JPH02184809A - Front stop telecentric projecting lens - Google Patents

Abstract

PURPOSE:To well correct various aberrations by constituting the above lens, successively from a chart side, of the 1st lens group having a positive refracting power, the 2nd lens group and the 3rd lens group having a negative refracting power, the 4th lens group of a positive meniscus lens, and the 5th lens group consisting of a positive lens. CONSTITUTION:The projector is constituted of an illuminating optical system 10, a projecting lens 21, a screen 22, a half mirror 30, a chart 41, and a stage 40. The projecting lens 21 is constituted, successively from the chart side, of the 1st lens group having the positive refracting power, the 2nd lens group and 3rd lens group having the negative refracting power, the 4th lens group which is the positive meniscus lens, and the 5th lens group consisting of the positive lens. The combination of the positive and negative two groups is required for the front group in order to eliminate a chromatic aberration and the positive lens group is used for the 1st lens group in order to eliminate a spherical aberration. The various aberrations are well corrected in this way and high imaging performance is obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a projection lens for a projector that illuminates a chart on a printed circuit board or the like through a lens, and projects an enlarged chart image onto a screen using the reflected light. In particular, it relates to a front aperture telecentric projection lens in which the aperture or entrance pupil is located closer to the screen than the lens system.

[Prior Art] In a projector that illuminates a chart and forms an image using reflected light, a bright image can be obtained most efficiently when an illumination method is adopted in which illumination light is incident on the chart from a direction perpendicular to the chart.

For this reason, in most projectors of this type, a half mirror is installed inside the projection lens system, and the illumination light from outside the projection optical path is reflected to the chart side by the mirror, and the illumination light is guided to the chart through the projection lens. It will be done. In this case, in order to improve the utilization efficiency of reflected light, the projection lens is required to be a telecentric system toward the chart side.

[Problem to be solved by the invention] In a telescend link projection lens, the sum of its total length and working distance (distance between the final surface of the lens on the chart side and the chart) is L, the focal length is f, and the chart seen from the light source side. When the magnification on the side is m and the distance between principal points is HH, the following relationship generally holds true.

L=(2-m)-f+HH However, in the above-mentioned projector, the distance between the mirror and the chart is fixed and it is necessary to ensure a constant working distance, so it is necessary to If lenses are to be exchanged, it may be necessary to keep the overall length of the lenses short in order to provide interchangeability with lenses of higher magnification. JP-A-63-1561 discloses a telecentric lens with a short L, but this lens has a problem of poor workability on a chart surface due to its short working distance.

Furthermore, the following conditions are required for the projection lens of this type of projector.

First, the image on the screen is uniformly bright.

In other words, the open F number is bright and the aperture efficiency is 100.
% is required.

Second, the imaging performance on the screen is high. That is, it is assumed that spherical aberration, coma aberration, astigmatism, axial and lateral chromatic aberration, etc. are well corrected.

Thirdly, it is required that the image on the screen has little distortion, that is, that the distortion aberration is small.

[Purpose] This invention was made in view of the above problems,
Provided is a telecentric projection lens that has a magnification of about 10 times, has various aberrations well corrected and has high imaging performance, has a relatively short overall length relative to the focal length, and has a relatively long working distance. The purpose is to

[Means for solving the problem] In order to make the lens system telecentric toward the chart side, it is necessary to divide the lens system into two main groups, converging the luminous flux in the front group, and ensuring telecentricity in the rear group. A suitable configuration is required.

Further, in order to eliminate chromatic aberration, the front group is required to be a combination of two positive and negative lenses, and in order to eliminate spherical aberration, the first lens group is required to be a positive lens group.

Furthermore, since positive distortion is produced by converging the light beam in the 1.2 lens group, a diverging system is required as the third lens group to correct this.

A convergence system is placed closest to the chart to converge the light beam diverged by the third lens group, but if the refraction is large, the imaging performance will deteriorate, so It is desirable to have a two-group configuration. Since positive distortion also occurs in these fourth and fifth lens groups, the third lens group is designed to be able to correct distortion including this aberration. It is necessary to generate negative distortion.

In accordance with these conditions, the front aperture telecentric lens according to claim 1 is provided with one lens in order from the side where the illumination light is reflected by the mirror and enters, and the reflected light from the illuminated chart is emitted toward the screen. A first lens group that has a positive refractive power as a whole by a positive lens or a combination of positive and negative lenses, a second lens group that has a negative refractive power with its concave surface facing the chart side, and a negative lens group with its concave surface facing the screen side. A third lens group having a refractive power of Claim 2 is characterized in that the refractive power φ of the entire system, the first lens group and the second lens group are
It is characterized in that the ratio of the combined refractive power of the lens group to φlX-11 satisfies 0.4×φ 1-sr/φ <1.3...■.

Equation (2) is a condition for making the total length shorter than the focal length and also making the working distance longer. In a projection lens having a five-group configuration as described above, the total length and working distance are determined by the combined refractive power of the first lens group and the second lens group, and the larger the combined refractive power, the shorter both of them become.

Equation (2) is a condition for achieving a balance between the total length and working distance by appropriately providing the combined refractive power of the first lens group and the second lens group. Below the lower limit of this formula, the metal length becomes too long, and above the upper limit, the working distance becomes too short.

Claim 3 is based on the refractive power φ of the entire system and the refractive power φ of the first lens group.
□, the refractive index nxφ of the positive lens of the first lens group is characterized by satisfying the following conditions: 0.9(φ, /φ<1.8...■ 1.55<1....■ .

■Formula
Among the lens groups and the second lens group, the first lens group has a positive refractive power.
By appropriately providing the refractive power of the lens group, the overall length can be kept short and spherical aberration can be favorably corrected. If the lower limit of this formula is not reached, the combined refractive power of the first lens group and the second lens group becomes too small, making it difficult to keep the total length short. Conversely, if the upper limit is exceeded, the negative refractive power of the second lens group increases, causing spherical aberration,
Coma aberration etc. become overcorrected.

Equation (2) is based on formula (2). Among the first lens groups given appropriate refractive power by Equation (2), by increasing the refractive index of the positive lens, the Petzval sum of the first lens group with large refractive power is kept small, and the field curvature is This is a condition for suppressing If the lower limit of this equation is exceeded, the Petzval sum of the first lens group becomes excessive, resulting in an excessive curvature of field.

Claim 4 is the refractive power φ of the entire system, and the refractive power φ of the third lens group.
III, refractive power φml of the first surface of the third lens group, 31st/
Assuming the refractive power φ, 2 of the second surface of the lens group, -3.5<φII
I, /φ<-2,0...■-3.5<φIII1
/φ〈-2,0...■-0,9＜φ, 2/φ〈0.7
...It is characterized by satisfying the condition [6].

Equation (2) is a condition for appropriately providing the refractive power of the third lens group having a large negative refractive power, so that the Petzval sum generated in all the lens groups approaches O, and curvature of field is suppressed. If the lower limit of the formula (2) is not reached, the curvature of field will be overcorrected, and the radius of curvature of each surface of the third lens group will be too small, resulting in significant occurrence of spherical aberration, coma, etc. Also,
If the upper limit is exceeded, it becomes difficult to achieve a positive Petzval sum, and field curvature cannot be corrected.

Equation (2) is a condition for properly correcting spherical aberration, comatic aberration, etc. by appropriately providing the refractive power of the first surface of the third lens group. When configuring a telecentric projection lens with a five-group configuration, spherical aberration and comatic aberration occur significantly on the first lens group, first on the first surface of the third lens group, so in order to correct this, the first surface of the third lens group It is necessary to give it strong negative refractive power. (2) If the lower limit of the formula is exceeded, spherical aberration and coma aberration will be overcorrected, and if the upper limit is exceeded, the correction will be insufficient.

Equation 0 is a condition for appropriately correcting distortion by appropriately providing the refractive power of the second surface of the third lens group. When constructing a front aperture telecentric projection lens with a five-group configuration, the first lens group converges the light beam, and the fourth and fifth lens groups bring the off-axis principal ray closer to the optical axis to maintain telecentricity. Distortion aberration occurs. In order to correct this, it is necessary to generate negative distortion at the second surface of the third lens group. When the lower limit of Equation 0 is exceeded, the distortion becomes over-corrected, and when the upper limit is exceeded, the distortion becomes under-corrected.

A fifth aspect of the present invention is characterized in that the following condition is satisfied, where the Abbe number of the fourth lens group is Vl and the Abe number of the fifth lens group is νV.

Equation (2) is a condition for suppressing the occurrence of chromatic aberration of magnification by appropriately giving the Abbe numbers of the fourth and fifth lens groups. As mentioned above, since the fourth and fifth lens groups have a small number of lenses and have the effect of bringing the off-axis chief ray closer to the optical axis, it is difficult to correct lateral chromatic aberration in the fourth and fifth lens groups. . However, the fourth lens group, the fifth
By giving a large Abbe number to the lens group, it is possible to suppress the occurrence of chromatic aberration of magnification. (2) When the lower limit of the formula is not reached, lateral chromatic aberration becomes noticeable.

[Example] The present invention will be described in detail below.

First, the overall configuration of a projection apparatus to which a projection lens is attached will be explained based on FIG.

As schematically shown in FIG. 1, this reflective illumination type projection apparatus includes an illumination optical system 10 having a light source 11 and a condenser lens 12, and a projection optical system having a projection lens 21, a screen 22, and a relay mirror 23, 24. Series 20 and
It consists of a half mirror provided at the intersection of both optical systems, and a stage 40 on which a chart 41 such as a printed circuit board is placed.

The projection lens 21 of the projection optical system 20 is a half mirror 30
The optical axis g2 of the projection optical system 20 indicated by the dashed line is located closer to the stage 40 than the stage 40.
, and also perpendicular to the optical axis g1 of the illumination optical system indicated by the two-dot chain line.

According to the configuration described above, the light flux emitted from the illumination optical system 10 is reflected by the half mirror 30 toward the chart 41 side, and the reflected light from the chart 41 forms an image of the chart 41 on the screen 22 via the projection lens 21. Form.

Nine specific design examples of the projection lens 21 will be shown below.

FIG. 2 is a sectional view of the lens according to the first example.

The specific numerical values of this lens are as shown in Table 1 on page 14.0 The symbols in the table are FNO, where F is the F number, f is the focal length at the d-line, H is the magnification, and ω is the half angle of view. ,
dφ is the distance from the aperture to the first surface, rl is the radius of curvature of the first surface from the illumination light incident side, and di is the distance between the first surface and the i+th surface.
The lens thickness or air gap between the first surface and the i+1th surface, ni is the refractive index at the d-line of the lens between the first surface and the i+1th surface, v
L is its Atsbe number.

Furthermore, the aberrations due to the above configuration are as shown in FIG.

Hereinafter, in the same manner, FIGS. 4, 5, and 2 are for the second embodiment, FIGS. 6, 7, and 3 are for the third embodiment, and FIGS. 8 and 9 are for the third embodiment.
Figures and Table 4 show the fourth embodiment, Figs. 10 and 11, Table 5 shows the fifth embodiment, Figs. Figure 15 and Table 7 show the seventh embodiment and the 16th example.
Figures 17 and 8 are examples of the 8th example, Figures 18 and 19.
However, Table 9 shows the lens cross section, aberration, and numerical configuration of the ninth embodiment.

The values of formulas (1) to (2) in each example are as shown in Table 10.

Table 1 FMO, = 1:4. Of=119.17ω=16.8°Table 2 FNO,=1:4. Of=1.19.36ω=16.8
″' Table 3 FNO,=174.Of=119.41ω=16.8” Table 4 FNO,=1:4. Of=119.27ω=16.8” FNO,=1:4.0 Table 7 f=118.03 ω=17.1” FNO,=1:4.0 Table 8 f=119.02 ω= 12.2 @ Table 5 FNO, = 1:4. Of=117.03ω=17.2' Table 6 FNO,=1:4. Of=117.15ω=17.1" FNO,=1:4.0 Table 9 f=119.08 ω=12.2 9,11,1
Figures 3, 15, 17, and 19 are aberration diagrams corresponding to each example.

[Effect] As explained above, according to the present invention, the magnification is about 10 times, various aberrations are well corrected, and high imaging performance is achieved, and the total length is relatively small compared to the focal length. It is possible to provide a telecentric projection lens that is short and has a relatively long working distance.

Also, by satisfying each condition, F number 1=4.
0, and the aperture efficiency is 100 up to an angle of view of 241 to 30”.
%, various aberrations are well corrected, it has high imaging performance, the total length L is 1.6f to 1.9f, which is relatively short compared to the focal length, and the working distance is 0.
．． 6f~1. Of, a relatively long telecentric projection lens can be provided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a projector to which a front aperture telecentric projection lens according to the present invention is applied. Figures 2 to 19 show embodiments of the front aperture telecentric projection lens of the present invention, and Figures 2.4, 6.
, 8, 10, 12, 14, 16.18 are the 9th actual figures from the first embodiment.

Claims (1)

[Claims] (1) One positive lens or a positive and negative lens laminated in order from the side where the illumination light is reflected by the mirror and enters, and the reflected light from the illuminated chart is emitted toward the screen. a first lens group having a positive refractive power as a whole; a second lens group having a negative refractive power with a concave surface facing the chart side; and a second lens group having a negative refractive power with a concave surface facing the screen side. 3 lens groups, a 4th lens group which is a positive meniscus lens with a convex surface facing the chart side, and a 5th lens group consisting of one or two positive lenses. Aperture telecentric projection lens. (2) The ratio of the refractive power φ of the entire system to the combined refractive power φ_(_ I _−_II_) of the first lens group and the second lens group is 0.4<φ_(_ I _−_II_ )/φ<1.3
The front aperture telecentric projection lens according to claim 1, wherein [1] is satisfied. (3) Refractive power φ of the entire system, refractive power φ_ of the first lens group
I, refractive index of the positive lens of the first lens group n_ I _+
The pre-diaphragm telecentric according to claim 1, characterized in that it satisfies the following conditions: 0.9<φ_ I /φ<1.8...[2] 1.55<n_ I __+...[3] projection lens. (4) Refractive power φ of the entire system, refractive power φ_ of the third lens group
III, the refractive power φ_III_1 of the first surface of the third lens group, and the refractive power φ_III_2 of the second surface of the third lens group, -
3.5<φ_III/φ<-2.0...[4]-3.5
<φ_III_1/φ<-2.0...[5]-0.9<
The front aperture telecentric projection lens according to claim 1, wherein the front aperture telecentric projection lens satisfies the following condition: φ_III_2/φ<0.7...[6]. (5) The Abbe number of the fourth lens group is ν_IV, and the Abbe number of the fifth lens group is ν_IV.
The front aperture telecentric projection lens according to claim 1, characterized in that, where the Abbe number of the lens group is ν_V, the following condition is satisfied: 45<(ν_IV+ν_V)/2...[7].