Optical: systems and elements – Lens – With viewed object support
Reexamination Certificate
2001-09-06
2004-06-08
Dang, Huang Xuan (Department: 2873)
Optical: systems and elements
Lens
With viewed object support
C359S760000
Reexamination Certificate
active
06747818
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming lens, an image forming lens unit, an original document reading module, an original document reading method, an original document reading apparatus and an image information processing apparatus.
2. Description of the Related Art
An image forming lens is used in original document reading parts of various image forming apparatuses such as copying machines, facsimile machines, multi-functional products, etc. The image forming lens is also used in image scanners for reading an original document. The resolution of reading an original document with such apparatuses has recently increased from 300 or 400 dpi (dots per inch) to 600 dpi, and more recently to 1200 dpi. With such increase in the resolution of reading an original document with such apparatuses, higher performance is demanded for the lenses for use in reading the original document.
It is known that Gauss type lenses can accomplish a high resolution with a relatively wide lens diameter. The Gauss type lenses are widely used in original document reading parts of digital copying machines, multi-functional products, etc. and high-end flatbed image scanners. However, for realizing the higher performance recently demanded for an image forming lens, at least 6 pieces of lenses are required, as described for example in Japanese Patent Laid-open Publication No. 2000-111794. Therefore, the cost of such an image forming lens is inevitably high.
Japanese Patent Laid-open Publication No. 7-56085 describes an image forming lens having a two-lens construction. However, the image forming lens having a two-lens construction has a limitation in realizing such a higher performance recently demanded for the image forming lens. Therefore, the image forming lens having a two-lens construction is not suitable for use in an original document reading part of digital copying machines and multi-functional products requiring a relatively high resolution, and is generally used in facsimile apparatuses or image scanners not requiring a high reading resolution.
Also, an image forming lens having an anamorphic lens surface is known to be used in original document reading parts of digital copying machines, etc., as described for example in Japanese Patent Laid-open Publication No. 2000-307800. However, in the image forming lens of JP No. 2000-307800, the lens having the anamorphic lens surface is not arranged close to the image surface of the image forming lens, and therefore the effect of the anamorphic lens surface is not sufficiently realized.
For enhancing the performance of an image forming lens, it is conceivable to form a surface thereof in a non-spherical shape. Further, when the above-described original document reading parts of digital copying machines, etc. and the image scanners include a one-dimensional light receiving element array (line sensor), in addition to forming a surface of the image forming lens in a non-spherical shape, another surface thereof can be formed in an anamorphic shape, as described in Japanese Patent Laid-open Publication No. 2000-307800. However, as described above, the effect of the anamorphic lens surface is not sufficiently realized.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a novel image forming lens that has a lesser number of lenses in comparison with Gauss type lenses and that yet has a performance higher than or equivalent to that of the Gauss type lenses.
Other preferred embodiments of the present invention provide an image forming lens that has the function and performance exceeding those of image forming lenses having a lens surface of an anamorphic shape and that is yet relatively low in cost.
According to a preferred embodiment of the present invention, an image forming lens for forming an image of an original document includes a front side lens group arranged at an object side and a rear side lens group arranged at an image forming side. The front side lens group includes from 2 to 4 individual lenses including at least one positive lens, and the rear side lens group includes one negative lens. The back-focus of the image forming lens when in use is equal to or smaller than 25% of an entire length of the image forming lens, and the air space, i.e., open space, between the front side lens group and the rear side lens group is equal to or greater than 50% of the entire length of the image forming lens. The front side lens group lens can include two, three or four lenses. By configuring an image forming lens with three individual lenses, correction of aberration is easy and relatively high performance can be realized.
In the above-described image forming lens, each lens can be spherical, so that manufacturing of each lens is relatively easy and thereby the image forming lens is realized at relatively low cost.
The above-described image forming lens can be configured such that at least one lens surface thereof is non-spherical. The non-spherical surface can be the incident side surface of the rear side lens group or the imaging side surface of the rear side lens group. That is, the rear side lens group can be configured such that the object side surface and/or the imaging side surface of thereof are non-spherical.
In the above-described image forming lens, the rear side lens group can be of plastic construction. In the above-described image forming lens, because the rear side lens group is disposed close to the image surface of the image forming lens, the rear side lens group is larger than the front side lens group. Accordingly, by using a plastic lens for the rear side lens group, the cost of the image forming lens can be further reduced. By using a plastic lens for the rear side lens group, the object side surface and/or the imaging side surface thereof can be easily formed in non-spherical shapes.
In the above-described image forming lens, because the rear side lens group is disposed close to the image surface of the image forming lens and a light receiving element array is arranged at the image surface, the outer shape of the rear side lens group can have a rotational asymmetry with respect to the optical axis of the image forming lens. In this case, the outer shape of the rear side lens group may be in a strip-like form having a long dimension in a main scanning direction. Here, the main scanning direction corresponds to the direction in which light receiving elements of the light receiving element array are arranged.
When the rear side lens group is plastic, an engaging part for positioning, supporting or fixing the image forming lens can be formed at a part of the rear side lens group. The engaging part can be protruding or concave.
In the above-described image forming lens, the back-focus of the image forming lens in the actual usage state thereof can be equal to or smaller than 10% of the entire length of the image forming lens. The smaller back-focus is advantageous in correcting aberration. However, if the back-focus is relatively large within the limit of 25% of the entire length of the image forming lens, for example, an adjusting mechanism for adjusting the position of a light receiving element array relative to the rear side lens group can be advantageously arranged within the back-focus.
In the above-described image forming lens, as described above, the outer shape of the rear side lens group can have a rotational asymmetry with respect to the optical axis of the image forming lens. However, the above-described image forming lens can be configured such that the outer shapes of the front side lens group and the rear side lens group have a rotational symmetry with respect to the optical axis of the image forming lens and thereby the entire image of an original document can be read at one time with an area sensor.
In the above-described image forming lens, for realizing high performance, the balance between the focal l
Itabashi Akihisa
Nishina Kiichiro
Ohashi Kazuyasu
Dang Huang Xuan
Dickstein Shapiro Mortin & Oshinsky LLP
Martinez Joseph
Ricoh & Company, Ltd.
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