Optical: systems and elements – Diffusing of incident light
Reexamination Certificate
1999-12-16
2001-11-27
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Diffusing of incident light
C359S618000, C355S052000
Reexamination Certificate
active
06324005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focusing optical system in which light is emitted from plural light sources in accordance with image information and which focuses light.
2. Description of the Related Art
Currently, there are image exposing devices in which plural light sources, which are disposed in a matrix-like arrangement at a predetermined position of the device, and a photosensitive material are moved relatively in a main scanning direction and a subscanning direction such that the photosensitive material is exposed. The light from the plural light sources is focused onto the photosensitive material by a focusing optical system. For example, semiconductor elements such as LEDs are used as the light sources, and these semiconductor elements are arranged in a matrix-like arrangement at a predetermined pitch.
However, in actuality, there are cases in which the light sources are not disposed at a predetermined pitch. Namely, there are cases in which positional offset (so-called pitch offset) occurs between the desired arrangement of positions of the light sources and the actual arrangement of positions. Due to this pitch offset, the distribution of the amount of light at the time of scanning the light sources and the photosensitive material relatively may be uneven and the image quality may deteriorate.
In order to reduce the unevenness in the distribution of the amount of light due to pitch offset, for example, reducing the focusing magnification of the lens forming the focusing optical system has been considered. Namely, by reducing the focusing magnification, the absolute amount of the pitch offset on the photosensitive material is reduced. However, if the focusing magnification of the lens is reduced, the spot size on the photosensitive material is also reduced, and even if the absolute amount of the pitch offset is low, the unevenness in the distribution of the amount of light will be great.
SUMMARY OF THE INVENTION
In view of the aforementioned, an object of the present invention is to provide a focusing optical system which can prevent unevenness in the distribution of the amount of light caused by positional offset of the light source, and which can focus with high precision.
A first aspect of the present invention is a focusing optical system, comprising: a plurality of light sources emitting light in accordance with image information; focusing device for focusing light from the plurality of light sources such that intervals between light from the plurality of light sources is at a predetermined focusing magnification with respect to intervals between the plurality of light sources; and spot size enlarging device for focusing focused spots of the plurality of light sources at a spot magnification which is larger than the focusing magnification by the focusing device.
Accordingly, light from the plurality of light sources is focused by the focusing device such that intervals between the light from the plurality of light sources are at a predetermined focusing magnification with respect to intervals between the plurality of light sources.
Each of the focused spots of the plurality of light sources is focused by the spot size enlarging device at a spot magnification which is greater than the focusing magnification. Namely, the spot size at the focused position is greater than a case in which focusing is carried out only by the focusing device. Thus, even if there is offset in the positions (pitch offset) of the plurality of light sources, unevenness in the distribution of the amount of light of the plurality of light sources on the whole is corrected, and as a result, highly precise focusing can be achieved.
In a second aspect of the present invention, in the first aspect, the spot size enlarging device comprises at least one diffraction grating.
In a third aspect of the present invention, in the first aspect, the spot size enlarging device comprises at least one material having a birefringent property.
In a fourth aspect of the present invention, in the first aspect, the spot size enlarging device is at least one lens forming the focusing device and has a predetermined spherical aberration.
The spot size enlarging device may comprise, as in the second aspect, a diffraction grating, or may comprise, as in the third aspect, a material having abirefringent property. In either case, a spot size enlarging device can be provided with a simple structure.
As in the fourth aspect, the spot size enlarging device may be a lens which forms the focusing device and which has a predetermined spherical aberration. In this way, the spot size enlarging device and the focusing device are made integral, and there is no need to provide a separate member such as a diffraction grating or a material having abirefringent property. Thus, the number of parts of the focusing optical system can be reduced, and the focusing optical system can be made light-weight and inexpensive.
In a fifth aspect of the present invention, in the invention of any of the first through fourth aspects, at least one diffusing member, which diffuses the light from the plurality of light sources, is disposed between the plurality of light sources and the focusing device.
Even if there is unevenness in the distribution of the amount of light due to the configuration of the light emitting surfaces of the light sources, the distribution of the amount of light from the light sources is made uniform (what is known as beam shaping) by the diffusing member. Even more highly precise focusing can thereby be realized.
In a sixth aspect of the present invention, in the invention of any of the first through the fifth aspects, the plurality of light sources is formed with at least two types of light sources each of different wavelengths, and the diffusing member has a degree of diffusion corresponding to the different wavelengths of the plurality of light sources.
In a case in which the diffusing member has a single degree of diffusion, the beam configuration of the light diffused by the diffusing member is different for each color. In contrast, by using a diffusing member which has degrees of diffusion corresponding to different wavelengths, the beam configuration of the light diffused by the diffusing member is the same for each of the colors.
In the seventh aspect of the present invention, in the invention of the first to sixth aspects, the plurality of light sources are arranged along a main scanning direction and a subscanning direction, and a spot magnification of the spot size enlarging device is set to be greater in the subscanning direction than in the main scanning direction.
Accordingly, the spot size is large in the subscanning direction, and unevenness in the distribution of the amount of light can be reduced. Because the spot size in the main scanning direction is smaller than in the subscanning direction, a sharper image can be obtained.
In the eighth aspect of the present invention, a focusing optical system comprises: a plurality of light sources emitting light in accordance with image information; focusing device for focusing light from the plurality of light sources such that intervals between light from the plurality of light sources is at a predetermined focusing magnification with respect to intervals between the plurality of light sources; and diffusing device provided at one of a pupil position of the focusing device or a vicinity thereof, for diffusing light from the plurality of light sources.
Accordingly, the intervals between the light from the plurality of light sources is focused by the focusing device at a predetermined focusing magnification with respect to the intervals between the light sources, respectively.
Further, the respective focused spot of each of the plurality of light sources is diffused by the diffusing device, which is disposed at the pupil position of the focusing device or vicinity thereof. Namely, the spot size at the focusing position is larger than in the case in which focusing is carried out simply by the focusing device alo
Fuji Photo Film Co. , Ltd.
Nguyen Thong
Sughrue Mion Zinn Macpeak & Seas, PLLC
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