FLASH IN STEREO 105M has about 50 percent greater brilliance, but on short exposures
some of this is lost by clipping out the peak brilliance with short
exposure.
Although these designations were received from an authori-
tative source, there seems to be some confusion about terms. As
used here “F” simply means the “empty” bulb and the “M” a
wire-filled bulb.
For general use with Kodachrome, the F bulb is probably the
best. Choice often depends upon various circumstances of course,
but without good reason for using another type, we recommend
the F bulb, unless your camera shutter is synchronized for other
bulbs. These bulbs provide an excellent color match for arti-
ficial light film without a filter.
We shall not give details of the equipment and its attachment
to the camera as this information is given with each flashgun as
it applies specifically, With the Realist, for example, the flash re-
flector slides into the “shoe” on top of the camera, the shutter set
at 1/25 or 1/50, a bulb inserted in the socket and the exposure
made as usual. The Personal and Stereo Vivid have synchronizing
contacts of somewhat different design. More elaborate externally
synchronized guns are attached according to the manufacturer’s
instructions. The Verascope uses a Busch gun of condenser type.
ExPosuRE.-The question constantly arises, “What exposure
shall I give with flash?”
Although the flash has high intensity, it is used so close to the
subject that its effect varies sharply with distance. According to
the inverse square law, the exposure at eight feet must be four
times that at four feet. For this reason, the flash exposure is based
upon “guide numbers.” These guide numbers take into considera-
tion the brilliance of the light, the sensitivity of the film, and the
distance of the subject. Thus the guide numbers change as the
film sensitivity changes.
Let us take the F bulb. used with film of 10-16 ASA sensitivity.
Reference to the exposure guide shows that up to i/ioo second
the guide number is 44. We now turn our attention to the sub-
ject. The focusing scale tells us that it is eight feet distant, We
therefore divide 44 by 8, which gives us 51h. We therefore set the
diaphragm at f5.6 which is close enough to the 5.5 as determined
by computation.