FLASH LIGHTING DEVICE

Abstract: A flash unit (10) comprises a flash lamp (11) in an umbrella shade/holder (12) with a converge/diverge optical element (13) disposed directly in front of the lamp (11). The function of this optical element (13) is to distribute light from the flash lamp evenly over the surface of an original.

Description: 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. 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 tructure, 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 Figure 2. Examples of these known types of illumination apparatus are shown in JP 58-195839, JP 57-46266, JP 59-177532 and JP 60-225136. 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 which is capable of uniformising to an acceptable extent the illuminance distribution on an original surface illuminated with flash lamps. In accordance with the present invention, a flash illumination apparatus for illuminating an original includes at least one flash lamp; reflection means for reflecting light emitted by the or each flash lamp positioned in the optical path of the light and arranged immediately in front of the flash lamp, and means for collecting and diffusing light emitted by the or each flash lamp, wherein light reflected by the original is focussed onto a light sensitive material for exposure thereof and is characterised in that the collecting and diffusing means is positioned relative to the reflection means so that it intercepts light from the or each flash lamp which has not been reflected by the reflection means and does not intercept light which has been reflected by the reflection means whereby light from the collecting and diffusing means and light from the reflection means is independently dispersed over the original. Preferably, the or each flash lamp is positioned within the volume of the reflection means. In the preferred example, the collecting and diffusing means is positioned within the volume of the reflection means. Figs. 1(A) and 1(B) are, respectively, an exploded perspective view and a sectional view showing an embodiment of the present invention, Fig. 2 shows a hitherto known original illuminating apparatus, Fig. 3 is a view showing distribution of illuminance on an original illuminated by the same, and Fig. 4 is a view showing an example of distribution of illuminance on an original illuminated with the illuminating apparatus according to the present 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 no 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. 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.

Claims: 1. A flash illumination apparatus for illuminating an original, the apparatus including at least one flash lamp (11); reflection means (12) for reflecting light emitted by the or each flash lamp; and means (13) for collecting and diffusing light emitted by the or each flash lamp positioned in the optical path of the light and arranged immediately in front of the flash lamp, wherein light reflected by the original is focussed onto a light sensitive material for exposure thereof characterised in that the collecting and diffusing means (13) is positioned relative to the reflection means (12) so that it intercepts light from the or each flash lamp which has not been reflected by the reflection means and does not intercept light which has been reflected by the reflection means whereby light from the collecting and diffusing means and light from the reflection means is independently dispersed over the original. 2. Apparatus according to claim 1, wherein the or each flash lamp is positioned within the volume of the reflection means. 3. Apparatus according to claim 1 or claim 2, wherein the collecting and diffusing means is positioned within the volume of the reflection means.

Inventors: ICHIMURA, HAJIME
Applicants: POLAROID CORPORATION
Application year: 1987
Main classification: G03B27
IPC codes: G03B27, G03G15