JPH0387823A - Exposing method for variable power type copying machine - Google Patents

Abstract

PURPOSE:To obtain excellent image formation performance over a wide power variation range by making the incidence and projection sides of an image forming lens system opposite from those of enlargement and reduction. CONSTITUTION:The image forming lens system 8 has lenses arranged asymmetrically about a stop and when a copy of life size is taken, the image forming lens system 8, and plane mirrors 5 and 6 are arranged at positions (a) in a figure. The image forming lens system 8 is displaced to an object-side position (c) for the enlargement and to an image-side position (b) for the reduction. When an enlarged copy is taken, the image forming lens system 8 is rotated and its incidence and projection side are opposite from those at the time of the life-size and enlargement copying operations and the side shown by a mark B is an incidence side. Consequently, the excellent conjugation relation between a document and a photosensitive body at the time of the unmagnification and reduction copying operation is realized even at the time of the enlargement.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to an exposure method in a variable magnification type copying machine.

[Prior Art] Conventionally, the imaging lens system of a copying machine has been mainly composed of an even number of lenses arranged symmetrically with respect to an aperture. There is also a constant demand for compactness and high performance in imaging lens systems for copying machines. From the viewpoint of compactness and high performance, an imaging lens system that has a symmetrical lens arrangement with respect to the aperture has a radius of curvature, which can be used for aberration correction.
There are problems in that the number of parameters such as surface spacing and glass material is small, and the degree of freedom in design is greatly restricted, making it difficult to downsize and improve performance.

For this reason, recently, imaging lens systems for copying machines have been proposed that have an asymmetric lens arrangement with respect to the aperture.

[Problems to be Solved by the Invention] On the other hand, recently, it has become common for copying machines to have a variable magnification function, and the range of variable magnification has expanded from enlargement to reduction magnification.

When using an imaging lens with the above-mentioned asymmetric lens arrangement in a copying machine having such a wide variable magnification range including enlargement/reduction magnification, it is difficult to achieve good imaging performance in the entire variable magnification range.

In other words, if good imaging performance is achieved at the enlargement magnification, the imaging performance tends to deteriorate at the reduction magnification, and conversely, if good imaging performance is achieved at the reduction magnification, the imaging performance at the enlargement magnification decreases. is prone to deterioration.

The present invention was made in view of the above-mentioned circumstances, and
The purpose of the present invention is to provide an exposure method for a variable magnification type copying machine that can achieve good imaging performance in a wide range of variable magnification including enlargement and reduction magnification by using an imaging lens having an asymmetric lens arrangement with respect to the aperture. .

[Means to solve the problem] The present invention will be explained below.

In the present invention, an imaging lens system for forming an original image on a photoreceptor has an asymmetric lens arrangement with respect to an aperture, and this imaging lens system is displaced along the optical axis and the image is transferred from the original to the photoreceptor. This is an exposure method used in a "variable magnification type copying machine" in which the copying magnification is changed by changing the optical path length, and the copying magnification includes an enlargement magnification and a reduction magnification.

The feature of this method is that ``the entrance and exit sides of the imaging lens system are reversed in magnification and reduction magnification.''

[Function] In the variable magnification method, which changes the copying magnification by displacing the imaging lens system along the optical axis and changing the optical path length from the original to the photoreceptor, the imaging lens system is a fixed focal length lens system. It is.

The fact that such an imaging lens system has good imaging performance at magnification (or reduction) magnification means that the image formation lens system provides good image formation performance between the document and the photoreceptor at magnification (or reduction) magnification. It means that they are connected in a conjugate relationship.

In this case, if the lens arrangement of the imaging lens system is asymmetric with respect to the aperture, it is difficult to maintain a good conjugate relationship between the original and the photoreceptor when the imaging lens system is used as it is at the reduction (or enlargement) rate. difficult.

However, at this time, the entrance side and exit side of the imaging lens system are
If you reverse the enlargement (or reduction) magnification, the enlargement (or reduction)
or reduction) magnification, it is possible to reproduce the goodness of the conjugate relationship.

[Embodiments] Hereinafter, specific embodiments will be described with reference to the drawings.

The figure schematically shows an example of an exposure optical system embodying the present invention.

Reference numeral 1 indicates an original glass, and an original to be copied is placed flatly on this original glass l.

The exposure optical path from the original placed on the original glass l to the photoreceptor 9 is formed by the plane [2, 3, 4, the imaging lens system 8, and the plane mirrors 5, 8.7.

The plane mirror 2 is used for scanning, and moves together with a document illumination lamp (not shown) to scan the document.

At this time, the plane mirror 3.4 moves together at a speed of 172 times the moving speed of the plane mirror 2, keeping the optical path length on the object side of the imaging lens system 8 constant.

Of the plane mirrors 5.6.7 disposed on the image side of the imaging lens system 8, the plane mirror 5.6 is displaced to adjust the optical path length as the magnification changes.

Now, when the copying magnification is equal to the same, the imaging lens system 8 and the plane mirror 5.6 are arranged at the position shown in (a) in the figure.

Further, the positions shown in (b) with respect to the planes R5 and R6 generally indicate a state in which they are displaced in order to adjust the optical path length during enlargement or reduction magnification.

Imaging lens system 8 has "asymmetric lens arrangement with respect to aperture"
For enlargement magnification, it is displaced to position (c) on the object side from position (a) at the same magnification, and for reduction magnification, it is displaced to position (b) on the image side. .

Further, the symbols A and B attached to the imaging lens system 8 are symbols for distinguishing between the front and rear of the imaging lens system 8.

The imaging lens system 8 is designed to have good imaging performance for the same magnification and reduction magnification, and for the same magnification and reduction magnification, the side indicated by the symbol A is the object side, that is, the incident side. There is.

On the other hand, when the magnification is increased, the imaging lens system 8 is rotated so that the entrance side and the exit side are reversed from those when the magnification is equal to or reduced, so that the side indicated by the symbol B is set as the entrance side.

As a result, it has been realized at the same magnification and reduced magnification.
A good conjugate relationship between the original and the photoconductor can be achieved even at magnification.

[Effects of the Invention] Therefore, according to this exposure method, good imaging performance can be achieved in a wide variable magnification range from enlargement to reduction, and copies of good image quality can always be obtained regardless of the copying magnification. In addition to the original scanning method described in the embodiment, the exposure method may be a method of displacing the original with respect to an exposure optical system, or a full-surface exposure method.

[Brief explanation of drawings]

The figure is a diagram for explaining one embodiment of the present invention.

Claims (1)

[Claims] An imaging lens system that forms an original image on a photoreceptor has an asymmetric lens arrangement with respect to an aperture, and the imaging lens system is displaced along the optical axis and transferred from the original to the photoreceptor. In a variable magnification type copying machine that changes the copying magnification by changing the total optical path length, and includes an enlargement magnification and a reduction magnification as the copying magnification, the input side and exit side of the imaging lens system are An exposure method characterized by reversing the reduction magnification.