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June. 1926
AMERICAN C I NE M AT OG R APHER
Eleven
4 00 ^JM
Violet Spectral Sensitivity o^ Film
500 fcOO 700u.(i
Blue Green Yellow Orange Red
TransmiHBd
*•* „_ Ser 0
SaFeligrrte
3er00
I ZOOOf !
06 2
E
Values enclosed m rectangles represent retatrve photographic effect onPanchroma+ic Film
t ?l-0
Above: Figure One. Curves showing relation between visual and photographic intensity of light transmitted by Wratten safelights.
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S
SPeCTRO-PHOTOMETRlC ABSORPTION GJRVE5 OF DE5EnSITIZER5
CONCfcWR>TION in parts per million
Figure Four
Figure Three
tended throughout the visible spectrum. The light transmitted by the Wratten Safelight Filters is represented in this diagram by blocks of which the extent of the base line corresponds to the wavelengths transmitted. The area, and the accompanying number, represent the relative photographic effectiveness of the light. This was measured by the effect produced on a panchromatic film when exposed to the different safelights for the same time through a step tablet (See Fig. 2). On the right are given the values in foot candles for the illumination given by the safelights and measured at a distance of 1 foot (30 cm.) when used in a Wratten safelight lamp containing a 25 W. bulb. The measurements were made with a Macbeth illuminometer. From this diagram it is evident that the yellowish green safelight, Series 3, is the most efficient for panchromatic materials, while for emulsions which are not red sensitive the red safelights Series 1 or 2 are better because of the relative insensitivity of the film to the light which they transmit. The extent to which these relations are modified by the use of desensitizers in development will be indicated later.
In Fig. 2 is shown the method by "which the relative photographic effect of the light transmitted by the different safelights was measured. A step tablet having a density range of 3.4 was placed over a sheet of Commercial Panchromatic Film. Narrow strips were then exposed to each of the different safelights for the same time and in the same manner, and the whole sheet developed.
From the densities of the step tablet corresponding in each case to the first visible image, the relative exposures were calculated.
The limits of safety in exposing Eastman Motion Picture Negative and Commercial Panchromatic Film to the various safelights is shown in Table I. The fog density produced with normal development by a ten seconds exposure to the safelight at a distance of one foot is given except where no effect was obtained in this time. In such cases the time required to produce a visible fog is recorded. Table t
Comparative -Safety of Untreated Film to
Wratten Safelights
Exposure at 30 cm. (1 ft.) from 8" x 10" Wratten
Safelight Lamp Containing 25 W. Bulb.
Relative Fog Density Produced by 10
seconds Exposure. Panchromatic Motion Picture Nega
Safelight. Film.
Series 00 2.2
0 2.0
1 1.5
2 1.5
3 0.2
4 1.0 From Table I it is evident that sufficient light cannot be used with panchromatic film without desensitizing
(Continued on Page IS)
tive Film.
1.9
1.2 Fog in 1 minute Fog in 2 minutes Fog in 15 seconds
0.8