110 THREE-DIMENSIONAL PHOTOGRAPHY
Then too, room walls affect the color, and as these are usually
a warm tint such as cream, ivory or tan, they tend to lower the
over-all color temperature. As this is so variable, we shall limit the
discussion to the actual flash color.
Standard Balance.-Daylight film is usually balanced for 5gooK,
the tungsten films are corrected for projection bulbs at about
3200 and photoflood are corrected for 3400. But in actual use
both the projection and flood bulbs tend to fall below this color,
photoflood bulbs particularly fall off rapidly with use.
Thus, if we assume the color temperatures of flashbulbs to be
accurate (and they are more accurate than the average tungsten
or photoflood), the corrections may be ascertained.
When using the F type bulb, use no filter with either type A
or tungsten films. The light is very slightly warm for A and cool
for tungsten, but the variation is not more than other variations
to be expected in commercial products, so with the F type, rapid
bulb, use no correcting filter when using either of the artificial
light film types.
For use with daylight film, use the usual filter which would be
used with this film for artificial light use.
The M type bulb, at 38ooK, is the standard flash color for other
bulbs except the blue series. For use with photoflood film (type
A), the H&H C 1/4 is used and with tungsten film the C 1/2 is indi-
cated. With daylight film a B2 filter would be indicated rather
than the Bq for F bulbs. Corresponding filters of other series will
provide similar corrections.
If the electronic flash is used, the color temperature may be as-
sumed to be 7000K more or less or one correction step more blue
than the light for which daylight film is corrected. Daylight film
would therefore call for a C 1/4 filter, photoflood would need the
C5 and tungsten film the C6 for correction. However, it is advisa-
ble to use an artificial light film type for flash work, rather than
the daylight type, unless electronic flash is used, when daylight
film is preferable.
Blue Bulbs.-There are times when it is necessary to use day-
light film, such as when balancing flash and daylight. In this case
it is better to filter the light at its source than to use a filter over
the camera lens.
The easiest way to do this is to use blue bulbs, but they are