_ T T T T TT T Tn > T TT 5 & STEP WEDGE EXPCSLRES! 3 AT EZFSNNAG OF FiLM, 3 AT END. on ee | OENSITY - TOT -30 ~20 -10 LOGRELATIVE EXPOSURE 0 Fig. 11.5--Control step wedges, film T-11. axis is called the inertia point. It is found that the inertia point position is quite insensitive to variation in developoent processing. The inertia point froa the calibration film was therefore used to place sn absolute energy scale om the D-log E curves obtained as follows. The exposure ratio between any two channels of a streak casera is known from the relative filter transmissions. Thus at any fixed time, four points on a density-versus-relative- exposure curve are obtained. By going to other times, other groups of points cao be obtained, and thus a complete curve can be built up. It-was found chat data from channels with ninicum exposure (and to a such saaller extent the one with the next greater exposure) did not fit well with che higher density chan- nels.) Subsequent laboratory tests have sbown chat there is sufficient scattericg in the fila and casera to cause a distortion of the channels which have been attecusted factors of 100 to 1000 as were the two least dense channels. Therefore, only data from the two most dense channels on each fila were con- sidered reliable acd used in subsequent analysis. ay The aucocalibrated curves