JP2005309251A - Projection lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection lens that corrects magnification chromatic aberration while suppressing the position variation of back focus due to temperature changes to a practical use level. <P>SOLUTION: The projection lens is characterized in that, in the projection lens for projecting a video of a rectangular image display micro device onto a screen surface, a first lens group having negative refracting power and a second lens group having positive refracting power are arranged from an expansion side to a reduction side in order, and at least part of the lens surface constituting the second lens group is a diffraction optical surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection lens, and is particularly suitable for a projection lens used in a rear projection type video display apparatus employing a micro device as an image display element.

  In recent years, projection video display devices have become widespread. As one of the projection video display devices, there is a rear projection type video display device that displays an image by projecting an image of an image display device onto a transmissive screen from the back side. This rear projection type image display device is known as a rear projection TV, for example.

  This rear projection type image display device color-separates light emitted from a white light source into three primary color components (red, blue, green), illuminates each color component light that has been color-separated on a reflective image display device, A color image is displayed by projecting video light of each color component reflected by the reflective image display device onto a transmissive screen by a projection lens.

  In recent years, such a rear projection TV has been requested to have a large display screen as the projection TV main body is thinned, and accordingly, the projection lens has been shortened to project a large screen at a short projection distance. -Wide angle of view is required.

  In order to meet such a demand, the ratio between the back focus and the focal length of the projection lens must be increased. On the other hand, in order to enlarge and project an image on a reflective image display device onto a screen with high contrast, it is necessary to use a light beam emitted from the reflective image display device at an angle close to vertical.

  Accordingly, it is necessary to have telecentricity so that the principal ray off the axis of the projection lens is perpendicular to the reflective image display device.

  Further, unlike a CRT (Cathode Ray Tube) method, a DMD (Digital Mirror Device) element or the like cannot electrically correct distortion due to dot matrix display.

  Therefore, a small distortion must be realized by the projection lens itself. However, this is an obstacle to realizing a wide angle projection lens and a long back focus.

  Furthermore, with the increase in the density (high definition) of pixels of the reflective image display device, it has become important to improve the optical performance of the projection lens, particularly to reduce the “chromatic aberration of magnification”.

Patent Document 1 is an invention proposed in view of such problems. In Example 1 of Patent Document 1, a technique for correcting various aberrations using two aspherical lenses made of acrylic resin among nine lenses is disclosed.
Japanese Patent Laid-Open No. 2003-156683

  However, with the recent increase in the density (high definition) of pixels of the image display microdevice, there is a strong demand in the market for improving the optical performance of the projection lens, in particular, for correcting the “chromatic aberration of magnification” to be small in the operating wavelength range.

  In the conventional projection lens shown in Patent Document 1, the chromatic aberration of magnification is 19 μm for blue light (450 nm) and 5 μm for blue-red light (450-620 nm), as shown in FIG. This blue lateral chromatic aberration corresponds to 0.11% of the focal length f = 17.373 mm.

  In order to correct lateral chromatic aberration, anomalous dispersion glass (for example, Abbe number νd is 81.6, 90.3, etc.) can be effectively corrected. However, such anomalous dispersion glass is very expensive, Further, since it is difficult to manufacture the lens, there is a problem that the cost of the projection lens is increased.

  Further, for example, a retrofocus type composed of a first group having a negative refractive power on the enlargement side (front group) and a second group having a positive refractive power on the reduction side (rear group) across the aperture stop. In the case of a wide-angle projection lens, since the refractive power arrangement of the lens is asymmetrical before and after the aperture stop, off-axis aberrations such as distortion and astigmatism are large, but these aberrations are caused by using an aspherical surface. Although it can be corrected, there is a problem that an aspherical surface cannot correct chromatic aberration.

  Therefore, in view of the above-described background, the present invention uses a large amount of resin-made aspherical lenses, and suppresses back focus position fluctuation due to temperature changes to a practical level, while reducing chromatic aberration of magnification. A wide-angle projection lens capable of projecting a fine image is provided.

  In order to solve such a problem, the projection lens of the present invention according to claim 1 is a projection lens that projects an image of a rectangular image display microdevice on a screen surface in order from the enlargement side to the reduction side. A first lens group having a negative refractive power and a second lens group having a positive refractive power are arranged, and at least one of the lens surfaces constituting the second lens group is a diffractive optical surface. Features.

  As described above, by configuring the projection lens, a projection lens with little lateral chromatic aberration can be realized by using only a general optical material with high mass productivity.

  In the projection lens according to the second aspect of the present invention, the first lens group is configured by arranging the first lens and the second lens in order from the magnification side to the reduction side, and the second lens group is a magnification lens. A negative meniscus lens having a double-sided aspherical surface in which the region near the optical axis of the enlargement side surface is a concave surface, in which the third lens to the seventh lens are arranged in order from the side toward the reduction side The second lens is a negative meniscus lens composed of a double-sided aspheric surface in which the region near the optical axis of the enlargement side surface is a concave surface, and the third lens is formed by bonding a biconcave lens to the reduction side surface of the biconvex lens. The fourth lens is a positive meniscus lens having a double-sided aspherical surface with a convex surface facing the reduction side and at least one surface having a diffractive optical surface, and the fifth lens is a biconvex lens. A biconcave lens is joined to the reduction side of The sixth lens is a positive lens with a strong convex surface facing the reduction side, the seventh lens is a positive lens with a strong convex surface facing the reduction side, and the first lens group and the second lens A feature is that a diaphragm is disposed between the groups.

  As described above, by configuring the projection lens, it is possible to realize a high-definition TV image with high imaging performance at a wide angle of view with little lateral chromatic aberration.

  In the projection lens according to the third aspect of the present invention, the first lens, the second lens, and the fourth lens are each formed of a synthetic resin, and the Abbe numbers ν1, ν2, and ν4 of these lenses are ν1, ν2, and In addition, ν4> 54 is satisfied, and Abbe numbers ν6 and ν7 of the sixth lens and the seventh lens satisfy ν6 and ν7 <73.

  As described above, if the Abbe number condition is satisfied, the chromatic aberration of magnification can be reduced by using only a general optical material because one surface of the fourth lens is a diffractive optical surface (DOE) without using anomalous dispersion glass.

  According to a fourth aspect of the present invention, the projection lens of the present invention suppresses back focus position fluctuation due to temperature change by balancing the negative refractive power of the first lens and the second lens and the positive refractive power of the fourth lens. It is characterized by doing.

  With this configuration, a change in temperature occurs in the opposite direction with almost the same value as the back focus position fluctuation caused by the first lens and the second lens, so that they cancel each other and suppress each other.

Projection lenses of the present invention according to claim 5, when the focal length of the first lens group and f _I, and the focal length of the fourth lens in the second lens group and f4, 3 <f4 / | f I | <13 conditions are satisfied.

Projection lenses of the present invention according to claim 6, the focal length of the entire system is f, the back focus of the entire system is B _FL, the focal length f _I of the first lens _group, the focal length of the second lens group When f _{II, the condition} is that 2 <B _FL / f and 1.0 <f _II / | f _I | <1.5 are satisfied.

  By satisfying the above conditions, by forming a long air gap between the first lens group and the second lens group, it is possible to bend the optical path, and has strong telecentricity, and even better Optical characteristics can be realized.

  The projection lens of the present invention according to claim 7 is characterized in that an optical path bending means is provided between the first lens group and the stop.

  With the above configuration, the depth of the rear projection TV or the like can be reduced by bending the optical path with the optical path bending means.

  According to the projection lens of the present invention, the following effects can be obtained.

(1) By using many synthetic resin aspherical lenses for the first lens group and the second lens group, and using a diffractive optical element (DOE) on one surface of the second lens group, the back focus caused by temperature change can be reduced. It is possible to project a high-definition image with smaller chromatic aberration of magnification onto the screen while suppressing the position variation to a practical level.

(2) A good correction of lateral chromatic aberration can be made with only a general optical material, and high-definition images can be mass-produced at low cost and light weight can be realized.

(3) It has a wide back angle and a long back focus, and can realize good telecentricity and good correction of distortion.

(4) It is possible to suppress back focus position fluctuations (focus plane changes) due to temperature changes.

  Hereinafter, the best mode for carrying out the projection lens of the present invention will be described with reference to the drawings.

  This embodiment demonstrates the case where it applies to the projection lens used for a rear projection type video display apparatus.

  Further, in the present embodiment, when a reflective image display microdevice is used as an image display device and a single-plate rear projection TV optical system is used as an optical system, the projection lens is a color image of the reflective image display microdevice. A case of enlarging and projecting on the screen will be described.

  In the following, first, the overall configuration of a rear projection type image display apparatus provided with a projection lens will be described, and then the projection lens and examples will be described.

(A) Overall Configuration FIG. 11 is a cross-sectional view for schematically explaining a configuration example of a rear projection type image display device.

  In FIG. 11, the rear projection type image display device 10 includes an optical engine b, a projection lens e, a bending mirror f, and a transmission screen c on the front surface of the cabinet a in a cabinet a.

  The light from the optical engine b is reflected by a first folding mirror d incorporated in the projection lens e, and the reflected light passes through the projection lens e and the second folding mirror f on the cabinet a side. And is projected onto the transmissive screen c. As a result, the TV set is made thinner and larger.

  Next, a configuration example of the single-plate rear projection TV optical system will be described with reference to FIG.

  In FIG. 12, a single plate rear projection TV optical system includes an arc amplifier (ultra-high pressure mercury lamp) 1 which is a white light source, a reflector 2, a color wheel 3, a light tunnel 4, a relay lens 5, a DMD (Digital Mirror Device) element 6, A cover glass 7, a TIR (Total Internal Reflection) prism 8, and a projection lens 9 are provided.

  The arc lamp 1 is arranged at the first focal point of the reflector 2 having an elliptical shape. The light emitted from the arc lamp 1 is reflected and collected by the reflector 2, passes through the color wheel 3, is time-divided into three primary colors, and is collected at the second focal point of the reflector 2.

  The color wheel 3 includes three primary color blue, green, and red color filters arranged in a disk shape, and is color-separated in a time-sharing manner by rotating light at high speed (for example, about 60 rotations per second). It is.

  The condensed light is guided by a light tunnel 4 having an aspect ratio of, for example, 16: 9 arranged on the condensing surface, thereby forming uniform rectangular illumination light and by the relay lens 5. The DMD element 6 is irradiated as illumination light of each color component efficiently and time-divided.

  The DMD element 6 is an image display element, and includes a two-dimensional micro mirror (for example, 14 μm square) whose reflection angle is controlled at high speed, and reflects incident light by adjusting the angle of the micro mirror. . That is, when the DMD element 6 reflects ON, the angle of the minute mirror is adjusted, and incident light is reflected toward the projection lens 9, and when the DMD element 6 reflects OFF, the angle of the minute mirror is adjusted and incident. The light is not reflected toward the projection lens 9 but is absorbed by, for example, a light absorbing member. In this way, in the case of ON reflection, the projection lens 9 reflects light.

  When the illumination light is irradiated onto the DMD element 6 by the relay lens 5, only the light in the ON state by the DMD element 6 is enlarged and projected onto the screen (not shown) by the projection lens 9.

  As described above, the light reflected by the DMD element 6 is enlarged and projected onto the screen via the projection lens 9.

(B) Projection Lens Next, the lens configuration of the projection lens of this embodiment will be described with reference to the drawings. FIG. 1 is a lens configuration diagram of a projection lens that enlarges and projects image light reflected by the DMD element 6 onto a screen (not shown).

  It is assumed that a screen (not shown) is provided on the left side of FIG. 1, and in the following description, the screen side is referred to as “enlarged side” and the DMD element 6 side (right side in FIG. 1) is referred to as “reduced side”. To do.

  In FIG. 1, the projection lens of this embodiment includes a first group I (also referred to as a first lens group) having negative refractive power and a second group II (second lens) in order from the enlargement side to the reduction side. (Also called a group). A TIR prism 8, a cover glass 7, and a DMD element 6 are disposed on the reduction side of the second group.

  The type of projection lens configured by arranging the first group I and the second group II is referred to as a “retro focus type”, which can increase the back focus and is suitable for widening the angle.

  In FIG. 1, in the projection lens, at least one of the lens surfaces constituting the second group is a diffractive optical surface.

  Here, a diffractive optical element (DOE) is an optical element having a chromatic aberration correction capability using a diffraction phenomenon, and for example, chromatic aberration of a lens used for an imaging lens, a CD, a DVD pickup, or the like. Is known as a technique for correcting the image with a combination of a diffractive optical element and a refractive lens.

  However, a wide-angle projection lens that applies a diffractive optical element (DOE) to a projection TV of an image display microdevice and has a high definition and a field angle of 90 ° has not yet been known.

  Further, the optical characteristics of the diffractive optical element (DOE), unlike the conventional refractive lens, have the characteristics of inverse dispersion and anomalous dispersion such as Abbe number ν = −3.45 and partial dispersion ratio θgF = 0.296. ing.

  In addition, the projection lens includes a diaphragm S between the first group I and the second group II, and a bending mirror M between the first group I and the diaphragm S.

  As shown in FIG. 1, the first group I is configured by arranging a first lens L1 and a second lens L2 in order from the enlargement side to the reduction side.

  Both the first lens L1 and the second lens L2 are negative meniscus lenses in which the area near the optical axis of the enlargement side surface is a concave surface and is a double-sided aspheric surface. The first lens L1 and the second lens L2 are molded of synthetic resin. As the synthetic resin material, for example, acrylic (PMMA), polyolefin resin, and the like are suitable materials.

  In FIG. 1, the second group II includes a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7 in order from the enlargement side to the reduction side. Arranged.

  The third lens L3 is a cemented lens formed by cementing a biconcave lens L32 to the reduction-side surface of the biconvex lens L31.

  The fourth lens L4 is a double-sided aspherical positive meniscus lens having a convex surface facing the reduction side. Further, at least one surface of the fourth lens L4 is a diffractive optical surface (DOE), and in this embodiment, the surface on the enlargement side of the fourth lens L4 is a diffractive optical surface. Furthermore, the fourth lens L4 is molded from a synthetic resin. As the synthetic resin material, for example, acrylic (PMMA), polyolefin resin, and the like are suitable materials.

  The diffractive optical surface (DOE) is preferably blazed (saw-shaped). For example, there is a method in which a plastic material or the like is injection-molded with a mold manufactured by ultra-precise cutting with a diamond tool. Further, for example, a method of forming a diffractive optical surface on a resin layer formed on a glass lens can be used.

  In this way, by setting at least one surface of the fourth lens L4 as a diffractive optical surface, achromaticity corresponding to the wavelength of incident light can be achieved.

  The fifth lens L5 is a cemented lens formed by cementing a biconcave lens L52 to the reduction-side surface of the biconvex lens L51.

  Both the sixth lens L6 and the seventh lens L7 are positive lenses having a strong convex surface facing the reduction side.

  In the first group I, the lens surfaces (four surfaces in the present embodiment) that are configured are all aspherical surfaces. In this way, by making the first group I aspherical on the entire surface, correction that improves distortion is performed, and further, the third lens L3 that is a cemented lens of the second group II in which the axial luminous flux is most expanded. The fourth lens L4, which is a double-sided aspherical meniscus lens having a positive weak refractive power disposed immediately after (reduction side), and the two lenses L1 and L2 of the first group I are coupled together to reduce off-axis aberrations. Astigmatism, coma and the like are corrected well, and a bright projection lens can be realized.

  Further, (a) each of the first lens I of the first group I, the second lens L2, and the fourth lens L4 of the second group II; and (b) the sixth lens L6 of the second group II and the fourth lens L6. Each of the seven lenses L7 is set so as to satisfy the following conditions. Note that ν is the Abbe number of the lens medium.

Condition (1) ν1, ν2, and ν4> 54
Condition (2) ν6 and ν7 <73
As is well known, the Abbe number ν is ν = (N _d −1) / (N _F −N _c ), where N _F , N _d , and N _c are the refractive indexes of the F, d, and C lines of the lens medium. Defined.

  In the light beam emitted from the first lens group I and directed to the screen, if the “change due to wavelength” of the angle formed by the principal beam with the optical axis is large, chromatic aberration with a large magnification occurs on the screen.

  On the other hand, in the two lenses on the reduction side of the first group I and the second group II, the distance from the optical axis to the principal ray of the off-axis light beam becomes large, and the influence on the chromatic aberration of magnification is large.

  The refractive index of the lens medium increases as the wavelength becomes shorter, but the medium satisfying the above conditions (1) and (2) has a small “ratio of increase in refractive index as the wavelength decreases”.

  If a material having such properties is used for “a lens having a high principal ray height and a strong refractive power” in the first group I and the second group II, the chief ray height exiting from the first group I is obtained. It is possible to reduce the “difference due to the wavelength” of the angle between the position of the point and the optical axis, and it is possible to satisfy the requirement for chromatic aberration of severe magnification.

  The first lens L1 of the first group I has a large distance from the optical axis with respect to the principal ray of the off-axis light beam, and thus the lens system tends to be large.

  By making the first lens L1 and the second lens L2 into synthetic resin lenses that satisfy the above condition (1), the first lens L1 and the second lens of the first lens group I can be suppressed while suppressing the influence on the chromatic aberration. L2 can be reduced in weight, further leading to a reduction in manufacturing costs.

  Since the first lens group I has a negative refractive power, if a synthetic resin lens is used only for the first lens group I, back focus position fluctuation (movement of the focus surface) occurs due to a temperature change of the refractive index.

  In order to cancel this, in the second group II, a synthetic resin lens element having a relatively weak positive refractive power must be inserted.

  In the present embodiment, the second lens group II is configured by inserting a fourth lens L4 as a synthetic resin lens element.

When the focal length of the first group I is f _I and the focal length of the fourth lens L4 in the second group II is f4, the following conditions are set.

Condition (3) 3 <f4 / | f _I | <13
The focal length of the entire system f, and a back focal length of the entire system with B _FL, also the focal length of the first group I when f _I, the focal length of the second lens group II and f _II, which satisfies the following conditions Set as follows.

Condition (4) 2.0 <B _FL / f
Condition (5) 1.0 <f _II / | f _I | <1.5
As in the projection lens of this embodiment, the back focus B is a retrofocus lens in which the first group I has a negative refractive power and the second group II has a positive refractive power. By securing a space where the TIR prism can be installed by _FL and forming a long air gap between the first group I and the second group II, the optical path can be bent and has a strong telecentricity. In order to realize better optical characteristics, it is desirable to satisfy the above conditions (4) and (5).

  Further, the cabinet of the projection TV apparatus can be made thinner as compared with the case where a projection lens apparatus having a configuration that does not perform optical path conversion is provided.

  Next, the lens configuration of the projection lens shown in FIG. 1 will be described. In FIG. 1, the radius of curvature of the i-th surface from the enlargement side is Ri, and the surface interval on the optical axis between the i-th surface and the (i + 1) -th surface is Di. Further, the refractive index and the Abbe number are values of the d line.

  Further, the focal length of the entire system is represented by f (e-line value), the brightness is F / no, the angle of view is 2ω, the lateral magnification is M, and the projection distance is L.

As is well known, an aspherical surface is an orthogonal coordinate system (X, Y, Z) in which the optical axis is the Z axis, R is a paraxial radius of curvature, K is a conic constant, and A3, A4,. When the fourth-order,..., And tenth-order aspheric coefficients are used, the surface shape at the coordinates h = (X ² + Y ² ) ^1/2 is represented by the following expression.

Z (h) = (h ² / R) / [1+ {1− (1 + K) · (h / R) ² } ^1/2 ]
+ A3 · h ³ + A4 · h ⁴ + A5 · h ⁵ + A6 · h ⁶
+ A7 · h ⁷ + A8 · h ⁸ + A9 · h ⁹ + A10 · h ¹⁰ (1)
Further, the diffractive optical element applied to the projection lens of the present invention has rotational symmetry, and the reference wavelength is an e-line of 546 nm. The equation for determining the aspheric phase amount (φ) is equation (2).

φ (h) = C1 · h ² + C2 · h ⁴ + C3 · h ⁶ + (2)
Here, φ (h) represents a phase amount at a height h from the optical axis, and C1 to C3 represent coefficients of a phase term having an aspherical effect.

  Next, Example 1 of the projection lens of the present embodiment using specific numerical values will be described with reference to the drawings.

  FIG. 2 is a diagram illustrating a lens configuration and a ray tracing diagram of the first embodiment. FIG. 4 is an explanatory diagram showing specific numerical values for constituting the projection lens in the first embodiment. Further, FIG. 13 is a diagram showing the phase amount of the diffractive optical surface (DOE).

  The lens configuration shown in FIG. 2 corresponds to the lens configuration shown in FIG. 1, and the corresponding components are denoted by the corresponding reference numerals.

In Example 1, as shown in FIG. 4, the focal length f of the entire system (value of e line) = 10.83 mm, brightness F / no = 2.4, back focus B _FL = 37.589 mm, This is a case where the angle of view 2ω = 90 °, the lateral magnification M = −1 / 53.21 ×, and the projection distance L = 542.0 mm.

  FIG. 6 is an aberration diagram illustrating the chromatic aberration of magnification of the projection lens of Example 1, and FIG. 7 is an aberration diagram illustrating the spherical aberration, astigmatism, and distortion of the projection lens of Example 1.

  As shown in FIG. 6, according to the projection lens of Example 1, the chromatic aberration of magnification is about 5 μm for light of 450 nm to 546 nm (blue-green light), and for light of 450 nm to 620 nm (blue-red light). These values are about −5 μm, and these values are 0.05% of the focal length f = 10.83 mm, which can be improved to half or less compared to the chromatic aberration of magnification due to the conventional projection lens of FIG.

  Further, as shown in FIG. 7, according to the projection lens of Example 1, good results can be obtained in terms of spherical aberration, astigmatism, and distortion.

  Next, Example 2 of the projection lens of the present embodiment will be described with reference to the drawings.

  FIG. 3 is a diagram illustrating a lens configuration and a ray tracing diagram of the second embodiment. FIG. 5 is an explanatory diagram showing specific numerical values for constituting the projection lens in the second embodiment. Further, FIG. 14 is a diagram showing the phase amount of the diffractive optical surface (DOE).

  The lens configuration shown in FIG. 3 corresponds to the lens configuration shown in FIG. 1, and corresponding components are denoted by corresponding reference numerals.

In Example 2, as shown in FIG. 5, the focal length f of the entire system (value of e line) = 9.96 mm, brightness F / no = 2.4, back focus B _FL = 25.284 mm, This is a case where the angle of view 2ω = 90 °, the lateral magnification M = −1 / 68.67 ×, and the projection distance L = 649.0 mm.

  FIG. 8 is an aberration diagram showing the chromatic aberration of magnification of the projection lens of Example 2, and FIG. 9 is an aberration diagram showing the spherical aberration, astigmatism, and distortion of the projection lens of Example 2.

  As shown in FIG. 8, according to the projection lens of Example 2, the chromatic aberration of magnification is about 2 μm for light of 450 nm to 546 nm (blue-green light), and for light of 450 nm to 620 nm (blue-red light). This value is about −3 μm, and these values are 0.03% of the focal length f = 9.96 mm, which can be improved to 1/3 or less compared to the chromatic aberration of magnification due to the conventional projection lens of FIG.

  Moreover, as shown in FIG. 9, according to the projection lens of Example 2, the spherical aberration, the astigmatism, and the distortion can be obtained with good results.

(C) Other Embodiments (C-1) In the above-described embodiments, the case where a DMD element is taken as an example as an image display demicrodevice has been described. Even when the liquid crystal display device according to the above and the LCOS (Liquid Crystal On Silicon) element of the reflective liquid crystal are used, the same operation and effect as the above-described embodiment can be obtained.

(C-2) In the above-described embodiment, the case where a single-plate optical system is applied as the optical system has been described. However, the present invention is not limited to this, and a three-plate optical system may be applied.

(C-3) In the above-described embodiment, the case where the diffractive optical surface is provided on one surface of the fourth lens L4 of the second group II has been described. However, the arrangement of the diffractive optical surface can exhibit a correction function for lateral chromatic aberration. If there is, it will not specifically limit, but it can apply to the 1 or several lens surface which comprises 2nd group II.

  Further, the diffractive optical surface may be applied to one or a plurality of lens surfaces constituting the first group I. At this time, since the constituent lens surface of the first group I is arranged on the enlargement side, the lens area is larger than that of the constituent lens of the second group II, and thus a burden may be caused in forming the lens surface.

(C-4) In the above-described embodiment, the magnification may be changed by changing the surface of the second lens of the first lens group or changing the distance between the first lens group and the second lens group. . Thereby, the magnification can be changed by the minimum change of the lens element of the projection lens.

It is explanatory drawing for demonstrating the lens structure of the projection lens of this embodiment. It is a figure which shows the lens structure and ray tracing of Example 1. It is a figure which shows the lens structure and ray tracing of Example 2. FIG. 6 is an explanatory diagram showing specific numerical values of the projection lens of Example 1. FIG. 6 is an explanatory diagram showing specific numerical values of the projection lens of Example 2. FIG. 6 is an aberration diagram showing chromatic aberration of magnification of the projection lens of Example 1. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the projection lens of Example 1. FIG. 6 is an aberration diagram showing lateral chromatic aberration of the projection lens of Example 2. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the projection lens of Example 2. It is an aberration diagram showing the chromatic aberration of magnification of a conventional projection lens. It is sectional drawing which shows the structural example of the rear projection type video display apparatus provided with the projection lens of this embodiment. It is a figure which shows the structural example of the optical system using the DMD element of this embodiment. FIG. 4 is a diagram illustrating a phase amount of a diffractive optical surface used in the projection lens of Example 1. FIG. 6 is a diagram illustrating a phase amount of a diffractive optical surface used in the projection lens of Example 2.

Explanation of symbols

I: First group (first lens group),
L1 ... 1st lens, L2 ... 2nd lens,
II ... 2nd group (2nd lens group),
L3 ... third lens, L4 ... fourth lens, L5 ... fifth lens,
L6 ... sixth lens, L7 ... seventh lens, R10 ... diffractive optical surface (DOE),
L31, L32 ... Lenses constituting the third lens,
L51, L52 ... Constituent lens of the fifth lens,
M ... Bending mirror, S ... Aperture, 6 ... DMD element, 7 ... Cover glass,
8 ... TIR prism.

Claims (7)

In the projection lens that projects the image of the rectangular image display microdevice on the screen surface,
In order from the enlargement side to the reduction side, a first lens group having negative refractive power and a second lens group having positive refractive power are arranged,
A projection lens, wherein at least one of the lens surfaces constituting the second lens group is a diffractive optical surface. The projection lens according to claim 1, wherein
The first lens group is configured by arranging a first lens and a second lens in order from the enlargement side to the reduction side,
The second lens group is configured by arranging the third lens to the seventh lens in order from the enlargement side to the reduction side,
The first lens is a negative meniscus lens composed of a double-sided aspheric surface in which a region near the optical axis of the surface on the enlargement side is a concave surface,
The second lens is a negative meniscus lens composed of a double-sided aspheric surface in which a region near the optical axis of the surface on the enlargement side is a concave surface,
The third lens is a cemented lens formed by cementing a biconcave lens to a reduction-side surface of the biconvex lens,
The fourth lens is a positive meniscus lens comprising a double-sided aspherical surface with a convex surface facing the reduction side, and at least one surface is provided with a diffractive optical surface.
The fifth lens is a cemented lens formed by cementing a biconcave lens to a reduction-side surface of the biconvex lens,
The sixth lens is a positive lens having a strong convex surface on the reduction side,
The seventh lens is a positive lens having a strong convex surface on the reduction side,
A projection lens, wherein a stop is disposed between the first lens group and the second lens group. The projection lens according to claim 2, wherein
The first lens, the second lens, and the fourth lens are each molded from a synthetic resin, and the Abbe numbers ν1, ν2, and ν4 of these lenses satisfy ν1, ν2, and ν4> 54, respectively, and
The projection lens, wherein the Abbe numbers ν6 and ν7 of the sixth lens and the seventh lens satisfy ν6 and ν7 <73, respectively. The projection lens according to claim 2 or 3,
A projection lens, wherein back focus position fluctuation due to temperature change is suppressed by a balance between the negative refractive power of the first lens and the second lens and the positive refractive power of the fourth lens. In the projection lens in any one of Claims 1-4,
When the focal length of the first lens group is f _I and the focal length of the fourth lens of the second lens group is f4, the condition 3 <f4 / | f _I | <13 is satisfied. Projection lens. In the projection lens in any one of Claims 1-5,
When the focal length of the entire system is f, the back focus of the entire system is B _FL , the focal length f _I of the first lens group, and the focal length of the second lens group is f _II , 2.0 <B A projection lens satisfying the conditions of _FL / f and 1.0 <f _II / | f _I | <1.5. In the projection lens in any one of Claims 1-6,
An optical path bending means is provided between the first lens group and the stop.

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