JPH05303033A - Microfilm projection lens system - Google Patents

Abstract

PURPOSE:To provide the improved projection lens system used for a microreader or a reader/printer for reproducing an image of a microfilm. CONSTITUTION:The microfilm projection lens system is constituted of a first focusing lens group I consisting of a cemented lens of a biconvex positive lens whose strong convex surface is turned to an enlargement side and a negative lens, a second divergent lens group II consisting of one piece of positive lens and one piece of negative lens whose strong concave surface is turned to the enlargement side, and a third convergent lens group III having a strong convergent component on the enlargement side, in order of the enlargement side, and an opening diaphragm is arranged in the vicinity of a first lens group I.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microfilm projection lens system used in a microreader or reader printer for reproducing an image on a microfilm.

[0002]

2. Description of the Related Art Many microfilms are recorded with each frame in which the orientations of the original characters are not unified vertically and horizontally at the time of its production, and in many cases, they are photographed irregularly. For this reason, conventionally, during image reproduction by a reader or reader printer, an image rotation prism is arranged between the projection lens and the screen, that is, on the enlargement side of the projection lens to correct the vertical and horizontal positions of the reproduced image projected on the screen. It is common to

However, in the conventional projection lens system, since the position of the aperture stop is located substantially at the center of the projection lens system, the image rotation prism to be inserted is attached to the magnifying side end surface of the projection lens system when the angle of view is wide. Even if the image rotation prism is arranged in the closest position, the light beam spreads, so that the image rotation prism becomes large. In addition, the image rotation prism is equivalent to a parallel plate placed at an angle of 45 degrees to the optical axis, and performance varies depending on the location even within the same image circle diameter. The larger the image rotation prism, the more the amount of axial astigmatism generated. Has a drawback in that (the axial astigmatism is proportional to the length of the prism bottom surface), the image is deteriorated, and the entire projection optical system including the mirror is enlarged.

Therefore, a so-called front diaphragm type projection lens system in which the aperture stop position where the light beam is most converged in the projection lens system is located near the end surface of the projection lens system has been proposed by the applicant of the present invention. For example, JP-A-2-
173712, JP-A-1-163713,
JP-A-1-163714, JP-A-63-1161
No. 12, JP-A-63-63012, JP-A-6-63012.
2-75609, JP-A-2-228621, and the like. The values of the F number F _NO , the angle of view 2ω, and the telephoto ratio ∞TL / f of these projection lens systems are shown in Table 1, respectively.

[0005]

[Table 1]

[0006]

By the way, generally, in a front diaphragm type projection lens system, the usable field angle cannot be widened and field curvature and astigmatism become large. It was difficult to correct the aberration. Moreover, there was a difficulty in compactness. Further, since it is a front stop, there is a very difficult design in that the combination of glass materials for simultaneously correcting axial chromatic aberration and lateral chromatic aberration is limited.

The present invention has been made in view of the above points, and is extremely compact with a telephoto ratio ∞TL / f of about 0.75, an angle of view 2ω = 20 °, and an effective F number F _NO. The objective of the present invention is to provide a new type of microfilm projection lens system in which various aberrations are well corrected at = 15 and the performance is good.

[0008]

According to the present invention, as shown in FIG.
As shown in the lens configuration in (A), in order from the magnification side, a converging first lens group I composed of a cemented lens of a biconvex positive lens with a strong convex surface facing the magnification side and a negative lens, and one positive lens And a divergent second lens group II consisting of a single negative lens with a strong concave surface facing the magnifying side, and a converging third lens group III having a strong converging component on the magnifying side. It is a microfilm projection lens system characterized by being arranged in the vicinity of the first lens group I 1. Further, the third lens group III is a single positive lens having a strong convex surface on the magnifying side, or the third lens group III is a positive lens and a negative lens having a strong concave surface on the magnifying side, or the third lens group. III
Is a microfilm projection lens system composed of a cemented lens of a positive lens and a negative lens with a strong concave surface facing the magnifying side.

Further, as a more specific form for carrying out the present invention, the focal length of the entire system is f, and the first lens group I
, And the focal length of the third lens group III is f
c, the converted surface distance between the first lens group I and the second lens group II is e
_{When set to 1} ,

1.5 <f / fa <2.5 ... 0.6 <f / fc <1.8 ... 2.5 <f / e ₁ <3.7 ...

It is desirable that the conditional expressions (1) and (2) are satisfied.

The present invention is a compact telephoto type projection lens system having a three-group structure consisting of a first lens group I to a third lens group III, and reducing the number of constituent lenses to 5 to 6.

The first lens group I on the magnifying side is suitable as a telephoto type front lens group. Since the first lens group I 1 has a relatively strong refractive power, the spherical aberration tends to be undercorrected, but the second lens group II has the above-described configuration to correct the spherical aberration. Further, while adopting the telephoto type, a divergent lens group having a negative lens with a concave surface facing the magnifying side is arranged behind the second lens group II so as to be advantageous for correction of coma aberration.

As shown in FIG. 1B, by increasing the conversion surface spacing e ₁ between the first lens group I and the second lens group II, the negative field curvature that tends to occur is corrected, and The telephoto ratio can be further reduced, and the projection lens system can be made compact.

The aperture stop S is arranged in the vicinity of the first lens group I, but the third lens group III has a converging refractive power having a strong convergent component on the magnifying side and is relatively distant from the aperture stop S. However, that is, by allowing the off-axis light rays to pass through at a position away from the optical axis, it becomes possible to bring the reduction-side pupil position to a position relatively away from the reduction-side image plane.

As a result, the pupil position P _{EXT based} on the reduction-side image plane is about -0.7f, which is relatively far from the image plane for the telephoto type. By making the pupil position P _EXT far, the exit angle of off-axis light decreases, and the lateral magnification β decreases to −.
The low magnification of 1 / 7.5 prevents the illumination lens system following the projection lens system from becoming large even though the image format is large. In addition, FIGS. 2A and 2B show the case where the third lens group III is composed of positive and negative power arrangements as in the present invention, and the third lens group III is a negative and positive power arrangement in the related art. It is shown by comparing the off-axis chief ray heights h ₁ and h ₂ in the case of being configured by the arrangement. From these figures, the off-axis chief ray height is positive for the third lens group III of the present invention,
It is well understood that the negative power arrangement can lower the off-axis chief ray height h ₁ on the final surface.

Therefore, the third lens group III is composed of a positive lens and a negative lens having a strong concave surface on the magnifying side.
Alternatively, by using the cemented lens, the lens outer diameter defined by the reduction end (final surface) of the third lens group III can be reduced. As a result, the projection lens system can be made compact.

The above conditional expression defines the refracting power of the first lens group I, and if the upper limit value is exceeded, the first lens group I
It becomes difficult for other lens groups to correct the negative spherical aberration generated by I. On the other hand, when the value is below the lower limit, the total lens length becomes long, and the compactness that is the object of the present application is lacking.

The above conditional expression defines the refractive power of the third lens group III, and if it exceeds the upper limit value, it becomes difficult to correct off-axis field curvature, coma aberration and distortion. On the other hand, when the value goes below the lower limit, the position of the exit pupil is changed to approach the reduction side image plane, and the illumination system installed subsequent to this projection lens system becomes large.

The above conditional expression defines the telephoto ratio. By satisfying this conditional expression, various aberrations are satisfactorily corrected, and the telephoto ratio is reduced to about 0.75 with 5 to 6 lenses. It becomes possible. If the lower limit is exceeded, the Pebbard sum will increase negatively, making it difficult to correct field curvature. Further, the coma aberration becomes large and cannot be completely corrected. On the other hand, when the value exceeds the upper limit, the total length of the lens system becomes large, which makes it difficult to make it compact. Deviating from this conditional expression requires a large number of lenses to correct various aberrations that occur, which is also disadvantageous to the compactness which is the object of the present invention.

[0021]

EXAMPLES Specific examples will be described below with reference to the drawings.
To do. 3 to 7 show the first to fifth embodiments of the present invention.
Example Microfilm Projection with Image Rotating Prism
It is sectional drawing which shows the structure of a lens system. In each of these figures
And the parallel flat glass on the right side shows the film holder,
The film is sandwiched with another parallel flat glass (not shown).
It is designed to hold clothes. Including this parallel flat glass
Tables 2 to 6 show detailed lens specifications. In these tables
And the radius of curvature is r₁ , R₂ ... ,
Axial surface spacing is d₁ , D₂ ・ ・ ・ , Refractive index of glass material at d-line
To N₁ , N₂・ ・ ・  , The Abbe number of the glass material is ν₁ , Ν₂ ・ ・ ・
・  And the film holders of Examples 1 to 5
It is a numerical value on each side including-. In addition, the conditions in the above tables
The numerical values of the respective examples in the formula are also shown. That
The spherical surface of the microfilm projection lens system of each example.
Aberration curve diagram showing each aberration situation of difference, astigmatism and distortion
Are shown in FIGS. 8 to 12, respectively.

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

[Table 5]

[0026]

[Table 6]

In these examples, the aperture efficiency is 100% within the effective angle of view. Further, the projection angle is a compact, low-magnification projection lens system with an excellent angle of view of 2ω = 20 ° and excellent aberration correction.

[0028]

As described above, the lens system for projecting the microfilm by disposing the image rotation prism on the magnifying side of the present invention has the entrance pupil position where the light beam converges most near the magnifying side of the projection lens system. By disposing the image rotation prism at a position close to the end face of the image rotation prism, deterioration of the projected image can be minimized, and the image rotation prism and the projection optical system as a whole can be made compact. Moreover,
Since the pupil position is relatively far from the film surface, it becomes easy to share the projection lens system with other magnifications with the illumination system.

Further, the number of constituent sheets is as small as 5 to 6, and
The outer diameter of the lens can be made small, and the telephoto ratio of about 0.75 has made it possible to make the conventional low-magnification projection lens extremely compact. Further, the projection lens system of the present invention is suitable for application to an optical system having an image rotation prism on the magnifying side, as described above, but it is also sufficient to be used for an optical system not using the image rotation prism. It goes without saying that it has performance.

[Brief description of drawings]

1A and 1B are a lens configuration diagram and a thin-walled power arrangement diagram of the present invention;

2A and 2B show the present invention in which the third lens group III is composed of positive and negative lenses, and the third lens group III is composed of negative and
Explanatory diagram of comparison of the off-axis chief ray height with the conventional one composed of positive,

FIG. 3 is a side sectional view showing the configuration of the first embodiment of the present invention,

4 is an aberration curve diagram of the projection lens system of FIG.

FIG. 5 is a side sectional view showing a configuration of a second embodiment of the present invention,

6 is an aberration curve diagram of the projection lens system of FIG.

FIG. 7 is a side sectional view showing the configuration of Embodiment 3 of the present invention,

8 is an aberration curve diagram of the projection lens system of FIG. 7,

FIG. 9 is a side sectional view showing a configuration of a fourth embodiment of the present invention,

10 is an aberration curve diagram of the projection lens system shown in FIG. 9;

FIG. 11 is a side sectional view showing the configuration of Example 5 of the present invention,

12 is an aberration curve diagram of the projection lens system of FIG.

Claims (5)

[Claims] 1. A first lens group I having a converging property consisting of a cemented lens of a biconvex positive lens and a negative lens with a strong convex surface facing the magnification side in order from the magnification side, and one positive lens and a strength to the magnification side. Divergent second consisting of one negative lens with concave surface
Lens group II, third convergence with strong convergence component on the magnifying side
Lens group III and the aperture stop is the first lens group
A microfilm projection lens system that is placed near I. 2. The microfilm projection lens system according to claim 1, wherein the third lens group III is composed of one positive lens having a strong convex surface facing the magnification side. 3. The microfilm projection lens system according to claim 1, wherein the third lens group III comprises a positive lens and a negative lens having a strong concave surface on the magnifying side. 4. The microfilm projection lens system according to claim 1, wherein the third lens group III is composed of a cemented lens of a positive lens and a negative lens having a strong concave surface facing the magnifying side. 5. The focal length of the entire system is f, the focal length of the first lens unit I is fa, the focal length of the third lens unit III is fc,
2. The microfilm projection lens system according to claim 1, wherein the following conditional expression is satisfied, where e ₁ is the conversion surface distance between the first lens group I and the second lens group II. 1.5 <f / fa <2.5 ... 0.6 <f / fc <1.8 ... 2.5 <f / e ₁ <3.7 ...