Photocopying – Projection printing and copying cameras – Illumination systems or details
Patent
1989-02-16
1990-12-18
Hix, L. T.
Photocopying
Projection printing and copying cameras
Illumination systems or details
G03B 2754
Patent
active
049789945
DESCRIPTION:
DESCRIPTION
BEST MODE OF CARRYING OUT THE INVENTION
In the following, an exemplary embodiment of the present invention will be described on the basis of the drawings.
In FIG. 1, the image forming apparatus includes an original holding press plate 2, a photographing camera 3 and a manipulating portion 4.
In FIG. 2, an original 1 is disposed on a contact glass surface 5 and held down by the press plate Z. The original 1 is illuminated by the flash lamp 6, wherein light reflected from the original 1 is reflected at a first mirror 7 and a second mirror 8 and focussed onto a film 10 by passing through a taking lens 9. The film 10 is placed within the camera 3 (FIG. 1) and exposed to the light upon opening of the shutter in synchronism with the emission of light from the flash lamp 6.
In FIG. 3, a pair of flash lamp units 11-1 and 11-2 are disposed substantially symmetrically as viewed in the longitudinal direction. The flash units include flash lamps 6-1 and 6-2, reflector Plates 13-1 and 13-2, and diffusing plates 12-1 and 12-2, respectively, and are oriented toward the original.
When a print key of the manipulating portion 4 is pressed with the original 1 having been disposed in place, a capacitor (not shown) is electrically charged, whereby the lamp 6-1 is first caused to emit light. After the lighting of the lamp 6-1, the capacitor is again charged, whereby the lamp 6-2 in turn is lit, whereupon the exposure is ended.
It is desirable that the exposure be as uniform in distribution as possible over the whole surface of the original. However, because of disposition of the lamp 6 within the limited inner space of the apparatus, the plane of the original 1 is located closely adjacent to tbe lamp 6, as tbe result of which great difficulty is encountered in preventing unevenness in the exposure with the single lamp 6. For this reason, the lamps are provided at two locations in this apparatus. Further, by lighting the two lamps 6-1 and 6-Z one by one rather than lighting them simultaneously, the quantities of light outputted by the front and rear lamps, respectively, in succession can be individually measured and controlled more accurately. Besides, the capacitor may be of a small capacity.
With this apparatus, nonuniformity of exposure over the surface of original could be substantially eliminated by employing the two lamps However, when a high contrast positive film "Polagraph" (trade name) available from the Polaroid Corporation was used and the transmission factor of the film was measured after development in succession to the photographing of an original having a constant density, it was found that the transmission factor is nonuniform over front to rear portions of the film. Hence, the sequence of lighting the lamps was reversed In that case, the transmittance distribution of the film showed an opposite tendency. The results are shown in FIG. 5.
The front lamp 6-1 tends to illuminate intensively the front surface of the original 1, while the rear lamp 6-2 illuminates more intensively the rear portion of the original 1. Thus, it is seen in view of the characteristics of tbe film that tbe portion subjected to the intensive illumination at the first lighting and feeble illumination upon the second lighting appears to have been more exposed than the portion illuminated with feeble light upon the first lighting and then intensively at the second lighting.
Under the circumstances, in conjunction with the realization of uniformity in the density after development over the whole area of the film, it has been found that the transmission factor of the film becomes constant when the total amount of exposure is controlled to be minimum at a portion (front portion in this case) which is subjected to the maximum exposure at the first illumination, as is shown in FIG. 4.
As a method of making the amounts of the first and second exposures asymmetrical to each other, the angles .theta..sub.1 and .theta..sub.2 at which the lamps are mounted, as shown in FIG. 3, may be so selected that .theta..sub.1 <.theta..sub.2 or the diffusing plat
REFERENCES:
patent: 3375752 (1968-04-01), Fairbanks et al.
patent: 4255046 (1981-03-01), Corona
patent: 4334767 (1982-06-01), Lehman
patent: 4551011 (1985-11-01), Yuasa et al.
L. J. Mason, "Aperture Control of Integrating Cavity Flash Lamp Exposure", Xerox Disclosure Journal, vol. 11, No. 2, Mar./Apr. 86, pp. 77-78.
H. M. Harris, "Adaptive Illumination Balancing System", Xerox Disclosure Journal, vol. 4, No. 6, Nov./Dec. 79, p. 787.
L. J. Mason, "Exposure Control with Multiple Flash Lamps", Xerox Disclosure Journal, vol. 10, No. 5, Sep./Oct. 89, pp. 295-296.
Corrigan Alfred E.
Hix L. T,.
Rutledge D.
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