JP2005173494A - Lens for projection and projection image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens for projection which has a wide field angle of ≥40° half field angle, high resolution, a log back focus, and high telecentric properties and is compact. <P>SOLUTION: A first lens group I having a negative refracting power and a second lens group II having a positive refracting power are arranged in order from an enlargement side to a reduction side, and the first lens group comprises a meniscus negative lens having both surfaces made aspherical and is convex toward the enlargement side and a negative lens having high curvature on the reduction side, in order from the enlargement side, and the second lens group II comprises one or two positive lenses having high curvature on the enlargement side, a cemented lens obtained by sticking a negative lens having high curvature on the reduction side and a positive lens having both surfaces made convex to each other, a meniscus negative lens having both surfaces made spherical and is convex toward the reduction side, and a positive lens having high curvature on the reduction side, in order from the enlargement side, and is telecentric on the reduction side, and these lenses satisfy conditions 2.4<Bf/f<3.4 and 1.5<¾f1/f¾<2.8 wherein f is the focal length of an entire system and f1 is the focal length of the first lens group and Bf is a back focus in air in the case of an infinite conjugate on the enlargement side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection lens for enlarging and projecting an original image on a screen, and a projection type image display apparatus equipped with the projection lens.

  2. Description of the Related Art Liquid crystal projectors that enlarge and project an image displayed on a liquid crystal panel or the like onto a display medium such as a screen have been widely used as general TV broadcasts, video playback images, and computer display devices.

  In particular, each color image of red, green, and blue is displayed on three independent liquid crystal panels (liquid crystal light valves, etc.), and the displayed color images are combined and enlarged and projected from the back of the transmissive screen with a wide angle of view. The “rear type three-panel liquid crystal projector” to be displayed has a large screen and is thin, and a high-definition image has increased the spread rate.

  In a three-panel liquid crystal projector, regardless of whether it is a front method or a rear method, light from a white light source is generally separated into red, green, and blue colors by a color separation optical system and guided to each liquid crystal panel, and light emitted from these liquid crystal panels (The intensity is two-dimensionally modulated by the image displayed on each liquid crystal panel) is synthesized by a color synthesizing optical system and is incident on a projection lens. A “color combining optical system including prisms” is disposed between the liquid crystal panels.

  For this reason, a “long back focus” is required for a projection lens used in a three-plate liquid crystal projector.

  Separately from the above three LCD projectors, a single reflective LCD panel is used, and a polarizing beam splitter, etc. is arranged between the LCD panel and the projection lens, and red, green, and blue light are scrolled onto the LCD panel. There is a so-called “LCOS single plate projector” that irradiates and projects the reflected light in an enlarged manner. In this case, since the liquid crystal panel is a reflection type, the liquid crystal panel and the projection are separated in order to separate the optical path of the illumination light beam irradiated from the illumination light source to the liquid crystal panel and the optical path of the imaging light beam whose intensity is modulated by the liquid crystal panel Therefore, in the case of this LCOS single-plate projector, the projection lens has a “long back” so that the optical path separating means can be arranged. You must have "focus".

  When the angle of the light beam incident on the color synthesis optical system from the liquid crystal panel changes, the spectral transmittance of the color synthesis optical system changes accordingly, and the brightness of each color in the projected color image changes according to the angle of view. The image becomes difficult to see. In order to avoid this, it is preferable that the projection lens has “a telecentric property that the angle of the principal ray is approximately parallel to the optical axis on the reduction side”.

  As a projection lens that has a long back focus and is telecentric on the reduction side, a so-called “negative refractive power lens group” and “positive refractive power lens group” are arranged in order from the enlargement side to the reduction side. Although a "retrofocus type" type is known, this type of projection lens tends to have a large overall length, and in particular, "a rear projection type image display apparatus that requires a compact thin outline in a direction perpendicular to the screen surface. The problem here is how to incorporate the projection lens without impairing the compactness of the image display device.

  As a method to solve this problem, rear-projection type projectors are designed by placing "reflecting means such as mirrors" between the lens groups of a retrofocus type projection lens having a large overall length and bending the optical path inside the projection lens. A device for making an image display device thin is known (Patent Documents 1 to 4, etc.).

  Further, in order to shorten the optical path of the imaging light flux as much as possible and “to make the projection image display device thin while increasing the display image size”, the projection lens needs to have a large angle of view. Of course, various aberrations must be corrected well and high resolution must be provided so that the displayed image has high image quality.

Japanese Patent Laid-Open No. 9-218379 JP200142211 Japanese Patent Application No. 2003-91682 Japanese Patent Application No. 2003-127187

  In view of the above, the present invention has a half angle of view: a wide angle of view of 40 degrees or more, a high resolution, a long back focus and high telecentricity, a compact projection lens, and a projection using this projection lens. It is an object of the present invention to realize a type image display device, particularly a thin-type rear type projection type image display device.

  As illustrated in FIG. 1, the projection lens of the present invention has a first lens group I having a negative refractive power from the enlargement side (left side in FIG. 1) toward the reduction side, and has a positive refractive power. “Retro focus type” with the second lens group II.

The first lens group I is composed of two lenses in order from the magnification side: “a meniscus negative lens having both aspheric surfaces and convex on the magnification side” and “a negative lens having a large curvature on the reduction side”.
The second lens group II is composed of one or two “positive lenses having a large curvature on the enlargement side (one in FIG. 1)”, “negative lens having a large curvature on the reduction side, and both surfaces in order from the enlargement side. The lens is composed of a cemented lens formed by bonding two convex positive lenses, a meniscus negative lens having both aspheric surfaces and convex on the reduction side, and a positive lens having a large curvature on the reduction side.

This projection lens is telecentric on the reduction side, the focal length of the entire system: f, the focal length of the first lens group: f1, and the back focus in air when the conjugate point on the enlargement side is infinity: Bf conditions:
(1) 2.4 <Bf / f <3.4
(2) 1.5 <| f1 / f | <2.8
(Claim 1).

  Example 1 to be described later is an example in which there is one positive lens disposed on the enlargement side with respect to the cemented lens in the second lens group. In Examples 2, 3, and 4, there are two examples of the same positive lens. ing. In FIG. 1, the symbol ST indicates “aperture stop”, the symbol P indicates “prism as a color synthesis optical system”, and the symbol LB indicates “image display surface of a light valve such as a liquid crystal panel”.

The projection lens according to claim 1, wherein a reflecting means for bending an optical path is disposed between the first and second lens groups, the focal length of the entire system: f, and the optical axes of the first lens group and the second lens group. The distance above: d is the condition:
(3) 5.0 <d / f <10.0
(Claim 2).

The projection lens according to claim 1 or 2, wherein in the second lens group, an average of Abbe numbers of “positive lenses arranged on the enlargement side of the cemented lens” in the second lens group (when the number of the positive lenses is one, the Abbe number). ): Ν _2A is the condition:
(4) 20 <ν _2A <40
Is preferably satisfied (Claim 3).

Further, a projection lens according to any one of claims 1 to 3, constituting the cemented lens in the second lens group, the Abbe number of the negative lens: [nu _2BN, the positive lens Abbe number: [nu _2BP is, conditions:
(5) 50 <ν _2BP −ν _2BN <75
Is preferably satisfied (claim 4).

The projection lens according to any one of claims 1 to 4, wherein the Abbe number: ν _{2C of the} “positive lens disposed on the most reduction side in the second lens group” is:
(6) 50 <ν _2C <95
Is preferably satisfied (Claim 5).

The projection lens according to any one of claims 1 to 5, wherein the “meniscus negative lens having an aspheric surface” in the first lens group is preferably a plastic lens, and in this case, its focal length is f _1P. The focal length of the entire system: f, the condition:
(7) 0 <| f / f _1P | <0.12
Is preferably satisfied.

In the projection lens according to any one of claims 1 to 6, the “lens having an aspheric surface” in the second lens group is preferably a plastic lens, and in this case, its focal length is f _2P , all System focal length: f, condition:
(8) 0 <| f / f _2P | <0.04
Is preferably satisfied (claim 7).

  The projection lens according to any one of claims 1 to 7, wherein in the first lens group, the "interval between the aspherical lens and the lens arranged on the reduction side of the aspherical lens" is variable and projected. It can be configured such that the curvature of the image plane that occurs with a change in the distance (distance from the projection lens to the screen) can be corrected by changing the interval.

  A projection type image display device according to the present invention has a configuration in which the projection lens according to any one of claims 1 to 8 is mounted (claim 9). This projection type image display apparatus can be implemented as a front type three-panel liquid crystal projector, and in particular, can be implemented as the above-mentioned “rear type three-plate liquid crystal projector”. .) Further, the present invention can also be suitably implemented as the aforementioned “LCOS single plate projector”.

  Since the projection lens of the present invention has a long back focus as described above, the “first lens group I having a negative refractive power” on the enlargement side and the “second lens having a positive refractive power” on the reduction side. “Lens Group II” is arranged, and the main point is moved to the rear (reduction side) of the lens.

Condition (1) is a condition for securing a sufficient back focus necessary for a projection lens of a three-plate liquid crystal projector while maintaining a “large field angle (40 degrees or more)”.
If the lower limit of the condition (1) is exceeded while maintaining the above “large angle of view”, the back focus: Bf becomes short, and a color synthesizing optical system such as a prism between the projection lens and the liquid crystal panel, or the above-mentioned polarization It becomes difficult to arrange optical path separating means such as a beam splitter. If the upper limit of the condition (1) is exceeded while maintaining the desired “sufficient back focus”, the focal length f of the entire system becomes small, and it becomes difficult to correct various aberrations.

The condition (2) is a condition for “making both sufficiently long back focus and good optical performance compatible”.
In the case of a retrofocus type lens, in general, the ratio of the back focus: Bf to the focal length: f of the entire system: Bf / f is the principal point interval: D between the negative first lens group and the positive second lens group. The focal length of the first lens group: f1 (<0)
Bf / f = 1-D / f1 (a)
It is represented by Accordingly, as the value of | f1 | becomes smaller, the value of back focus: Bf becomes larger.

  If the parameter: | f1 / f | exceeds the upper limit of the condition (2), | f1 | becomes too large and the negative refractive power of the first lens group becomes small, and the second term on the right side of the above formula (a) becomes The right side itself becomes smaller and it becomes difficult to obtain a desired back focus.

  If the lower limit of the condition (2) is exceeded, | f1 | becomes too small and the “negative refractive power of the first lens group” becomes excessive, so that off-axis aberrations such as coma and field curvature are kept good. Becomes difficult.

Condition (3) is a condition for “appropriately securing a space necessary for arranging a reflecting means for bending the optical path and a long back focus”.
When the distance between the first lens group and the second lens group: d is increased, the “main point distance: D” in the above formula (a) increases, so that a long back focus can be realized and a “space for disposing the reflecting means” Can also be secured. However, if the interval d is too large and the parameter d / f exceeds the upper limit of the condition (3), the lens disposed on the enlargement side becomes large, which increases the cost of the projection lens. Conversely, when the parameter d / f exceeds the lower limit of the condition (3), it becomes difficult to secure a long back focus and a space for arranging the reflecting means.

  As described above, since the refractive power arrangement of the retrofocus type projection lens is asymmetric when viewed from the center of the lens (aperture stop position), distortion is likely to occur greatly.

  Since the lens on the most magnified side of the first lens group has a "high off-axis principal ray height (distance from the optical axis) compared to other lenses", an aspheric lens is used for this lens. Thus, distortion can be effectively corrected.

  The light beam traveling from the enlargement side to the reduction side enters the second lens group while diverging from the first lens group having negative refractive power. In the second lens group, “one or two pieces having a large curvature on the enlargement side” Is converted from a divergent state into a converged light beam. Then, it is converted again to a “divergent light beam” at the cemented surface of “a cemented lens formed by bonding two negative lenses having a large curvature on the reduction side and a positive lens having convex surfaces on both sides” following the positive lens. By repeating convergence and divergence in this way, it is possible to obtain an image with good aberration correction.

  In the second lens group, an aspherical surface is disposed at a position away from the aperture stop toward the reduction side (“a meniscus negative lens convex on the reduction side” following the cemented lens). It enables effective correction of aberrations.

Condition (4) represents “a suitable range of the average Abbe number of the positive lens disposed on the magnification side of the cemented lens” in the second lens group. Exceeding the upper and lower limits of condition (4) makes it difficult to correct longitudinal chromatic aberration and lateral chromatic aberration.
Condition (5) represents “the range of the Abbe number difference between the negative lens and the positive lens constituting the cemented lens” in the second lens group. If the upper and lower limit values of the condition (5) are exceeded, it will be difficult to correct axial chromatic aberration and lateral chromatic aberration as in the condition (4).

  The off-axis chief ray incident on the projection lens from the liquid crystal panel has high telecentricity, so it is “bent largely in the direction of the optical axis” by the second lens group having a positive refractive power. When the difference in the “degree of bending” due to the difference in wavelength is large, the lateral chromatic aberration is greatly generated.

In the projection lens according to the fifth aspect, the Abbe number of “the most positive lens disposed on the reduction side” in the second lens group is appropriately selected according to the condition (6), thereby suppressing the occurrence of lateral chromatic aberration.
In the projection lens according to claim 6, the aspherical lens in the first lens group is made as a plastic aspherical lens made of a plastic material that is inexpensive and easy to mold. However, the plastic lens is made of optical glass. In contrast, since the “change in focal length due to temperature” is large, if the refractive power of the plastic lens is large, the “change in focal length / focus position due to temperature change” becomes large in the entire projection lens.

  In particular, the projection lens in a rear-type liquid crystal projector is sealed in the housing after being installed in the device housing, so it is difficult to readjust the focus position and magnification (focal length). It is necessary to give due consideration to the deterioration of

Condition (7) is a condition that regulates the “degree of change in focal length due to temperature” of the plastic aspheric lens in the first lens group in view of this point.
When the parameter of condition (7): | f / f _1P | exceeds the upper limit, the focal length of the plastic aspheric lens: f _1P changes with temperature change, the “image magnification” changes, and the large focus It is not preferable because a deviation occurs.

  In the projection lens according to claim 7, the aspherical lens in the second lens group is made of plastic, and the condition (8) regulates the “degree of change in focal length due to temperature” of the plastic aspherical lens. Yes.

Although the upper limit value of the condition (8) is smaller than the upper limit value of the condition (7), it is for the reason described below.
The “movement amount of the focus position of the projection lens: ΔL” due to the change in the focal length due to the temperature change of the plastic lens is the focal length of the plastic lens: f _P , the incident light height to the plastic lens: h _P , and temperature dispersion. Number: By ω _P
ΔL = h _P ² / f _P · ω _P (b)
It is represented by

The light bundle emitted from one point of the liquid crystal panel is incident on the second lens group while spreading, but after reaching the maximum in the second lens group, the light bundle diameter is converged and becomes a small light bundle diameter. Incident into the lens group. Assuming that the light incident heights of the plastic lenses in the first lens group and the second lens group are h _P1 and h _P2 , respectively, h _P2 is larger than h _P1 , and the ratio of 2 Power: ε ² (= (h _P2 / h _P1 ) ² ) takes a value of 3 or more.

The amount of movement of the focus position due to temperature change: ΔL is “light incident height: proportional to the square of h _P ” as apparent from the above formula (b), so the focal length of the plastic lens in the second lens group is It must be at least three times larger than the plastic lens in the first lens group. For this reason, the upper limit value 0.04 of the condition (8) is smaller than the upper limit value 0.12 of the condition (7).

  In a rear projection type image display apparatus, in order to meet the demands of consumers, “enhancing the product lineup by changing the screen size as a display screen step by step” is generally performed. However, if the projection distance (distance from the projection lens to the screen) is changed in accordance with the screen size, the curvature of the image plane occurs around the screen and the image quality deteriorates.

  For example, in the projection lens of Example 1, when the projection distance: 650 mm is extended to 1200 mm and the “projection display size” is enlarged, the image is understood from the astigmatism diagram of FIG. 13 and the coma aberration diagram of FIG. As shown, a large curvature of the image plane is generated.

  In this case, astigmatism when the distance between the aspherical lens in the first lens group (the lens on the most magnifying side) and the lens arranged on the reduction side of the aspherical lens is “shortened by 0.5 mm” FIG. 15 is a diagram, and FIG. 16 is a coma aberration diagram. As can be understood from FIGS. 15 and 16, the shortening of the interval eliminates the curvature of the image surface and restores good image performance. The same correction is possible when the projection distance is shortened and the size of the projection display is reduced. This function is the same in other embodiments.

  That is, as in the projection lens described in claim 8, by changing the lens interval, the curvature of the image plane can be easily corrected for each size screen, and a good image can be projected.

  According to the present invention, as shown in a specific example described later, a high angle of view of a half angle of view of 40 degrees or more is maintained while maintaining a high resolving power, a long back focus, and a high telecentricity. It is possible to realize a projection lens having good performance, compactness and low cost, and a projection type image display apparatus equipped with the projection lens.

Hereinafter, four specific examples will be given as the best mode of the projection lens.
In each embodiment, “S” represents the surface number counted from the enlargement side, and “R” represents the radius of curvature of each surface (including the surface of the aperture stop ST and the surface of the prism P that is the color synthesizing optical system). In the case of a spherical surface, it represents a paraxial radius of curvature), and “D” represents a surface interval on the optical axis.

  “Nd” and “νd” indicate the refractive index and Abbe number of each lens material with respect to the d-line. “F” is the focal length of the projection lens, “F / No” is the F value representing brightness, “ω” is the half angle of view, and “obd” is the first surface of the lens (first lens group) from the object (screen) “Bf” represents the back focus in the air (without the prism). The unit of the quantity having the length dimension is “mm”.

The aspherical shape has an intersection with the optical axis as the origin, height relative to the optical axis: h, optical axis direction shift: Z, paraxial radius of curvature: R, conic constant: K, aspheric coefficient of higher order terms: As A, B, C, D, E, the well-known formula:
Z = (1 / R) · h ² / [1 + √ {1- (1 + K) · (1 / R) ² · h ² }]
+ A ・ h ⁴ + B ・ h ⁶ + C ・ h ⁸ + D ・ h ¹⁰ + E ・ h ¹²
The above-mentioned R, K, A, B, C, D, E are given and specified.

  FIG. 1 shows the lens configuration of the projection lens of Example 1.

  A first lens group I, an aperture stop ST, and a second lens group II are arranged from the enlargement side (left side of the figure), and a prism P that is a color synthesis optical system is provided between the projection lens and the light valve LB. Has been inserted.

f = 11.575, F / No = 2.4, ω = 40.6 °, obd = 650,
bf = 34.880
S R D Nd νd
1 51.224 5.000 1.49154 57.8
2 24.708 17.480
3 1500.000 2.700 1.49700 81.6
4 24.156 69.940
5 ∞ (Aperture) 13.830
6 31.228 5.180 1.80809 22.8
7 1130.820 8.900
8 −70.390 1.600 1.84666 23.8
9 20.141 9.460 1.49700 81.6
10 −32.911 0.170
11 −86.444 3.990 1.49154 57.8
12 −210.874 0.170
13 68.827 10.520 1.45600 90.3
14 −26.238 5.000
15 ∞ 36.000 1.51680 64.2
16 ∞ 6.341.

Aspherical first surface K = 0.8074, A = −0.8193 × 10 ⁻⁶ , B = −0.6124 × 10 ⁻⁹ , C = 0.1154 × 10 ⁻¹¹ ,
D = −0.6006 × 10 ⁻¹⁵ , E = 0.1585 × 10 ⁻¹⁹
Second surface K = −0.7086, A = 0.1268 × 10 ⁻⁵ , B = −0.6224 × 10 ⁻⁸ , C = 0.1381 × 10 ⁻¹⁰ ,
D = −0.1202 × 10 ⁻¹³ , E = 0.3684 × 10 ⁻¹⁷
11th surface K = 18.2802, A = −0.4669 × 10 ⁻⁴ , B = 0.4626 × 10 ⁻⁷ , C = −0.1393 × 10 ⁻⁹ ,
D = −0.3005 × 10 ⁻¹² , E = 0.2409 × 10 ⁻¹⁴
Twelfth surface K = 148.43, A = −0.2886 × 10 ⁻⁴ , B = 0.6839 × 10 ⁻⁷ , C = −0.1331 × 10 ⁻⁹ ,
D = 0.3849 × 10 ⁻¹² , E = 0.

Value of conditional expression (1) Bf / f = 3.013
(2) | f1 / f | = 2.617
(3) d / f = 7.237
(4) ν _2A = 22.8
(5) ν _2BP −ν _2BN = 57.8
(6) ν _2C = 90.3
(7) | f / f _1P | = 0.112
(8) | f / f _2P | = 0.038.

FIG. 2 shows a diagram of spherical aberration, astigmatism and distortion obtained by evaluating the projection lens of Example 1 on the reduction side, and FIG. 3 shows a diagram of coma aberration.
Each aberration diagram shows “aberration of green light having a wavelength of 546 nm”, but spherical aberration diagrams and coma aberration diagrams also show aberrations of wavelengths of 610 nm and 470 nm, representing red and blue light. In the astigmatism diagram, S represents the sagittal image surface, and M represents the aberration of the meridional image surface. The same applies to the aberration diagrams of the other examples.

FIG. 4 shows the lens configuration of the projection lens of Example 2 according to FIG.
A first lens group I, a reflection mirror (planar mirror) M that bends the optical path, an aperture stop ST, and a second lens group II are arranged from the enlargement side (obliquely upper right in the figure).

f = 11.575, F / No = 2.4, ω = 44.5 °, obd = 650,
bf = 31.300
S R D Nd νd
1 54.521 5.000 1.49154 57.8
2 28.680 23.380
3 −128.627 2.300 1.65844 50.9
4 26.633 70.240
5 ∞ (Aperture) 0.170
6 45.958 4.280 1.75520 27.5
7 −446.047 8.630
8 26.547 3.880 1.62004 36.3
9 40.830 8.820
10 −142.745 3.000 1.84666 23.8
11 16.467 7.680 1.45650 90.3
12 −37.115 0.170
13 −99.824 3.940 1.49154 57.8
14 −150.221 4.550
15 210.806 8.330 1.61800 63.4
16 −26.453 4.000
17 ∞ 36.000 1.51680 64.2
18 ∞ 3.760.

Aspherical first surface K = 0.9395, A = −0.0.2006 × 10 ⁻⁵ , B = 0.6093 × 10 ⁻⁹ , C = 0.1552 × 10 ⁻¹² ,
D = −0.139 × 10 ⁻¹⁵ , E = 0.1661 × 10 ⁻¹⁹
Second surface K = −0.5924, A = −0.2654 × 10 ⁻⁵ , B = −0.4287 × 10 ⁻⁸ , C = 0.4217 × 10 ⁻¹¹ ,
D = −0.2353 × 10 ⁻¹⁵ , E = −0.1644 × 10 ⁻¹⁷
13th surface K = 46.8534, A = −0.4063 × 10 ⁻⁴ , B = 0.2643 × 10 ⁻⁷ , C = −0.2303 × 10 ⁻⁹ ,
D = −0.9169 × 10 ⁻¹² , E = 0.8887 × 10 ⁻¹⁴
14th surface K = 107.7504, A = −0.2213 × 10 ⁻⁴ , B = 0.3736 × 10 ⁻⁷ , C = −0.2333 × 10 ⁻⁹ ,
D = 0.7881 × 10 ⁻¹² , E = 0.

Value of conditional expression (1) Bf / f = 2.704
(2) | f1 / f | = 2.042
(3) d / f = 6.083
(4) ν _2A = 31.9
(5) ν _2BP −ν _2BN = 66.5
(6) ν _2C = 63.4
(7) | f / f _1P | = 0.088
(8) | f / f _2P | = 0.199.

  FIG. 5 shows a diagram of spherical aberration, astigmatism, and distortion obtained by evaluating the projection lens of Example 2 on the reduction side, and FIG. 6 shows a diagram of coma aberration.

  FIG. 7 shows the lens configuration of the projection lens of Example 3 according to FIG.

f = 11.579, F / No = 2.4, ω = 44.4 °, obd = 646,
bf = 38.097
S R D Nd νd
1 84.687 5.000 1.49154 57.8
2 37.678 29.850
3 −159.025 2.300 1.66672 48.3
4 23.739 58.900
5 ∞ (Aperture) 5.140
6 55.723 4.400 1.75211 25.1
7 −132.944 0.170
8 51.035 3.430 1.71736 29.5
9 78.624 14.030
10 −63.675 3.000 1.84666 23.8
11 22.412 7.570 1.45650 90.3
12 −26.112 0.170
13 −78.346 4.410 1.49154 57.8
14 −131.162 2.140
15 −791.911 9.470 1.49700 81.6
16 −20.560 6.000
17 ∞ 40.000 1.51680 64.2
18 ∞ 5.921.

Aspheric surface 1st surface K = 3.0252, A = 0.1841 × 10 ⁻⁵ , B = −0.562 × 10 ⁻⁹ , C = 0.3614 × 10 ⁻¹² ,
D = −0.1555 × 10 ⁻¹⁵ , E = 0.525 × 10 ⁻¹⁹
Second surface K = −0.375, A = 0.1109 × 10 ⁻⁵ , B = −0.5196 × 10 ⁻⁹ , C = 0.7981 × 10 ⁻¹² ,
D = −0.4733 × 10 ⁻¹⁵ , E = −0.3273 × 10 ⁻¹⁸
13th surface K = 38.3042, A = −0.4873 × 10 ⁻⁴ , B = 0.9652 × 10 ⁻⁸ , C = −0.4018 × 10 ⁻⁹ ,
D = −0.7022 × 10 ⁻¹² , E = 0.3828 × 10 ⁻¹⁴
14th surface K = 71.3368, A = −0.2314 × 10 ⁻⁴ , B = 0.4611 × 10 ⁻⁷ , C = −0.2338 × 10 ⁻⁹ ,
D = 0.914 × 10 ⁻¹² , E = 0.

Value of conditional expression (1) Bf / f = 3.290
(2) | f1 / f | = 1.844
(3) d / f = 5.531
(4) ν _2A = 27.3
(5) ν _2BP −ν _2BN = 66.5
(6) ν _2C = 81.6
(7) | f / f _1P | = 0.081
(8) | f / f _2P | = 0.028.

  FIG. 8 shows a diagram of spherical aberration, astigmatism and distortion obtained by evaluating the projection lens of Example 3 on the reduction side, and FIG. 9 shows a diagram of coma aberration.

  FIG. 10 shows the lens configuration of the projection lens of Example 4 according to FIG.

f = 9.877, F / No = 2.4, ω = 42.4 °, obd = 696,
bf = 29.291
S R D Nd νd
1 48.888 5.600 1.49154 57.8
2 27.700 23.440
3 −146.830 2.800 1.74330 49.2
4 25.894 85.640
5 49.900 4.260 1.72825 28.3
6 -694.120 0.200
7 ∞ (Aperture) 5.300
8 31.200 4.080 1.59551 39.2
9 63.860 13.800
10 −189.650 1.500 1.84666 23.8
11 15.180 6.850 1.49700 81.6
12 −42.020 2.640
13 −96.916 3.000 1.49154 57.8
14 −136.080 4.000
15 2144.880 6.860 1.56883 56.0
16 −23.030 4.000
17 ∞ 33.000 1.51680 64.2
18 ∞ 3.667.

Aspherical first surface K = 0.7053, A = −0.109 × 10 ⁻⁵ , B = −0.1899 × 10 ⁻⁸ , C = 0.26 × 10 ⁻¹¹ ,
D = −0.1267 × 10 ⁻¹⁴ , E = 0.2084 × 10 ⁻¹⁸
Second surface K = −0.5157, A = −0.1645 × 10 ⁻⁵ , B = −0.8583 × 10 ⁻⁸ , C = 0.7812 × 10 ⁻¹¹ ,
D = −0.4456 × 10 ⁻¹⁵ , E = −0.2911 × 10 ⁻¹⁷
13th surface K = 41.123, A = −0.7144 × 10 ⁻⁴ , B = 0.8345 × 10 ⁻⁷ , C = −0.7079 × 10 ⁻⁹ ,
D = −0.4672 × 10 ⁻¹¹ , E = 0.3405 × 10 ⁻¹³
14th surface K = 110.1549, A = −0.4876 × 10 ⁻⁴ , B = 0.1207 × 10 ⁻⁶ , C = −0.8291 × 10 ⁻⁹ ,
D = 0.1906 × 10 ⁻¹¹ , E = 0.441 × 10 ⁻¹⁴ .

Value of conditional expression (1) Bf / f = 2.966
(2) | f1 / f | = 2.218
(3) d / f = 8.671
(4) ν _2A = 33.75
(5) ν _2BP −ν _2BN = 57.8
(6) ν _2C = 56.0
(7) | f / f _1P | = 0.069
(8) | f / f _2P | = 0.014.

  FIG. 11 shows a diagram of spherical aberration, astigmatism and distortion obtained by evaluating the projection lens of Example 4 on the reduction side, and FIG. 12 shows a diagram of coma aberration.

Each of the projection lenses of Examples 1 to 4 listed above includes a first lens group I having a negative refractive power and a second lens group II having a positive refractive power from the enlargement side toward the reduction side. The first lens group I is composed of two lenses, a meniscus negative lens having both aspheric surfaces and convex on the magnification side, and a negative lens having a large curvature on the reduction side, in order from the magnification side. 2 (a positive lens having a large curvature on the magnification side, one negative lens (Example 1) or two (Examples 2 to 4) from the magnification side, a negative lens having a large curvature on the reduction side, and a positive lens having convex surfaces on both sides. A cemented lens formed by laminating sheets, a double-sided aspherical meniscus negative lens on the reduction side, a positive lens with a large curvature on the reduction side, telecentric on the reduction side, and the focal length of the entire system: f, When the focal length of the first lens unit I is f1, and the conjugate point on the enlargement side is infinity Back in the air focus: Bf is, conditions:
(1) 2.4 <Bf / f <3.4
(2) 1.5 <| f1 / f | <2.8
(Claim 1).

In the projection lenses of Examples 1 to 4, the focal length of the entire system is f, and the distance on the optical axis between the first lens group I and the second lens group II is d.
(3) 5.0 <d / f <10.0
And the projection lenses of Examples 2 to 4 have a compact outer shape by disposing reflecting means for bending the optical path between the first lens group I and the second lens group II (Claim 2). .

In addition, in the projection lenses of Examples 1 to 4, the average Abbe number of positive lenses disposed on the magnification side from the cemented lens of the second lens group II: ν _2A is as follows:
(4) 20 <ν _2A <40
(Claim 3) and the Abbe number of the negative lens: ν _2BN and the Abbe number of the positive lens: ν _2BP constituting the cemented lens are as _follows :
(5) 50 <ν _2BP −ν _2BN <75
(Claim 4).

Furthermore, the Abbe number: ν _2C of the positive lens disposed closest to the reduction side of the second lens group II is:
(6) 50 <ν _2C <95
(Claim 5).

In the projection lenses of Examples 1 to 4, the meniscus negative lens having an aspheric surface in the first lens group I is a plastic lens, the focal length is f _1P , and the focal length of the entire system is f.
(7) 0 <| f / f _1P | <0.12
(Claim 6), the lens having an aspheric surface in the second lens group II is a plastic lens, and its focal length: f _2P is:
(8) 0 <| f / f _2P | <0.04
(Claim 7).

  Furthermore, in any of the projection lenses of Examples 1 to 4, the distance between the aspherical lens in the first lens group I and the lens disposed on the reduction side of the aspherical lens is variable, so that the projection distance can be changed. The accompanying curvature of the image plane can be corrected by changing the interval.

  Therefore, the light of the white light source is separated into three lights of red, green and blue, passed through three independent liquid crystal panels, and the light having the image information is synthesized by the prism of the color synthesis optical system, Using a projection-type image display device that displays an enlarged projection from the back of a transmissive screen or a reflective liquid crystal panel, a red, green, and blue light is scrolled onto the liquid crystal panel, and the reflected light is transmitted to the transmissive screen. By mounting the projection lens of Examples 1 to 4 on a projection-type image display device that magnifies and projects from the back of the projector, it is possible to display a high-definition image while being compact. ).

1 is a lens configuration diagram of Example 1. FIG. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration of Example 1. FIG. 6 is a diagram showing coma aberration in Example 1. 6 is a lens configuration diagram of Example 2. FIG. It is a figure which shows the spherical aberration of Example 2, astigmatism, and a distortion aberration. FIG. 6 is a diagram showing coma aberration in Example 2. 6 is a lens configuration diagram of Example 3. FIG. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration of Example 3. FIG. 6 is a diagram showing coma aberration in Example 3. 6 is a lens configuration diagram of Example 4. FIG. It is a figure which shows the spherical aberration of Example 4, astigmatism, and a distortion aberration. FIG. 6 is a diagram showing coma aberration in Example 4. It is a figure which shows spherical aberration, astigmatism, and distortion aberration when the projection distance is extended to 1200 mm in Example 1. It is a figure which shows the coma aberration when the projection distance is extended to 1200 mm in Example 1. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, and distortion when the projection distance is extended to 1200 mm and image plane correction is performed in Example 1. It is a figure which shows a coma aberration when the projection distance is extended to 1200 mm in Example 1, and image surface correction | amendment is carried out.

Explanation of symbols

I First lens group
II Second lens group M Reflection mirror
ST Aperture stop
Prism LB light valve as P color synthesis optical system

Claims (9)

A first lens group having negative refractive power and a second lens group having positive refractive power are arranged from the enlargement side to the reduction side,
The first lens group, in order from the magnifying side, is composed of two lenses, a meniscus negative lens having both aspheric surfaces and convex on the magnifying side, and a negative lens having a large curvature on the reducing side,
The second lens group consists of two lenses, a positive lens having a large curvature on the one or two magnification sides from the magnification side, a negative lens having a large curvature on the reduction side, and a positive lens having convex surfaces on both sides. It consists of a cemented lens, a meniscus negative lens that is aspheric on both sides and convex on the reduction side, and a positive lens with a large curvature on the reduction side.
Telecentric on the reduction side, focal length of the entire system: f, focal length of the first lens group: f1, back focus in air when the magnification side conjugate point is at infinity: Bf
(1) 2.4 <Bf / f <3.4
(2) 1.5 <| f1 / f | <2.8
Projection lens characterized by satisfying The projection lens according to claim 1,
Reflecting means for bending the optical path between the first and second lens groups,
Focal length of the entire system: f, distance on the optical axis between the first lens group and the second lens group: d is a condition:
(3) 5.0 <d / f <10.0
Projection lens characterized by satisfying The projection lens according to claim 1 or 2,
In the second lens group, the average Abbe number of positive lenses arranged on the magnification side from the cemented lens: ν _2A is the condition:
(4) 20 <ν _2A <40
Projection lens characterized by satisfying The projection lens according to any one of claims 1 to 3,
The negative lens Abbe number: ν _2BN and the positive lens Abbe number: ν _2BP constituting the cemented lens in the second lens group are the conditions:
(5) 50 <ν _2BP −ν _2BN <75
Projection lens characterized by satisfying In the projection lens according to any one of claims 1 to 4,
Abbe number ν _2C of the positive lens disposed closest to the reduction side in the second lens group is:
(6) 50 <ν _2C <95
Projection lens characterized by satisfying In the projection lens according to any one of claims 1 to 5,
The meniscus negative lens having an aspheric surface in the first lens group is a plastic lens, and its focal length is f _1P and the focal length of the entire system is f.
(7) 0 <| f / f _1P | <0.12
Projection lens characterized by satisfying The projection lens according to any one of claims 1 to 6,
The lens having an aspheric surface in the second lens group is a plastic lens, and its focal length is f _2P and the focal length of the entire system is f.
(8) 0 <| f / f _2P | <0.04
Projection lens characterized by satisfying The projection lens according to any one of claims 1 to 7,
In the first lens group,
The interval between the aspheric lens and the lens disposed on the reduction side of the aspheric lens is variable,
A projection lens characterized in that a curvature of an image plane generated by changing a projection distance (distance from a projection lens to a screen) can be corrected by changing the interval. A projection-type image display device comprising the projection lens according to any one of claims 1 to 8.

Images