1. Field of the Invention
The present invention relates to an original scanning apparatus used with a copying machine and the like, and more particularly, it relates to an illuminating or lighting apparatus for scanning an original, wherein a point light source is fixed and a reflection member is shifted.
2. Related Background Art
Conventionally, a lighting apparatus wherein a point light source is fixed and a reflection optical system is shifted to scan an area to be illuminated has already been known, as disclosed in the Japanese Patent Publication No. 53-41976.
FIGS. 20-22 show a lighting mechanism of such lighting apparatuses, in which FIG. 20 is a perspective view of such lighting apparatus, FIG. 21 is a plan view of the apparatus of FIG. 20, and FIG. 22 is a side view of the apparatus of FIG. 20. By the way, when the point light source is used, it is necessary to convert scattered light beams into parallel light beams in order to prevent the reduction in a light amount due to the shifting movement of a reflection hood. In the lighting apparatus shown in FIGS. 20-22, it is so designed that light beams scattered from a light source 100 are converted into parallel beams by a reflection mirror 120 having a parabolic surface which can focus light beams onto the light source. By shifting a reflection hood 110 with a scanning movement, an area to be illuminated is scanned.
Incidentally, in such a conventional lighting apparatus, the scattered light beams from the light source 100 were collimated (i.e., converted into parallel beams) at a time only by using the parabolic reflection mirror 120, as mentioned above.
However, as shown in FIG. 20, the parabolic reflection mirror 120 for collimating the light beams has an elongated shape. That is, the collimated light beams by the parabolic reflection mirror have a longitudinal length of 200-300 mm, but have a width or height of 30-40 mm which is greater than a width of a slit merely by several times. Thus, a distance between the light source and an apex of the parabolic reflection mirror is substantially determined by the longitudinal length of the reflection mirror, and, this distance cannot be considerably reduced. That is to say, in order to arrange the light source nearer to the parabolic reflection mirror, the latter must be bent considerably along its longitudinal length. If to do so, since the parabolic reflection mirror is also bent along the widthwise direction, it is distorted at a central portion thereof, with the result that the light beams cannot be collimated correctly.
Accordingly, the conventional lighting apparatus has a drawback that the efficiency for gathering the light beams in the widthwise direction is considerably reduced, since the light source cannot be arranged in the vicinity of the parabolic reflection mirror. Further, if the light source is arranged in the vicinity of the parabolic reflection mirror, since the scattered light beams can be gathered by the parabolic reflection mirror within a greater angular range along the longitudinal direction, the difference in the light amount between longitudinal end portions and the central portion of the reflection mirror will be too great.
In order to match the light amount at the central portion with those at the end portions of the reflection mirror, the light amount of the central portion must be greatly reduced by using a filter, light amount correcting plate and the like. As a result, the available light amount was considerably reduced.