JPS60209713A - Microfilm projection optical system - Google Patents

Abstract

PURPOSE:To obtain a projection lens with high performance by providing the 1st convergent lens group, the 2nd negative meniscus lens group, the 3rd biconvex lens group which has the larger-curvature convex surface on a reduction side, and the 4th divergent lens group which has the larger-curvature concave surface on the reduction side. CONSTITUTION:Negative spherical aberration generated by the 1st lens group A is compensated by the negative meniscus lens of the 2nd group B positively by a proper quantity, and positive Petzval generated by the 3rd group C is compensated negatively by the 2nd group B. A positive-negativae cemented lens is used as the 1st group A with large incident light height to compensate the chromatic aberration of spherical aberration and a cemented lens is used for the 4th group D to easily compensate power chromatic aberration. Then, 0.9f<f1< 2.0f, where f1 is the focal length of the 1st lens group A and (f) is the focal length of the whole system. Further, -10.0f<f4<-3.0f, where f4 is the focal length of the 4th lens group. Furthermore, 1.5r6<r5>2.5r6 and 0.6f<f34<0.75f, where r5 and r6 are the radii of curvature of both surfaces of the 2nd lens group B and f34 is the composite focal length of both the 3rd and the 4th lens groups.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical system for a microreader or reader printer for reproducing images of microfilm.

Many prior art microfilms are recorded without aligning the orientation of the characters in the original document in the vertical and horizontal directions when they are created. For this reason, micro league printers or league printers have been used in which an image rotation prism is inserted between a projection lens and a screen so that the direction of the image on the screen can be rotated.

However, in conventional reader printers of this type, the exit pupil of the projection lens is located at the center of the lens. This has the disadvantage that the optical system becomes larger, leading to image deterioration, and the entire optical system including the mirror becomes larger.

Let me explain the above points in a little more detail. Figure 3 shows the general configuration of Microleague, where 1 is a microfilm, 2 is a projection lens, 3 is an image rotation prism, and 4.5.6 is ρa and 7
is the screen. Figure 4A is an image rotating prism.
, B are also available, but since the type used in Figure 3 is more compact as long as the angle of view is large, this type is used in microreaders. However, this type of prism is optically equivalent to a parallel flat glass plate tilted at 45 degrees to the optical axis, and produces aberrations for the converging light beam. The degree of aberration differs between a light beam incident in a direction more inclined to the surface and a light beam incident in a direction less inclined. The degree of aberration (such as axial astigmatism) is proportional to the length of the bottom surface of the prism. For this reason, it is better for the prism 3 to be as small as possible, but in the conventional configuration, the exit pupil of the projection lens 2 is located near the center of the lens.
Near the prism 3, the light beams coming from each point on the microfilm are spread over a wide range as shown in the figure.
had to be made larger to cover this spread of luminous flux.

The above-mentioned problem can be improved by arranging the aperture position of the projection lens to be outside the screen-side edge of the lens surface (in the screen-side space). Regarding this point, the special public
A proposal has been made in No.-35028. However, the projection lens proposed by this proposal has a narrow angle of view and is less bright than a normal projection lens.

In other words, by using a front aperture, field curvature and astigmatism become large, and coma correction becomes insufficient at a wide angle of view, making it difficult to obtain a lens with a wide angle of view. It is difficult to correct 7 chromatic aberrations and lateral aberrations simultaneously, the combinations of glass materials are limited, and comprehensive correction of various other aberrations becomes difficult. It is dark, around 0, and if you try to correct aberrations to a considerable degree, the telephoto ratio, that is, the value obtained by dividing the distance from the image side edge of the lens to the film surface by the composite focal length f of the projection lens, will be about 1.5. The entire lens becomes larger.

The smaller the telephoto ratio, the more compact the lens.

Purpose The present invention aims to provide a high-performance projection lens suitable for downsizing an image rotation prism by arranging an aperture on the magnification side (screen side) of the projection lens.

Construction: As a projection lens that performs magnification projection, in order from the magnification side, there is an aperture stop, a convergent lens group made of a combination of a positive lens and a negative lens, and a '2nd lens made of a negative meniscal lens with its convex surface facing the magnification side. This lens uses a projection lens consisting of four groups: a third lens group consisting of a biconvex lens with a strongly convex surface facing the reduction side, and a diverging fourth lens group with a strongly concave surface facing the reduction side. An image rotating prism is placed close to the end surface on the enlarged side.

Embodiment FIGS. 1A and 1B show a projection lens according to the present invention, where E7 is an aperture, A is a lens group, B is a second lens group, C is a third lens group, and D is a fourth lens group. G is a parallel plane glass plate that presses the microfilm M to keep it flat, and there is a screen on the left side of the figure. To designate each surface of the lens, a number is assigned to each surface, and specific specifications are shown in the table below. Tables 1 to 4 correspond to FIG. 1A, and Table 5 corresponds to FIG. 1B. In FIG. 1A, the fourth lens group is composed of a cemented lens. In these tables, CR is the radius of curvature of the lens surface, T is the ω spacing on the axial surface, Ncl is the refractive index, νd is the Atsube number, \ is the angle of view measured to one side from the optical axis, and f is the angle of view of the entire lens system. It is the focal length. In addition, each table includes reference data such as the total length SUMT from the aperture to the film surface, and the focal length fl of each lens group.
, the ratio of f4, etc. to the composite focal length f, the ratio of curvature radii of both sides of the second lens group B, r5/r6, the difference in the Atsube numbers of the two lenses constituting the fourth lens group, shear a - b, etc. This is an additional note.

The characteristics of this lens FJ formation will be explained. The negative meniscus lens of the second group B corrects the negative spherical aberration generated in the second lens group A by an appropriate amount in the positive direction, and the second group B corrects the negative Petzval aberration that occurs in the third lens group C. It is corrected in the negative direction. By using a positive/negative cemented lens for the first group A, which has a high incident light beam height, it is easy to correct chromatic aberration due to spherical aberration.
By rubbing the fourth group with the cemented lens V, correction of chromatic aberration of magnification is facilitated. In addition, the lens configuration satisfies the following conditions: 〇(1) The focal length f1 of the lens group A, and the focal length f of the entire lens system is 0.9 f (f l (2, Of fl is above When fl is smaller than the above condition, the negative field curvature that occurs in the first group cannot be corrected by other lens groups. Also, the occurrence of upper coma becomes larger.On the other hand, when fl becomes larger than the above condition, the wide angle °″l″1oiqi at the angle of view image point=-
ib~6・4(2) Focal length f4 and t of the fourth lens group
The relationship between -10,0f (f4 (-3,0f) When f4 exceeds the upper lower limit, astigmatism increases, and when it exceeds the upper limit, distortion in the positive direction cannot be corrected completely0t3) second lens Regarding the ratio of the radius of curvature r5.r6 of 5.6 on both sides of group B, 1.5 r 6 (r 5 (2,5 r'6 When r5 exceeds the lower limit, the coma at a wide angle of view increases and exceeds the upper limit. and the first
．． It is difficult to correct the deviation of the Petzval sum in the negative direction in both the second lens groups with other lens groups, and the curvature of image increases.

(4) Combined focal length f of both the third and fourth lens groups,
Relationship between 34 and f 0.6 f (f 34 (0,75 f As a result, the image surface properties deteriorate, and when the value exceeds the upper limit, downward coma and distortion become significant.

If the fourth lens group is constructed by cementing a biconvex lens and a biconcave lens, and the Atsbe number on the convex lens side is νa, and the Atsbe number on the concave lens side is νb, the glass material should be such that shear a - b〉12. By selecting , it becomes easy to correct chromatic aberration.

1 ω=12.8゜F N O, /2.8 -3L9 Radius of curvature Axis-to-plane distance Refractive index Atsbe number CRT Na
vL 2 14.422 3.500 1.6'i'003 4'i', 15 2
3 -40.546 :L, 200 1. 'i'o154 41.15 34
26.60'7 2.300 4 5 22.937 1.000 1. 'i'8560 42.81 56
11, 'i"i" / 9.300 6 'i' 46.005 4.500 1.60311 60.74 "i'8
-23.265 0.500 8 9 '12.504 4.500 167'i'90 53.38 910
114.542 1.500 1.681. uゝ 36.64 1011
, 9.306 16.690 11 12 lNF 3.000 '1.51680 64.12 1213
INF SUMT-4'7.990 f/f=1.51 f4/f=-6,46r5/r6=
'1.95f34/f=0. '72 νa-+zb=1
6.744 (2 ω-15,0°F N O, /4.0 f=32.4 Radius of curvature Axis spacing Refractive index Atsube number CRT Nd
νd 2 13·652, 2 3.54'8 1.67003 4", '15.

39.605. 3 1.214 1.70154 41.15.

4 2L472,4 2.322 5 20.560, 5 1.012’1. '7B560 42.81.

°11°2°" 16 9.958 """"13.500: L, 603□, 60.7
4 ”9 13.853, 9 5.50OL65844 50.88 10 -28.684 L215.1.6B150 36.64 1 1011
9.859 13.162 111 12 Engineering NF 3.000 i, 51sao 6-4.12 1 12
13 Engineering NF 13 EIUMT=45.444 f/f=1. '72 f4/f--3, 42r5/r6
=1.83f34/f=o, 68 sea b=14.
24 Table 3 ω-work 12.8 F, No, /4.0 f=3.1.9 Radius of curvature Axial surface spacing Refractive index Atsube number CRT Na
vd 13.451 3.500 1.67003 47.15 2-9.6
31 1.200 1. 'i'0154 41.15 322
．． 727 2, 300 4 21.351 1.000 L'78560 42.81 510.9
81 9.300 6 31.561 3.900 L60311 60. '74 '7-25
．． 188 0.500 8 12,'i' 48 4.500 1.6'7'i'90 53.38 9-
8'7. '749 1.500 1.68150 36.64 109.0
57 16.690 11 Engineering NF 3,,OOO1,5168064,1212NF SUMT,=4'i',390 f/f =1.55 f4/f =-4,02r5/r
6 =1.94f34/f=o, 68 va-shib=1
6. '74 Table 11- ω= 1 '7.90 FNo, /4.0 F=31.9 Radius of curvature Axis spacing Refractive index Atsube number CRT Nd
νd 13 INF SUMT,,=46.310 f/f=L93 f4/f,=-6,38r5/r6-
2.14f34/f=0.64 va-νb=15.0
Table 9 also shows ω-12,8°FNO, /4.0 f=32.0 Radius of curvature Upper axis distance Refractive index Atsbe number CRT Nd
νd Aperture 0.0 1 13.287 3.500 1.66'755 41.98 2-9.
838 1.198 1. '70154 4:L, 15 338
．． 145 2.299 4 24.1'/2 1.000 1.78472 25°75 59,'7
30 9.836 6 30.32 '7 2.800 1.49520 '79. '74 '7-
19.253 1.000 8 12.5B';' 6.000 1.64050 60.08 9B, 99
B 13.000 10 NF 3.000 1.51680 64.12 11st NF SUMT=43.633 f/f=1.0o f4/f=-4,45ra/rb-
2,48f34/f=0.69 FIG. 2 shows the aberrations of each example shown in the previous example. In these figures, the curve of the solid line d in spherical aberration is the d line, and the dashed line g
is the wavelength of the g-line, and the chain double-dashed line C is the wavelength of the d-line. The astigmatism is for the d-line, and the solid line 1) s indicates the aberration of the spherical section, and DT indicates the aberration of the meridional section.

In microreader printers where the image rotation prism is miniaturized by using a front-calibration projection lens as the effect projection lens, it is difficult to correct field curvature, astigmatism, and coma with this type of lens, and therefore the F number is also low. It was dark at about 4.0, and the telephoto ratio was about 1.5, making the entire lens system large.However, according to the present invention, the angle of view is 2ω-26°~
It has a wide angle of view of 36 degrees, a bright F number of 2.8 to 4.0, a compact telephoto ratio of about 1.4, and a front aperture projection lens with excellent performance. - The reader printer as a whole can be made smaller, and the quality of the projected image can also be improved due to better lens performance and smaller image rotation prism.

[Brief explanation of drawings]

FIGS. 1A and 1D are side sectional views of an example lens of the present invention, 01
! Figure 2 A1. A2. A3. Bl, B2. B3, CI, C
2, C3, DI, D2. D3. El. B2. B3 is a graph showing the aberrations of each embodiment of the present invention, and FIG. 3 is a side view showing the overall configuration of the microreader printer. Figure 4 A and B are image rotation pre-2 lens groups, C...
・Third lens group, D...Fourth lens group, G...Film holding glass plate, M...Micro film, 2~
13... Numbers of surfaces of lenses, etc. In Figure 13, 1... Microfilm, 2... Projection lens, 3... Image rotation prism, γ... Screen. Agent Patent Attorney Hiroshi Agata 2 figures

Claims (1)

[Claims] (1) In a configuration in which an aperture diaphragm is disposed at the magnification side end of the magnification projection lens, and an image rotation prism is disposed close to the magnification side end of the magnification projection lens, the magnification projection lens is placed at the magnification side end. In this order, the aperture diaphragm, the convergent lens group consisting of a junction of positive and negative lenses, the second lens group consisting of a negative meniscus lens with its convex surface facing the magnification side, and the biconvex lens group having its strongly convex surface facing the reduction side. A microfilm projection optical system comprising a third lens group and a diverging fourth lens group with a strongly concave surface facing the reduction side. (2) For the projection lens, f is the focal length of the lens, fl is the focal length of the lens group, f4 is the focal length of the fourth lens group, f34 is the combined focal length of both the third and fourth lens groups, and r5
When r6 is the radius of curvature of the enlarged side surface of the second lens group and r6 is the radius of curvature of the reduced side surface, the following condition is satisfied. Microfilm projection optical system. - 0,9f (f 1<2.Of -10,Of (f 4(-3,Of l,5r6(r 5(2,5r6 (curvature convexity is taken as positive) 0.6 f(f 34 (0,'i'5f(3) The fourth lens group of the projection lens is a combination of a biconvex lens and a biconcave lens.The Atsube number on the convex lens side is νb.If the Atsube number on the concave lens side is νb, then shear b) The microfilm projection optical system according to claim 2, characterized in that the microfilm projection optical system is selected so as to have a diameter of 12.0.