JPS63116112A - Projection lens for microfilm - Google Patents

Abstract

PURPOSE:To obtain the titled lens which is compact and whose each aberration has been corrected so as to be well-balanced, by providing five lens groups of biconvex, biconcave, positive, negative meniscus and convex shapes in order from the enlargement side, and satisfying prescribed conditions. CONSTITUTION:The titled lens is constituted of the first lens group I consisting of a biconvex lens, the second lens group II consisting of a positive lens whose convex surface is turned to the reduction side, the third lens group III consisting of a positive lens whose surface is turned to the reduction side, the fourth lens group 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. Also, this projection lens for a microfilm is constituted so as to satisfy the conditions of the inequality I and the inequality II. In this regard, in the expressions, (f) : f123 : and f45 denote a focal distance of the whole system, a composite focal distance of the first, the second and the third lens groups I, II and III, and a composite focal distance of the fourth and the fifth lens groups IV, V, 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 are recorded without aligning the orientation of the characters in the original document vertically and horizontally at the time of creation. Therefore, conventionally, a microreader or reader printer has been used in which an image rotation 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, in such devices, the space for inserting the projection lens cannot be made very large from the viewpoint of operability and the overall size of the device. It becomes difficult to secure space for the image rotation prism. Therefore, a compact lens is desired. The so-called telephoto ratio TL/f is used as a measure of the compactness of a projection lens. , TL is the total length of the lens when the object point is at infinity, and f is the focal length.

As a compact microfilm projection lens with a small telephoto ratio, for example, the Japanese Patent Publication No. 47-3502
There is one known from Publication No. 8.

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

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

The above purpose is to first
a second lens group consisting of a biconcave lens, a third lens group consisting of a positive lens with its convex surface facing the reduction side, a fourth 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. This is achieved by a microfilm projection lens composed of a lens group.

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 fifth lens group), the overall length is shortened and compact, and the positive power of the front group is mainly generated in the first lens group. However, the negative spherical aberration generated in the first lens group is mainly corrected in the second lens group, and the negative spherical aberration generated in the third lens is mainly corrected in the fourth lens group. ing.

Furthermore, compactness of the projection lens of the present invention is guaranteed by satisfying the following conditional expression K.

(1) 1.5<///123 <1.5 (2) −
1,6<////45 <-1, 1 set, 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, (1)
, Equation (2) defines the power of the front and rear groups.

Here, in order to make the lens system compact, it is necessary to increase the power of the front group. On the other hand, in order to reduce the curvature of field, the power of the front group must be reduced. Equations (1) and (2) are conditions 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 0.9, as is clear from the examples described later.
8~i,06, which is extremely small, indicating 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-x)//rA<2.2, Nl
, N2. N4: 1st. Second. Refractive index of the fourth lens group rA: Radius of curvature of the magnification side surface of the 1171st group rB: Radius of curvature of the demagnification side surface of the 1171st group rC: Radius of curvature of the magnification side surface of the second lens group rD: Radius of curvature of the magnification side surface of the 4th lens group As mentioned above, in the projection lens of the present invention, the power of the front group is generated in the 1171st group, but the negative spherical aberration generated in this group is mainly This is corrected by the second lens group, especially its magnification side surface. In this way the second
When spherical aberration is captured by the magnifying side surface of the lens group, off-axis aberrations, particularly coma aberration, occur, but this is balanced by the demagnifying side surface of the 1171st lens group. this is,
This is achieved by satisfying equation (5). Equation (3) defines the power of the enlarged side surface of the 1171st group.2.
If it exceeds 2, it becomes difficult to correct the above-mentioned spherical aberration and comatic aberration at the same time. Equation (4) defines the power of the magnifying side surface of the fourth lens group, and when it becomes larger than -3.0, it becomes difficult to correct various aberrations generated in the front group in a well-balanced manner.

Furthermore, if the formula (4) is not met, the error sensitivity to eccentricity becomes large, resulting in a lens that is difficult to manufacture.

The projection lens of the present invention was originally developed for the purpose of being combined with a small image rotation prism, and therefore the aperture stop is placed on the front side (enlargement side). however,
The projection lens of the present invention can be fully 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, in front of the third lens group or You can do it later. This also applies when a large image rotation prism is used due to the circumstances of the projection system.

Further, when the aperture stop is provided on the front side, the image rotation prism can be made smaller on the front side, but the sensitivity to errors such as lens eccentricity becomes more severe on the negative side. Therefore, in the first to fourth embodiments of the present invention, the aperture stop is placed in front of the 1171st lens group so that the image rotation prism can be sufficiently miniaturized, and furthermore, in the fifth embodiment, the aperture stop is placed in front of the 1171st lens group. It is placed after.

In this sense, the term "front side" used in the present invention means
This includes not only the front aperture outside the lens system, but also the position of the aperture located on the front side within the lens system.

FIG. 6 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 between 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 undergoes an image rotation action by an image rotation prism 3, and is 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 fifth embodiments of the present invention will be described using FIGS. 1 to 5. In each figure, fAl indicates the lens configuration, and 4 indicates an aberration diagram of the lens. Each figure fA showing the lens configuration
), I, II, III, ff, and V are the first lens group, the second lens group, the third lens group, and the fourth lens group, respectively.
The fifth lens group is shown. A is the aperture stop, and the 1st, 2nd, 3rd, .
In the fourth embodiment, it is arranged before the 1171st lens group, and in the fifth embodiment, it is arranged after the second lens group. Note that G is a flat glass plate that holds the microfilm 1, and only one of them is shown.

On the other hand, in each figure showing aberration (Bl), the solid line d of spherical aberration shows the aberration for each wavelength of the d-line, the -dashed line gl'ig line, and the two-dot chain line C shows the aberration for each wavelength of the C-line. is d
Regarding lines, the solid line DS is a spherical cross section, and the dotted line DT
indicates the aberration of the meridional 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 F number, telephoto ratio (TL//), ///123°///45, (Nl-1) f/rA, ( N4 1
)f/rpt ((1-Nl)/r, +(Nz-1)f
Each value of ro)/ is an indication. Further, the focal length is normalized to 1.

Table 1 (First example) Radius of curvature Axial surface spacing Refractive index (Nd) Atsube number (νd) (Nl -1) f/rA=2.02 (N4-1) f/rp=-2,44 Table 2 (Second example) Radius of curvature Distance between upper surfaces of the shaft Refractive index (Nd) A-Sobe number (νd) FN0. =5.6TL//
=1.06β=-1/19 ///123=1.65 7//45=-1,
55(N+-1)f/rA=1.59 (Na1) //'D=2.54Table 3
(Third example) Radius of curvature Distance between upper surfaces of the shaft Refractive index (Nd) A-Sobe number (νd) FN0. =5.6TL/
/=1.04β=-1/19 f/fL23=1.74 f/f45 =-
1,58(Nl-1)f/rA=1.93 (N4-1)//r,=-2,77 Table 4 (Fourth Example) FN0. = 5.6 TL// = 1.
06β=-1/19 f/f123 = 175 f/f45 =-
1,54 (Nl-1) f/rA = 1.86 (N4 1) f/rD = 2.74 'B ''C Table 5 (Fifth Example) Radius of curvature Upper axis spacing Refractive index (Nd) Atsube number (
νd)FN0. =5,6TL//=0
．． 98β=-1/17.5 f/f123 =1.58 f/f45 =
-1,19(Ni-1)f/rA=2.18 (N4-1)f/rp=-2,94 FIG.

1... 1st lens group ■... 2nd lens group ■... 3rd lens group ■... 4th lens group ■... 5th lens group A... Aperture diaphragm Applicant Minolta Camera Co., Ltd. Fig. 1 (A) Fig. 1 (β) Fig. 2 (A) Fig. 2 (B) Elimination 1φυE Astigmatism q or difference -, 1
藺ψFigure 3 (A> Figure 3 (B) 1MIJ'llL
41&,,'SL
, i-bend/Q Fig. 4 (A> Fig. 4 CB) Fig. 5 (A)

Claims (1)

[Claims] 1. In order from the magnification side, a first lens group consisting of a biconvex lens, a second lens group consisting of a biconcave lens, a third lens group consisting of a positive lens with a convex surface facing the reduction side, and a concave lens group that magnifies the concave surface. A microfilm projection lens composed of a fourth lens group consisting of a negative meniscus lens facing the 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<1.8 -1.6<f/f_4_5<-1.1, f: focal length of the entire system f_1_2_3: combined focal length of the first, second, and third lens groups f_4_5: A projection lens for microfilm according to claim 2, characterized in that the composite focal length of the fourth and fifth lens groups is 3, and the following conditional expression is satisfied. (N_1-1) f/r_A<2.2 -3.0<(N_4-1) f/r_D {(1-Ni)/r_B+(N_2-1)/r_C}f
<-0.1 set, N_1, N_2, N_4: 1st, 2nd
, refractive index of the fourth lens group r_A: radius of curvature of the magnification side surface of the first lens group r_B: radius of curvature of the demagnification side surface of the first lens group r_C: radius of curvature of the magnification side surface of the second lens group r_D: The microfilm according to any one of claims 1 to 3, characterized in that the radius of curvature of the magnifying side surface of the fourth lens group is 4, and the aperture stop is provided on the front side of the lens system. projection lens. 5. The microfilm according to claim 4, wherein the aperture stop is disposed in front of the first lens group, between the first lens group and the second lens group, or after the second lens group. projection lens.