JPS62237414A - Zoom lens system for finite distance - Google Patents

Abstract

PURPOSE:To freely execute framing, and also, to make the titled system small in size and compact, by constituting it so that an aperture stop is fixed, the first positive lens group and the second negative lens group move along an optical axis, and a distance between an object and an image is kept constant in a finite distance, at the time of zooming. CONSTITUTION:The titled lens system is a finite distance use zoom lens system for constituting a projection lens of a microfilm reader, etc. It is constituted by arranging an aperture stop S, the first positive lens group I, and the second negative lens group II, in order from the magnification side. In this state, the aperture stop S is fixed, and the first positive lens group and the second negative lens group II move along an optical axis at the time of zooming and keep a distance between an object and an image constant in a finite distance. The interval between an object and an image is kept constant irrespective of zooming and out-of-focus (a movement of an image point) due to zooming is not generated, therefore, the projecting magnification can be changed continuously within a range of about 20X-25X.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a microfilm reader, a microfilm printer, or a finite distance device that is incorporated into the optical system of a microfilm reader/printer to change the projection magnification in the range of about 20x to 25x. Regarding zoom lens systems.

-a, there are lens systems for microfilm readers, microfilm printers, and microfilm readers/printers, such as those disclosed in Japanese Patent Publication No. 47-35028, Japanese Patent Application Laid-open No. 57-4016, and Japanese Patent Application Laid-open No. 57-4016. 7371
The one disclosed in Publication No. 5 is known.

However, Japanese Patent Publication No. 47-35028 and Japanese Unexamined Patent Publication No. 57-
The one disclosed in Japanese Patent No. 4016 is a microlens system with a fixed magnification, so the framing is constant and it is not easy to use. On the other hand, the latter, published in Japanese Patent Application Laid-Open No. 57-73715, is a zoom lens system for finite distance use, but since it has an aperture built into the lens system, it can be used to zoom to the magnification side (screen side). The effective F-number of the camera changes, and the amount of light on the screen changes greatly, giving a visually strange feeling. The reason is as follows.

In other words, as shown in FIG.
An aperture (
Considering a model with S), the effective F-number on the magnifying side is the 1171st group (1) seen from the magnifying side.
It is determined by the size of the virtual image (V) (entrance pupil) of the diaphragm (S). Now, if the half angle of the tension angle of the axial light beam is U, then the effective F number is determined by sin u. Therefore, due to the zooming movement of the 1171st group (I), the diameter and position of the virtual image (V) of the diaphragm (S) by the 1171st group (I) change, and the half angle U also changes.
This is because the effective F number changes.

In addition, USP336032 is available as a lens with built-in prism.
5 has a doped prism that itself has its own aberration-generating factor built in between the lenses, so a large number of lenses are required to correct the aberrations of the entire system, making the entire lens system large. Furthermore, since the diaphragm is disposed between the movable lens groups, the effective F-number on the enlargement side changes during zooming.

The finite-distance zoom lens system according to the present invention has been developed in view of the points detailed above. (b) The effective F-number on the magnification side can be kept constant regardless of zooming; (c) The prism for image rotation can be made smaller; (d) The point is that it can be configured compactly.

Therefore, in the present invention, the aperture stop, the first
It is composed of a positive lens group and a second negative lens group arranged side by side, and during zooming, the aperture stop is fixed and the first positive lens group and the second negative lens group move along the optical axis to move over a finite distance. The present invention has provided a finite distance zoom lens system that is characterized by keeping the object-to-image distance constant, thereby achieving the above-mentioned objective.

That is, regardless of zooming, the object image interval is kept constant and there is no blurring (image point movement) due to zooming, so the projection magnification can be continuously changed in the range of about 20X to 25X.

Moreover, since the aperture stop is installed on the magnifying side,
By arranging the aperture diaphragm close to the image rotation prism, the image rotation prism can be miniaturized, and as shown in FIG. The half-angle U remains constant regardless of zooming, and the effective F-number on the enlargement side does not vary.

Furthermore, among the lens groups that move with zooming,
The first lens group counting from the magnification side is a positive lens group,
The second lens group is a negative lens so that it becomes a telephoto type on the long focal point side, and since it does not include a built-in prism for image rotation, it can be constructed compactly.

Next, the present invention will be specifically explained.

As shown in Figure 1, microfilm holder (1)
, a projection lens (2), an image rotation prism (3), a first mirror (4), a second mirror (5), a third mirror (6), and a screen (7). This is a finite distance zoom lens system that constitutes the projection lens (2) of the microfilm league printer, and this is shown in Fig. 2 (A) and (El
), an aperture stop (S), a first positive lens group (1), and a second negative lens group (II) are juxtaposed in order from the magnification side, and the aperture at a predetermined magnification is Aperture (
The lens is configured so that TL/fL<1.2, where TL is the distance between S) and the image plane, and ft is the longest focal length.

The aperture stop (S) is fixed, and the first positive lens group (I) and the second negative lens group (II) move along the optical axis and move over a finite distance during zooming. The object-to-image distance is kept constant. Specifically, the first positive lens group (1) is close to the aperture stop (S) at the longest focal length end (L end), and the first positive lens group (1) is close to the aperture stop (S) at the longest focal length end (L end). ) and the second negative lens group (If) when zooming from the longest focal length end (L end) to the shortest focal length end (S end).
Distance (d) between the positive lens group (I) and the second negative lens group (n)
9) moves toward the reduction side while expanding it.

The first positive lens group (I) is configured by juxtaposing a positive lens, a biconcave lens, and a positive lens group including at least one positive lens in order from the magnification side, that is, a positive-negative-positive triplet type, or This is a modified type of lens group that also serves as a front aperture to correct spherical aberration and coma aberration.

The second negative lens group (If) is configured by juxtaposing, in order from the magnification side, a positive lens group having at least one positive lens and a negative lens group having at least one negative lens. This is a lens group that contributes to correction of various aberrations during zooming, especially astigmatism and off-axis coma aberration.

Examples in which the present invention is applied to the zoom lens system described above will be shown below.

Table 1 shows the radius of curvature, axial spacing, refractive index at the d-line, and Abbe number of the lenses corresponding to the examples.

Note that the distance between the top surfaces of the shafts is the lateral magnification (the reciprocal of the projection magnification, which is a negative value)
is β, β=-0,049, β=-0,045,
The fluctuation value at β=-0,040 is shown.

β in this example -0,049, β=-0,04
5. The longitudinal aberration at β=-0,040 is shown in Figure 3, respectively.
It is shown in FIGS. 4 and 5. Among the aberrations, spherical aberration is di,
The F-line and C-line are shown, and astigmatism and distortion are shown on the d-line. SC is the amount of dissatisfaction of the sine condition, and Fe is the effective F on the reduction side.
The number ω indicates a half angle of view.

Σd=73.286~73.286~73.286 In summary, when the present invention is incorporated as a projection lens in a microfilm reader, microfilm printer, or microfilm reader/printer, Synergistically with rotation, we have developed a finite-distance zoom lens system that allows free framing, eliminates changes in the brightness of the projected image due to zooming, and can be configured to be small and compact, including the image rotation prism. We have now been able to provide it.

[Brief explanation of drawings]

Figures 1 to 5 show embodiments of the present invention, with Figure 1 being a schematic diagram of the microfilm reader, and Figures 2 (a) and (El) showing the L and S ends of the lens system, respectively. The cross-sectional views of FIGS. 3 to 5 each have a magnification β of −
It is an aberration curve diagram at the time of 0,049, -0,045, -0,040. FIG. 6 is a cross-sectional view of the lens system referred to in the description of the prior art, and FIG. 7 is a cross-sectional view of the lens system referred to in the description of the present invention. (S)...Aperture stop, (1)...First
Positive lens group, (formerly... second negative lens group,

Claims (3)

[Claims] (1) An aperture stop, a first positive lens group, and a second negative lens group are juxtaposed in order from the magnification side, and when zooming, the aperture stop is fixed, and the first positive lens group and the second negative lens A finite-distance zoom lens system characterized by a group that moves along the optical axis to maintain a constant object-to-image distance over a finite distance. (2) The first positive lens group is close to the aperture stop at the longest focal length end, and when zooming from the longest focal length end to the shortest focal length end, the first positive lens group and the second negative lens group The finite distance zoom lens system according to claim 1, wherein the first positive lens group and the second negative lens group move toward the reduction side while increasing the distance between them. (3) The first positive lens group is configured by juxtaposing a positive lens, a biconcave lens, and a positive lens group including at least one positive lens in order from the magnification side, and the second negative lens group is
Claim (1) is configured by juxtaposing a positive lens group having at least one positive lens and a negative lens group having at least one negative lens in order from the magnification side. Zoom lens system for finite distances.