American cinematographer (Jan-Dec 1926)

July. 192C A M E R I C A N C I N E M A TOGP. A P H E R Eleven Effect of Desensitizers in Deuelopment Continued from Last Month. Additional Tables and Charts Used in Investigation Given. Bij m. L. Dundon and J. 1. Crabtree Of the Eastman Research Laboratory. Full Details as Announced in Transactions of Society of Motion Picture Engineers. PANCHROMATIC FILM BEFORE DESENSITIZING PANCHROMATIC FILM AFTER DESENSITIZING MOTION PICTURE NEGATIVE FILM BEFORE DESENSITIZING MOTION PICTURE FILM AFTER DESENSITIZING Figure Six: Effect of Pinakryptol green on color sensitivity of Panchromatic and motion picture negative film. Desensitized films were given 200 times as much exposure as the untreated films. (Continued from last month) In Fig. 5 are shown similar results for motion picture negative film with 2 minutes bathing. The effect of pinakryptol green on the relative color sensitivity of panchromatic film is shown by Fig. 6. Pieces of panchromatic and motion picture negative film were bathed for 2 minutes in pinakryptol green 1-10,000 dried and exposed in a spectrograph. The desensitized samples were given about 200 times as much exposure as the untreated film. It is evident that desensitizing with pinakryptol green reduces color sensitivity much more than it does the original blue sensitivity of the emulsion. The effect of different dyes in this respect varies greatly. Pinakryptol yellow is more effective and phenosafranine less effective in reducing color sensitivity than pinakryptol green. In fact phenosafranine is actually a color sensitizer to a slight degree and confers a definite color sensitivity on ordinary plates with a maximum effect at 580 mm. in the green-yellow region. Basic scarlet N also extends slightly the sensitivity in the green. The effect of time of bathing on sensitivity may be seen from typical curves of Fig. 7 in which sensitivity of panchromatic film is plotted against time of bathing. It is evident that sensitivity falls off very rapidly for the first minute or two but diminishes very slowly after 5 minutes. 2. Limits of Safety in Exposing Desensitized Film to Different Safelights. In Table I the comparative safety of untreated film to safelight exposure was indicated. In Table II are given similar data for film desensitized for 2 minutes and 5 minutes with various concentrations of pinakryptol green. The numbers represent time in minutes for which exposures were made without producing visible fog. Tests were only extended to 8 minutes, as it was considered that this was sufficient time of exposure to cover any practical need, although in many cases the time of safety was much longer. F. indicates fog in less than y2 minute, and the numbers show the time in minutes for which the film could be exposed without visible fog, after a treatment corresponding to the time and concentration given at the top of the column. From these figures it is seen by bathing panchromatic film in a 1-10,000 solution of pinakryptol green, or after the film has been in the developer containing 1 part in 25,000 of the desensitizer, inspection of the film may be conducted with safety with a Series 4 Wratten safelight containing a 25 W. bulb at a distance of 12 inches. Under the same conditions motion picture negative film may be safely examined with a Series 0 safelight. 3. Bleaching of the Latent Image on Desensitized Film ' by Red Light. It is a well known fact that when an exposed plate is treated with certain dyes and then exposed to red light the latent image of the first exposure is destroyed. Ordinary desensitizing dyes promote this action very strongly. In fact, as Luppo-Cramer24 has shown, if a plate is given 23. A. Hubl, "A Contribution to the Knowledge of Development In Bright Light," Phot. Rund. G2, 235, (1925). 24. Luppo-Cramer, "Desensitizing and Duplicate Negatives," B. J. Phot. 69, 765, (1922) (Abs.) Phot. Rund, 59, 269, (1922).