Page:JOSA-Vol 06-06.djvu/47

Table 12

Transmissions of Approved Photographic Taking Filters

λ=Wave-length in mμ.
Τ=Fraction of incident radiation transmitted.

No. 1		No. 2		No. 3		No. 4
λ	Τ	λ	Τ	λ	Τ	λ	Τ
700	.82	620	.01	400	.07	460	.02
680	.82	600	.03	410	.09	470	.09
660	.82	580	.18	420	.11	480	.19
640	.82	560	.30	430	.15	490	.35
620	.80	540	.46	440	.21	500	.49
610	.75	530	.53	450	.28	510	.58
600	.60	520	.37	460	.26	520	.59
590	.25	510	.52	470	.19	530	.55
585	.10	500	.35	480	.10	540	.49
580	.02	490	.12	490	.04	550	.38
. . .	. . .	480	.02	580	.01	560	.25
. . .	. . .	. . .	. . .	. . .	. . .	570	.74
. . .	. . .	. . .	. . .	. . .	. . .	580	.07
. . .	. . .	. . .	. . .	. . .	. . .	590	.02

photographically, as closely as possible, the mixing proportions of the corresponding reproducing filters which are required to match the colors of the photographed objects. The production of such photographic records of the values in question will evidently depend not only upon the transmissions of the filters but also upon the spectral distribution of sensitiveness of the given photographic emulsion. Similar general principles apply to the choice of two-color taking filters if the blue-violet values of the photographed objects are left out of consideration, since two-color taking filters are ordinarily selected so as to neglect those values of the scene which are poorly represented in yellowish, artificial illumination.

(c) Photographic Reproducing Filters. Filters necessary for three-color and two-color additive projection of photographic positives printed from color separation negatives, or for use in such instruments as the Ives Chromscope (54, 218) depend in quality upon the character of the light source which is employed. Since the sources vary widely, it is difficult to specify the transmissions of the filters very exactly. Filters for three-color addi-