JPH10177138A - Projection lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the constituting number of lenses so as to realize an inexpensive lens system, and to obtain a projection lens that is hardly influenced by temperature change and can include the wide angle of view excellently compensated in aberration, and that can be made compact and can be reduced in cost, by using an aspherical lens consisting of a plastic lens in the most part of the constituting lenses. SOLUTION: In this projection lens, a diverging lens group 1, a converging lens group 2 and a Fresnel lens group 3 are arranged from an enlarging side. Two negative lenses G1 and G2 on the front side of the lens group 1 are the lens consisting of plastic material and at lest one of them is made aspherical. The positive lens G5 and the negative lens G7 of the lens group 2 are the lens consisting of the plastic material. By using the lenses G1 , G2 , G5 and G7 consisting of the plastic material in a part of the constitution in such a way and correcting the shortcoming of the plastic lens, the power of each lens in the constitution is appropriately set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens used for magnifying projection and the like, in particular, has a brightness of about F1: 4.0, covers a half angle of view of about 40 °, and is excellent in a variable power range. The present invention relates to a projection lens capable of obtaining excellent performance.

[0002]

2. Description of the Related Art In a recent enlargement projection apparatus, for example, the resolution of a liquid crystal used as an image modulation element has been increased,
There is a demand for high resolution in the entire magnifying projection device. or,
As the apparatus itself has been reduced in size, there has been a demand for a wider angle of view and a smaller size, and also a lower cost.

In order to meet the demand for higher resolution and wider angle of view, the number of lenses has been increased or the refractive index of lens materials has been increased. It has become.

As one method of reducing the number of lenses, there is known a method of using a plastic molded lens having an aspherical lens. However, a lens formed of a plastic material has a large refractive index due to a temperature change. It has the property of changing. For this reason, there is a problem that the back focus of the lens changes and the resolution is deteriorated.

[0005]

In view of such circumstances, the present invention makes it possible to cover a wide angle of view of about half angle of view ω = 40 °, and uses an aspherical plastic lens for the majority of the number of components. A projection lens that reduces the number of components, realizes an inexpensive lens system, is less susceptible to changes in temperature, and can cover a wide angle of view in which various aberrations are well corrected. Is provided.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a variable magnification projection lens having a divergent lens unit, a convergent lens unit, and a Fresnel lens unit from the enlargement side. Two negative lenses G ₁ and G ₂ having at least one negative meniscus lens with the convex surface facing the enlargement side;
And a positive lens G _3, the convergent lens group includes a positive lens G _4, G ₅ in order from the magnifying side, a lens G _6, a negative meniscus lens G ₇ having a concave surface facing the magnification side, G ₁ and G ₂ of the diverging lens group are made of a plastic material, and at least one surface is made of an aspherical lens. G ₅ and G ₇ of the converging lens group are made of a plastic material.
At least one surface has an aspherical lens configuration, and the Fresnel lens group includes a Fresnel lens having a positive refractive power and a Fresnel surface on a reduction side, and a distance between the divergent lens group and the convergent lens group. The magnification is changed by changing the distance between the converging lens group and the Fresnel lens group, and relates to a projection lens satisfying the following conditions. _{(1) -1.1 <f 12 /f<-0.86} (2) 1.05 <f 5 /f<1.35 (3) -22.5 <f 7 /f<-3.0 ( 4) 40 <ν ₃ <55, where f: focal length of the entire wide-side lens system f ₁₂ : composite focal length of lenses G ₁ and G ₂ f ₅ : focal length of lens G ₅ f ₇ : focal length of lens G ₇ Distance ν ₃ : Abbe number of lens G ₃

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a projection lens according to the present embodiment. In the projection lens, a divergent lens group 1, a convergent lens group 2, and a Fresnel lens group 3 are arranged from the enlargement side (front side). This is a so-called retrofocus type projection lens having a configuration.

The two negative lenses G ₁ and G ₂ on the front side of the divergent lens group 1 are made of plastic material, and at least one of them is made aspherical. Further, the positive lens G ₅ of the convergent lens 2, a negative lens G ₇ and lens of plastic material.

In order to brighten F _No with the configuration of the projection lens shown in FIG. 1, it is preferable to increase the focal length of each lens unit and the interval between each lens unit. It does not become compact. Further, since the half angle of view is about 40 ° and the angle is widened, the correction of the aberration of the off-axis light beam is not so positive. Conversely, if the focal length of the divergent lens unit is increased to reduce the size, the negative power is increased and the negative distortion is increased. The two negative lenses G ₁ and G ₂ on the front side of the divergent lens group 1 are made of a plastic material, and at least one of them is made aspherical to correct such distortion.

In general, when plastic is used as a lens material, the refractive index of the plastic changes with a change in temperature, so that the back focus changes and the resolving power deteriorates. The positive lens G ₅ of the convergent lens group 2;
Structure a negative lens G ₇ and a lens of plastic material, to offset the change in the back focus due to a change in temperature.

The conditional expressions for the lenses constituting the projection lens are shown below.

[0013]

[Conditional expression]

_{(1) -1.1 <f 12 /f<-0.86} (2) 1.05 <f 5 /f<1.35 (3) -22.5 <f 7 /f<-3.0 ( 4) 40 <ν ₃ <55, where f: focal length of the entire wide-side lens system f ₁₂ : composite focal length of lenses G ₁ and G ₂ f ₅ : focal length of lens G ₅ f ₇ : focal length of lens G ₇ Distance ν ₃ : Abbe number of lens G ₃

Conditional expression (1) defines the combined focal length f ₁₂ of the negative lenses G ₁ and G ₂ .

[0015] Negative power the composite focal length f ₁₂ exceeds the upper limit becomes strong, negative distortion increases. Also it is difficult to offset the change in the focal length due to a temperature change in the lens G _5. Conversely, when the combined focal length f ₁₂ exceeds the lower limit for the focal length becomes longer, increasing chromatic aberration in the divergent lens group 1, the chromatic aberration in the entire becomes resolution deteriorates sufficiently corrected.
In addition, the total length of the divergent lens group 1 is increased, and it is not possible to reduce the size of the entire lens.

[0016] Condition (2) is a focal length f ₅ of the positive lens G ₅
Is defined.

If the focal length f ₅ exceeds the upper limit, the power becomes weak. If the composite focal length of the positive lenses G ₄ and G ₅ is to be kept constant, the power of the lens G ₄ becomes strong and astigmatism increases. Good performance at the angle of view cannot be maintained. Conversely the focal length f ₅ increases the aberrations of the off-axis since the power of the lower limit lens G ₄ becomes strong, can not be maintained better performance.

[0018] Condition (3) is the focal length f ₇ of the negative lens G ₇
Is defined.

[0019] the angle focal length f ₇ is emitted from the negative power becomes too strong lens G ₇ exceeds the upper limit increases.
In the Fresnel lens group 3 thereafter, if the light beam emitted from the Fresnel lens surface is made to approach a substantially parallel light beam, the prism cutting angle on the Fresnel lens surface becomes sharp, and the light amount loss becomes large and processing becomes difficult. Absent. Entire flange back is lengthened device the focal length f ₇ conversely exceeds the lower limit is not preferable because becomes long.

Conditional expression (4) defines the Abbe number ν ₃ of the lens G ₃ .

[0021] The present invention is being used for plastic material lens G _1, G _2, the chromatic aberration of the negative lens group of the lens G _1, G ₂ would be approximately determined. Therefore, the Abbe number [nu ₃ of the lens G ₃ is deteriorated chromatic aberration is outside this range, the resolution deteriorates.

[0022]

Examples of the present invention will be described below. In the table, r indicates the radius of curvature, d indicates the surface interval, n indicates the refractive index, and ν indicates the Abbe number. Note that the expression for the aspherical surface is

[0023]

X = Y ² (1 / r) / [1 + √ ｛1- (1+
K) Y ² (1 / r) ² }] + C2Y ⁴ + C4Y ⁶ + C6Y ⁸
+ C8Y ¹⁰

K, C2, C4, C
6, C8 are shown.

Example 1 f = 1 to 1.05 conversion F _NO = 4.0 2ω = 81 ° to 76 ° rd nu 1 3.806 0.102 1.4913 58.0 2 0.644 0.147 3 0.857 0.087 1.4913 58.0 4 0.487 0.297 5 0.773 0.085 1.7206 47.7 6 0.978 d6 (variable) 7 0.921 0.141 1.7162 53.6 8 7.246 0.332 9 0.625 0.078 1.4913 58.0 10 83.132 0.092 11 -1.021 0.108 1.7044 29.9 12 0.809 0.119 1.7443 52.4 13 -1.135 0.061 14 -0.648 0.073 1.4913 58.0 15 -0.927 d15 (variable) 16 ∞ 0.043 1.4913 58.0 17 -1.217

Aspheric coefficient 4 plane 9 plane 15 plane 17 plane K -0.621 0.638 -3.245 -0.582 C2 0.285 0.281 0.134 × 10 -0.685 C4 -0.131 × 10 0.205 × 10 0.641 × 10 0.129 × 10 C6 0.641 × 10 0.675 × 10 0.176 × 10 ² -0.131 × 10 C8 -0.185 × 10 ² -0.112 × 10 ³ -0.814 × 10 ² 0.454 d6 = 0.095 to 0.048 d15 = 1.012 to 1.058 f ₁₂ / f = − _{0.906 f 5 /f=1.278 f 7 /f=-4.788 ν} 3 = 47.7

Example 2 f = 1.0 to 1.05 conversion F _NO = 4.0 2ω = 81 ° to 76 ° rd ν 1 3.911 0.102 1.4913 58.0 2 0.654 0.141 3 0.842 0.087 1.4913 58.0 4 0.478 0.309 5 0.755 0.084 1.7206 47.7 6 0.943 d6 (variable) 7 0.887 0.138 1.694 54.6 8 5.403 0.336 9 0.602 0.079 1.4913 58.0 10 129.952 0.108 11 -0.946 0.069 1.7044 29.9 12 0.839 0.136 1.7443 52.4 13 -1.106 0.048 14 -0.662 0.075 1.4913 58.0 15 -0.919 d15 (variable) 16 ∞ 0.043 1.4913 58.0 17 -1.216

Aspherical surface coefficient 4 9 9 15 17 17 K -0.592 0.587 -3.407 -0.580 C2 0.251 0.241 0.138 × 10 -0.641 C4 -0.108 × 10 0.265 × 10 0.714 × 10 0.113 × 10 C6 0.551 × 10 -0.691 × 10 0.183 × 10 ² -0.107 × 10 C8 -0.161 × 10 ² -0.371 × 10 ² -0.865 × 10 ² 0.338 d6 = 0.095 to 0.048 d15 = 1.029 to 1.075 f ₁₂ / f = −0.911 f ₅ /f=1.231 f ₇ /f=−5.340 ν ₃ = 47.7

Example 3 f = 1.0 to 1.05 conversion F _NO = 4.0 2ω = 81 ° to 76 ° rd ν 1 3.857 0.101 1.4913 58.0 2 0.695 0.114 3 0.874 0.087 1.4913 58.0 4 0.488 0.371 5 0.737 0.076 1.7206 47.7 6 0.870 d6 (variable) 7 0.871 0.141 1.6940 54.6 8 5.722 0.289 9 0.599 0.105 1.4913 58.0 10 22.345 0.090 11 -0.965 0.056 1.7044 29.9 12 0.772 0.145 1.7443 52.4 13 -1.075 0.073 14 -0.608 0.050 1.4913 58.0 15 -0.927 d15 (variable) 16 ∞ 0.043 1.4913 58.0 17 -1.286

Aspheric coefficient 4 plane 9 plane 15 plane 17 plane K -0.540 0.577 -4.039 -0.404 C2 0.294 0.230 0.148 × 10 -0.599 C4 -0.764 0.268 × 10 0.853 × 10 0.105 × 10 C6 0.453 × 10 -0.188 × 10 ^{2 0.175 × 10 2 -0.101 × 10} C8 -0.103 × 10 2 0.250 × 10 3 -0.131 × 10 3 0.321 d6 = 0.074~0.029 d15 = 0.987~1.032 f 12 / f = -0 _{.961 f 5 /f=1.251 f 7 /f=-3.790 ν} 3 = 47.7

Example 4 f = 1.0 to 1.05 conversion F _NO = 4.0 2ω = 81 ° to 76 ° rd ν 1 4.084 0.102 1.4913 58.0 2 0.690 0.068 3 0.748 0.087 1.4913 58.0 4 0.429 0.317 5 0.784 0.089 1.7206 47.7 6 0.993 d6 (variable) 7 1.051 0.146 1.6940 54.6 8 52.050 0.360 9 0.644 0.093 1.4913 58.0 10 -11.512 0.113 11 -0.912 0.074 1.7044 29.9 12 0.934 0.133 1.7443 52.4 13 -1.195 0.047 14 -0.705 0.075 1.4913 58.0 15 -0.795 d15 (variable) 16 ∞ 0.043 1.4913 58.0 17 -1.217

Aspherical coefficient 1 plane 4 plane 9 plane 15 plane 17 plane K -20.320 -0.609 0.723 -2.263 -0.564 C2 -0.207 × 10 ^-1 0.242 0.346 0.122 × 10 -0.848 C4 -0.162 × 10 ^-1 -0.125 × 10 0.262 × 10 0.659 × 10 0.158 × 10 C6 -0.118 × 10 ^-1 0.492 × 10 -0.159 × 10 ² 0.150 × 10 ² -0.133 × 10 C8 0.148 × 10 ^-1 -0.166 × 10 ² 0.165 × 10 ³ -0.530 × 10 ² 0.354 d6 = 0.109 to 0.062 d15 = 1.032 to 1.080 f ₁₂ /f=−0.924 f ₅ /f=1.245 f ₇ /f=−17.272 ν ₃ = 47.7

Example 5 f = 1.0 to 1.05 conversion F _NO = 4.0 2ω = 81 ° to 76 ° rd n ν 1 3.761 0.101 1.4913 58.0 2 0.650 0.135 3 0.842 0.087 1.4913 58.0 4 0.471 0.302 5 0.742 0.086 1.7206 47.7 6 0.933 d6 (variable) 7 0.890 0.136 1.6940 54.6 8 4.841 0.349 9 0.600 0.083 1.4913 58.0 10 -20.637 0.105 11 -0.944 0.088 1.7044 29.9 12 0.843 0.126 1.7443 52.4 13 -1.205 0.043 14 -0.745 0.075 1.4913 58.0 15 -0.976 d15 (variable) 16 ∞ 0.043 1.4913 58.0 17 -1.143

Aspheric coefficient 4 plane 9 plane 15 plane 17 plane K -0.614 0.547 -3.711 -0.663 C2 0.287 0.216 0.141 × 10 -0.737 C4 -0.129 × 10 0.166 × 10 0.712 × 10 0.146 × 10 C6 0.656 × 10 0.232 × 10 ² 0.127 × 10 ² -0.144 × 10 C8 -0.180 × 10 ² -0.461 × 10 ³ -0.612 × 10 ² 0.487 d6 = 0.097 to 0.050 d15 = 1.037 to 1.084 f ₁₂ / f = −0.900 f ₅ /f=1.188 f ₇ /f=−7.175 ν ₃ = 47.7

[0035]

As described above, according to the present invention, since a plastic lens is used for a part of the structure and the defect of the plastic lens is corrected, the power of each lens of the structure is appropriately set. Therefore, the number of lenses can be reduced, the size can be reduced, the wide-angle range around half angle of view of about 40 ° can be covered at a low cost, and excellent performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a layout diagram of a lens according to an embodiment of the present invention.

FIG. 2 is an aberration diagram of the first example according to the present invention.

FIG. 3 is an aberration diagram of a second example according to the present invention.

FIG. 4 is an aberrational diagram of the third embodiment according to the present invention.

FIG. 5 is an aberration diagram of a fourth embodiment according to the present invention.

FIG. 6 is an aberration diagram of a fifth embodiment according to the present invention.

[Explanation of symbols]

 1 divergent lens group 2 convergent lens group 3 Fresnel lens group

Claims (1)

[Claims] In a variable power projection lens having a divergent lens group, a convergent lens group, and a Fresnel lens group from the enlargement side, the divergence lens group has at least a convex surface facing the enlargement side in order from the enlargement side. It has two negative lenses G ₁ , G ₂ having one negative meniscus lens and a positive lens G _3, and the convergent lens group includes positive lenses G ₄ , G _{5 in} order from the enlargement side.
And a lens G ₆ , a negative meniscus lens G ₇ having a concave surface facing the enlargement side, wherein G ₁ and G ₂ of the divergent lens group are made of a plastic material, and at least one surface is made of an aspheric surface. , G _5, G ₇ of the convergent lens group is made of a plastic material, and at least one surface with a lens structure consisting of a non-spherical surface, the Fresnel lens is a Fresnel lens having a Fresnel surface on the reduction side has a positive refractive power Wherein the magnification is changed by changing the distance between the divergent lens group and the convergent lens group, and the distance between the convergent lens group and the Fresnel lens group. Projection lens characterized by satisfaction. _{(1) -1.1 <f 12 /f<-0.86} (2) 1.05 <f 5 /f<1.35 (3) -22.5 <f 7 /f<-3.0 ( 4) 40 <ν ₃ <55, where f: focal length of the entire wide-side lens system f ₁₂ : composite focal length of lenses G ₁ and G ₂ f ₅ : focal length of lens G ₅ f ₇ : focal length of lens G ₇ Distance ν ₃ : Abbe number of lens G ₃