Telecentric projection lenses

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to telecentric projection lenses which are intended to use at a magnification of about 1/10 and which are precise in terms of their F number and have their aberrations well corrected.
2. Description of the Prior Art
In recent years there have been developed and used original scanning methods in which solid image pick-up elements are employed as scanning means for reading apparatus with the solid image pick-up elements are arranged in the image plane as scanning photo-receptor elements to scan the original.
To carry out the above known scanning methods, a projection lens must be used to transmit the original image to the solid image pick-up elements and further a color separation prism must be interposed between the projection lens and the focal plane containing the elements to transmit the color signals of the original to the solid image pick-up elements. If a common non-telecentric lens is used as the projection lens in this case, the off-axial rays are obliquely incident upon the color separation prism and shading is caused thereby. To overcome the problem of shading there is used a projection lens having a telecentric property. By using such lens, the principal rays of the incident light pass through the focal point on the side of object field and therefore the principal rays of the exit light including off-axial rays on the side of image field can run in parallel with the optical axis. This is one effective method already known for overcoming the problem of shading caused by the color separation prism.
However, projection lenses useful for carrying out the above scanning method have to satisfy many requirements at the same. In general, such a projection lens has to satisfy the following requirements:
(1) The F number of the lens should be relatively precise. To carry out a high speed scanning employing solid image pick-up elements it is preferable to increase, as much as possible, the quantity of exposure light to the elements per unit time. On the other hand, it is also preferable to use, as an original illumination lamp, a light source whose illumination is as low as possible. For this reason, the projection lens is required to have a relatively precise F number.
(2) For the purpose of reduction in size of the apparatus, namely reduction of the distance between the original surface and the focal plane, the lens should have a wide angle of field.
(3) The lens should have a high resolving power because the size of solid image pick-up element is very small which is in the order of 15.mu..
(4) The lens should be suitable for use with its apperture efficiency for off-axis being 100%. This is because the distribution of light intensity must be uniform over all of the solid image pick-up elements.
(5) The lens should be able to project the original surface uniformly. In other words, the distortion of the lens should be of low level.
(6) Since a color separation prism must be interposed between the lens and the solid image pick-up elements, the lens should have a long back focal length.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide telecentric projection lenses which satisfy the above requirements.
It s a more specific object of the present invention to provide such telecentric lenses which are precise in terms of F number and which have high resolving power, as well as contrast, as the result of well corrected spherical aberration, coma, curvature of field and distortion and which are suitable for use at aperture efficiency of 100% and at a magnification of about 1/10.
To attain the above objects according to the first embodiment of the present invention, there is provided a projection lens which has a pupil located at the focal point on the side of object field of the whole lens system and comprises a first lens or group composed of a positive single lens or lens elements, a second lens or group composed of a double concave single lens and a third lens group or composed of two positive lenses or lens elements arranged in this order as viewed from the object field side, wherein one of the two positive lenses in the third lens group has a cemented surface whose center of curvature lies on the side of object field, and which projection lens is so designed as to satisfy the following conditions:
(1) 1.69.ltoreq..vertline.f.sub.1 /f.sub.2 .vertline..ltoreq.2.55
(2) -0.33.ltoreq.f.sub.2 /f.ltoreq.-0.19
(3) 0.41.ltoreq.f.sub.3 /f.ltoreq.0.59
where, f.sub.1, f.sub.2 and f.sub.3 are focal lengths of the first, first lens and the second and third lens groups, respectively, and f is the focal length of the whole system.
The second embodiment of the invention is directed to a projection lens which has a pupil located at the focal point on the side of object field of the whole lens system and comprises a first lens composed of a positive single lens, a second lens group composed of a double concave singal lens and a third lens group composed of three or four lenses, arranged in this order as viewed from the object field side, wherein any one of the lenses in the third group has a cemented surface, and which projection lens is so designed as to satisfy the following conditions:
(1') 1.72.ltoreq..vertline.f.sub.1 /f.sub.2 .vertline..ltoreq.2.58
(2') -0.33.ltoreq.f.sub.2 /f.ltoreq.-0.19
(3') 0.41.ltoreq.f.sub.3 /f.ltoreq.0.59
wherein, f.sub.1, f.sub.2 and f.sub.3 are focal lengths of the first lens and the second and third lens groups, respectively, and f is the focal length of the whole system.
Other and further objects, features and advantages of the present invention will appear more fully from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1A is a cross-sectional view of the lens described in Example 1;
FIG. 1B shows aberrations thereof;
FIG. 1C shows transverse aberrations on Gaussian image plane thereof;
FIG. 2A is a cross-sectional view of Example 2 and FIG. 2B shows aberrations thereof;
FIG. 3A is a cross-sectional view of Example 3 and FIG. 3B shows aberrations thereof;
FIG. 4A is a cross-sectional view of Example 4 and FIG. 4B shows aberrations thereof;
FIG. 5A is a cross-sectional view of Example 5 and FIG. 5B shows aberrations thereof;
FIG. 6A is a cross-sectional view of Example 6 and FIG. 6B shows aberrations thereof;
FIG. 7A is a cross-sectional view of Example 7 and FIG. 7B shows aberrations thereof;
FIG. 8A is a cross-sectional view of Example 8 and FIG. 8B shows aberrations thereof;
FIG. 9A is a cross-sectional view of Example 9 and FIG. 9B shows aberrations thereof;
FIG. 10A is a cross-sectional view of Example 10 and FIG. 10B shows aberrations thereof;
FIG. 11A is a cross-sectional view of Example 11 and FIG. 11B shows aberrations thereof;
FIG. 12A is a cross-sectional view of Example 12 and FIG. 12B shows aberrations thereof;
FIG. 13A is a cross-sectional view of Example 13 and FIG. 13B shows aberrations thereof and FIG. 13C shows transverse aberrations on Gaussian image plane thereof;
FIG. 14A is a cross-sectional view of Example 14 and FIG. 14B shows aberrations thereof;
FIG. 15A is a cross-sectional view of Example 15 and FIG. 15B shows aberrations thereof;
FIG. 16A is a cross-sectional view of Example 16 and FIG. 16B shows aberrations thereof;
FIG. 17A is a cross-sectional view of Example 17 and FIG. 17B shows aberrations thereof;
FIG. 18A is a cross-sectional view of Example 18 and FIG. 18B shows aberrations thereof;
FIG. 19A is a cross-sectional view of Example 19 and FIG. 19B shows aberrations thereof;
FIG. 20A is a cross-sectional view of Example 20 and FIG. 20B shows aberrations thereof; and
FIG. 21A is a cross-sectional view of Example 21 and FIG. 21B shows aberrations thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS
Initially, there is described conditions (1) to (3) relating to the projection lens according to the first embodiment of the present invention.
By satisfying the condition (1) the spherical aberration can be well corrected while keeping the balance of the refractive powers of the first and second lens groups. The lens of the present invention is used in a telecentric system and the distance between the principal points of the second and third groups is larger than the distance between those of the first and second groups. Therefore, positions at which the paraxial rays pass through the first lens group are greatly spaced apart from the optical axis, which produces a large quantity of spherical aberration.
When .vertline.f.sub.1 /f.sub.2 .vertline. is below the lower limit 1.69, then the refractive power of the first group becomes high and the paraxial rays passing through the surface are intensely refracted in the direction toward the optical axis. As the result of it, a large quantity of negative spherical aberration is produced. On the contrary, when .vertline.f.sub.1 /f.sub.2 .vertline. exceeds the upper limit of 2.55, the refractive power of the second lens group becomes high and the second group produces such a level of positive spherical aberration which overly compensates the negative spherical aberration produced in the first group.
The condition (2) must be satisfied to correct the curvature of field of the lens system.
When f.sub.2 /f is larger than the upper limit, -0.19, then Petzval sum is overcompensated and curvature of field is overly currected. To correct it, the refractive power of the second lens group must be increased in absolute value. However, as described hereinafter in connection with the condition (3), if the absolute value of the refractive power of the second group is so increased, then there is produced in the second group a large quantity of distortion which is difficult to correct.
On the contrary, when f.sub.2 /f is less than the power limit of -0.33, it becomes difficult to correct Petzval sum of the whole system and thereby undercorrection of the curvature of field is caused.
Condition (3) is necessary for correction of the curvature of field and distortion. Since the lens is used in a telecentric system, the positions at which principal rays pass through the third lens group are greatly spaced apart from the optical axis. When f.sub.3 /f is smaller than the lower limit of 0.4, the refractive power of the third lens group becomes high and principal rays passing through the third group are intensely refracted in the direction toward the optical axis. Thereby, a large quantity of distortion is produced. On the contrary, if f.sub.3 /f is larger than the upper limit of 0.59, then curvature of field becomes worse to the extent that it may be hardly corrected.
Now, the shape of lens according to the first embodiment of the invention is described in detail.
As described above, the lens system of the present invention must be precise in terms of F number. To attain the object, it is most advantageous to effectively correct the spherical aberration of the first lens group which is the group at which paraxial rays are most apart from the optical axis. To this end, the surface of the first lens group on the side of object field is so shaped as to be convexed toward the object field side.
In the lens system of the present invention, the lens group which corrects Petzval sum is only the second group. Therefore, the condition of power to the second group becomes severe. For this reason, the negative lens of the second group is shaped as a double concave lens to reduce aberrations in the second group.
Since a color separation prism is to be interposed between the image plane and the nearest lens surface to the image field, the lens system is required to have a long back focal length. To this end, the third lens group is composed of two positive lenses and is formed in such manner that the air lens formed by the two positive lenses has a shape of double concave lens.
The following examples, Examples 1 to 12 together with FIGS. 1 to 12 illustrate the design of above projection lenses according to the first aspect of the invention and demonstrate the effect of the invention.
In the examples,
Ri is the radius of curvature of the i-th surface of the lens system;
Di is the thickness of air spacing on axis between the i-th surface and the i+1-th surface;
.omega. is angle of field;
.beta. is magnification of focus;
Ni is the refractive index of the i-th lens to D ray;
.nu.i is Abbe's number of the i-th lens;
fi is the focal length of the i-th group; and
D0 is the air spacing on axis from the pupil SL to the R1 surface.
For all of Examples 1 to 12 the F number is 1:5.
EXAMPLE 1
______________________________________f = 1 angle of field = 25.2.degree. .beta. = 0.12343______________________________________R1 = 0.3986 D1 = 0.134 N1 = 1.72 .nu.1 = 50.2R2 = -5.6178 D2 = 0.1653R3 = -0.3958 D3 = 0.0701 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4543 D4 = 0.1345R5 = -2.8306 D5 = 0.1384 N3 = 1.697 .nu.3 = 48.5R6 = -0.3292 D6 = 0.1588 N4 = 1.72825 .nu.4 = 28.5R7 = -0.6113 D7 = 0.0181R8 = 0.8726 D8 = 0.1635 N5 = 1.7725 .nu.5 = 49.6R9 = -3.6073.vertline.f.sub.1 /f.sub.2 .vertline. = 2.0161 f.sub.2 /f = -0.2543 f.sub.3 /f = 0.4971 DO = 0.0213______________________________________
EXAMPLE 2
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4403 D1 = 0.1682 N1 = 1.72 .nu.1 = 50.2R2 = -1.8559 D2 = 0.13R3 = -0.4636 D3 = 0.0329 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5059 D4 = 0.1492R5 = -1.6321 D5 = 0.2362 N3 = 1.697 .nu.3 = 48.5R6 = -0.4315 D6 = 0.0414 N4 = 1.72825 .nu.4 = 28.5R7 = -0.5964 D7 = 0.0528R8 = 1.0092 D8 = 0.0925 N5 = 1.7725 .nu.5 = 49.6R9 = -5.1222.vertline.f.sub.1 /f.sub.2 .vertline. = 1.723 f.sub.2 /f = -0.296 f.sub.3 /f = 0.5764 DO = 0.1764______________________________________
EXAMPLE 3
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3446 D1 = 0.1461 N1 = 1.72 .nu.1 = 50.2R2 = 4.6621 D2 = 0.1688R3 = -0.3246 D3 = 0.0205 N2 = 1.80518 .nu.2 = 25.4R4 = 0.3854 D4 = 0.0696R5 = 1.3077 D5 = 0.2144 N3 = 1.674 .nu.3 = 48.5R6 = -0.3306 D6 = 0.2108 N4 = 1.72825 .nu.4 = 28.5R7 = 0.5451 D7 = 0.0697R8 = 0.9435 D8 = 0.1443 N5 = 1.7725 .nu.5 = 49.6R9 = 28.7464.vertline.f.sub.1 /f.sub.2 .vertline. = 2.3587 f.sub.2 /f = -0.216 f.sub.3 /f = 0.4485 DO = 0.0219______________________________________
EXAMPLE 4
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4822 D1 = 0.1456 N1 = 1.72 .nu.1 = 50.2R2 = -35.0608 D2 = 0.2244R3 = -0.4207 D3 = 0.0325 N2 = 1.80518 .nu.2 = 25.4R4 = 0.6509 D4 = 0.0834R5 = -1.3008 D5 = 0.1128 N3 = 1.697 .nu.3 = 48.5R6 = -0.2572 D6 = 0.1755 N4 = 1.72825 .nu.4 = 28.5R7 = -0.4887 D7 = 0.0625R8 = 0.8924 D8 = 0.1618 N5 = 1.7725 .nu.5 = 49.6R9 = -5.1437.vertline.f.sub.1 /f.sub.2 .vertline. = 2.1135 f.sub.2 /f = -0.3131 f.sub.3 /f = 0.4966 DO =0 0.0399______________________________________
EXAMPLE 5
______________________________________f = 1 angle of field = 25.2.degree. .beta.= -0.12343______________________________________R1 = 0.3052 D1 = 0.1736 N1 = 1.72 .nu.1 = 50.2R2 = -1.5021 D2 = 0.089R3 = -0.3001 D3 = 0.0837 N2 = 1.80518 .nu.2 = 25.4R4 = 0.3522 D4 = 0.1376R5 = 3.8193 D5 = 0.1725 N3 = 1.697 .nu.3 = 48.5R6 = -0.5969 D6 = 0.167 N4 = 1.72825 .nu.4 = 28.5R7 = -0.7671 D7 = 0.0713R8 = 0.6312 D8 = 0.0988 N5 = 1.7725 .nu.5 = 49.6R9 = 4.6414.vertline.f.sub.1 /f.sub.2 .vertline. = 1.9285 f.sub.2 /f = -0.1904 f.sub.3 /f = 0.4961 DO = 0.04______________________________________
EXAMPLE 6
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4186 D1 = 0.0891 N1 = 1.72 .nu.1 = 50.2R2 = -9.096 D2 = 0.197R3 = -0.4351 D3 = 0.0279 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4955 D4 = 0.1493R5 = -1.6863 D5 = 0.1956 N3 = 1.697 .nu.3 = 48.5R6 = -0.3195 D6 = 0.1151 N4 = 1.72825 .nu.4 = 28.5R7 = -0.5561 D7 = 0.0153R8 = 0.9878 D8 = 0.0852 N5 = 1.7725 .nu.5 = 49.6R9 = -4.6263.vertline.f.sub.1 /f.sub.2 .vertline. = 1.9652 f.sub.2 /f = -0.2844 f.sub.3 /f = 0.5261 DO = 0.0437______________________________________
EXAMPLE 7
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4165 D1 = 0.1912 N1 = 1.72 .nu.1 = 50.2R2 = -3.39 D2 = 0.1481R3 = -0.3872 D3 = 0.0785 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4866 D4 = 0.1315R5 = -0.7668 D5 = 0.0804 N3 = 1.697 .nu.3 = 48.5R6 = -0.251 D6 = 0.1176 N4 = 1.72825 .nu.4 = 28.5R7 = -0.4241 D7 = 0.0631R8 = 0.7723 D8 = 0.1651 N5 = 1.7725 .nu.5 = 49.6R9 = -6.2772.vertline.f.sub.1 /f.sub.2 .vertline. = 2.0437 f.sub.2 /f = -0.2571 f.sub.3 /f = 0.4901 DO = 0.0373______________________________________
EXAMPLE 8
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3482 D1 = 0.1182 N1 = 1.72 .nu.1 = 50.2R2 = -4.0406 D2 = 0.1449R3 = -0.3748 D3 = 0.0764 N2 = 1.80518 .nu.2 = 25.4R4 = 0.3816 D4 = 0.1265R5 = 1.7347 D5 = 0.2061 N3 = 1.697 .nu.3 = 48.5R6 = -0.4603 D6 = 0.1757 N4 = 1.72825 .nu.4 = 28.5R7 = -0.7049 D7 = 0.0618R8 = 0.8119 D8 = 0.1439 N5 = 1.7725 .nu.5 = 49.6R9 = 8.081.vertline.f.sub.1 /f.sub.2 .vertline. = 2.0039 f.sub.2 /f = -0.2247 f.sub.3 /f = 0.4957 DO = 0.0344______________________________________
EXAMPLE 9
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4429 D1 = 0.0335 N1 = 1.72 .nu.1 = 50.2R2 = -4.1849 D2 = 0.204R3 = -0.5629 D3 = 0.0209 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4844 D4 = 0.2198R5 = -2.4032 D5 = 0.2335 N3 = 1.697 .nu.3 = 48.5R6 = -0.4017 D6 = 0.0267 N4 = 1.72825 .nu.4 = 28.5R7 = -0.6186 D7 = 0.0515R8 = 1.0314 D8 = 0.0917 N5 = 1.7725 .nu.5 = 49.6R9 = -6.7698.vertline.f.sub.1 /f.sub.2 .vertline. = 1.741 f.sub.2 /f = -0.3205 f.sub.3 /f = 0.5832 DO = 0.0585______________________________________
EXAMPLE 10
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3693 D1 = 0.1981 N1 = 1.72 .nu.1 = 50.2R2 = 2.5301 D2 = 0.1765R3 = -0.2971 D3 = 0.0161 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4745 D4 = 0.0643R5 = 1.9365 D5 = 0.1127 N3 = 1.697 .nu.3 = 48.5R6 = -0.2642 D6 = 0.2305 N4 = 1.72825 .nu.4 = 28.5R7 = -0.4824 D7 = 0.07R8 = 0.9622 D8 = 0.1526 N5 = 1.7725 .nu.5 = 49.6R9 = -9.8269.vertline.f.sub.1 /f.sub.2 .vertline. = 2.5728 f.sub.2 /f = -0.2248 f.sub.3 /f = 0.4199 DO = 0.0248______________________________________
EXAMPLE 11
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3879 D1 = 0.1531 N1 = 1.72 .nu.1 = 50.2R2 = -9.0167 D2 = 0.165R3 = -0.3786 D3 = 0.0698 N2 = 1.80518 .nu.2 = 25.4R4 = 0.4629 D4 = 0.1477R5 = 21.2811 D5 = 0.1962 N3 = 1.697 .nu.3 = 48.5R6 = -0.3036 D6 = 0.1701 N4 = 1.72825 .nu.4 = 28.5R7 = -0.5721 D7 = 0.052R8 = 0.7612 D8 = 0.1554 N5 = 1.7725 .nu.5 = 49.6R9 = 6.2487.vertline.f.sub.1 /f.sub.2 .vertline. = 2.0849 f.sub.2 /f = -0.2494 f.sub.3 /f = 0.4834 DO = -0.2064______________________________________
EXAMPLE 12
______________________________________f = 1 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3756 D1 = 0.1325R2 = -3.3599 D2 = 0.145R3 = -0.3905 D3 = 0.0774R4 = 0.4348 D4 = 0.1877R5 = -2.0321 D5 = 0.1835R6 = -0.578 D6 = 0.0618R7 = 0.8196 D7 = 0.1767R8 = -1.6015 D8 = 0.1025R9 = -3.9946.vertline.f.sub.1 /f.sub.2 .vertline. = 1.9421 f.sub.2 /f = -0.2452 f.sub.3 /f = 0.5112 DO = 0.0327______________________________________
Ternary aberration coefficients of the above examples are shown in the following table, Table 1. In the table, I is spherical aberration, II is coma, III is astigmatism, P is Petzval sum and V is distortion.
TABLE 1______________________________________coefficient Example______________________________________ Example 1 Example 2 Example 3 Example 4______________________________________I 0.12406 0.46004 -0.14528 0.02664II 0.1735 0.1418 0.40244 0.26765III 0.01027 0.03254 0.17935 0.05713P 0.17223 0.27954 0.09523 0.21265V -0.05443 0.13357 -0.01235 -0.02325______________________________________ Example 5 Example 6 Example 7 Example 8______________________________________I 0.31882 0.16961 0.22606 0.32845II 0.16566 0.24766 0.36047 0.19517III 0.13201 0.05117 0.12012 0.09247P 0.13286 0.13695 0.1091 0.24124V 0.10842 -0.0848 -0.32938 0.04887______________________________________ Example 9 Example 10 Example 11 Example 12______________________________________I 0.87371 -0.31711 0.08399 0.08932II 0.18237 0.45304 0.37468 0.19056III 0.00096 0.22948 -0.04541 -0.00143P 0.30255 0.06921 0.2076 0.21645V 0.05155 0.05192 0.01822 -0.08943______________________________________
Hereinafter, description is made of the conditions (1') to (3') previously given for the lens according to the second embodiment of the invention.
Condition (1') is necessary for good correction of spherical aberration while maintaining the balance of refractive powers of the first and second lens groups. The lens of the present invention is of telecentric system and the spacing between the principal points of the second and third groups is broader than that between those of the first and second groups. Therefore, positions at which paraxial rays pass through the first group are greatly spaced apart from the optical axis and thereby a large quantity of spherical aberration is produced. If .vertline.f.sub.1 /f.sub.2 .vertline. is below the lower limit of 1.72, then the refractive power of the first group becomes high and therefore the paraxial rays passing through the surface will be intensely refracted in the direction toward the optical axis so that a large quantity of negative spherical aberration may be produced. On the contrary, when .vertline.f.sub.1 /f.sub.2 .vertline. is over the upper limit, 2.58, the refractive power of the second lens group becomes high and the second group will produces such a level of positive spherical aberration which may overly compensate the negative spherical aberration produced by the first lens group.
Condition (2') is for correction of curvature of field. When f.sub.1 /f.sub.2 exceeds the upper limit, -0.19, the Petzval sum is overcorrected and the correction of the curvature of field becomes excessive. To overcome the drawback, the absolute value of refractive power of the third group must be increased. However, as described later in connection with condition (3'), by increasing the absolute value of refractive power there is produced in the third lens a large quantity of distortion the correction of which is very difficult. On the contrary, if f.sub.2 /f is smaller than the lower limit, then the correction of Petzval sum of the whole system becomes difficult and curvature of field is undercorrected.
Condition (3') should be satisfied to correct the curvature of field and distortion. This is because the lens of the present invention is of telecentric system and the principal rays pass through the third lens group at positions far away from the optical axis. If f.sub.3 /f is below the lower limit of 0.41, then the refractive power of the third group becomes high and the principal rays passing through the third group are intensely refracted in the direction toward the optical axis. As a result, a large quantity of distortion is produced. On the contrary, when f.sub.3 /f is over the upper limit of 0.59, curvature of field becomes worse to the extent that it is no longer possible to correct the aberration.
Now, the shape of the above projection lens according to the second embodiment of the invention is described in detail.
As previously described, the projection lens of the present invention is required to be precise in terms of F number. To meet the requirement, it is advantageous that spherical abberation be corrected at the first group in which paraxial rays are most apart from the optical axis of the lens. To this end, the lens surface on the side of object field of the first group is convexed toward the object field side.
In this type of lens, Petzval sum is corrected primarily by the power of the second group. Therefore, the condition of power for the second group often becomes very severe and the second group is apt to produce various aberrations. To reduce the aberrations as much as possible, the second lens group is shaped as a double concave lens.
Since the lens of the present invention is a telecentric lens, off-axial principal rays should be spaced at a large distance from the optical axis by the third lens group. It is preferred that the nearest lens to the object field of the third group be shaped as a positive meniscus lens whose concaved surface is facing the side of object field. Further, it is preferred that the lens located nearest to the image field of the third group be shaped as a meniscus lens whose concaved surface is facing the image field side. By doing so, the principal rays are made spaced apart from the optical axis by the first mentioned meniscus lens and aberrations are corrected by the concave surface of the second mentioned meniscus lens. In addition, since the lens has no negative power, the requirement of lengthening the back focal length of the whole lens system can be attained at the same time.
The following examples, Example 13 to 21 together with FIGS. 13 to 21 illustrate the design of the projection lenses of the above second embodiment of the present invention. In all the following examples, focal length f is standarized to 1, F number to 5.0, angle of field .omega. to 25.2.degree. and focus magnification .beta. to -0.12343.
Again, Ri is the radius of curvature of the i-th surface;
Di is the thichness on axis or air spacing on axis between the i-th surface and the i+1-th surface;
Ni is the refractive index of the i-th lens to D ray;
.nu.i is Abbe's number of the i-th lens;
fi is the focal length of the i-th lens group; and
D0 is the air spacing on axis from pupil SL to the R1 surface.
EXAMPLE 13
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4235 D1 = 0.1596 N1 = 1.72 .nu.1 = 50.2R2 = -2.934 D2 = 0.156R3 = -0.4137 D3 = 0.0658 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5172 D4 = 0.1378R5 = -0.5814 D5 = 0.1784 N3 = 1.60311 .nu.3 = 60.7R6 = -0.5646 D6 = 0.0037R7 = 1.7452 D7 = 0.1295 N4 = 1.757 .nu.4 = 47.9R8 = -1.0784 D8 = 0.0037R9 = 2.934 D9 = 0.1099 N5 = 1.697 .nu.5 = 48.5R10 = -1.6199 D10 = 0.141 N6 = 1.72825 .nu.6 = 28.5R11 = 7.2159 D11 = 0.1119R12 = 0.6834 D12 = 0.1345 N7 = 1.7725 .nu.7 = 49.6R13 = 1.0343.vertline.f.sub.1 /f.sub.2 .vertline. = 1.895 f.sub.2 /f = -0.2767 f.sub.3 /f = 0.5216 DO = 0.0291______________________________________
______________________________________f = 1 1:5 angle of field = 25.2.degree. .GAMMA. = -0.12343______________________________________R1 = 0.4309 D1 = 0.1372 N1 = 1.72 .nu.1 = 50.2R2 = -3.3104 D2 = 0.1659R3 = -0.4118 D3 = 0.068 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5596 D4 = 0.1133R5 = -0.5297 D5 = 0.1596 N3 = 1.60311 .nu.3 = 60.7R6 = -0.4196 D6 = 0.0948R7 = 1.2334 D7 = 0.1282 N4 = 1.697 .nu.4 = 48.5R8 = -0.7865 D8 = 0.1423 N5 = 1.72825 .nu.5 = 28.5R9 = -1.5704 D9 = 0.0168R10 = 0.8342 D10 = 0.1341 N6 = 1.7725 .nu.6 = 49.6R11 = 1.4571.vertline.f.sub.1 /f.sub.2 .vertline. = 1.8826 f.sub.2 /f = -0.2857 f.sub.3 /f = 0.5303 DO = 0.0069______________________________________
EXAMPLE 15
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4227 D1 = 0.1398 N1 = 1.72 .nu.1 = 50.2R2 = -3.6537 D2 = 0.1709R3 = -0.402 D3 = 0.0714 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5558 D4 = 0.0827R5 = -0.5313 D5 = 0.0414 N3 = 1.76182 .nu.3 = 26.6R6 = -1.0604 D6 = 0.1282 N4 = 1.60311 .nu.4 = 60.7R7 = -0.414 D7 = 0.1031R8 = 1.335 D8 = 0.2223 N5 = 1.697 .nu.5 = 48.5R9 = -1.5253 D9 = 0.0315R10 = 0.7952 D10 = 0.1356 N6 = 1.7725 .nu.6 = 49.6R11 = 1.5874.vertline.f.sub.1 /f.sub.2 .vertline. = 1.904 f.sub.2 /f = -0.2804 f.sub.3 /f = 0.5184 DO = 0.0195______________________________________
EXAMPLE 16
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3957 D1 = 0.1939 N1 = 1.72 .nu.1 = 50.2R2 = 2.4014 D2 = 0.1921R3 = -0.3159 D3 = 0.0303 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5107 D4 = 0.0846R5 = -1.0159 D5 = 0.0546 N3 = 1.60311 .nu.3 = 60.7R6 = -0.4331 D6 = 0.0037R7 = 2.5196 D7 = 0.1745 N4 = 1.757 .nu.4 = 47.9R8 = -0.5692 D8 = 0.0037R9 = -0.6627 D9 = 0.1387 N5 = 1.697 .nu.5 = 48.5R10 = -0.4418 D10 = 0.1477 N6 = 1.72825 .nu.6 = 28.5R11 = -0.5971 D11 = 0.0856R12 = 0.71 D12 = 0.1196 N7 = 1.7725 .nu.7 = 49.6R13 = 0.7761.vertline.f.sub.1 /f.sub.2 .vertline. = 2.6519 f.sub.2 /f = -0.2385 f.sub.3 /f = 0.4206 DO = 0.0158______________________________________
EXAMPLE 17
______________________________________f = 1 1:5 angle of field = 25.2.degree. .GAMMA. = -0.12343______________________________________R1 = 0.4103 D1 = 0.0989 N1 = 1.72 .nu.1 = 50.2R2 = -2.1886 D2 = 0.1497R3 = -0.4378 D3 = 0.0595 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5473 D4 = 0.1499R5 = -0.5567 D5 = 0.1904 N3 = 1.60311 .nu.3 = 60.7R6 = -0.5263 D6 = 0.0036R7 = 5.6929 D7 = 0.1218 N4 = 1.757 .nu.4 = 47.9R8 = -1.368 D8 = 0.0036R9 = 3.3639 D9 = 0.1172 N5 = 1.697 .nu.5 = 48.5R10 = -1.539 D10 = 0.1 N6 = 1.72825 .nu.6 = 28.5R11 = 35.1532 D11 = 0.0915R12 = 0.6849 D12 = 0.0815 N7 = 1.7725 .nu.7 = 49.6R13 = 1.4832.vertline.f.sub.1 /f.sub.2 .vertline. = 1.6578 f.sub.2 /f = -0.2941 f.sub.3 = 0.5815 DO = 0.02______________________________________
EXAMPLE 18
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4616 D1 = 0.1423 N1 = 1.72 .nu.1 = 50.2R2 = -2.5065 D2 = 0.1625R3 = -0.4707 D3 = 0.0522 N2 = 1.80518 .nu.2 = 25.4R4 = 0.6353 D4 = 0.1537R5 = -0.5035 D5 = 0.1863 N3 = 1.60311 .nu.3 = 60.7R6 = -0.5187 D6 = 0.0037R7 = 3.1351 D7 = 1.1227 N4 = 1.757 .nu.4 = 47.9R8 = -1.4508 D8 = 0.0037R9 = 2.1422 D9 = 0.1286 N5 = 1.697 .nu.5 = 48.5R10 = -1.3417 D10 = 0.1032 N6 = 1.72825 .nu.6 = 28.5R11 = 27.4187 D11 = 0.0895R12 = 0.7259 D12 = 0.1182 N7 = 1.7725 .nu.7 = 49.6R13 = 1.2478.vertline.f.sub.1 /f.sub.2 .vertline. = 1.6798 f.sub.2 /f = -0.3289 f.sub.3 /f = 0.5736 DO = 0.0156______________________________________
EXAMPLE 19
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.3092 D1 = 0.1798 N1 = 1.72 .nu.1 = 50.2R2 = -1.3737 D2 = 0.0857R3 = -0.2973 D3 = 0.085 N2 = 1.80518 .nu.2 = 25.4R4 = 0.3564 D4 = 0.1288R5 = -0.5992 D5 = 0.0897 N3 = 1.60311 .nu.3 = 60.7R6 = -0.6701 D6 = 0.0037R7 = 2.6866 D7 = 0.138 N4 = 1.757 .nu.4 = 47.9R8 = -0.6575 D8 = 0.0037R9 = -2.5082 D9 = 0.0833 N5 = 1.697 .nu.5 = 48.5R10 = -3.5115 D10 = 0.101 N6 = 1.72825 .nu.6 = 28.5R11 = -11.326 D11 = 0.089R12 = 0.5951 D12 = 0.0767 N7 = 1.7725 .nu.7 = 49.6R13 = 2.425.vertline.f.sub.1 /f.sub.2 .vertline. = 1.9288 f.sub.2 /f = -0.1903 f.sub.3 /f = 0.496 DO = 0.0152______________________________________
EXAMPLE 20
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.298 D1 = 0.188 N1 = 1.72 .nu.1 = 50.2R2 = -1.3058 D2 = 0.0778R3 = -0.2875 D3 = 0.0574 N2 = 1.80518 .nu.2 = 25.4R4 = 0.3573 D4 = 0.1482R5 = -0.5748 D5 = 0.0653 N3 = 1.60311 .nu.3 = 60.7R6 = -0.4784 D6 = 0.1083R7 = 1.1557 D7 = 0.1496 N4 = 1.697 .nu.4 = 48.5R8 = -1.383 D8 = 0.1051 N5 = 1.72825 .nu.5 = 28.5R9 = -1.6648 D9 = 0.0158R10 = 0.7112 D10 = 0.1017 N6 = 1.7725 .nu.6 = 49.6R11 = 2.7318.vertline.f.sub.1 f.sub.2 .vertline. = 1.8621 f.sub.2 /f = -0.1903 f.sub.3 /f = 0.5096 DO = 0.0099______________________________________
EXAMPLE 21
______________________________________f = 1 1:5 angle of field = 25.2.degree. .beta. = -0.12343______________________________________R1 = 0.4133 D1 = 0.1413 N1 = 1.72 .nu.1 = 50.2R2 = -2.4883 D2 = 0.1479R3 = -0.4097 D3 = 0.0848 N2 = 1.80518 .nu.2 = 25.4R4 = 0.5148 D4 = 0.1134R5 = -0.5332 D5 = 0.1512 N3 = 1.60311 .nu.3 = 60.7R6 = -0.4298 D6 = 0.1092R7 = 1.1578 D7 = 0.1559 N4 = 1.697 .nu.4 = 48.5R8 = -2.0472 D8 = 0.1053R9 = 0.9246 D9 = 0.0956 N5 = 1.7725 .nu.5 = 49.6R10 = -24.8952 D10 = 0.1017 N6 = 1.80518 .nu.6 = 25.4R11 = 2.4866.vertline.f.sub.1 /f.sub.2 .vertline. = 1.8463 f.sub.2 /f = -0.2722 f.sub.3 /f = 0.5321 DO = 0.0079______________________________________
Ternary aberration coefficients of the above examples are given in the following table, Table 2 wherein I is spherical aberration, II is coma, III is astigmatism, P is Petzval sum and V is distortion.
TABLE 2______________________________________coefficient Example______________________________________ Example 13 Example 14 Example 15 Example 16______________________________________I 0.02847 -0.08302 0.06864 -0.3336II 0.09015 0.1896 0.15269 0.49706III -0.00516 -0.00769 -0.01428 0.12913P 0.14767 0.21517 0.19111 0.13869V 0.18112 0.01496 0.0142 -0.0607______________________________________ Example 17 Example 18 Example 19 Example 20______________________________________I 0.15339 0.09436 0.13221 0.15643II 0.09323 0.10385 0.2282 0.17737III -0.01272 0.00036 0.17019 0.07046P 0.25299 0.25626 0.07882 0.11143V 0.14735 0.20489 0.20353 0.12851______________________________________ Example 21______________________________________I 0.0236II 0.15886III -0.03366P 0.24261V -0.02899______________________________________

Number	Date	Country	Kind
55-27735	Mar 1980	JPX
55-27736	Mar 1980	JPX

Number	Name	Date	Kind
2685229	Schulz et al.	Aug 1954
4093348	Yasukuni	Jun 1978

Telecentric projection lenses

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