Projection lens system

Abstract

A projection lens system which produces a smaller amount of residual chromatic aberrations and which will exhibit satisfactory performance even if it is used as a long-focus lens. The projection lens system is composed of a front group and a rear group. The front group includes, in order from the object side, a positive first lens element, a positive second lens element and a negative third lens element. The lens system satisfies the following conditions:-0.0015<(.theta.2-.theta.3)/(.nu.2-.nu.3)<0where .theta.2 and .nu.2 denote the dispersion index of the second lens element and .theta.3 and .nu.3 denote the dispersion index of the third lens element, with .theta. and .nu. being defined by:.theta.=(ng-nF)/(nF-nC).nu.=(nd-1)/(nF-nC)where ng, nF, nC and nd denote the refractive indices of a lens element at the g, F, C and d lines, respectively.

Description

BACKGROUND OF THE INVENTION

This application is based on and claims priorities from Japanese Patent Applications No. Hei-3-347594 and No. 3-347595 both filed Oct. 29, 1991.

The present invention relates to a projection lens system that is principally intended to be used in platemaking to project and duplicate patterns.

A known platemaking projection lens system of the type contemplated by the present invention is described in Japanese Patent Publication No. Sho 56-53728. The projection lens system disclosed in the publication exhibits satisfactory imaging performance at life size and at magnifications in its neighborhood and features a compact lens geometry.

However, the prior art projection lens system described above has the problem that chromatic aberrations are not completely corrected and that if it is used as a long-focus lens, a drop in contrast occurs to make it impossible to insure satisfactory performance.

The present invention has been accomplished in the light of these problems of the prior art and has as an object providing a projection lens system that is designed to produce a smaller amount of residual chromatic aberrations and which, hence, will exhibit satisfactory performance even if it is used as a long-focus lens.

SUMMARY OF THE INVENTION

The above-stated and other objects of the present invention can be attained by a projection lens system that is composed of a front group and a rear group, the front group comprising, in order from the object side, a positive first lens element, a positive second lens element and a negative third lens element, the rear group comprising a negative fourth lens element, a positive fifth lens element and a positive sixth lens element, the lens system satisfying the following conditions:

-0.0015&lt;(.theta.2-.theta.3)/(.nu.2-.nu.3)&lt;0 (1) -0.0015&lt;(.theta.5-.theta.4)/(.nu.5-.nu.4)&lt;0 (1') where .theta.2 and .nu.2 denote the dispersion index of the second lens element, .theta.3 and .nu.3 denote the dispersion index of the third lens element, .theta.4 and .nu.4 denote the dispersion index of the fourth lens element and .theta.5 and .nu.5 denote the dispersion index of the fifth lens element and, with .theta. and .nu. being defined by: .theta.=(ng-nF)/(nF-nC) .nu.=(nd-1)/(nF-nC) where ng, nF, nC and nd denote the refractive indices of a lens element at the g, F, C and d lines, respectively.

According to another aspect of the invention, there is provided a projection lens system that is composed of a front group and a rear group, the front group comprising, in order from the object side, a positive first lens element, a negative second lens element and a positive third lens element, the rear group comprising a positive fourth lens element, a negative fifth lens element and a positive sixth lens element, the lens system satisfying the following conditions:

-0.0012&lt;(.theta.1-.theta.2)/(.nu.1-.nu.2)&lt;0 (1A) -0.0012&lt;(.theta.6-.theta.5)/(.nu.6-.nu.5)&lt;0 (1A') where .theta.1 and .nu.1 denote the dispersion index of the first lens element, .theta.2 and .nu.2 denote the dispersion index of the second lens element, .theta.5 and .nu.5 denote the dispersion index of the fifth lens element and .theta.6 and .nu.6 denote the dispersion index of the sixth lens element, with .theta. and .theta. and .nu. being defined by: .theta.=(ng-nF)/(nF-nC) .nu.=(nd-1)/(nF-nC). where ng, nF, nC and nd denote the refractive indices of a lens element at the g, F, C and d lines, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a simplified cross-sectional view showing the projection lens system of Example 1;

FIG. 2 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 1;

FIG. 3 is a simplified cross-sectional view showing the projection lens system of Example 2;

FIG. 4 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 2;

FIG. 5 is simplified cross-sectional view showing the projection lens system of Example 3;

FIG. 6 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 3;

FIG. 7 is a simplified cross-sectional view showing the projection lens system of Example 4;

FIG. 8 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 4;

FIG. 9 is a simplified cross-sectional view showing the projection lens system of Example 5;

FIG. 10 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 5;

FIG. 11 is a simplified cross-sectional view showing the projection lens system of Example 6;

FIG. 12 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 6;

FIG. 13 is a simplified cross-sectional view showing the projection lens system of Example 7;

FIG. 14 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 7;

FIG. 15 is a simplified cross-sectional view showing the projection lens system of Example 8;

FIG. 16 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 8;

FIG. 17 is a simplified cross-sectional view showing the projection lens system of Example 9;

FIG. 18 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 9;

FIG. 19 is a simplified cross-sectional view showing the projection lens system of Example 10;

FIG. 20 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 10;

FIG. 21 is a simplified cross-sectional view showing the projection lens system of Example 11; and

FIG. 22 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of the projection lens system of the present invention are described below.

As typically shown in FIG. 1, each of the lens systems according to the examples is composed of 6 elements as divided between a front group and a rear group, the front group comprising, in order from the object side, a positive first lens element, a positive second lens element and a negative third lens element, the rear group comprising a negative fourth lens element, a positive fifth lens element and a positive sixth lens element, and each lens system satisfies the conditions (1) and (1') set forth above. If this condition is satisfied, residual aberration can be suppressed to a sufficiently low level to produce a sharp image.

In order to insure flatness for the image plane, the projection lens system of the present invention desirably satisfies the following conditions:

0.25&lt;f2/f&lt;0.40 (2) 0.25&lt;f5/f&lt;0.40 (2') -0.30&lt;f3/f&lt;-0.20 (3) -0.30&lt;f4/f&lt;-0.20 (3') 0.03&lt;(nF1+nF2)/2-nF3 (4) 0.03&lt;(nF6+nF5)/2-nF4 (4') 0.15&lt;L/f&lt;0.25 (5) where f denotes the focal length of the overall system, fi the focal length of the ith lens element, nFi the refractive index of the ith lens element at the F-line, and L the overall lens length.

Conditions (2), (2'), (3) and (3') specify the distribution of power between the second and third lens elements and fourth and fifth lens elements, respectively. If the upper limit of either condition is exceeded, the spherical aberration and curvature of the field that develop will be overcorrected. If the lower limit of neither condition is reached, the two kinds of aberration will be undercorrected.

Condition (4) and (4') specify the Petzval sum. If these conditions are not met, the Petzval sum increases to cause greater curvature of the field and astigmatism.

Condition (5) specifies the overall lens length. If the upper limit of this condition is exceeded, the overall lens length becomes excessive. If the lower limit of this condition is not reached, the field curvature will increase.

If conditions (2) to (5) and (2') to (4') are satisfied, the flatness of the image plane is insured and within a half-view angle range of 12.degree., a uniform and high resolution can be attained to produce an image having no unevenness in density.

Further, in order to suppress spherical aberration and field curvature, the projection lens system of the present invention desirably satisfies the following conditions:

3.5&lt;f.multidot.{(nF3-1)/r6}&lt;5.5 (6) 3.5&lt;f.multidot.{(nF4-1)/r7}&lt;5.5 (6') 5.0&lt;f.multidot.{(nF1-1)/r1+(nF2-1)/r3}&lt;10.0 (7) 5.0&lt;f.multidot.{(nF6-1)/r12+(nF5-1)/r10 }&lt;10.0 (7') 0.07&lt;d6/f&lt;0.15 (8) where ri denotes the radius of curvature of the ith surface as counted from the object side, and d6 the space between the front and rear groups.

Conditions (6), (6'), (7) and (7') specify the balance between refractive index and curvature radius for various lens elements. If the upper limit of conditions (6) and (6') is exceeded, the spherical aberration and curvature of the field that develop will be overcorrected. If the lower limit of these conditions is not reached, those kinds of aberration will be undercorrected. If the upper limit of conditions (7) and (7') is exceeded, the spherical aberration and curvature of the field that develop will be undercorrected. If the lower limit of these conditions is not reached, those kinds of aberration will be overcorrected.

Condition (8) specifies the space between the front and rear groups. If the upper limit of this condition is exceeded, not only is curvature of the field undercorrected but also the overall lens length will increase. If the lower limit of condition (8) is not reached, curvature of the field will be overcorrected.

As typically shown in FIG. 15, according to another aspect of the invention, each of the lens systems according to the examples is composed of 6 elements as divided between a front group and a rear group, the front group comprising, in order from the object side, a positive first lens element a negative second lens element and a positive third lens element, the rear group comprising a positive fourth lens element, a negative fifth lens element and a positive sixth lens element, the rear group being located completely symmetrical to the front group with respect to a stop diaphragm, and each lens system satisfies the conditions (1A) and (1A') set forth above. If this condition is satisfied, residual aberration can be suppressed to a sufficiently low level to produce a sharp image.

In order to insure flatness for the image plane, the projection lens system of the present invention desirably satisfies the following conditions:

0.25&lt;f1/f&lt;0.40 (2A) 0.25&lt;f6/f&lt;0.40 (2A') -0.40&lt;f2/f&lt;-0.30 (3A) -0.40&lt;f5/f&lt;-0.30 (3A') 0.04&lt;(nF1+nF3)/2-nF2 (4A) 0.04&lt;(nF6+nF4)/2-nF5 (4A') 0.15&lt;L/f&lt;0.25 (5)

Conditions (2A), (2A'), (3A) and (3A') specify the distribution of power between the second and third lens elements and fourth and fifth lens elements, respectively. If the upper limit of either condition is exceeded, the spherical aberration and curvature of the field that develop will be overcorrected. If the lower limit of neither condition is reached, the two kinds of aberration will be undercorrected.

Condition (4A) and (4A') specify the Petzval sum. If these conditions are not met, the Petzval sum increases to cause greater curvature of the field and astigmatism.

If conditions (2A) to (5) and (2A') to (4A') are satisfied, the flatness of the image plane is insured and within a half-view angle range of 12.degree., a uniform and high resolution can be attained to produce an image having no uneveness in density.

Further, in order to suppress spherical aberration and field curvature, the projection lens system of the present invention desirably satisfies the following conditions:

3.5&lt;f.multidot.{(nF2-1)/r4}&lt;5.5 (6A) 3.5&lt;.vertline.f.multidot.{(nF5-1)/r9}.vertline.&lt;5.5 (6A') 7.0&lt;f.multidot.{(nF1-1)/r1+(nF3-1)/r5}&lt;10.0 (7A) 7.0&lt;.vertline.f.multidot.{(nF6-1)/r12+(nF4-1)/r8}.vertline.&lt;10.0(7A') 0.05&lt;d6/f&lt;0.09 (8A) where ri denotes the radius of curvature of the ith surface as counted from the object side, and d6 the space between the front and rear groups.

Conditions (6A), (6A'), (7A) and (7A') specify the balance between refractive index and curvature radius for various lens elements. If the upper limit of conditions (6A) and (6A') is exceeded, the spherical aberration and curvature of the field that develop will be overcorrected. If the lower limit of these conditions is not reached, those kinds of aberration will be undercorrected. If the upper limit of conditions (7A) and (7A') is exceeded, the spherical aberration and curvature of the field that develop will be undercorrected. If the lower limit of these conditions is not reached, those kinds of aberration will be overcorrected.

Condition (8A) specifies the space between the front and rear groups. If the upper limit of this condition is exceeded, not only is curvature of the field undercorrected but also the overall lens length will increase. If the lower limit of condition (8A) is not reached, curvature of the field will be overcorrected.

EXAMPLE 1

FIG. 1 is a simplified cross-sectional view showing a projection lens system according to Example 1 of the present invention. Specific data for this example are shown in Table 1, in which f denotes the focal length at the F line (486 nm), m the magnification, fB the back focus, FNo. the F number, r the radius of curvature, d the lens thickness or airspace, nF, ng, nC and nd the refractive indices at the F, g, C and d lines, respectively, and .nu. the Abbe number.

FIG. 2 is a set of graphs plotting the curves of various aberrations as obtained with the projection lens system of Example 1, i.e., spherical aberration SA, sine condition SC, chromatic aberrations as represented by spherical aberrations at the F, g, e, h and d lines, astigmatism (S, sagittal; M, meridional), and distortion.

TABLE 1______________________________________f = 599.00 m = -1.00 fB = 1134.91 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 126.935 6.50 1.81994 40.9 1.83115 1.80025 1.806102 168.626 0.503 100.408 8.00 1.62757 60.3 1.63316 1.61728 1.620414 587.154 1.875 496.672 5.00 1.62310 44.2 1.63089 1.60924 1.613406 80.121 74.277 -80.121 5.00 1.62310 44.2 1.63089 1.60924 1.613408 -496.672 1.879 -587.154 8.00 1.62757 60.3 1.63316 1.61728 1.6204110 -100.408 0.5011 -168.626 6.50 1.81994 40.9 1.83115 1.80025 1.8061012 -126.935______________________________________

EXAMPLE 2

FIG. 3 is a simplified cross-sectional view showing a projection lens system according to Example 2 of the present invention. Specific data for this example are shown in Table 2. FIG. 4 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 2.

TABLE 2______________________________________f = 599.00 m = -1.00 fB = 1135.22 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 127.368 6.50 1.84852 42.7 1.85953 1.82898 1.834812 178.260 0.503 112.883 8.00 1.62757 60.3 1.63316 1.61728 1.620414 861.149 1.985 765.130 5.00 1.62310 44.2 1.63089 1.60924 1.613406 85.937 74.037 -85.937 5.00 1.62310 44.2 1.63089 1.60924 1.613408 -765.130 1.989 -861.149 8.00 1.62757 60.3 1.63316 1.61728 1.6204110 -112.883 0.5011 -178.260 6.50 1.84852 42.7 1.85953 1.82898 1.8348112 -127.368______________________________________

EXAMPLE 3

FIG. 5 is a simplified cross-sectional view showing a projection lens system according to Example 3 of the present invention. Specific data for this example are shown in Table 3. FIG. 6 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 3.

TABLE 3______________________________________f = 599.06 m = -1.00 fB = 1135.07 FNo. 1:11SurfaceNo. r d nF .nu. ng nC nd______________________________________1 153.183 6.50 1.81719 35.0 1.83061 1.79428 1.801002 197.561 0.503 88.274 8.00 1.62757 60.3 1.63316 1.61728 1.620414 567.520 1.895 490.298 5.00 1.62310 44.2 1.63089 1.60924 1.613406 75.615 74.227 -75.615 5.00 1.62310 44.2 1.63089 1.60924 1.613408 -490.298 1.899 -567.520 8.00 1.62757 60.3 1.63316 1.61728 1.6204110 -88.274 0.5011 -197.561 6.50 1.81719 35.0 1.83061 1.79428 1.8010012 -153.183______________________________________

EXAMPLE 4

FIG. 7 is a simplified cross-sectional view showing a projection lens system according to Example 4 of the present invention. Specific data for this example are shown in Table 4. FIG. 8 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 4.

TABLE 4______________________________________f = 599.00 m = -1.00 fB = 1134.85 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 121.726 6.50 1.81994 40.9 1.83115 1.80025 1.806102 168.872 0.503 107.003 8.00 1.62383 62.8 1.62917 1.61401 1.617004 620.006 1.895 529.711 5.00 1.62310 44.2 1.63089 1.60924 1.613406 81.771 74.237 -81.771 5.00 1.62310 44.2 1.63089 1.60924 1.613408 -529.711 1.899 -620.006 8.00 1.62383 62.8 1.62917 1.61401 1.6170010 -107.003 0.5011 -168.872 6.50 1.81994 40.9 1.83115 1.80025 1.8061012 -121.726______________________________________

EXAMPLE 5

FIG. 9 is a simplified cross-sectional view showing a projection lens system according to Example 5 of the present invention. Specific data for this example are shown in Table 5. FIG. 10 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 5.

TABLE 5______________________________________f = 598.77 m = -1.00 fB = 1138.52 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 195.000 8.50 1.84982 37.2 1.86278 1.82738 1.834002 273.800 0.543 111.252 13.00 1.62757 60.3 1.63316 1.61728 1.620414 -4593.852 1.995 -13639.246 7.00 1.62310 44.2 1.63089 1.60924 1.613406 92.300 55.947 -92.300 7.00 1.62310 44.2 1.63089 1.60924 1.613408 13639.246 1.999 4593.852 13.00 1.62757 60.3 1.63316 1.61720 1.6204110 -111.252 0.5411 -273.800 8.50 1.84982 37.2 1.86278 1.82738 1.8340012 -195.000______________________________________

EXAMPLE 6

FIG. 11 is a simplified cross-sectional view showing a projection lens system according to Example 6 of the present invention. Specific data for this example are shown in Table 6. FIG. 12 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 6.

TABLE 6______________________________________f = 599.04 m = -1.00 fB = 1134.17 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 200.658 8.50 1.73689 37.9 1.74801 1.71783 1.723422 300.011 0.503 105.634 13.00 1.62757 60.3 1.63316 1.61728 1.620414 4512.049 2.925 2332.373 7.00 1.62310 44.2 1.63089 1.60924 1.613406 87.569 59.927 -87.569 7.00 1.62310 44.2 1.63089 1.60924 1.613408 -2332.373 2.929 -4512.049 13.00 1.62757 60.3 1.63316 1.61728 1.6204110 -105.634 0.5011 -300.011 8.50 1.73689 37.9 1.74801 1.71783 1.7234212 -200.658______________________________________

EXAMPLE 7

FIG. 13 is a simplified cross-sectional view showing a projection lens system according to Example 7 of the present invention. Specific data for this example are shown in Table 7. FIG. 14 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 7.

TABLE 7______________________________________f = 599.04 m = -1.00 fB = 1127.68 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 232.573 8.50 1.79831 36.1 1.81103 1.77665 1.783002 345.456 0.503 100.536 13.00 1.62757 60.3 1.63316 1.61728 1.620414 1872.935 2.025 1519.569 7.00 1.62310 44.2 1.63089 1.60924 1.613406 85.980 71.947 -85.980 7.00 1.62310 44.2 1.63089 1.60924 1.613408 -1519.569 2.029 -1872.935 13.00 1.62757 60.3 1.63316 1.61728 1.6204110 -100.536 0.5011 -345.456 8.50 1.79831 36.1 1.81103 1.77665 1.7830012 -232.573______________________________________

EXAMPLE 8

FIG. 15 is a simplified cross-sectional view showing a projection lens system according to Example 8 of the present invention. Specific data for this example are shown in Table 8. FIG. 15 also illustrates stop diaphragm 20 of the projection device. FIG. 16 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 8.

TABLE 8______________________________________f = 599.20 m = -1.00 fB = 1138.66 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 91.368 12.00 1.57464 71.3 1.57899 1.56666 1.569072 251.725 1.503 193.485 8.00 1.53933 48.9 1.54541 1.52845 1.531724 73.228 10.805 102.280 7.00 1.75566 44.8 1.76505 1.73905 1.744006 115.000 39.767 -115.000 7.00 1.75566 44.8 1.76505 1.73905 1.744008 -102.280 10.809 -73.228 8.00 1.53933 48.9 1.54541 1.52845 1.5317210 -193.485 1.5011 -251.725 12.00 1.57464 71.3 1.57899 1.56666 1.5690712 -91.368______________________________________

EXAMPLE 9

FIG. 17 is a simplified cross-sectional view showing a projection lens system according to Example 9 of the present invention. Specific data for this example are shown in Table 9. FIG. 18 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 9.

TABLE 9______________________________________f = 598.98 m = -1.00 fB = 1139.11 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 91.479 12.00 1.57464 71.3 1.57899 1.56666 1.569072 283.153 1.503 233.901 8.00 1.55654 45.8 1.56331 1.54457 1.548144 74.955 10.005 109.830 7.00 1.81719 35.0 1.83061 1.79428 1.801006 128.083 40.807 -128.083 7.00 1.81719 35.0 1.83061 1.79428 1.801008 -109.830 10.009 -74.955 8.00 1.55654 45.8 1.56331 1.54457 1.5481410 -233.901 1.5011 -283.153 12.00 1.57464 71.3 1.57899 1.56666 1.5690712 -91.479______________________________________

EXAMPLE 10

FIG. 19 is a simplified cross-sectional view showing a projection lens system according to Example 10 of the present invention. Specific data for this example are shown in Table 10. FIG. 20 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 10.

TABLE 10______________________________________f = 599.02 m = -1.00 fB = 1138.02 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 87.527 12.00 1.57464 71.3 1.57899 1.56666 1.569072 260.160 1.503 189.174 8.00 1.57664 42.8 1.58421 1.56339 1.567324 69.686 8.905 92.649 7.00 1.73462 29.5 1.74915 1.71032 1.717366 106.428 43.007 -106.428 7.00 1.73462 29.5 1.74915 1.71032 1.717368 -92.649 8.909 -69.686 8.00 1.57664 42.8 1.58421 1.56339 1.5673210 -189.174 1.5011 -260.160 12.00 1.57464 71.3 1.57899 1.56666 1.5690712 -87.527______________________________________

EXAMPLE 11

FIG. 21 is a simplified cross-sectional view showing a projection lens system according to Example 11 of the present invention. Specific data for this example are shown in Table 11. FIG. 22 is a set of graphs plotting the aberration curves obtained with the projection lens system of Example 11.

TABLE 11______________________________________f = 599.05 m = -1.00 fB = 1137.60 FNo. 1:11Sur-faceNo. r d nF .nu. ng nC nd______________________________________1 85.883 12.00 1.57464 71.3 1.57899 1.56666 1.569072 241.460 1.503 177.182 8.00 1.55654 45.8 1.56331 1.54457 1.548144 68.116 10.605 91.548 7.00 1.65293 34.5 1.66383 1.63437 1.639806 104.494 39.807 -104.494 7.00 1.65293 34.5 1.66383 1.63437 1.639808 -91.548 10.609 -68.116 8.00 1.55654 45.8 1.56331 1.54457 1.5481410 -177.182 1.5011 -241.460 12.00 1.57464 71.3 1.57899 1.56666 1.5690712 -85.883______________________________________

Table 15 below shows how conditions (1) to (8) and (1A) to (8) discussed hereinabove are satisified in Examples 1 to 11.

__________________________________________________________________________Condition Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7__________________________________________________________________________(1) -0.00117 -0.00117 -0.00117 -0.00099 -0.00117 -0.00117 -0.00117(2) 0.32 0.34 0.28 0.34 0.29 0.29 0.28(3) -0.26 -0.26 -0.24 -0.26 -0.25 -0.24 -0.25(4) 0.10 0.10 0.10 0.10 0.12 0.06 0.09(5) 0.20 0.20 0.20 0.20 0.20 0.21 0.22(6) 4.65 4.36 4.95 4.55 4.05 4.27 4.33(7) 7.60 7.32 7.46 7.52 5.98 5.77 5.79(8) 0.12 0.12 0.12 0.12 0.09 0.10 0.12__________________________________________________________________________Condition Ex. 8 Ex. 9 Ex. 10 Ex. 11__________________________________________________________________________(1A) -0.00065 -0.00080 -0.00093 -0.00080(2A) 0.37 0.38 0.37 0.38(3A) -0.34 -0.34 -0.33 -0.34(4A) 0.13 0.14 0.08 0.06(5) 0.20 0.20 0.20 0.20(6A) 4.41 4.49 4.96 4.89(7A) 8.17 8.22 8.68 8.28(8A) 0.07 0.07 0.07 0.07__________________________________________________________________________

The conditions expressed by prime, for example (1'), (2') . . . (1A'), (2A') . . . have the same calculated value as listed above.

The projection lens systems of the examples have an F number as large as 1:11 and depth of focus can be sufficiently increased to prevent the drop of image resolution even if the ambient temperature or the thickness of the object to be projected varies. Therefore, when using those lens systems as projection lens in a platemaker, the need for readjustments due to changes in the ambient temperature and other parameters is eliminated to reduce the load on platemaking operators.

As described on the foregoing pages, the projection lens system of the present invention causes a smaller amount of residual chromatic aberrations and, hence, is capable of producing a contrasty image even if it is used as a long-focus lens. In addition, by satisfying specified conditions, the lens system is capable of producing a flat image plane and a uniform image without any uneveness in density.

Claims

1. A projection lens system comprising a front group and a rear group, said front group comprising, in order from an object side, a positive first lens element, a positive second lens element and a negative third lens element, said rear group comprising a negative fourth lens element, a positive fifth lens element and a positive sixth lens element, said lens system satisfying the following conditions:

-0.0015&lt;(.theta.2-.theta.3)/(.nu.2-.nu.3)&lt;0

-0.0015&lt;(.theta.5-.theta.4)/(.nu.5-.nu.4)&lt;0

where .theta.2 and .nu.2 denote the dispersion index of the second lens element, .theta.3 and .nu.3 denote the dispersion index of the third lens element, .theta.4 and .nu.4 denote the dispersion index of the fourth lens element and .theta.5 and .nu.5 denote the dispersion index of the fifth lens element and, with .theta. and .nu. being defined by:

.theta.=(ng-nF)/(nF-nC)

.nu.=(nd-1)/(nF-nC)

where ng, nF, nC and nd denote the refractive indices of a lens element at the g, F, C and d lines, respectively.

2. A projection lens system according to claim 1 which further satisfies the following conditions:

0.25&lt;f2/f&lt;0.40

0.25&lt;f5/f&lt;0.40

-0.30&lt;f3/f&lt;-0.20

-0.30&lt;f4/f&lt;-0.20

0.03&lt;(nF1+nF2)/2-nF3

0.03&lt;(nF6+nF5)/2-nF4

0.15&lt;L/f&lt;0.25

where f denotes the focal length of the overall system, fi the focal length of the ith lens element, nFi the refractive index of the ith lens element at the F-line, and L the overall lens length.

3. A projection lens system according to claim 2 further satisfies the following conditions:

3.5&lt;f.multidot.{(nF3-1)/r6}&lt;5.5

3.5&lt;f.multidot.{(nF4-1)/r7}&lt;5.5

5.0&lt;f.multidot.{(nF1-1)/r1+(nF2-1)/r3}&lt;10.0

5.0&lt;f.multidot.{(nF6-1)/r12+(nF5-1)/r10}&lt;10.0

0.07&lt;d6/f&lt;0.15

where ri denotes the radius of curvature of the ith surface as counted from the object side, and d6 a distance between the front and rear groups.

4. A projection lens system comprising a front group and a rear group, said front group comprising, in order from the object side, a positive first lens element, a negative second lens element and a positive third lens element, said rear group comprising a positive fourth lens element, a negative lens element and a positive sixth lens element, said lens system satisfying the following conditions:

-0.0012&lt;(.theta.1-.theta.2)/.nu.1-2.nu.2)&lt;0

-0.0012&lt;(.theta.6-.theta.5)/.nu.6-.nu.5)&lt;0

where .theta.1 and .nu.1 denote the dispersion index of the first lens element, .theta.2 and .nu.2 denote the dispersion index of the second lens element, .theta.5 and .nu.5 denote the dispersion index of the fifth lens element and .theta.6 and .nu.6 denote the dispersion index of the sixth lens element and, with .theta. and .nu. being defined by:

.theta.=(ng-nF)/(nF-nC)

.nu.=(nd-1)/(nF-nC)

where ng, nF, nC and nd denote the refractive indices of a lens element at the g, F, C and d lines respectively.

5. A projection lens system according to claim 4 which further satisfies the following conditions:

0.25&lt;f1/f&lt;0.40

0.25&lt;f6/f&lt;0.40

-0.40&lt;f2/f&lt;-0.30

-0.40&lt;f5/f&lt;-0.30

0.04&lt;(nF1+nF3)/2-nF2

0.04&lt;(nF6+nF4)/2-nF5

0.15&lt;L/f&lt;0.25

where f denotes the focal length of the overall system, fi the focal length of the ith lens element, nFi the refractive index of the ith lens element at the F-line, and L the overall lens length.

6. A projection lens system according to claim 5 further satisfies the following conditions:

3.5&lt;f.multidot.{(nF2-1)/r4}&lt;5.5

3.5&lt;.vertline.f.multidot.{(nF5-1)/r9}.vertline.&lt;5.5

7.0&lt;f.multidot.{(nF1-1)/r1+(nF3-1)/r5}&lt;10.0

7.0&lt;.vertline.f.multidot.{(nF6-1)/r12+(nF4-1)/r8}.vertline.&lt;10.0

0.05&lt;d6/f&lt;0.09

where ri denotes the radius of curvature of the ith surface as counted from the object side, and d6 a distance between the front and rear groups.