JP3376153B2 - Zoom lens - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a micro film reader or a micro that reproduces an image of a micro film, for example, in which zooming is performed while maintaining a distance between objects at a fixed finite distance. The present invention relates to a zoom lens suitable for a film reader printer or the like.

[0002]

2. Description of the Related Art Conventionally, in a projection optical system such as a microfilm reader or a microfilm reader printer, a projection optical system has been used in which the magnification is changed while the object-image distance is maintained at a fixed finite distance, and the projection magnification is continuously changed. Various zoom lenses have been proposed.

Generally, the lower the projection magnification of a zoom lens for projection is, the longer its focal length is, and therefore the zoom lens itself tends to be large.

However, if the projection size is up to about A4 size, the apparatus itself does not become so large. Therefore, the object-to-image distance does not become so long as about 1000 mm, so that the focal length of the projection lens at the time of low magnification does not have to be extremely long. As a result, it is possible to keep the zoom lens for projection with low magnification substantially the same size as other zoom lenses with high projection magnification without having a complicated lens structure.

However, if it is attempted to project the projection size up to about A3 size, the size of the apparatus itself increases to some extent. Therefore, the object-to-image distance must be long to some extent, and the focal length of the projection lens itself must be set long according to the object-to-image distance. Therefore, there is a problem that it becomes very difficult to obtain good optical performance without increasing the size of the lens.

In general, in a projection optical system such as a microfilm reader printer, an image rotation prism (hereinafter referred to as "rotation prism") rotatable near the exit side (screen side) of a zoom lens for projection. Are arranged. This makes it possible to rotate the projected image at an arbitrary angle and easily adjust the inclination of the image in the plane of the film. The size of the rotation prism is generally required to be about 80 to 100 mm.

On the other hand, in the present situation, a zoom lens for projection with a low magnification capable of projecting up to A3 size, for example, a zoom lens with a projection magnification of about 7 to 16 times, generally has a long focal length, so that a film is used. The distance from the film surface (object surface) of the projected image such as to the first lens surface on the magnifying side of the projection lens is required to be about 150 mm.

That is, when the rotation prism and the zoom lens for projection are arranged in the apparatus, it is about 250.
A space of about mm is required to be secured on the main body of the apparatus, and as a result, there are problems that the position of the screen for observing the projected image is high and the size of the entire apparatus is large.

Therefore, in order to avoid the above-mentioned problems, conventionally, when a zoom lens for projection with a low magnification is used, the rotation prism is detached from the apparatus main body so that the image rotation function cannot be used, and the projected image is observed. Was there.

By the way, when using a device such as a microfilm reader printer, for example, certain data is retrieved by a fish film (microfiche film), and then a roll film is used based on the retrieved data.
A series of operations of browsing the searched data is often performed.

The magnification for enlarging and projecting this fish film is about 24 times, and at this time, the zoom range is 20.
A zoom lens for projection with a so-called medium magnification of about 30 times is used. The magnification for enlarging and projecting the roll film is about 14 to 15 times, and at this time, a so-called low-magnification projection zoom lens having a zoom range of about 9 to 16 times is used.

In the series of operations described above, in order to magnify and project the film image at a projection magnification suitable for the film, the zoom lens for projection must be frequently replaced according to the type of the film. There was an inconvenience.

Further, as described above, when the zoom lens for projection with low magnification is used, the rotation prism must be removed from the main body of the apparatus. Therefore, the rotation prism can be attached to the main body of the apparatus every time the lens is exchanged.
I had to remove it. Therefore, there is a problem that the work efficiency is very poor for the user.

According to the present invention, the lens configuration of each lens group of the two-group zoom lens composed of two lens groups as a whole is appropriately set, and the zoom range often used for magnifying and projecting a fish film is about 20 to 30 times. With a zoom lens for medium magnification, by expanding the zoom range on the low magnification side to secure a variable magnification range of about 14 to 30 times so that roll film can also be magnified and projected, it is possible to use only one zoom lens. It is an object of the present invention to provide a zoom lens capable of enlarging and projecting both a fish film and a roll film and having extremely high work efficiency, which is suitable for, for example, a microfilm reader.

Further, according to the present invention, the size of the projection lens is 20 to 30 even though the low magnification range of about 14 times is covered.
By making it about the same size as a lens that secures a variable power range only about twice, it is possible to use a rotation prism having an image rotation function, which makes it easy to observe a projected image and has good operability. For example, an object of the present invention is to provide a zoom lens suitable for a microfilm reader or the like.

[0016]

A zoom lens according to a first aspect of the invention is a first lens unit L having a negative refractive power in order from the magnification side.
1. Having two lens groups of the second lens unit L2 having a positive refractive power, the first lens unit L1 has a concave locus on the enlargement side with zooming from the short focal length end to the long focal length end. In the zoom lens having the second group L2 moving from the reduction side to the enlargement side with a monotonous locus, the first group L1 includes a negative lens L11 having a concave surface facing the enlargement side and a positive lens L12. A second lens unit L2 having a cemented lens L1a
Is an aperture stop SP, a positive lens L21, a positive lens L22, a negative lens L23, and a biconvex positive lens L2 in order from the enlargement side.
4. Positive lens L25 and negative lens L with concave surface facing the reduction side
And a negative lens L27 having a concave surface facing the magnifying side, and a positive lens L28. The focal length of the second lens unit L2 is fB, and the negative lens L2a is negative. Lens L27 and positive lens L
When the composite focal length of 28 is fB2 and the focal length of the negative lens L27 is f7, -1.2≤fB2 / fB≤-0.6 (1) 0.6≤f7 / fB2≤1.3 ... (2) is characterized by satisfying the following condition.

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2, 3, and 4 are sectional views of lenses of Numerical Embodiments 1 to 4 of the present invention, respectively, FIGS. 5, 6, 7, and 8.
[Fig. 3] is an aberration diagram of Numerical Examples 1 to 4, respectively. In the same aberration diagram, (A) shows the short focal length end and (B) shows the long focal length end.

In the figure, L1 is the first group having negative refractive power,
L2 is a second group having a positive refractive power, and the first group L1
The side is the enlargement side, and the second group L2 side is the reduction side.

MF is a projected object such as a microfilm,
G is a plate glass for pressing the projection target, SP is a diaphragm that moves integrally with the second lens unit L2, and S is a screen.

Each of the lens groups L1 and L2 moves so as to maintain a good optical performance while keeping a constant object-image distance during zooming, and a locus (moving locus) satisfying this is shown in FIGS. 4 is indicated by an arrow.

In this embodiment, when zooming from the short focal length end to the long focal length end, the first lens unit L1 has a concave locus toward the enlargement side and the second lens unit L2 is a straight line from the reduction side to the enlargement side as shown by the arrow. It moves so as to have a specific (monotonic) trajectory. As a result, in the present embodiment, a zoom lens having a high resolving power with a small variation in aberration during zooming over the entire screen at various projection magnifications is obtained.

The first lens unit L1 in this embodiment is composed of a cemented lens L1a in which a negative lens L11 having a concave surface facing the enlargement side and a positive lens L12 are cemented together, and has a negative refracting power as a whole. . The two lenses of the first lens unit L1 mainly correct axial chromatic aberration and coma in a well-balanced manner.

The second lens unit L2 includes an aperture stop SP in order from the enlargement side.
A front positive lens group L2F having three lenses, a positive lens L21 having convex surfaces on both sides, a meniscus-shaped positive lens L22 having convex surfaces facing the enlargement side, and a negative lens L23 having concave surfaces on both sides, and both lens surfaces. Is a cemented lens L2a in which an intermediate positive lens group L2M composed of a positive lens L24 having a convex surface, a positive lens L25 having a convex surface on both surfaces and a negative lens L26 having a concave surface on both surfaces are cemented, and the concave surface is directed to the enlargement side. The rear negative lens unit L2R has three lenses (a cemented lens is counted as one lens) including a negative lens L27 and a positive lens L28, and the second lens unit L2 has a positive refracting power as a whole. ing. In this embodiment, the second lens unit L2
By appropriately setting the refractive power of the rear negative lens unit L2R, the overall length of the entire lens is set to be shorter than the focal length at the long focal length extremity, and good optics with little aberration variation in each zoom range. We have obtained a zoom lens with high performance.

In particular, in this embodiment, the front positive lens unit L2F is mainly configured to correct axial chromatic aberration and spherical aberration, and the rear negative lens unit L2R is configured to have the above-described predetermined shape. Mainly corrects astigmatism over the entire zoom range. Conditional expression (1) is intended to suppress the total lens length short and to mainly improve the aberration correction at the long focal length end by appropriately setting the refractive power of the rear negative lens unit L2R in the second lens unit L2. It is a thing. If the upper limit of conditional expression (1) is exceeded, astigmatism at the long focal length extremity will occur remarkably and coma will also occur, making it difficult to satisfactorily correct these aberrations. If the lower limit of conditional expression (1) is exceeded, it becomes difficult to keep the total lens length short and it becomes difficult to correct both lateral chromatic aberration and astigmatism at the long focal length end, which is not preferable.

[0026]

[0027]

[0028]

[0029]

Conditional expression (2) appropriately adjusts the ratio between the refractive power of the second lens unit L2 and the refractive power of the negative lens L27 in the rear negative lens unit L2R, thereby performing well-balanced aberration correction in the entire zoom range. It is for the purpose.

If the upper limit of conditional expression (2) is exceeded, spherical aberration will occur remarkably at the short focal length extremity, and it will be very difficult to correct it well, which is not desirable.
If the lower limit of conditional expression (2) is exceeded, large astigmatism will occur at the long focal length extremity, and inward coma will occur extremely, which makes correction of aberration difficult.

Next, the case where the zoom lens of this embodiment is applied to a microfilm reader will be described with reference to FIG.

In the figure, reference numeral 2 is a zoom lens according to the present invention, which projects the microfilm MF in an enlarged manner onto the screen S through the rotation prism 3 and the folding mirrors 4, 5, and 6.

The rotation prism 3 is rotatably arranged near the enlargement side exit of the zoom lens 2.
By this rotation (rotation in the XZ plane in the figure), the projected image is rotated by a required angle and emitted. That is, microfilm M
Rotate to make it easier to observe the projected image when the vertical direction (vertical / horizontal position) of the F image information is not recorded correctly (X in the figure).
-Rotation in the Z plane).

In the present embodiment, for example, in a series of operations in which certain data is retrieved by, for example, a fish film, and then the retrieved data is browsed by a roll film, each film is obtained by using only one zoom lens 2. The image information recorded on the screen can be enlarged and projected on the screen S surface, whereby the projected image can be observed without making the operation troublesome. A rotation prism 3 having an image rotation function
The micro film reader is very easy to use because it can be installed in the device.

Next, numerical examples of the present invention will be shown. In the numerical examples, ri is the radius of curvature of the i-th lens surface in order from the expansion side, di is the i-th lens thickness and air gap from the expansion side, and Ndi and νdi are of the i-th lens in order from the expansion side. The refractive index of glass and the Abbe number. The last two lens surfaces r20 and r21 represent the plate glass G.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0038]

[Outer 1]

[0039]

[Outside 2]

[0040]

[Outside 3]

[0041]

[Outside 4]

[0042]

[Table 1]

[0043]

According to the present invention, as described above, the lens configuration of each lens unit of the two-group zoom lens is appropriately set, and the zoom range is about 20 to 30 times. By expanding the zoom range to cover the low magnification range of about 14 times, both fish film and roll film can be enlarged and projected by using only one zoom lens, which is very efficient. A zoom lens suitable for a microfilm reader or the like can be achieved.

Further, according to the present invention, since the total lens length can be set short even though the low magnification range is covered as described above, a rotation prism having an image rotating function can be used. Therefore, it is possible to achieve a zoom lens which is easy to observe a projected image and has good operability, and which is suitable for a microfilm reader or the like.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is a diagram of various types of aberration in Numerical example 1 of the present invention.

FIG. 6 is a diagram of various types of aberration in Numerical example 2 of the present invention.

FIG. 7 is a diagram of various types of aberration of Numerical example 3 of the present invention.

FIG. 8 is a diagram showing various types of aberration in Numerical Example 4 of the present invention.

FIG. 9 is a schematic view of a main part when the zoom lens of the present invention is applied to a microfilm reader.

[Explanation of symbols]

L1 first group L2 second group SP aperture G plate glass M Projected object d d line FF line C C line ΔS sagittal image plane ΔM Meridional image plane H entrance pupil height Y height

Claims (2)

(57) [Claims] 1. A first lens element having a negative refractive power in order from the enlargement side.
It has two lens groups, a lens unit L1 and a second lens unit L2 having a positive refractive power, and the first lens unit L1 has a concave locus on the enlargement side in association with zooming from the short focal length end to the long focal length end. And the second
In the zoom lens in which the group L2 moves from the reduction side to the expansion side with a monotonous locus, the first group L1 includes a negative lens L11 having a concave surface facing the expansion side.
Lens L1a in which the positive lens L12 and the positive lens L12 are cemented
The second lens unit L2 includes a stop SP and a positive lens L in order from the enlargement side.
21, a positive lens L22, a negative lens L23, a biconvex positive lens L24, a cemented lens L2a in which a positive lens L25 and a negative lens L26 having a concave surface facing the reduction side are cemented.
It has a negative lens L27 with the concave surface facing the enlargement side, and a positive lens L28, and the focal length of the second lens unit L2 is f
B, the composite focal length of the cemented lens L2a, the negative lens L27, and the positive lens L28 is fB2, and the negative lens is
A zoom lens characterized by satisfying the following condition : -1.2≤fB2 / fB≤-0.6 0.6≤f7 / fB2≤1.3 when the focal length of L27 is f7 . 2. The zoom lens according to claim 1, wherein the zoom range is 14 to 30 times.