GB1326931A - Apparatus for making prints from colour negatives - Google Patents

Abstract

1326931 Photographic colour printing CIBA-GEIGY A G 26 Aug 1970 [28 Aug 1969] 41137/70 Heading G2A The spectral composition of a colour printing light beam # 0 is controlled by comparing the spectral composition of the beam before and after passage through a colour negative positioned at 5. The integral density of the negative can thus be assessed irrespective of fluctuations of the light source or filters. A light source 1 is positioned within a number of cold light mirrors 9 and a heat filter 10. The beam passes yellow, magenta and cyanogen filters 2, 3, 4 which can be swung into the beam to a selected extent by drive motors 11, 12 and 13. The beam is blended or mixed by passage through mirror tunnels 14, 16 interconnected by a pyramid 15 of material with low diffusion capacity to illuminate a ground glass screen 17. Printing light intensities # 0 , # 1 are measured using fibre optic light guides 19, 20a, 20b, 21 and 22. The guides terminoate opposite a photo-cell 24 in front of which a disc 25 containing regions of different coloured filters is rotated by a motor 23. In addition, the photocell receives a signal periodically from a reference lamp 32. The thus seven successive outputs from photo-cell 24 are applied to a logarithmic converter 34, which is adjusted by comparator 42 according to reference light source 32, and thence via a distributor 35 to stores, e.g. 37, 38 for the blue component. A blue difference signal D KB is produced at a summation stage 44 and the difference signal after various corrections is applied to motor 11 controlling the position of yellow filter 2 and to a blocking stage 71 which releases an exposure timer 74 only when the difference signal is below a certain threshold value. Timer 74 controls the operation of a shutter 7 and is fed with a signal from a summation stage 64 representative of the overall brightness of the printing beam. Stages 58, 54, 55 provide corrections to the measured signals for manual correction, negative parameters and printing material parameters respectively. Stage 47 adjusts the slope of the print material characteristic to take account of the Schwarzchild effect and development conditions, and stage 45 permits undercorrection if the negative has a colour dominant or colour cast.