Patent GB-711590-A (GB)
Abstract: 711,590. Photographic projection printing. TECHNICOLOR MOTION PICTURE CORPORATION. Sept. 26, 1952 [Oct. 2, 1951], No. 24172/52. Classes 97(1) and 98(1) A method of printing from a photographic record with increased contrast by projection on to photographic light-sensitive material is characterized by the steps of illuminating the record to form a beam carrying an image thereof, illuminating the record a second time by means of the light from a luminiferous image of the record derived from the imagecarrying beam, and projecting an image of the record so illuminated on the material, Apparatus for carrying out the method has a first gate for the record, a second gate for the light-sensitive material, and a light source for illuminating one side of the record, and is characterized by an optical system for directing light from the source, once passed through the record, a second time through the record with the image carried thereby in register with the record; and bv an optical system for forming an image of the record so illuminated on the material. The beam may pass through the record more than twice, and may be combined with another beam passing through the record a different number of times, so that the contrast of the image projected on the light-sensitive material may be varied by varying the relative intensities of the beams. As shown in Fig. 1, a negative film N passes through a gate Gn and a positive film A passes through a gate Gp, the films being driven intermittently in the usual manner. A semi-silvered mirror B, is placed just behind film N in gate Gn, and another semi-silvered mirror B 2  is placed at an angle between the gate Gn and a lens C. A beam of light b 1  from a lamp L 1  passes through the negative N and mirrors B 1 , B 2 , and an image of negative N is formed on film A by lens C. A beam b 2  from a lamp L 2  is reflected at mirror B 2 , and passes through negative N twice, being reflected by mirror B 1 , and then passes through mirror B, and is focused by lens C on to film A. Since beam b 2  passes through the negative twice, the image formed by beam b 2  alone is of twice the contrast of the image formed by beam b 1  alone. The contrast of the combined image may be varied by varying the relative intensibles of beams b 1 , b 2 , as by means of variable resistors R 1 , R 2  in the lamp circuits, or variable wedge filters F 1 , F 2  in the beams b 1 , b 2 . In a first modification, light reflected from the surface of negative 'N is eliminated by polarizing beams b 1 , b 2  in perpendicular planes, introducing a quarter-wave plate between lamp L, and mirror B 1 , another quarter-wave plate between mirror B, and the negative N, and a polarizing screen between lens C and film A. By rotating the quarter-wave plates in unison, the relative intensities of beams b 1 , b 2  reaching film A, and hence the contrast, can be varied. Mirror B 2  may be replaced by a semi-reflecting surface in a cubical prism. In a second modification, the light sources are at the side of the apparatus and the beams are reflected along the optical axis by semi-reflecting surfaces. Mirror b 1  is reflected by a cube-corner reflector placed at a distance from the negative. A lens is required in the back-reflected beam to form an image upon and in register with the record on negative N, and the beams are separately controlled by means of polarizers and quarter-wave plates. In a third modification, the beam emerging from the negative is split by a semi-reflecting surface. The reflected part is reflected by two mirrors to another semi-reflecting surface which reflects it through the negative again, in the same direction as before lenses in the path of the diverted beam form an image in register with the record. Polarizers and a half-wave plate control the direct and diverted beams separately. When the negative N bears a coloured record, filters may be placed in one of the beams to control separately different colour aspects of the record. To reduce light loss, the semi-reflecting surfaces and associated polarizers may be replaced by surfaces which reflect light polarized in one plane and transmit light polarized in the perpendicular plane. In a fourth modification, the mirror b 1  is replaced in the arrangement shown by a translucent fluorescent screen or moving fluorescent strip, and beam b 2  consists of ultra-violet light only. This beam is reflected through negative N and stimulates the fluorescent screen or strip. The resulting light, passing through negative N, forms with beam b 1  an image on film A. A filter absorbing ultra-violet light is placed between mirror B 2  and film A.