Optical: systems and elements – Collimating of light beam
Reexamination Certificate
1999-06-18
2001-05-22
Phan, James (Department: 2872)
Optical: systems and elements
Collimating of light beam
C359S717000, C359S795000
Reexamination Certificate
active
06236512
ABSTRACT:
RELATED APPLICATIONS
This application claims the priority of Japanese Patent Application No. 10-193827 filed on Jul. 9, 1998, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a collimator lens usable in a light-scanning apparatus such as copier, laser printer, or the like which scans a laser beam in order to record or display an image; and, in particular, to a collimator lens for converting a divergent luminous flux emitted from a light source such as semiconductor laser into a parallel luminous flux, and a light-scanning apparatus using the same.
2. Description of the Prior Art
Various kinds of light-scanning apparatus such as copier, laser printer, and the like for scanning a laser beam in order to record or display an image have conventionally been known.
Such a light-scanning apparatus is configured such that a laser beam emitted from a semiconductor laser is converted by a collimator lens into a parallel luminous flux, which is then deflected in response to the rotation of a rotary polygon mirror, and thus deflected luminous flux is focused by an f&thgr; lens onto an imaging surface.
Here, as the collimator lens, those of a two-group/two-element configuration have been known as disclosed, for example, in Japanese Unexamined Patent Publication Nos. 58-14109, 58-38915, 61-279820, 61-273520, and 2-73324, so as to reduce the weight and dimensions of lens.
In general, it is necessary for the collimator used in such a light-scanning apparatus to be a bright lens system in order to enhance the efficiency of utilization of the light from the light source and increase the illuminance on the photosensitive drum surface. As a consequence, the collimator lens would have a numerical aperture greater than that of f&thgr; lens systems in general, whereby aberrations generated thereby are likely to increase. Therefore, in the collimator lens, it is necessary to favorably correct these aberrations such as wavefront aberration.
Meanwhile, as the light-scanning apparatus, there has been known a multibeam system which uses a plurality of light sources so as to carry out multibeam scanning, thereby achieving a higher scanning speed and enabling a plurality of different information items to be recorded at the same time in a single scanning operation. In the case where this multibeam system is employed or the like, it is desirable that aberrations be favorably corrected within the range of about 2 degrees in terms of half angle of view &ohgr;.
In the collimator lenses disclosed in the above-mentioned publications, most of examples have a narrow angle of view, for instance, such that their performances with respect to off-axis light are taken into consideration only for an angle of view on the order of installation errors. Aberrations are so large in examples with a large angle of view that it is difficult for the collimator lenses to be employed in a multibeam scanning optical system having a plurality of light sources disposed on a plane perpendicular to the optical axis, for example.
Further, in the collimator lenses disclosed in the above-mentioned publications, back focus, i.e., the distance from the lens on the light source side to the light source, is short, i.e., about 0.4f to 0.6f.
If the back focus is short, however, then the collimator lens is disposed near the light source (semiconductor laser or the like), whereby the temperature of the collimator lens is likely to increase due to the heat from the light source. Therefore, it is desired that the distance from the collimator lens to the light source be made greater in order for the collimator lens to be less susceptible to the heat from the light source.
SUMMARY OF THE INVENTION
In view of the above-mentioned circumstances, it is an object of the present invention to provide a collimator lens which, while in a simple lens configuration of two groups and two elements, can favorably correct off-axis aberrations to about 2 degrees in terms of half angle of view &ohgr; and secure necessary back focus; and a light-scanning apparatus using the same.
The collimator lens in accordance with the present invention comprises, successively from a parallel luminous flux side, a first lens having a negative refracting power and a second lens having a positive refracting power, wherein at least one surface of the second lens is formed as an aspheric surface.
Preferably, the surface of the second lens on a light source side is formed as a convex surface.
Preferably, the surface of the first lens on the parallel luminous flux side is formed as a concave surface.
Further, the collimator lens is preferably configured so as to satisfy the following conditional expression (1):
−0.87<R
1
/ƒ<−0.38 (1)
where
R
1
is the paraxial radius of curvature of the surface of the first lens on the parallel luminous flux side; and
f is the focal length of the whole lens system.
The light-scanning apparatus in accordance with the present invention uses the above-mentioned collimator lens.
In the light-scanning apparatus in accordance with the present invention, four semiconductor laser light sources for red, green, blue, and monochrome may be disposed on a plane perpendicular to an optical axis of the collimator lens.
Also, in the light-scanning apparatus in accordance with the present invention, a plurality of semiconductor laser light sources for monochrome may be arranged in a sub-scanning direction of a light beam.
When the surface of the second lens on the light source side is formed as an aspheric surface, the above-mentioned “convex surface” refers to a surface in which the radius (hereinafter referred to as approximate radius of curvature) of the arc connecting three points in total consisting of a point on the optical axis of this aspheric surface and two points at end parts of the effective diameter is negative.
REFERENCES:
patent: 5216550 (1993-06-01), Rudeen
patent: 5491587 (1996-02-01), Iwaki et al.
patent: 5550668 (1996-08-01), Appel et al.
patent: 58-14109 (1983-01-01), None
patent: 58-38915 (1983-03-01), None
patent: 61-279820 (1986-12-01), None
patent: 61-273520 (1986-12-01), None
patent: 63-226085 (1990-03-01), None
Fuji Photo Optical Co., Ltd.
Phan James
Snider Ronald R.
Snider & Associates
LandOfFree
Collimator lens and light-scanning apparatus using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Collimator lens and light-scanning apparatus using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Collimator lens and light-scanning apparatus using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2538603