Flash illumination apparatus

A flash illumination apparatus in which an original is simultaneously illuminated over the whole surface thereof by means of a single or plurality of flash lamps, wherein light reflected by the original is focused onto a light sensitive material for exposure thereof, characterized in that a collecting and diffusing optical element is disposed immediately before the flash lamp within a range of luminous flux so that the luminous flux illuminates a particular range of the original thereby improving the uniformity in illumination on the original.

TECHNICAL FIELD 
The present invention relates to a flash illumination apparatus for a 
copying machine and the like in which an original is illuminated 
simultaneously over the whole surface thereof by a single or a plurality 
of flash lamps, wherein light reflected from the original is focused onto 
a light sensitive material through an optical system for thereby carrying 
out exposure 
BACKGROUND ART 
A so-called strobe flash illumination apparatus employing a xenon discharge 
tube is utilized in various fields as a convenient light source of high 
efficiency. When used as the original illuminating apparatus in a copying 
machine, the above-mentioned apparatus is advantageous in respects to low 
heat generation, excellent color rendering properties and others, assuring 
a high utility. However, in the case of the copying machine in which an 
original is simultaneously illuminated over the whole surface thereof, it 
is necessary to illuminate uniformly the original as a whole. Since such 
uniform illumination cannot be accomplished solely with the flash lamp by 
itself, it has heretofore been practiced to make use of a reflector or the 
like. By using the reflector, a greater proportion of light rays emitted 
from the lamp can be caused to reach the surface of the original, whereby 
the utilization efficiency of light energy can be enhanced. However, with 
regards to the uniform information over the whole surface of the original, 
this arrangement was inadequate. 
When used as strobe flash in the photographing, such a structure is 
generally adopted in which a collecting and diffusing optical element 
(stepped concave or convex lens such as a Fresnel lens) is provided on the 
front side of the reflector. In the case of this structure, the light rays 
emitted directly from the lamp as well as those reflected by the reflector 
equally undergo diffusing action. Thus, this structure is dissatisfactory 
as the means for realizing uniform illumination even though it can change 
the range within which light rays can reach, because the light rays 
directly emitted by the lamp and those reflected by the reflector are 
equally collected and diffused. 
FIG. 3 is a view showing an example of illuminance distribution over an 
original surface obtained by illuminating the original surface from below 
with inclination by means of lamp units 1 each having a collecting and 
diffusing optical element 2 and disposed below the original 3 at both 
sides thereof. Curves shown in the figure represent equi-illuminance 
curves, wherein numerals inserted between the curves indicate the relative 
values of illuminance in the associated areas on the assumption that 
illuminance in the vicinity of the lamp 1 is given by 10. It will be seen 
that illuminance is decreased to 2 at both side ends in FIG. 2. 
In view of the aforementioned drawbacks of the hitherto known original 
illuminating apparatus employing the flash lamps for use in the copying 
machine and others, it is an object of the present invention to provide a 
flash illumination apparatus for use in the copying machines and others 
which is capable of uniformizing to an acceptable extent the illuminance 
distribution on an original surface illuminated with flash lamps. 
DISCLOSURE OF THE INVENTION 
For accomplishing the object mentioned above, the flash illumination lamp 
according to the present invention is characterized in that a luminous 
flux collecting and diffusing optical element is disposed immediately 
before said flash lamp within a range of luminous flux emitted by said 
lamp and illuminating directly the surface of said original for collecting 
and diffusing said luminous flux so that said luminous flux illuminate a 
particular range of the original.

BEST MODE FOR CARRYING OUT THE INVENTION 
In the following, an exemplary embodiment of the present invention will be 
described in detail by referring to the drawings. 
Referring to FIGS. 1(a) and (b) showing an embodiment of the present 
invention, a flash lamp unit 10 is composed of a flash lamp 11, a 
reflector 12 opened at the side facing an object to be illuminated, and a 
collecting and diffusing optical element 13 disposed immediately in front 
of the flash lamp. The collecting and diffusing optical element 13 may be 
constituted by a concave lens or a stepped concave lens or convex lens or 
stepped convex lens and is so disposed in the range of the luminous flux 
emitted from the lamp 11 and illuminating directly the original surface 
that the diffused luminous flux illuminates a particular range of an 
original surface. The particular range is so established that the portion 
which is illuminated with low illuminance only with the light rays 
reflected by the reflector 12 can be additionally and correctively 
illuminated with the light rays collected and diffused by the collecting 
and diffusing optical element at high luminance. 
With the arrangement of the apparatus described above, the light rays 
reflected by the reflector 12 do not pass through the collecting and 
diffusing optical element 13 but reach directly the original surface, 
whereby design of the reflector is facilitated because there is no need 
for taking into consideration the variation in the optical path due to the 
collecting and diffusing lens. Further, due to the action of the 
collecting and diffusing optical element 13, only the portion on the 
original surface which would be illuminated with low illuminance with only 
the light rays reflected by the reflector can be illuminated directly by 
light emitted from the lamp 11, whereby uniform illumination can be 
accomplished with improved efficiency. 
FIG. 4 is a view showing an example of illuminance distribution on an 
original surface obtained in the case where the flash illumination 
apparatus 10 according to the present invention is mounted in place of the 
lamp unit shown in FIG. 2 for illumination of the original surface. When 
compared with the illuminance distribution realized through illumination 
by the hitherto known apparatus shown in FIG. 3, it will be seen that the 
quantity of light is increased in the center portion and both lateral side 
portions of the original 3, falling within an allowable range of 
illuminance, whereby substantially uniform distribution of illuminance is 
realized as a whole. 
INDUSTRIAL APPLICABILITY 
As will be seen from the foregoing, it is possible according to the 
invention to uniformize the distribution of illuminance on a surface of an 
original with a simple structure in which a collecting and diffusing 
optical element is provided immediately before a flash lamp within a range 
of luminous flux directly emitted by the flash lamp. By using this flash 
illumination lamp in a copying machine of a type in which the original is 
illuminated over the whole surface and apparatus for preparing 
diapositives for projectors, copies or diapositives for projection can be 
obtained which have image density distributions duplicating the original 
with high fidelity.