Handbook of High Speed Photography - IET Labs, Inc.

such as the 1531-P2 Flash Delay to introduce a variable time delay
between the trigger signal and the strobe flash. Such a device may be
used with repetitive events to stop the motion as explained in para
graph 5.3.1, or with non-repetitive events to ensure that the strobe
flash occurs when the subject is in the proper position. For example,
to take the milk-drop pictures of Figure 1-3, the photographer used a
photoelectric pickoff to produce a synchronizing pulse for the Flash
Delay. Then by varying the delay he could photograph any part of the
drop's descent.
Another type of phase adjustment is obtained by varying the
position of thesignal-producing device itself. For example, by changing
the subject to microphone distance in the acoustic triggering system
mentioned earlier, a variation of the occurrence in time of the flash is
obtained.
o
z
o
o
W 200-
DELAY AFTER CONTACTS CLOSE
'(OR NEGATIVE-GOING PULSE)
s
z
I
<
_J
"- 100-
o-l
DELAY AFTER
CONTACTS OPEN
(OR POSITIVE-GOING
PULSE
(SEE TEXT)
T-
0
90
(FULLY CLOCKWISE) |
"I—
180
FLASH POINT
RPM DIAL POSITION
1 T"
270 360
(FULLY COUNTERCLOCKWISE)
IN DEGREES
Figure 5-11. Internal delay characteristics
of the Type 1531-A Strobotac electronic stroboscope.
5.3.3 OBTAINING A FLASH BURST FOR A MULTIFLASH PHOTO
GRAPH. In many cases the stroboscope with its free-running internal
oscillator may be employed to take a multiple-flash picture, in which
several exposures are made on a single piece of stationary film. Other
53