JPS6363012A - Projection lens for microfilm - Google Patents

Abstract

PURPOSE:To correct each aberration so as to be well-balanced, and to obtain the titled lens being compact and bright, by constituting said lens of a front group having a positive power and a rear group having a negative power. CONSTITUTION:The titled lens is constituted of the first lens group I consisting of a positive meniscus lens whose convex surface has been turned to an enlargement side, the second lens group II consisting of a negative lens whose concave surface has been turned to a reduction side, the third lens group III consisting of a positive lens whose convex surface has been turned to the enlargement side, the fourth lens groups IV consisting of a negative meniscus lens whose concave surface has been turned to the enlargement side, and the fifth lens group V consisting of a convex lens, in order from the enlargement side. In this state, a positive power of the front group is generated mainly by the first lens group, and a negative spherical aberration which has been generated by said first lens group is corrected mainly by the fourth lens group. Also, by satisfying inequalities, the compactness is secured. In this regard, (f), f123, and f45 in the inequalities denote a focal distance of the whole system, a composite focal distance of the first, the second and the third lens groups, and a composite focal distance of the fourth and the fifth lens groups, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microfilm projection lens used in a microreader or reader printer to reproduce images of microfilm.

Many microfilms were created by recording the characters in the original document without aligning the orientation of the characters horizontally and vertically. Therefore, conventionally, microreaders or reader printers have been used in which an image rotating prism is disposed between a projection lens and a screen so that the direction of the image on the screen can be rotated. On the other hand, the space for inserting the projection lens is too large from the viewpoint of operability and the overall size of the device (it cannot be taken), and for low-magnification lenses, the total length of the lens (the length from the film surface to the front edge of the lens)
becomes longer, making it difficult to secure space for the image rotation prism. Therefore, a compact lens is desired. A so-called telephoto ratio TL/1 is used as a measure of compactness.

Here, TL is the total length of the lens when the object point is at infinity, and f is the focal length.

An example of a microfilm projection lens with a small telephoto ratio is known from Japanese Patent Publication No. 47-35028.

However, in general, when trying to reduce the telephoto ratio, it becomes difficult to correct axial and external aberrations and on-axis aberrations in a well-balanced manner, and the projection lens described in the above publication also has incomplete correction of off-axis aberrations, especially coma aberration. .

Therefore, an object of the present invention is to provide a compact and bright microfilm projection lens in which each aberration is corrected in a well-balanced manner.

The above objectives are, in order from the magnification side, the 1171st lens group consisting of a positive meniscus lens with a convex surface facing the magnification side, the second lens group consisting of a negative lens with a concave surface facing the magnification side, and the positive lens group with a convex surface facing the magnification side. This is achieved by a microfilm projection lens constructed of a third lens group consisting of a third lens group consisting of a negative meniscus lens with its concave surface facing the magnification side, and a fifth lens group consisting of a convex lens.

The lens configuration of the present invention has a front group (first .
Second. 3rd lens group) and a rear group with negative power (4th lens group).
By adopting a so-called telephoto type configuration consisting of two groups (the 5th lens group), the overall length is shortened and compactness is achieved, and the positive power of the front group is mainly due to the 117th lens group.
The negative spherical aberration generated in the first lens group or the 1171st lens group is mainly corrected in the fourth lens group.

Further, the projection lens of the present invention is guaranteed to be compact by satisfying the following conditional expression.

(1) 1.5<f//f1□3<2.2(2)-
1,2<44.<.

However, f: focal length of the entire system/123: 1st. Second. Synthetic focal length f45 of the third lens group: 4th. Synthetic focal length of the fifth lens group As mentioned above, the projection lens of the present invention is a telephoto type consisting of a front group with positive power and a rear group with negative power, or (1)
Equation (2) defines the power of the after-melting group. That is, in order to make the lens system compact, it is necessary to increase the power of the front group. On the other hand, you have to comb it. Equation (1) is a condition for achieving both compactness and correction of field curvature within an appropriate range. The telephoto ratio of the projection lens of the present invention is 0.85 to 1.0, as is clear from the examples described later.
026, which shows that the lens system can be made compact.

The projection lens of the present invention further satisfies the following conditional expression to ensure well-balanced correction of axial aberrations and off-axis aberrations.

(3) (Nl, -1) //, < 3.2 (4)
-5,7<(N4-1) f/rB<-4,5 However, Nl, N4: 1st. Refractive index of the fourth lens group r A
, r e : 1st. Radius of curvature of the magnification side surface of the fourth lens group As mentioned above, in the projection lens of the present invention, the power of the front group is generated by the 1171st lens group, especially its first surface (the magnification side surface). However, the negative spherical aberration that occurs on this surface is mainly corrected on the first surface (the surface on the magnification side) of the fourth lens group.

If the power of the first surface of the first lens group defined by equation (3) exceeds 3.2, it becomes difficult to correct the negative spherical aberration generated at this surface using other surfaces. On the other hand, if the power of the first surface of the fourth lens group defined by equation (4) becomes smaller than -57, it becomes difficult to satisfactorily correct the negative spherical aberration generated in the front group. Also, the power of equation (4) is −4,
When the value is larger than 5, it becomes difficult to balance spherical aberration and off-axis aberration, especially coma aberration.

The projection lens of the present invention was originally developed for the purpose of being combined with a small image rotating prism, and therefore the aperture stop is placed on the front side (enlargement side).

However, the projection lens of the present invention can also be sufficiently applied to a projection system that does not use an image rotation prism, and in this case, the aperture stop does not need to be located on the front side; for example,
It may be before or after the third lens group. This also applies when a large image rotation prism is used due to the circumstances of the projection system.

In addition, when an aperture stop is provided on the front side, the image rotation prism can be made smaller at the front side (but on the other hand, the sensitivity to errors such as lens eccentricity becomes more severe).

Therefore, in the fourth, sixth, and twelfth embodiments of the present invention, the image rotation prism can be sufficiently miniaturized, and the error sensitivity is also moderate (the aperture stop is placed after the first lens group, and the fifth , 7 embodiment, it is arranged after the second lens group. In this sense, the term "front side" used in the present invention refers not only to the front aperture outside the lens system (it also refers to the front aperture located on the front side in the lens system). This also includes the position of the aperture.

FIG. 13 shows an example of a projection optical system of a microreader in which the projection lens of the present invention is used. In the figure, a microfilm 1 is held by two flat glass plates, and a projection lens 2 of the present invention is positioned directly above them. The light flux exiting the projection lens 2 is subjected to an image rotation action by an image rotation prism 3, and then projected onto a screen 7 via mirrors 4, 5, and 6.

The projection lens of the present invention is suitable for a projection optical system having such an image rotation prism 3, but as described above, it can also be applied to a normal projection optical system that does not perform image rotation.

Next, first to twelfth embodiments of the present invention will be described using FIGS. 1 to 12. tA+ in each figure indicates the lens configuration,
fBl indicates an aberration diagram of the lens. Each figure showing the lens configuration (in A+, I, II, III, IV, and V indicate the first lens group, second lens group, third lens group, fourth lens group, and fifth lens group, respectively. At the aperture stop, the first
, 2 , 3 , 8 , 9 , 10.11 In Examples, the lens is placed before the first lens group, in Examples 4, 6, and 12, it is placed after the first lens group, and in Examples 5 and 7, the lens is placed before the first lens group. It is placed after the lens group. In addition, G is microfilm 1
Only one of the flat glass plates sandwiching the is shown.

On the other hand, in each figure +13) showing aberrations, the solid line d of spherical aberration shows the aberration for each wavelength of the d-line, the dashed-dotted line g shows the aberration for the g-line, and the dashed-double-dotted line C shows the aberration for each wavelength. The astigmatism is for the d-line, and the solid line DS indicates the aberration of the spherical cross section, and the dotted line DT indicates the aberration of the calf cross section.

Below is a table showing specific specifications of each example.

In addition to the radius of curvature, axial spacing, refractive index, and Atsube number, each table includes the F number, telephoto ratio (CTL/f), f/f1□3f
/f4s, (N+-1)f/rA, (N4-1
Each value of >f/rB is an indication. Further, the magnification is 1/14.5 in each example, and the focal length is normalized to 1.

Margin Table 1 (First Example) Radius of curvature Distance between top surfaces of the shafts Refractive index (Nd) Atsube number (νd) d9 0.013 FNo, = 5.5 TL/ f = 0.
927f/ /+23= 1.592 f/f45 =-0,931 (Nt-1)f/rA =2.651(N4-1)/
/rB =-5,261 Table 2 (Second Example) Radius of curvature Axial surface spacing Refractive index (Nd) Atsube number (νd) FNo, = 5,5 TL/
f=0.920f/f1□3 =1.866 f/f45--1.125 (Nl-1)//rA =2.732(N4-1)/
/rB=-5.226 Table 3 (Third Example) Radius of curvature Axis top surface spacing Refractive index (Nd) Axial number (νd) FNo, = 5.6 TL/7
=1.026f/I, □3 =1.558 f/f45=-0,390 (Nl-1)//rA =3.037CNa-1,)
f/rB=-4,771 Table 4 (4th example) Radius of curvature Axis top surface interval Refractive index (Nd) Atsube number (νd) FNo, = 5.6 TL
/ / = 0.995/ // I□3 = 1.59
0 f/f45=-0,388 (''1)//'A =3.037CN4-1)f
/rB =-4,915Table 5 (Fifth Example) Radius of curvature Axial surface spacing Refractive index (Nd) Atsube number (νd)FNo, =5,5 TL/
f=0.992f/f,,,3=1.639 f/f,5=-0,597(Nl-1)f/rA=3.025(N4-1)
f/rB = -4,915 Table 6 (Sixth Example) Radius of curvature Axial surface spacing Refractive index (Nd) Atsube number (νd) FNO- = 5.6 TL/f
=0.91f/f, □3=1.838 f/f<s= 1.086 (Nl -1) f/rA=2.744(N4-1)f
/rB--5,328 Table 7 (Seventh Example) Radius of curvature Upper axis distance Refractive index (Nd) Atsube number, (νd)FNo, = 4,5 TL
/f=o, 97f/fx23=1.649 f/f<s-0,663 (Nl-1)f/rA=2.926 (N4-1)f/rB=-4,944 Table 8 ( 8th Example] Radius of curvature Upper surface spacing Refractive index (Nd) Atsube number (νd) FNo, =5,5 TL/
f=Q, 92f/f 123 = 1.792 f/f4S=-1,066 (Nl-1) f/rA=2.732 (N4-1) f/rB--5,227 Table 9 (9th Example) Radius of curvature Axial surface spacing Refractive index (Nd) Atsube number (νd) FNo, -5,6TL/f=0.91 f/f u3=1.866 f/f 45=7.1.145 (Nl -1) f/rA=2.720 (N4-1) f/rB=-5,226 Table 10 (10th
Example) “Radius of curvature Axis top surface spacing Refractive index (Nd) A/B number (νd) FNo, = 5,6 TL/f
=0.98f/f 123=1.698 f/f 45 =-0,661 CN1-1) f/rA=3.028 (N4-1) f/rs=-5,069Table 11 (
11th Example] Radius of curvature Distance between axial surfaces Refractive index (hed) A Nope number (νd) FNo, =5.6 TL/
f=0.85f/f 123=2.132 f/f 4s=-0,024 (Nl-1)f/rA=3.138 (N<-1)f/rs=-5,681 Table 12 ( 12th Example) Radius of curvature Axis top surface distance Refractive index (Nd) Atsube number (νd) FNo, =5,6 TL/f
=0.988f/V1z3=1.572 f/f <5-=0.368 (Nl-1)f/rA=3.052 (N4-1)f/rB=-4,975

[Brief explanation of drawings]

1 to 12 show the first to twelfth embodiments of the present invention, and in each figure (A) is a diagram showing the lens configuration, and (B) is an aberration diagram. FIG. 13 is a schematic cross-sectional view showing a projection optical system of a microreader to which the present invention is applicable. I...First lens group ■...Second lens group ■...Third lens group ■...Fourth lens group ■1...Fifth lens group A...Aperture diaphragm Applicant Minolta Camera Co., Ltd. Fig. 1 (A) Fig. 1 (B) Beaded grain Astigmatism Distortion
West 2 Figure 2 T C) Figure 2 (8) Figure 3 (C) Series 3 Figure (B) Figure 4 (A Figure 4 Raw & 1st 5th
Diagram (A) Diagram 1 (B) Diagram 6 (A) Diagram 6 (B) Diagram 7 (A) Diagram 7 (B) Senju Shuyou Astigmatism Shugo Namakyoku%
! 8 Figure (c) 1k [phase] U matari L lP burn nu L stop a curse q diagram (A) Figure 9 (B) 1 O diagram (A) keiq matari L non-or raw Me 1, d
b ζ Figure 11 (A) Figure 11 (8) Figure 12 (A) Figure 12 (8)

Claims (1)

[Claims] 1. In order from the magnification side, a first lens group consisting of a positive meniscus lens with its convex surface facing the magnification side, a second lens group consisting of a negative lens with its concave surface facing the magnification side, and a second lens group consisting of a negative lens with its convex surface facing the magnification side. A projection lens for microfilm comprising a third lens group consisting of a positive lens facing toward the magnification side, a fourth lens group consisting of a negative meniscus lens having its concave surface facing the magnifying side, and a fifth lens group consisting of a convex lens. 2. A projection lens for microfilm according to claim 1, which satisfies the following conditional expression. 1.5<f/f^1^2^3<2.2 -1.2<f/f^4^5<0 However, f: Focal length of the entire system f^1^2^3: 1st , a composite focal length of the second and third lens groups f_4_5: a composite focal length of the fourth and fifth lens groups 3, and the microfilm according to claim 2, which satisfies the following conditional expression: projection lens. (N_1-I)f/r_A<3.2 -5.7<(N_4-1)f/r_8<-4.5However,
N_1, N_4: refractive index r_A of the first and fourth lens groups,
r_B: The radius of curvature of the enlargement side surface of the first and fourth lens groups is 4, and the lens system has an aperture stop on the front side, according to any one of claims 1 to 3. Projection lens for microfilm. 5. The microfilm projection lens according to claim 4, wherein the aperture stop is disposed before or after the first lens group.