GB830954A - Improvements in and relating to photographic projection printers - Google Patents

Abstract

830,954. Photographic projection printers. EASTMAN KODAK CO. March 4. 1958 [March 4, 1957], No. 6870/58. Class 98(1) A photographic projection printer comprises means for illuminating a transparency, the illuminating system being adapted to project a predetermined pattern of light on to the plane of the extrance pupil of the projection objective, said pattern including a predetermined amount of light inside the entrance pupil and a ring of light surrounding it, whereby optimum elimination of shadows on the image due to scratches on the transparency is obtained; a plurality of interchangeable objectives are mounted on a turret. As shown, several objectives such as 16 or 26, for different degrees of magnification, are mounted on a turret 50, 51, and can be rotated into the operating position, in which position the entrance pupils always lie in the same fixed plane. The transparency, mounted in a gate 13, is positioned in a plane conjugate to the image plane 17. Light from a source 10 passes through a system of condenser and field lenses 11, 12, 14, in which is incorporated the'transparent screen 19 shown in more detail in Fig. 3. The screen is embossed with tiny conical dots 31-37, of the order of a million per sq. in. These cones have a very obtuse apex angle, so that light rays passing through their sides are deviated by about 10 degrees, as shown by rays 30<SP>1</SP>, 30<SP>11</SP>. The cones are separated by flat areas 38 through which rays pass undeviated, as at 30. The effect of the screen is to allow part of the rays, shown by full lines, to proceed undeviated to the projection lens 16, and to deviate others, shown by broken lines, to form the surrounding ring of light required for scratch-mark elimination. Between 4% and 20% of the light proceeds directly into the lens 16, the remainder being deviated. The diameter of the light nng may be varied by axial movement of the screen, and the film gate is also movable axially. A formula is given relating the focal length of the objective lens with the magnification and other constants of the system.