COLOR IN STEREO 123a light which has too little blue. How can you make up the de-
ficiency of blue in the photoflood? You cannot build up the blue
content of the light, but you can remove enough of the red to
leave the blue in proper balance. So you use a red-absorbing filter
(bluish) of the correct density.
But what if you are using daylight film and an SF flashbulb,
5900K film and 33ooK light?
The light is 3300K, Type A film is balanced for 34ooK. The
difference is insignificant, so you can safely use the same filter
you use for balancing daylight film to photoflood light, and by
the same reasoning you need no filter to balance Type A film to
SF or SM flashbulbs.
Thus adequate color control depends upon just two things,
knowing how to determine the. color of the light used and how to
determine the filter necessary to balance this light to the film you
are using.
Fortunately artificial light sources may be assumed to conform
to published ratings which means the difference between actual
and nominal rating is not enough to spoil the color effect. In fact
most light sources conform to average ratings. Therefore your
light measuring problem is limited largely to daylight conditions.
The measurement is done by a color temperature meter. This
may either be a visual meter, an electric CT meter or an attach-
ment for the G.E. exposure meter.
If you can distinguish between purple and blue, that is, whether
a blue color has any tinge of red in it or not, you can use the
visual meter successfully. You simply find three visual filters one
of which is purple, one of which is pure blue and one of which
is neutral or in-between.
If you doubt your color sensitivity, then use the attachment for
the exposure meter which gives you a definite reading unaffected
by personal visual error, or an electric CT meter.
As to the filters necessary, yo; can obtain filters from Eastman
and from Ansco for certain corrections of their films, but the
writer prefers the Harrison & Harrison correction set which has
11 blues, 11 reds or a total of 22 filters for each lens, a grand
total of 44 filters for the stereo camera. These filters make it possi-
ble to correct the balance of any light from 28ooK to 9500K for