JP2003057543A - Zoom lens for projection and image projecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a zoom lens for projection suitable for a DMD projector. SOLUTION: This zoom lens is constituted by arranging a 1st lens group I having negative refractive power and a 2nd lens group II having positive refractive power from an enlargement side to a reduction side, and arranging an aperture diaphragm ST in the vicinity of a lens nearest to the reduction side in the 2nd lens group. The 2nd lens group has two positive lenses on the enlargement side, and either of the two positive lenses is an aspherical lens, and the focal distance of the 1st lens group I: f1 and the focal distance of the 2nd lens group II: f2 satisfy a condition: (1) 0.6<f2 /|f1 |<0.9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection zoom lens and an image projection apparatus.

[0002]

2. Description of the Related Art Recently, an image projection apparatus (generally referred to as "DMD projector") using a digital micromirror device (hereinafter referred to as "DMD") has been widely used.

In the DMD, mirror elements (small mirrors corresponding to one pixel) are arranged in a lattice, and the directions of the individual mirrors are independently ± 10 degrees or more (± 12 in the latest type).
The optical device is designed to be changed.

By controlling the direction of each mirror element of the DMD by an image signal in a state where the light beam from the light source side is incident on the DMD, image information can be added to the reflected light beam by the DMD (of the image information). Since the luminous flux component necessary for reproduction is separated from the unwanted luminous flux component by the difference in the reflection direction), the luminous flux to which the image information is added is projected and imaged on the display medium such as a screen by the projection lens. By doing so, an image can be displayed.

The DMD projector can display an image with extremely high definition in combination with the improvement of the function of the DMD. Further, unlike “a liquid crystal panel in which image information is added due to a difference in light transmittance”, light reflection is used to add image information, so that the DMD projector has high light use efficiency and produces a bright image. Being able to display is also a great advantage.

In order to take advantage of the "display of a bright image" of such a DMD projector, the luminous flux from the light source side is directly D (without passing through a semi-transparent mirror).
It is preferable that the reflected light flux having the image information applied thereto be directly incident on the projection lens. For this,
The projection lens is required to have a shape that does not cause the illumination light flux incident on the DMD to be vignetting.

In consideration of the change area of the direction allowed for each mirror element in the DMD, the DMD
It is preferable that the incident angle of the illuminating light on is as small as possible.
Further, the effective lens diameter on the reduction (DMD) side of the projection lens must be divided into effective light (a light beam having image information added) reflected by the DMD and ineffective light by the difference in the traveling direction. , The size needed to capture the effective light is required. For this purpose, the projection lens must have a somewhat long back focus.

It is desired that the projection lens also has a variable power (zoom) function of about 1.2 to 1.3 and a compact size that can be easily carried.

[0009]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to realize a projection zoom lens suitable for a DMD projector. Another object of the present invention is to realize a compact image projection device (DMD projector) capable of displaying a good image by using the projection zoom lens.

[0010]

As shown in FIG. 1, a projection zoom lens of the present invention has a negative refracting power from the enlargement side (left side in the figure) toward the reduction side (right side). The first lens group I and the second lens group II having a positive refractive power are arranged, and the aperture stop S is provided in the vicinity of the most reduction side lens in the second lens group II.
The second lens group II has two positive lenses on the magnification side, one of these two positive lenses is an aspherical lens, and the focal length of the first lens group I is f ₁ and the focal length f ₂ of the second lens group II satisfy the condition: (1) 0.6 <f ₂ / | f ₁ | <0.9 (claim 1).

In FIG. 1, the aperture stop ST is on the "reduction side" of the lens on the most reduction side of the second lens group II, but it may be arranged on the enlargement side of this most reduction lens. In FIG. 1, reference numeral CG is “DMD cover glass”, and reference numeral SF is “mirror element array surface”.
Is shown.

In the zoom lens for projection according to the first aspect, the focal length of the entire system at the wide-angle end is fw and the focal length of the first lens group is f _{1. The} condition is: (2) 1.5 <| f ₁ It is preferable that | / fw <2.0 is satisfied (claim 2).

Further, in the projection zoom lens according to the first or second aspect, the length of the entire lens system at the wide-angle end is L.
It is preferable that the focal length of the whole system at w and the wide-angle end: fw satisfies the condition: (3) 3.3 <Lw / fw <4.0 (claim 3).

Further, in the projection zoom lens according to any one of claims 1 to 3, the first lens group includes “two negative lenses having a large curvature on the reduction side in order from the enlargement side, It is possible to use a positive lens having a large curvature on the magnifying side and to use one of the two negative lenses as an aspherical lens ”(claim 4).

According to the image projection apparatus of the present invention, "a light beam from a light source is applied to a digital micromirror device whose orientation of mirror elements is controlled according to an image signal, and image information is generated by the digital micromirror device. An image projecting device for projecting an image of a light flux given thereto by a projection lens onto a display medium to display an image, wherein the projection lens is any one of claims 1 to 4. (Claim 5).

The projection zoom lens of the present invention has a "retro focus type" two-group zoom lens system having a first lens unit having a negative refracting power and a second lens unit having a positive refracting power in order to have a long back focus. It was a lens. Then, by arranging the aperture stop “in the vicinity of the lens closest to the reduction side of the second lens group”, the effective diameter of the lens is “decreased gradually from the enlargement side to the reduction side” to illuminate the DMD. The light flux is allowed to enter the DMD with a small angle of incidence without being eclipsed by the projection zoom lens. With this configuration, the size of the lens closest to the reduction side of the second lens group is set to "effective light reflected from the DMD (light flux given image information) is effectively changed from invalid light. The size can be divided.

Further, by constructing two "magnification-side positive lenses" which are responsible for most of the refracting power of the second lens group II and using one of these as an aspherical lens, spherical aberration and coma are extremely small. I am trying.

The condition (1) is a condition for obtaining a long back focus required for the projection zoom lens while ensuring good optical performance and a desired zoom ratio, and a lower limit value: 0.
When it exceeds 6, the “refractive power of the first lens group” to the second lens group becomes small, so the back focus becomes short, and if the intention is to secure the back focus, the principal point spacing between the first and second lens groups Inevitably, the overall length of the projection zoom lens becomes longer, and the outer diameter of the lens on the magnifying side also increases accordingly, resulting in a costly lens.

Upper limit of condition (1): When 0.9 is exceeded,
Since the refracting power of the first lens group becomes excessive, it becomes difficult to correct spherical aberration and coma, and it becomes difficult to secure a desired zoom ratio.

The condition (2) is for achieving both a long back focus and good optical performance, and the lower limit value:
If it exceeds 1.5, the refracting power of the first lens group becomes excessive, and as described above, it is difficult to correct spherical aberration and coma, and it is difficult to secure good optical performance. Condition (2)
If the upper limit of 2.0 is exceeded, the refracting power of the first lens group becomes small, and the desired back focus cannot be obtained.

The condition (3) relates to the compactness of the zoom lens for projection and the balance of the image performance. When the lower limit value: 3.3 of the condition (3) is exceeded while securing a desired angle of view, each lens. The refractive power of the group becomes excessive, and it becomes difficult to correct spherical aberration, coma aberration, astigmatism, and the like. On the other hand, when the upper limit value: 4.0 is exceeded, the total length of the projection zoom lens becomes long and the compactness is lost.

In general, the first lens group of the "retro focus type" projection lens has a large effect of bending the principal ray, so that a large amount of distortion also occurs. In order to correct this distortion, it is generally arranged to arrange a lens having a positive refractive power at a position where the height of the off-axis chief ray on the magnifying side is high, and to cancel it by the high-order distortion of the opposite sign generated by this. Is being done,
This method is also used in Examples 2 and 4 described later.

As described above, in the projection zoom lens according to the fourth aspect, the "positive lens arranged at a position where the off-axis chief ray height on the enlargement side is high" is not used in the first lens group, and the "lens in order from the enlargement side" is used. By disposing two negative lenses having a large curvature on the reduction side and using one of them as an aspherical lens, it is possible to satisfactorily correct distortion with a small number of lenses.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, five examples will be given as specific embodiments.

In each embodiment, "S" represents the surface number, "R" represents the radius of curvature of each surface (paraxial curvature radius in the case of an aspherical surface), and "D" represents the surface spacing on the optical axis. . As for the surface spacing that changes due to zooming, the values at the wide-angle end and the telephoto end are also shown as “wide-angle end / telephoto end”.

“Nd” and “νd” represent the refractive index and Abbe number of the material of each lens with respect to the d-line. "Fw",
“Ft” is the focal length of the entire system at the wide-angle end and the telephoto end, “f ₁ ” is the focal length of the first lens group, and “f ₂ ”.
Is the focal length of the second lens group, “F / No” is the F value representing the brightness at the wide-angle end, and “obd” is the screen (display medium).
To the first surface of the lens (the lens surface on the most magnifying side of the first lens group), "Bfw" represents the back focus at the wide-angle end, and "Lw" represents the length of the entire system at the wide-angle end. In addition,
The unit of the quantity having the dimension of length is "mm".

The shape of the aspherical surface is, with the intersection point with the optical axis being the origin, the height relative to the optical axis: h, the displacement in the optical axis direction: Z, the paraxial curvature: c (the reciprocal of the paraxial radius of curvature), the cone Constant: K,
Well-known expressions for aspherical coefficients of higher order terms: A, B, C, D, E: Z = c · h ² / [1 + √ {1− (1 + K) · c ² · h ² }] + A · h ⁴ + B ・ h ⁶ + C
・ It is represented by h ⁸ + D ・ h ¹⁰ + E ・ h ¹² , and is specified by giving the values of c, K, and AE.

[0028]

EXAMPLES Example 1 FIG. 1 shows the lens configuration of a projection zoom lens of Example 1.

From the enlargement side (left side of the drawing), the first negative refractive power
The lens group I and the second lens group II are included, and the aperture stop ST is arranged on the reduction side of the second lens group. As described above, the code CG is the DMD cover glass and the code SF.
Indicates the array surface of the mirror elements. The meanings of these reference numerals are the same in the drawings showing the lens configurations of other examples.

Fw = 24.00, ft = 31.00, f ₁ = −46.86, f ₂ = 33.07, F / No = 3.0, obd = 2500, Bfw = 35.38, Lw = 81.95 S RD Nd νd 1 68.963 3.000 1.49154 57.8 2 20.366 7.212 3 60.927 3.000 1.71300 53.9 4 27.929 11.419 5 31.901 6.000 1.80518 25.5 6 44.322 28.205 / 13.623 7 22.106 4.500 1.62041 60.3 8 73.099 0.300 9 32.509 53.958 1.78 0.300 11 −267.267 4.566 1.67790 55.5 12 −45.919 6.051 1.74077 27.8 13 22.077 1.190 14 −128.253 2.255 1.78590 43.9 15 −25.182 0.000 16 ∞ (aperture) 32.850 / 37.945 17 ∞ 3.000 1.50847 61.2 18 ∞ 0.539 Aspheric second surface K = − 0.204660, A = -0.139657 × 10 ⁻⁵ , B = −0.108241 × 10 ⁻⁷ , C = 0.655403 × 10 ⁻¹² , D = 0.105 61 × 10 ⁻¹³ , E = −0.134059 × 10 ⁻¹⁵ 10th surface K = − 102.475167, A = 0.133455 × 10 ⁻⁴ , B = 0.502643 × 10 ⁻⁷ , C = −0.726386 × 10 ⁻¹⁰ , D = −0.581301 × 10 ⁻¹² , E = 0.3139 50 × 10 ⁻¹⁴ Parameter value of conditional expression (1) f ₂ / | f ₁ | = 0.71 (2) | f ₁ | /fw=1.95 (3) Lw / fw = 3.41 3, the wide-angle end of the projection zoom lens of Example 1,
Shows spherical aberration, astigmatism, and distortion at the telephoto end,
4 and 5 show coma aberrations at the wide-angle end and the telephoto end.
Each aberration diagram shows the aberration of green light having a wavelength of 546 nm, but the spherical aberration diagram and the coma aberration diagram also show the aberrations of wavelengths of 610 nm and 460 nm on behalf of red and blue light. In the astigmatism diagram, S is the aberration of the sagittal image plane, M is the aberration of the meridional image plane, and the same applies to the aberration diagrams of other examples.

Example 2 FIG. 6 shows the lens configuration of the projection zoom lens of Example 2 in the same manner as in FIG.

Fw = 24.00, ft = 31.00, f ₁ = −38.91, f ₂ = 32.09, F / No = 3.0, obd = 2500, Bfw = 33.61, Lw = 82.38 SRD Nd νd 1 96.973 3.770 1.78590 43.9 2 346.849 0.300 3 67.939 3.000 1.71300 53.9 4 23.656 6.999 5 18182.514 2.500 1.71300 53.9 6 30.701 17.089 7 44.870 3.651 1.75520 27.5 8 75.565 16.447 / 4.700 9 21.6081.39.953 1.589 11 48.218 4.173 1.49154 57.8 12 −65.590 0.300 13 2846.436 5.493 1.67790 55.5 14 −33.926 3.848 1.74077 27.8 15 20.579 1.554 16 ∞ (aperture) 0.000 17 −111.865 3.000 1.78590 43.9 18 −27.062 31.084 / 37.013 19 ∞ 3.000 1.50847 61.2 20 ∞ 0.539 Non Spherical surface 11th surface K = -19.511965, A = -0.157482 × 10 ⁻⁴ , B = −0.110765 × 10 ⁻⁶ , C = 0.126882 × 10 ⁻⁹ , D = 0.186271 × 10 ⁻¹¹ , E = −0.576168 × 10 ^{− 14} Value of conditional expression (1) f ₂ / | f ₁ | = 0.82 (2) | f ₁ | / fw = 1.62 (3) Lw / fw = 3.43 FIGS. 7 and 8 show the wide-angle end of the projection zoom lens of Example 2.
Shows spherical aberration, astigmatism, and distortion at the telephoto end,
9 and 10 similarly show coma.

Example 3 FIG. 11 shows the lens arrangement of a projection zoom lens of Example 3 in the same manner as in FIG.

Fw = 24.00, ft = 31.00, f ₁ = −38.57, f ₂ = 32.59, F / No = 3.0, obd = 2500, Bfw = 35.38, Lw = 81.15 S RD Nd νd 1 49.920 3.000 1.49154 57.8 2 20.117 11.689 3 158.321 3.000 1.71300 53.9 4 27.914 12.112 5 36.255 6.000 1.80518 25.5 6 56.082 18.503 / 6.675 7 21.831 7.359 1.62041 60.3 8 6415.610 2.103 9 50.719 4.069 1.49154. 0.489 11 −2532.379 4.146 1.67790 55.5 12 −31.883 2.538 1.74077 27.8 13 21.954 1.978 14 −99.466 4.164 1.78590 43.9 15 −26.085 0.000 16 ∞ (aperture) 32.850 / 38.920 17 ∞ 3.000 1.50847 61.2 18 ∞ 0.540 Aspheric second surface K = − 0.219096, A = -0.752019 x 10 ^-6 , B = -0.819655 x 10 ^-8 , C = 0.231799 x 10 ^-11 , D = 0.187472 x 10 ^-13 , E = -0.145556 x 10 ^-15 9th surface K =- 22.449074, A = -0.169469 x 10 ^-4 , B = -0.114740 x 10 ^-6 , C = 0.125784 x 10 ^-9 , D = 0.181846 x 10 ^-11 , E = -0.504 477 × 10 ⁻¹⁴ Value of conditional expression (1) f ₂ / | f ₁ | = 0.84 (2) | f ₁ | /fw=1.61 (3) Lw / fw = 3.38 FIGS. 14A and 14B show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 3, and FIGS.

Example 4 FIG. 16 shows the lens arrangement of the projection zoom lens of Example 4 in the same manner as in FIG.

Fw = 24.00, ft = 31.00, f ₁ = −37.37, f ₂ = 31.57, F / No = 3.0, obd = 2500, Bfw = 35.38, Lw = 80.61 SRD Nd νd 1 92.748 3.770 1.83500 43.0 2 265.294 0.300 3 61.098 2.500 1.69680 55.5 4 22.243 7.331 5 467.433 2.000 1.69680 55.5 6 29.831 17.811 7 38.434 4.986 1.75520 27.5 8 53.433 15.801 / 4.700 913 61.00 9.559 11 49.287 4.627 1.49154 57.8 12 −72.399 0.300 13 4042.909 4.459 1.67790 55.5 14 −31.626 3.406 1.74077 27.8 15 21.762 1.297 16 −98.378 2.164 1.83400 37.3 17 −27.056 0.000 18 ∞ (aperture) 32.850 / 38.918 19 ∞ 3.000 1.50847 61.2 20 ∞ 0.540 non Spherical 11th surface K = −20.995528, A = −0.172942 × 10 ⁻⁴ , B = −0.115102 × 10 ⁻⁶ , C = 0.164359 × 10 ⁻⁹ , D = 0.189393 × 10 ⁻¹¹ , E = −0.613979 × 10 ^{− 14} the value of the conditional expression _{(1) f 2 / | f} 1 | = 0.84 (2) | f 1 | / fw = 1 56 (3) Lw / fw = 3.36 FIGS. 17 and 18 show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 4, and FIGS. Shows coma aberration.

Embodiment 5 FIG. 21 shows the lens arrangement of the projection zoom lens of Embodiment 3 in the same manner as in FIG.

Fw = 24.00, ft = 31.00, f ₁ = −42.52, f ₂ = 33.87, F / No = 3.0, obd = 2500, Bfw = 35.26, Lw = 89.99 RD Nd νd 1 71.576 3.000 1.49154 57.8 2 20.950 6.637 3 56.064 3.000 1.71300 53.9 4 26.048 15.687 5 32.838 6.000 1.80518 25.5 6 41.811 19.931 / 6.381 7 33.020 6.000 1.49154 57.8 8 −518.134 4.379 9 36.288 10 530 1.65 1.602 11 62.922 4.579 1.67790 55.5 12 −46.370 4.901 1.74077 27.8 13 21.724 1.126 14 133.265 3.919 1.78590 43.9 15 −37.413 0.000 16 ∞ (aperture) 32.737 / 38.467 17 ∞ 3.000 1.50847 61.2 18 ∞ 0.540 Aspheric second surface K = −0.211346, A = -0.205330 x 10 ^-5 , B = -0.113088 x 10 ^-7 , C = -0.132977 x 10 ^-11 , D = 0.493989 x 10 ^-14 , E = -0.104775 x 10 ^-15 8th surface K = -5338.272168 , A = 0.599876 x 10 ^-5 , B = 0.140110 x 10 ^-7 , C = 0.360360 x 10 ^-11 , D = -0.910921 x 10 ^-13 , E = 0.218422 x 10 ^-15 Value of conditional expression (1) f ₂ / | f ₁ | = 0.80 (2) | f ₁ | /fw=1.77 (3) Lw / fw = 3.58 Implemented in FIGS. The spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the projection zoom lens of Example 5 are shown, and FIGS. 24 and 25 similarly show coma.

In each of the projection zoom lenses of Examples 1 to 5 mentioned above, the first lens group I having a negative refractive power and the second lens group having a positive refractive power are arranged from the enlargement side to the reduction side. II is arranged, and the aperture stop ST is arranged in the vicinity of the lens on the most reduction side in the second lens group II. The second lens group II has two positive lenses on the enlargement side. One of the positive lenses is an aspherical lens, and the focal length of the first lens group I: f ₁ , the focal length of the second lens group II: f ₂ , the focal length of the entire system at the wide-angle end: fw, length: Lw _{condition: (1) 0.6 <f 2} / | f 1 | <0.9 (2) 1.5 <| f 1 | / fw <2.0 (3) 3.3 <Lw /Fw<4.0 is satisfied (claims 1 to 3).

In the first, third and fifth embodiments, the first lens group I has two negative refractive power lenses having a large curvature on the reduction side and a large curvature on the enlargement side in order from the expansion side. Consists of 3 lenses with positive refractive power, 1 from the magnification side
The second lens is an aspherical lens (claim 4).

FIG. 26 is a schematic diagram showing an embodiment of the image projection apparatus. The luminous flux emitted from the light source 1 is condensed by the condenser lens 2, passes through the color wheel 3, and enters the DMD 5 via the relay lens 4.

The light beam reflected by the DMD 5 is projected and imaged on a display medium such as a screen (not shown) by the projection zoom lens 6.

Image signals of red, green and blue are sequentially applied to the DMD 5 to control the orientation of the mirror elements, thereby giving image information to the reflected light flux. The color wheel 3 is a filter of three colors of red, green, and blue, and rotates to separate the light flux from the light source side according to the color of the image information applied to the DMD 5.

In this way, red, green, and blue three-color images are sequentially switched and displayed on the display medium, and the afterimages of the respective color images are combined and visually recognized as a color image.

As the projection zoom lens 6, any one of the above-mentioned first to fifth embodiments can be used. As shown in the figure, the projection zoom lens 6 has a lens diameter that gradually decreases from the enlargement side to the reduction side. Therefore, as shown in the figure, the illumination light is incident on the DMD without being “viked”. The angle can be effectively reduced, and the lens diameter of the lens on the most reduction side can be set to "a size required to separate a reflected light beam having image information from an unnecessary light beam".

[0046]

As described above, according to the present invention, it is possible to realize a compact and high-performance zoom lens for projection having a shape suitable for an image projection apparatus using a DMD, having a long back focus. By using this projection zoom lens, a compact image projection device using DMD can be realized.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a projection zoom lens of Example 1. FIG.

FIG. 2 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 1.

FIG. 3 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end in the first embodiment.

FIG. 4 is a diagram showing coma aberration at the wide-angle end in Example 1.

FIG. 5 is a diagram showing coma aberration at the telephoto end in the first embodiment.

6 is a lens configuration diagram of a projection zoom lens of Example 2. FIG.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 2.

FIG. 8 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the second embodiment.

FIG. 9 is a diagram showing coma at the wide-angle end according to the second embodiment.

FIG. 10 is a diagram showing coma at the telephoto end according to the second embodiment.

FIG. 11 is a lens configuration diagram of a projection zoom lens of Example 3;

FIG. 12 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 3.

FIG. 13 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of Example 3;

FIG. 14 is a diagram showing coma at the wide-angle end according to the third embodiment.

FIG. 15 is a diagram showing coma at the telephoto end according to the third embodiment.

16 is a lens configuration diagram of a projection zoom lens of Example 4. FIG.

FIG. 17 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 4.

FIG. 18 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the fourth embodiment.

FIG. 19 is a diagram showing coma aberration at the wide-angle end according to Example 4;

FIG. 20 is a diagram showing coma aberration at the telephoto end of the fourth embodiment.

21 is a lens configuration diagram of a projection zoom lens of Example 5. FIG.

FIG. 22 is a diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of Example 5.

FIG. 23 is a diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the fifth example.

FIG. 24 is a diagram showing coma aberration at the wide-angle end according to Example 5;

FIG. 25 is a diagram showing coma aberration at the telephoto end of Example 5;

FIG. 26 is a diagram for explaining the first embodiment of the image projection apparatus.

[Explanation of symbols]

I First lens group II Second lens group ST aperture stop CG cover glass SF DMD mirror element array surface

Continued front page    F-term (reference) 2H087 KA06 PA07 PA08 PA18 PB08                       PB09 QA02 QA07 QA12 QA17                       QA22 QA25 QA26 QA32 QA34                       QA42 QA45 RA05 RA12 RA13                       RA35 RA36 RA42 SA07 SA09                       SA62 SA63 SB04 SB05 SB26

Claims (5)

[Claims] 1. A first lens unit having a negative refracting power and a second lens unit having a positive refracting power are arranged from the enlargement side to the reduction side in the vicinity of the most reduction side lens in the second lens unit. The second lens group has two positive lenses on the magnifying side, one of these two positive lenses is an aspheric lens, and the focal length of the first lens group is f ₁ The focal length: f ₂ of the second lens group satisfies the condition: (1) 0.6 <f ₂ / | f ₁ | <0.9. 2. The zoom lens for projection according to claim 1, wherein the focal length of the entire system at the wide-angle end: fw and the focal length of the first lens group: f ₁ satisfy the condition: (2) 1.5 <| f _{1. A} zoom lens for projection, characterized by satisfying ₁ | / fw <2.0. 3. The projection zoom lens according to claim 1, wherein the length of the entire lens system at the wide-angle end is L.
w, the focal length of the entire system: fw, the condition: (3) 3.3 <Lw / fw <4.0. 4. The zoom lens for projection according to any one of claims 1 to 3, wherein the first lens group comprises, in order from the enlargement side, two negative lenses having a large curvature on the reduction side and an enlargement side. A zoom lens for projection, comprising a positive lens having a large curvature, and one of the two negative lenses is an aspherical lens. 5. A light flux from a light source is applied to a digital micromirror device whose orientation is controlled according to an image signal, and the light flux to which image information has been added by the digital micromirror device. An image projecting device for projecting an image onto a display medium by a projecting lens to display an image, wherein the projecting lens according to any one of claims 1 to 4 is used.