JP2006113446A - Projection optical system and image projection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a telecentric retrofocus lens having simple constitution, made bright and compact and to have a wide angle, restraining the occurrence of chromatic aberration of magnification and distortion to be little, easily used for an enlarging and projecting projection device and realizing high-definition image projection. <P>SOLUTION: The projection lens has a 1st positive lens group having two negative lenses being concave meniscus lenses, a biconcave lens and at least one convex lens, and a 2nd lens group set behind the longest space and having positive refractive power in order from an enlargement side, and satisfies the following expression; 1<f2/f<4, provided that the focal distance of an i-th lens group is (fi) and the focal distance of an entire system is (f). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wide-angle projection lens that is used in a projection apparatus or the like that magnifies and projects an image onto a screen at a fixed finite distance, and in particular, uses a plurality of liquid crystal devices or the like for each color light as a display body to perform color synthesis. The present invention relates to a small telecentric zoom lens that has a simple configuration for projecting high-definition images through a single projection lens, has a long back focus, a wide angle of view of 90 ° or more, and a small distortion. .

  A negative lead type retrofocus lens preceded by a lens unit having a negative refractive power is relatively easy to widen the angle of view, but on the other hand, it has a large amount of distortion and a short back focus. Yes.

  The present applicant has conventionally proposed wide-angle lenses in Japanese Patent Laid-Open Nos. 10-48513 and 11-72700. However, in recent projection apparatuses, a color synthesizing system such as a cross dichroic prism is required. Big glass material is not considered. Therefore, a lens system with a short back focus has been proposed.

  For example, Japanese Patent Laid-Open Nos. 09-26542, 2001-116990, and 2003-233000 propose lenses that attempt to improve these drawbacks. The present applicant has also proposed a wide-angle lens with a long back focus in Japanese Patent Laid-Open No. 2001-42211. However, Japanese Patent Application Laid-Open No. 09-26542 is composed of three lens groups of negative, positive, and positive in order from the enlargement side, and FNo is dark and the angle of view is 80 ° or less and does not reach a wide angle.

  Japanese Patent Laid-Open No. 2001-116990 is composed of three negative and positive groups, and the first lens group is composed of only negative lenses, which is advantageous for ensuring a large back focus. The generation was large and sufficient characteristics were not obtained.

  In Japanese Patent Application Laid-Open No. 2003-233000, two negative and positive group configurations are used, the angle of view is not sufficient, and distortion is not fully corrected.

In addition, other similar projection lenses are disclosed in Japanese Patent Application Laid-Open No. 2001-42211.
Japanese Patent Laid-Open No. 10-048513 JP-A-11-072700 JP 09-026542 A JP 2001-116990 A JP 2003-233000 A JP 2001-042211 A

  In consideration of the above-mentioned advantages and disadvantages of the prior art, the present invention provides a high-definition, easy-to-use, high-definition projection apparatus with a simple configuration that is bright and compact, has a wide angle, and has little chromatic aberration of magnification and distortion. It is to provide a telecentric retrofocus lens that performs effective image projection.

In order to solve the above problems, the projection optical system of the present invention includes, in order from the enlargement side, two negative meniscus negative lenses, a biconcave lens, and a positive first lens group having at least one convex lens, It has a second lens group having a positive refractive power after a long interval and satisfies the following expression.
1 <f2 / f <4
Here, the focal length of the i-th lens group is fi, and the focal length of the entire system is f.

  Moreover, the image projection apparatus of this invention has at least 1 image forming element and the projection optical system in any one of Claims 1 thru | or 3 which projects the light from the said at least 1 image forming element. It is a feature.

  With the configuration described above, it is possible to provide a projection lens that has a simple configuration, is bright and small, has a wide angle, has a low chromatic aberration of magnification, and has little distortion.

  First, when a display image formed by an image display element such as a liquid crystal panel (especially a TN liquid crystal) or a micromirror device is enlarged and projected onto a screen as in the present invention, the liquid crystal display is particularly arranged for each of a plurality of color lights. When separately used, and combining each color light and projecting with one projection lens (projection optical system), it is necessary to satisfy the following conditions.

1) The light distribution characteristic of the liquid crystal or the influence of the angle dependency of the color synthesis dichroic mirror when synthesizing a plurality of color lights is eliminated, and the pupil on the panel side (exit pupil) according to the light flux emitted from the liquid crystal panel to the lens ) Is a so-called telecentric optical system in the distance.
2) A long back focus is required to secure a space for the color composition element interposed between the display body and the projection lens.
3) A lens made of a material that is easily damaged is not disposed on the surface (enlarged side) of the lens system (for example, it is preferable that the lens is not touched with plastic).
4) A sufficiently wide angle (angle of view of 90 ° or more) must be secured in a so-called rear projection type lens that projects from behind the screen.

  In contrast to the above requirements, the conventional example is insufficient for telecentricity, insufficient for downsizing and widening, and dark for FNo and not sufficient as a bright projector.

  The purpose of the present embodiment is to achieve a telecentric retrofocus lens that performs high-definition image projection, which is used in an enlarged projection projection apparatus, with a simple configuration that is bright and small, has a wide angle, has little chromatic aberration of magnification, and has little distortion. is there.

Therefore, in the projection optical system of the present embodiment, a positive first lens group having two concave meniscus negative lenses, a biconcave lens, and at least one convex lens in order from the enlargement side (the lens group described here is It is desirable that the lens is composed of a plurality of lenses, but it may be a single lens), and after the longest interval, a second lens group having a positive refractive power has It is to be configured to satisfy.
(1) 1 <f2 / f <4
Here, the focal length of the i-th lens group is fi, and the focal length of the entire system is f.

  This formula makes the distribution of the focal length of the entire system appropriate. Accordingly, the first lens group sufficiently corrects the distortion, and a large amount of power in the entire system is concentrated in the second lens group, thereby achieving an appropriate performance. If the lower limit of the expression (1) is exceeded, the power of the first lens group becomes weak, the distortion becomes large, and a long back focus cannot be achieved. On the other hand, if the upper limit is exceeded, the size is increased and a wide angle cannot be obtained.

  In particular, the second concave meniscus lens in order from the magnification side has an aspherical surface. Originally, in order to appropriately correct distortion, the most magnified lens is made aspherical as in Japanese Patent Application Laid-Open No. 10-48513 and Japanese Patent Application Laid-Open No. 11-72700 proposed by the present applicant. The distortion is controlled by the lens on the most magnified side where off-axis rays h ~ pass through the periphery, but it is better not to place a lens made of a material that is easily scratched on the surface (magnifying side) of the lens system. Preferred when considered. In particular, when an aspherical surface is formed on such a large-diameter lens, it is often made of a plastic material or the like. However, since plastic material is easily scratched and dusty, in the present invention, off-axis rays constitute an aspherical surface on the second lens from the magnification side, and the first lens from the magnification side in the present invention. In order to ensure back focus and reduce distortion, a concave meniscus lens is made of glass with a high refractive index, and an aspherical surface is formed at a position where it cannot be touched from the outside of the second lens, thereby correcting distortion well. Thus, the sharing is clarified, and the shape of the aspherical surface is set to the optimum shape for the second lens. In addition, by adopting such a configuration, the diameter of the second lens, which tends to be a plastic lens, can be reduced, and in producing by molding, the mold shape can be reduced, and the projection lens can be provided at low cost.

  In particular, it is preferable to reduce the focus on the reduction side in accordance with the distance fluctuation of the conjugate point on the enlargement side by moving the second lens group in the optical axis direction in order to downsize the entire system.

  This is because when the distance is adjusted in the first lens group or the whole, the front lens moves due to the variation in distance, and it is necessary to increase the diameter of the front lens in order to secure the peripheral light quantity in the vicinity. On the other hand, when the distance is adjusted with the second lens group, the front lens does not move, and as shown in Equation (1), a large amount of power in the entire system is concentrated in the second lens group, so the distance is adjusted as a whole. The distance can be as close as possible with a feed amount that is not significantly different from the case of, and it is effective for miniaturization without a decrease in the amount of peripheral light in the vicinity.

  The aperture stop is preferably arranged on the enlargement side of the second lens group and in the vicinity of the front principal point position of the second lens group. With such a configuration, telecentricity can be secured on the reduction side of the third lens group.

  Further, it is preferable that the second lens group is constituted by a larger number of lenses than the first lens group, and the lenses constituting the second lens group are constituted by 6 or more lenses.

In particular, in order to correct lateral chromatic aberration, it is preferable to have a positive lens made of a low dispersion glass material on the reduction side of the second lens group. Specifically (2) ν2p> 70
Where ν2p is the Abbe number of the positive lens constituting the second lens group, more specifically, the positive lens on the reduction side of the second lens group. In particular, there are at least two positive lenses satisfying (2) in the second lens group, and (2-a) ν2p> 80.
More preferably, it is comprised.

  Further, it is preferable for further correction of chromatic aberration that the second lens group has at least two bonded surfaces.

When the Abbe number of the third biconcave lens from the magnifying side in the first lens group is ν13 (3) ν13> 70
This is preferable for correcting chromatic aberration of magnification in the first lens group.

In particular, when the Abbe number of the concave meniscus lens on the most enlarged side of the first lens unit is ν11 (4) ν11 <40
It is preferable to comprise. At this time, in particular, (4-a) ν11 <30
It is preferable for further chromatic aberration correction to satisfy the above. Similarly, when the refractive index of the concave meniscus lens closest to the enlargement in the first lens group is N11 (5) N11> 1.7
It is preferable to ensure the back focus and reduce the occurrence of distortion.
Preferably (5-a) N11> 1.8
It is more preferable that the above is satisfied. In particular, it is preferable to dispose the most magnified lens G1 made of a material under the conditions (4) and (5).

In particular, it is preferable to satisfy the following formula.
(6) D / f> 15
(7) 4 <D / bf <8
However, here, bf means the back focal length of the air conversion length without a prism, a filter, etc., f is the focal length of the entire system, and D is the length from the first lens surface to the final lens surface.

  This formula describes the total length and back focus when aiming at widening the angle.

  If it deviates from the equations (6) and (7), it becomes impossible to achieve a wide angle with a desired lens size.

Furthermore, it is preferable to satisfy the following conditional expression.
(8) 2.5 <bf / f <5.0
(9) f1 / f2> 2.0
Equation (8) sets the back focus and focal length appropriately. Although related to equation (7), in order to increase the back focus, it is a simple method to increase the focal length of the entire system. However, the desired wide angle cannot be achieved. In order to obtain a desired angle of view by inserting a color synthesizing prism, it is preferable to construct a configuration satisfying this equation after arranging the lens configuration.

Moreover, it is preferable to satisfy the following conditional expression (10) 7 <f1 / f
This expression (10) describes the role sharing of the first lens group that is substantially afocal.

  Deviating from this range increases distortion and is not appropriate.

The second lens group having a large number of constituent lenses is a lens group that bears much of the power of the entire system as described above. As can be seen from the relationship of equation (1), specifically, the following relationship should be maintained.
(11) 0.8 <f2 / bf <1.2
If there is an aperture stop in the vicinity of the front principal point position of the second lens group, and the focal length of the first lens group is almost afocal as shown in equation (10), the second lens group functions as a relay lens. The device surface can achieve a telecentric configuration over the entire angle of view. Here, these expressions (1) and (10) are conditions that are satisfied when the aperture stop is in the vicinity of the front principal point position of the second lens group and the first lens group is substantially afocal. If this formula is deviated, the telecentricity cannot be ensured, and the lens is too large to be suitable.

  Further, the second lens group is a group for adjusting the distance, and since it has a configuration like a relay lens, it is preferable that the number of constituent lenses is the largest. As described above, at least six lenses are necessary for miniaturization and high performance.

  Specifically, the second lens group preferably includes at least two biconvex lenses and at least one negative lens having a concave surface on the reduction side.

  In addition, although it is stated that it is preferable that the positive lens on the reduction side in the second lens group has an Abbe number of 70 or more, more preferably 80 or more, it has a negative lens having an Abbe number of 30 or less on the reduction side. It is preferable. With this configuration, it is possible to reduce lateral chromatic aberration that occurs in the second lens group. Further, in the second lens group, a positive lens having a large Abbe number and a negative lens having a small Abbe number may be bonded together to further contribute to correction of chromatic aberration of magnification. On the enlargement side of the second lens group, that is, in the vicinity of the aperture stop, a negative lens having a large Abbe number and a positive lens having a small Abbe number are conversely arranged to suppress the occurrence of longitudinal chromatic aberration. Is preferred.

  At this time, these positive lenses and negative lenses may be bonded together.

Also, in order to eliminate the influence of the light distribution characteristics of the liquid crystal or the angle dependency of the color composition dichroic mirror when combining multiple color lights, the panel side pupil (exit pupil) must be a so-called telecentric optical system. Is effective for a lens as an efficient illumination means. In particular, it is necessary that the pupil (exit pupil) of the lens on the display panel side (reduction side) is far away. Specifically, in order to eliminate the angle dependency, the following conditions should be satisfied.
(12) | tk | / f> 10.0
The following conditions are more preferable: (12a) | tk | / f> 30.0
Hereinafter, Examples 1 to 6 will be briefly described.

(Examples 1-6)
The construction of the projection lens of Examples 1-6 is shown in FIGS. 1-6, the aberration diagrams of Examples 1-6 are shown in FIGS. 7-12, Numerical Examples 1-6 are shown in Tables 1-6, and the above of each example. Table 7 shows the values of the conditional expressions.

  In this numerical example table, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing in order from the object side, and Ni and νi are in order from the object side. The refractive index and Abbe number of the glass of the i-th lens. Further, the flat lens GB closest to the image plane in Numerical Examples 1 to 5 represents a glass block such as a color synthesis prism, a polarizing filter, or a color filter.

  1 to 6 show sectional views at the wide-angle end of Examples 1 to 6, in which G denotes a glass block such as a color synthesis prism, a polarizing filter, a color filter, or the like.

  7 to 12, solid lines, broken lines, alternate long and short dash lines, and alternate long and two short dashes lines are as illustrated in FIG. 7. That is, in the drawings showing spherical aberration and lateral chromatic aberration, the solid line shows the aberration of light with a wavelength of 550 nm, the two-dot chain line shows the aberration of light with a wavelength of 430 nm, and the one-dot chain line shows the aberration of light with a wavelength of 650 nm. In the drawing showing the curvature of field, the solid line indicates the aberration on the sagittal image plane, and the broken line indicates the aberration on the meridional image plane.

  Further, the projection distance of each embodiment is assumed to be 570 mm.

  Table 7 shows the relationship between the aforementioned conditional expressions and various numerical values in the numerical examples. The aspherical shape has an X axis in the optical axis direction, an H axis perpendicular to the optical axis, a positive light traveling direction, R is a paraxial radius of curvature, and each aspheric coefficient is K, B, C, D, E, When F

It is expressed by the following formula.

  The first to fifth embodiments have a plastic lens in which the concave side surface of the second lens from the magnification side is aspherical. Further, the second lens group also has a plastic lens having a positive power of a plastic double-sided aspheric surface. These two plastic lenses are configured to cancel the refractive index change due to temperature change. Of course, it is difficult to cancel completely, so the influence of the change in the optical characteristics due to the temperature change of a specific lens on the optical characteristics of the entire projection lens is affected by the change in the optical characteristics due to the temperature change of other lenses. The configuration is such that the change can be reduced by the influence on the entire projection lens. The aspherical surface of the second lens can be a double-sided aspherical surface. The lens has an FNo of 2.2.

  Each of the embodiments includes one having a substantially equal angle of view (focal length and image circle are the same) and different prism thicknesses introduced on the reduction side of the lens. In the first embodiment, a space that can be bent by a mirror is provided between the first lens group and the aperture stop. When rear projection is used in this way, it is possible to reduce the size by bending.

The sixth embodiment has an aspherical surface only in the first lens group.
The aspherical surface may be a compound aspherical lens (replica aspherical surface) having an aspherical surface made of a thin concave plastic layer on a spherical surface of glass.

  In these embodiments, an aperture efficiency of 300% or more and a peripheral light amount of 65% are secured.

  In Examples 1 to 6, the lens arranged on the most enlargement side is a negative meniscus lens convex on the enlargement side, and the lens arranged second from the most enlargement side is also on the enlargement side. It is desirable to use a convex negative meniscus lens.

  Further, the configuration of the present embodiment is not limited to the first to sixth embodiments. Even if a lens having a sufficiently weak power is inserted into the lens configuration of the first to sixth embodiments, it is within the scope of the present embodiment. Think of it as being within.

  The projection lens described so far is not limited to use only as a projection lens, but may of course be used as a photographing lens (camera, video camera, etc.) or an observation lens (telescope, binoculars, etc.).

(Example 7)
An example of an image projection apparatus using the projection lens of Examples 1 to 6 will be described. Light from a light source illuminates an image forming element that can modulate incident light, such as a liquid crystal panel or DMD, and the light from the image forming element is projected onto a projection surface such as a screen using the projection lens described above. It is the structure which projects to. Here, one image forming element may be used, and each color may be displayed in a time-sharing manner, and a color separation optical system that separates light from a light source into color light such as red, green, and blue, It may be configured to have a color synthesis optical system that color-synthesizes the light from the image forming elements for each color light, and to project the light from the color synthesis optical system by the projection lens described above. The image projection apparatus may be either a front projection system or a rear projection system.

  By constructing the projection lens as described in the present embodiment, a high-definition image projection used in an enlarged projection projection apparatus with a simple configuration that is bright and small in size, wide-angle, low in chromatic aberration of magnification and little distortion. A projection lens (telecentric retrofocus lens) can be achieved. In particular, it has become possible to provide a projector lens with a bright FNo that is sufficiently telecentric and achieves downsizing and widening of the angle with respect to the prior art.

1 is a schematic diagram of a projection lens configuration of Example 1. FIG. 6 is a schematic diagram of a configuration of a projection lens of Example 2. FIG. 6 is a schematic diagram of a configuration of a projection lens of Example 3. FIG. 6 is a schematic diagram of a projection lens configuration of Example 4. FIG. 6 is a schematic diagram of a projection lens configuration of Example 5. FIG. 10 is a schematic diagram of a projection lens configuration of Example 6. FIG. FIG. 4 is an aberration diagram of the projection optical system according to Example 1. FIG. 6 is an aberration diagram of the projection optical system according to Example 2. FIG. 6 is an aberration diagram for the projection optical system according to Example 3. FIG. 10 is an aberration diagram of the projection optical system according to Example 4. FIG. 10 is an aberration diagram of the projection optical system according to Example 5. FIG. 10 is an aberration diagram of the projection optical system according to Example 6.

Explanation of symbols

  Glass block for G color composition

Claims (4)

In order from the magnifying side, a positive first lens group having two negative meniscus lenses, a biconcave lens, and at least one convex lens, and a second lens group having a positive refractive power after the longest interval. Have
A projection optical system satisfying the following expression:
1 <f2 / f <4
Here, the focal length of the i-th lens group is fi, and the focal length of the entire system is f.   The projection optical system according to claim 1, wherein the second concave meniscus lens in order from the magnification side has an aspherical surface.   2. The projection optical system according to claim 1, wherein correction of defocusing on the reduction side accompanying variation in the distance of the conjugate point on the enlargement side is performed by moving the second lens group in the optical axis direction.   An image projection apparatus comprising: at least one image forming element; and the projection optical system according to claim 1 that projects light from the at least one image forming element.

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