Patent GB-355241-A (GB)
Title: Improvements in or relating to photographic printing apparatus
IPC: G03B27/72
Filed: 1930-05-12
Abstract: 355,241. Projection printing-apparatus. ROSE, W. H. T. R., 23, Bridge Street Row, Chester. May 12,1930, Nos. 14500 and 36282. [Class 98 (i).] In a projection printing-apparatus means are provided for adjusting the diaphragm of the projecting lens or the effective light therethrough, in accordance with the density of the negative as determined by the visible effect on a screen when illuminated by the projected beam and also by a standard source of light. In one arrangement the diaphragm is adjusted until a projected image is flooded out by the standard lamp. In another arrangement a grease spot is illuminated from opposite sides. The Specification also describes (1) an automatic timing device in conjunction with the pressure platen for the sensitive paper and comprising a tube with a rolling ball which can be inclined at different angles : and (2) a slide holder with automatic clamping means for introducing a film negative into the apparatus. In one apparatus the printing lamp B, Fig. 1, and a red inspection lamp B<1> are in a case A<2> below a frame A<1> with an aperture A<3> over which a sliding film holder is mounted. The lamp B is lit by contacts B<4> only when the holder is introduced. The negative is illuminated through a condenser B2. The cabinet A contains the projecting lens D, a translucent screen F, a pivoted mirror E<2> connected with the printing platen E, and a standard lamp G the circuit of which can be made and broken by the rod D<1> which is used to adjust the lens diaphragm, through a contact bar D<2> which may be below or above the rod. In operation the diaphragm is adjusted until the projected image on the screen F is just flooded out by the lamp G, which is then cut out. The sensitized paper is then placed on the plate A<7> and exposed by depressing the platen E<2> which swings down the mirror E<2>. In a second construction the printing lamp J and red lamp J<1> and its apertured plate J<2> are mounted on an adjustable bracket J<3> moved by a screw J<4>, J<5>. A frame N<3> holding a grease spot screen, or a piece of watered silk or other material having the same visual effect is carried by a wire frame N<5>, N<2>, N<1>, N<4> on a side horizontal pivot N, and normally swings down in front of the lens when the pivoted shutter L is raised by the spring L<1> on raising the pressure platen L<4>. The upper surface of the grease spot or screen is illuminated direct from the standard lamp O through the lower part of a shield O<1> which shields the observation window H<8> from direct illumination. The lens diaphragm controlling rod K<2> is adjusted until the grease spot is invisible and the contact K<2>, P is broken. On depressing the platen L<4> for an exposure the arm M swings the shutter L down, and the shutter rocks the grease spot frame from the lens. Alternatively the grease spot may be removed and the light through the lens projected on to the under surface of the shutter L which is also illuminated by direct light from the lamp O. The projection surface is observed by reflection from the mirror O<1> and the lens diaphragm adjusted until the high lights are just flooded out. A rheostat O<3> may be provided for preliminarily adjusting the standard lamp. Exposure timing device. This comprises a tube L<6>, Fig. 3, pivoted at L<5> to the platen frame L<3> and containing a ball or sliding member L<10> which moves to the right-hand end of the tube when the platen is raised. The effective inclination of the tube when the platen is down is controlled by a cam lever L<8>, and the exposure period is indicated audibly by the ball striking the left-hand end of the tube. Film negative holder. This comprises a base frame R, Figs. 3 and 5, having a printing aperture and fitted with blocks R<1> forming guideways for a sliding carriage R<2>. This carriage has an aperture with a glass plate R<4>; a spring plate R<5> for clamping the film at one edge and automatically released when withdrawn by the wedge strip R<6> on the plate R<5> engaging the wedge block R' on the base R ; brackets S slotted at S<1> for a swinging frame S<4> which has curved arms S<3> and projecting legs S<5>, and a block U with a contact strip U<1> for completing a circuit U<2> through the printing lamp when the carriage is pushed in. In the withdrawn position the frame S<4> is raised clear of the plate R<4> by rollers T on a fixed shaft T<1> and the legs S<5>. After placing a negative film on the plate R<4>, and pushing in the carriage, the spring R<5> first clamps one edge, and just before end of the movement, the rear edge of the frame S<4> engages the other end of the film and draws it out flat before it is finally clamped down by the frame and the contact strip U<1> completes the lamp circuit.