of the off-axis ray is large. In the present invention, at least two aspheric plastic lenses are preferably used. In the present embodiment, two aspheric plastic lenses L12 and L14 are used. Of the two aspherical plastic lenses, the aspherical plastic lens L12 which is a lens closer to the first group Ii is referred to as a first aspherical lens L12 here. In addition, the aspheric plastic lens L14 that is a lens closer to the second optical system II is referred to as a second aspheric lens L14 here.

  The projection optical system 100a according to the present embodiment effectively corrects the screen distortion and the field curvature aberration that tend to occur with the wide angle by the first aspheric lens L12 and the second aspheric lens L14. Yes. An odd-order aspheric surface is preferably used as the aspheric surface for aberration correction. As described above, an aspheric plastic lens has different properties from a normal glass lens with respect to temperature changes. For this reason, the two aspherical plastic lenses in the second group I-ii of the projection optical system 100a according to the present embodiment are also designed with an appropriate shape and refractive power, and in particular, aberration correction for off-axis image height. Thus, an optical system that suppresses aberration fluctuations in the off-axis image height due to temperature changes is realized.

Unlike the aspheric plastic lens in the first group I-i, the off-axis ray height is high in the second group I-ii, so that the lens thickness on the off-axis aberration and the maximum off-axis effective ray height are high. It is preferable to consider the lens characteristics by the relative ratio of the lens thickness. Regarding the first aspherical lens L12 and the second aspherical lens L14, the values of the above mathematical expressions (2) and (3) are calculated as follows.
(E — 21a) / (t — 21a) = 1.50 Equation (2)
(E — 22a) / (t — 22a) = 2.70 (3)

  If the value of Equation (2) deviates from the range of 1.4 to 1.9, and further the value of Equation (3) deviates from the range of 2.5 to 2.8, it is caused by screen distortion and temperature change. The image plane variation cannot be corrected by canceling with other optical members. For this reason, the value of Equation (2) is in the range from 1.4 to 1.9, and the value of Equation (3) is in the range from 2.5 to 2.8. desirable.

  Note that either an aspheric plastic lens in the first group that mainly corrects on-axis aberrations or an aspheric plastic lens in the second group that mainly corrects off-axis aberrations is used. Is also possible. Moreover, assembly adjustment can be facilitated by configuring all optical members with the same optical axis as in the present embodiment.

(effect)
Next, the effects brought about by the projection optical system according to the present embodiment will be described with reference to FIGS. FIG. 3 shows the through focus MTF when the image height ratio is 0.1, 0.3, 0.6, 0.8, 1.0 on the image display element side before the temperature change. 40 lp / mm corresponds to a pixel of 12.5 μm. In FIG. 4, the screen distortion at this time is indicated by a 21 × 21 grid.

  Next, FIG. 5 shows an MTF diagram after temperature change. This is a result of calculating the temperature distribution of the projection optical system 100a by analysis and calculating the optical performance variation by applying the analysis result to the optical data. Specifically, the refractive index change (dn / dt) for each material due to temperature rise and the surface shape change and lens interval change calculated from the linear expansion coefficient were input to the lens data for analysis. At this time, it is assumed that the temperature rise from the design temperature is + 40 ° C. in the first group I-i of the first optical system I, + 20 ° C. in the second group I-ii, and + 10 ° C. in the second optical system II. Analysis was performed. The reflecting member of the second optical system II is assumed to be plastic. Referring to FIG. 5, it can be seen that the fluctuation of the through focus MTF from the design value is very small, and the MTF at the reference focus position (0.0 mm position) is maintained at 50% or more of the MTF before and after the temperature rise.

  FIG. 6 shows screen distortion after temperature change. Referring to FIG. 6, even when the projection optical system 100a undergoes a temperature change and the aspheric plastic lens included in the projection optical system 100a undergoes performance fluctuation, the degree of screen distortion does not deteriorate so much. Recognize.

Furthermore, although the case where the projection screen size is 90 inches has been described above as an example, the projection screen size can be changed while focusing by moving the lens group in the first optical system I in the optical axis direction. Is possible. Therefore, it is preferable in terms of versatility of the image projection apparatus. For example, when projecting to 80 inches, the projection screen size can be changed without deteriorating aberration performance and temperature fluctuation by moving the lens group as follows. The projection distance (from the reflection surface RS1 of the second optical system II to the projection screen) is 350 mm.
L10 to L13 Move 1.86mm toward image display element L14 Move 1.03mm toward image display element

<3. Second Embodiment>
Next, a projection optical system according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 7 is an explanatory diagram for explaining the outline of the projection optical system according to the second embodiment of the present invention. FIG. 8 is a configuration diagram of the projection optical system according to the embodiment. FIG. 9 is an MTF diagram showing the performance of the projection optical system according to the embodiment before the temperature change. FIG. 10 is a lattice diagram showing screen distortion before temperature change of the projection optical system according to the embodiment. FIG. 11 is an MTF diagram showing the performance of the projection optical system according to the embodiment when the temperature changes. FIG. 12 is a lattice diagram showing screen distortion at the time of temperature change of the projection optical system according to the embodiment.

(Constitution)
First, referring to FIG. 7, a projection optical system 100b according to a second embodiment of the present invention is shown. The projection optical system 100b includes a first optical system I that is a refractive optical system and a second optical system II that is a reflective optical system. Light incident on the first optical system I from the image display element is transmitted through the first optical system I and then reflected by the second optical system II. An intermediate image is formed between the first optical system I and the second optical system II. The light reflected by the second optical system is magnified and travels to the screen.

  Next, a detailed lens configuration of the projection optical system 100b will be described with reference to FIG. The first optical system I includes a first group I-i (L21 to L29) closer to the image display element, and a second group I- disposed on the second optical system II side than the first group I-i. ii (L30 to L34). The first group Ii includes one aspheric plastic lens L27. The first group I-i has a stop D.

  The second group I-ii that transmits the light incident from the first group I-i to the second optical system II side includes three aspheric plastic lenses (L32 to L34). The three aspheric plastic lenses L32 to L34 are formed of odd-numbered aspheric surfaces, particularly for correcting screen distortion. The projection optical system 100b according to this embodiment is different from the projection optical system 100a according to the first embodiment in that the second group I-ii further includes one aspheric plastic lens L34. The aspheric plastic lens L34 can mainly correct distortion.

  The reflecting surface RS2 of the second optical system II has a concave shape and is formed of an odd-order aspheric surface. All optical members are coaxial optical systems in which the optical axes coincide. If the projection distance is 390 mm and the screen is 90 inches and 16: 9 screen, the slow ratio is 0.2 or less. Therefore, the projection optical system 100b is an ultrashort focus projection optical system. Here, the slow ratio is a numerical value obtained by dividing the projection distance by the horizontal size of the projection screen.

  Table 4 below shows numerical data of the projection optical system 100b according to the embodiment. This numerical data includes a radius of curvature, a surface interval, a d-line refractive index, and an Abbe number with respect to a surface number and a lens number. The lens numbers shown here correspond to the symbols in FIG.

  Next, an aspheric lens surface or reflection surface included in the first group I-i is expressed by the following mathematical formula (4). By substituting the values in Tables 5 and 6 into this aspherical expression, the lens surface or the reflective surface is represented. In Table 5, the surface numbers 16, 27 to 29 are described, and in Table 6, the surface numbers 30 to 33 are described.

・・・数式（４）

... Formula (4)

Here, the function and characteristics of the projection optical system 100b having the above-described configuration will be further examined. The operational effects of the aspheric plastic lens L27 of the first group I-i and the aspheric plastic lenses L32 and L33 of the second group I-ii are the same as those of the aspheric plastic lenses L07, L12 and L14 according to the first embodiment. It is. Here, when the value of the above mathematical formula (1) is calculated for the aspheric plastic lens L27 of the first group I-i of the projection optical system 100b according to the second embodiment, it is as follows.
(F_1a) / (f_1) = 7.02 Formula (1)

Further, when the values of the above formulas (2) and (3) are calculated for the aspheric plastic lenses L32 and L33 of the second group I-ii of the projection optical system 100b according to the second embodiment, the values are as follows. is there.
(E — 21a) / (t — 21a) = 1.82 Formula (2)
(E_22a) / (t_22a) = 2.52 Formula (3)

  The aspheric plastic lens L32 of the second group I-ii corresponds to the first aspheric lens L12 in the projection optical system 100a according to the first embodiment, and is a lens closer to the first group I-i. is there. The aspheric plastic lens L33 corresponds to the second aspheric lens L14 in the projection optical system 100a according to the first embodiment, and is a lens closer to the second optical system II. The aspheric plastic lens L34 has a function of correcting distortion.

(effect)
Next, an example of the effect brought about by the projection optical system 100b according to the present embodiment will be described with reference to FIGS. FIG. 9 shows the through focus MTF when the image height ratio is 0.1, 0.3, 0.6, 0.8, 1.0 on the image display element side before the temperature change. 40 lp / mm corresponds to a pixel of 12.5 μm. In FIG. 10, the screen distortion at this time is indicated by a 21 × 21 grid.

  Next, FIG. 11 shows an MTF diagram after temperature change. This is a result of calculating the temperature distribution of the projection optical system 100b by analysis and applying the analysis result to the optical data to calculate the optical performance variation. Specifically, the refractive index change (dn / dt) for each material due to temperature rise and the surface shape change and lens interval change calculated from the linear expansion coefficient were input to the lens data for analysis. At this time, it is assumed that the temperature rise from the design temperature is + 40 ° C. in the first group I-i of the first optical system I, + 20 ° C. in the second group I-ii, and + 10 ° C. in the second optical system II. Analysis was performed. The reflecting member of the second optical system II is assumed to be plastic. Referring to FIG. 11, it can be seen that the variation of the through focus MTF from the design value is extremely small, and the MTF at the reference focus position (0.0 mm position) is kept at 50% or more of the MTF before and after the temperature rise.

  FIG. 12 shows screen distortion after temperature change. Referring to FIGS. 10 and 12, it can be seen that distortion is corrected even when compared with the projection optical system 100a according to the first embodiment. It can also be seen that the degree of screen distortion does not deteriorate so much even when the performance of the aspheric plastic lens included in the projection optical system 100b is changed due to a temperature change.

Furthermore, although the case where the projection screen size is 90 inches has been described above as an example, the projection screen size can be changed while focusing by moving the lens group in the first optical system I in the optical axis direction. Is possible. Therefore, it is preferable in terms of versatility of the image projection apparatus. For example, when projecting to 80 inches, the projection screen size can be changed without deteriorating aberration performance and temperature fluctuation by moving the lens group as follows. The projection distance (from the reflection surface RS1 of the second optical system II to the projection screen) is 350 mm.
L30 to L32 Move 1.63 mm in the direction of the image display element L33 and L34 Move 0.88 mm in the direction of the image display element

<4. Application example>
Either the projection optical system 100a according to the first embodiment or the projection optical system 100b according to the second embodiment (hereinafter referred to as the projection optical system 100) can be applied to an image projection apparatus. . Here, some application examples of such an image projection apparatus will be described with reference to FIGS. FIG. 13 is an explanatory diagram showing a configuration of a three-plate liquid crystal projector using the projection optical system according to an embodiment of the present invention. FIG. 14 is an explanatory diagram showing a configuration of a single-plate DLP (Digital Light Processing) projector using the projection optical system according to an embodiment of the present invention. FIG. 15 is a side view showing a configuration of a front projection type image projection apparatus using a projection optical system according to an embodiment of the present invention. FIG. 16 is a plan view of the front projection type image projection apparatus of FIG. FIG. 17 is a side view showing a configuration of a rear projection type image projection apparatus using a projection optical system according to an embodiment of the present invention. 18 is a plan view of the rear projection type image projection apparatus of FIG.

  First, referring to FIG. 13, there is shown an example of an optical system from a light source to an LCD panel when using a three-plate transmissive LCD (Liquid Crystal Display) panel. The three-plate liquid crystal projector 10 mainly includes a light source, a dichroic mirror 11, a liquid crystal panel 12, a dichroic prism 13, and a projection optical system 100. The dichroic mirror 11 has a function of separating and transmitting and reflecting light from the light source. When separated into red, blue, and green light by the dichroic mirror 11, this light is incident on the respective liquid crystal panels 12. The liquid crystal panel 12 has a function of generating image light using light of any one color of red, blue, and green. Then, the image light generated by the liquid crystal panel 12 by light of any one of red, blue, and green is combined by the dichroic prism 13 and input to the projection optical system 100.

  Referring to FIG. 14, an example of a single-plate DLP projector 20 in the case of using a single-plate DMD (Digital Micromirror Device) panel is shown. The single-plate DLP projector 20 mainly includes a lens group 21 that relays light from a light source unit that outputs RGB light by a time sequential method, a DMD panel 22, and a projection optical system 100.

  15 and 16, a front projection type image projection apparatus 30 is shown. Although a light source and an illumination optical system that relays light from the light source are not shown here, the front projection image projection apparatus 30 mainly includes a light source, an illumination optical system, and a projection optical system 100. Here, in the projection optical system 100, by using the reflecting member 31 that deflects the optical path between the first group I-i and the second group I-ii, the apparatus size can be further reduced. is there.

  17 and 18, a rear projection type image projection apparatus 40 is shown. Although a light source and an illumination optical system that relays light from the light source are not shown here, the rear projection image projection apparatus 40 mainly includes a light source, an illumination optical system, and a projection optical system 100. Here, similarly to the front projection type image projection apparatus 30, by using the reflecting member 41 that deflects the optical path between the first group I-i and the second group I-ii in the projection optical system 100, It is possible to make the apparatus size more compact.

  Here, it is specifically shown that the projection optical system 100 according to an embodiment of the present invention can be applied to a main image projection apparatus currently implemented. However, the present invention is not limited to this example, and the projection optical system according to the embodiment of the present invention can be applied to other image projection apparatuses.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the technical scope of the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field of the present invention can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that it belongs to the technical scope of the present invention.

  For example, the numerical examples shown in the above embodiment are merely examples, and various configurations for realizing the same function can be taken.

100a, 100b Projection optical system L01-L14 Lens L21-L34 Lens RS1, RS2 Reflecting surface I First optical system I-i First group I-ii Second group II Second optical system

Claims (7)

A first optical system that is a refractive optical system that transmits light incident from the image display element side;
A second optical system that is a reflective optical system that reflects light incident from the first optical system side by a reflective surface;
With
The first optical system includes:
A first group comprising at least one aspheric plastic lens;
A second group that is disposed closer to the reflective optical system than the first group and includes at least two aspheric plastic lenses;
Have
The lens thickness e_21a at the light ray maximum height of the first aspheric plastic lens included in the second group, and the lens thickness t_21a on the optical axis of the first aspheric plastic lens are:
1.4 <(e_21a) / (t_21a) <1.9
Meet the requirements of
The second aspheric plastic lens included in the second group and disposed closer to the reflective optical system than the first aspheric plastic lens has a lens thickness e_22a at the maximum light ray height, and the second The lens thickness t_22a on the optical axis of the aspheric plastic lens is
2.5 <(e_22a) / (t_22a) <2.8
A projection optical system characterized by satisfying the following conditions. The focal length f_1a of the aspheric plastic lens included in the first group is given by f_1 as the focal length of the first group.
(F_1a) / (f_1)> 7.0
The projection optical system according to claim 1, wherein the following condition is satisfied.   The projection optical system according to claim 1, wherein an intermediate image is formed between the first optical system and the second optical system.   The projection optical system according to claim 1, wherein the reflection surface of the second optical system has a concave shape.   The projection optical system according to claim 1, wherein the first group has a stop.   The projection optical system according to claim 1, wherein the first optical system is a coaxial optical system. A first optical system that is a refractive optical system that transmits light incident from the image display element side;
A second optical system that is a reflective optical system that reflects light incident from the first optical system side by a reflective surface;
With
The first optical system includes:
A first group comprising at least one aspheric plastic lens;
A second group that is disposed closer to the reflective optical system than the first group and includes at least two aspheric plastic lenses;
Have
The lens thickness e_21a at the light ray maximum height of the first aspheric plastic lens included in the second group, and the lens thickness t_21a on the optical axis of the first aspheric plastic lens are:
1.4 <(e_21a) / (t_21a) <1.9
Meet the requirements of
The second aspheric plastic lens included in the second group and disposed closer to the reflective optical system than the first aspheric plastic lens has a lens thickness e_22a at the maximum light ray height, and the second The lens thickness t_22a on the optical axis of the aspheric plastic lens is
2.5 <(e_22a) / (t_22a) <2.8
An image projection apparatus provided with a projection optical system, characterized in that:

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