106 THREE-DIMENSIONAL PHOTOGRAPHYYou may avoid complex mental computation by using a guide
number close to that given. Thus, for a nine foot distance, you
may use 45 instead of 44, and the error will not be at all serious.
In fact surroundings often alter the effective light intensity to a
considerable degree, yet there is enough tolerance to give, usually,
good results from an approximate guide number.
There are conditions which call for some departure from the
computed exposure. For objects which are very dark, use one-half
stop larger aperture, for those which are light, one-half stop
smaller. Note that this also applies to rooms. In a small room with
white walls a reduction is required, but in a large room particu-
larly with dark walls, use the increase in exposure. For outdoor
work, use a full stop increase. To do this compute the exposure
first and then add one stop, do not use one-half the original guide
number.
It may be that you will find it necessary to alter the guide num-
bers after some experience. Different types of reflector make a
difference in the intensity of light reflected from the subject, and
that is the factor of importance. If the light is concentrated it will
be brighter, but if a wide beam reflector is used, it will be less
brilliant.
FLASH PosITroN.-There is a distinct relationship between the
effect produced and the position of the flash bulb in relation to
the lens. If the light is close to and directly above the lenses, the
lighting will be very flat, and projections along the camera axis,
or in the direction of the camera, will be minimized. For example
if a model is facing the camera directly, the nose will be short-
ened, the facial expression altered, the eyes set flush in the face
instead of being in their sockets. In short the face is flattened and
robbed of expression.
If the flash is supported at the side of the camera, and lies at the
same side of both lenses, there will be enough cast shadow to
remedy, to some extent the fault just noted. This is the position
used in most press photography, and for purely record work it is
acceptable, but it is still far from good.
The best position for the flash is above and at one side of the
camera, the distance from the lens at least 30 inches, and more
if the subject is more than four feet from the camera.
The illustrations which illustrate these points were made with