Handbook of High Speed Photography - IET Labs, Inc.

4-3). If the reflectors are placed 6 inches from the spindle the effective
separation is 2.0 feet. The bellows-extension correction is determined
from Figure 4-5.
0*v A ( 1 Q\
Bellows Ext. = '—— = 3, Image Size = 2,
and the correction factor K « 0.3-
The addition of a second lamp complicates the calculation, but
a reasonable first-order guess is that it will cause nI~2 (a 40%) increase
of f/number. The calculated f/number would be:
f =(0.3) ^~ (1.4) =18.9,
which can be approximated, or the nearest indicated number (f/16 or
f/22) may be used.
A final consideration is the shutter speed.
This must be fast
enough to prevent ambient-light exposure, which appears as blur and
reduced contrast in the final photo. The shutter must be fully open for
at least a full cycle of the spindle (see paragraph 5-3.1). In this case,
one revolution takes
1 1
25°>000 - 4^00 SCC
60
and the between-the-lens shutter speed may be the fastest indicated
(e-«- msec)*
The required f-stop must be calculated for pictures to be taken
on negative film. In this example Kodak Royal-X Pan film with an ASA
rating of 1250 is used. The required camera f-stop is:
f =(0.3) y(U) = H.5
If depth-of-field is unimportant, a finer-grained, slower speed
film can also be employed with correspondingly lower f-stop setting.
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