Single-Flash Triggering; Photography With The 4912 - BRUEL & KJAER 4912 Instruction Manual

than reciprocating, one of the high-µ discs supplied with the Transducer may be cem-
ented to the moving object or secured with a double-sided self-adhesive disc YO 0073.
The Transducer is supplied with a 1,2 m connecting cable AO 0038, requiring adaptor
JP 0145 (not supplied) to connect the 10-32 UNF miniature screw-locking coaxial plug
on the cable to the EXT. TRIG. INPUT socket on the 491 2.
The Magnetic Transducer is especially to be preferred for triggering in dirty environ-
ments or in general where the optical technique of the MM 0012 is not suitable. For
more detailed information, refer to the Product Data for the MM 0002.
3.4.4. Single-Flash Triggering
A single flash can be obtained when FUNCTION SELECTOR is set to "Ext . Trigger" by
connecting together the tip and the ring of the EXT. TRIG. INPUT socket, momentarily.
TRIGGER LEVEL should be set with the white mark on the knob slightly to the left of the
central position. This facility may be used to trigger the flash from the flash contacts of a
camera.
For correct synchronization of the shutter, the "X" contacts should be used on the cam-
era. Select the shutter speed in accordance with the recommendations in the camera's
instruction manual for its use with electronic flash. In general, any shutter speed may
be used with a between-the-lens shutter. With a camera having a focal-plane shutter,
the highest speed which may be used is usually limited to some setting between 1 /30
and 1 /125 s, depending on the characteristics of the shutter. This setting will be stated
in the instruction manual. If in doubt, use a setting of 1 / 30 s or longer.
Photography with the 4912 is discussed in section 3.5.
3.5. PHOTOGRAPHY WITH THE 4912
14
The recommended exposures for photographing objects illuminated by the flash of the
4912 are given in Table 3.2. The conditions in which they will be found optimum are:
subject-to-lamp distance, 250 mm (10 in); subject elements illuminated, up to 2,5° off
axis.
The 491 2 may be set to give a single flash in synchronism with the opening of the cam-
era shutter, as explained in section 3 .4.4. In this case the exposures given in the first
column of the Table should be used.
If the camera is not synchronized with the 491 2, then a shutter speed must be selected
which is slow enough to ensure that at least one flash occurs while the shutter is open.
It is preferable to ensure that at least three occur, to minimize the effect of the uncer-
tainty of the timing on the actual number of flashes which do occur. If the flash fre-
quency F is less than 25 Hz, then the number of flashes which occur during shutter-
open time should be calculated, and the exposure read from the corresponding column
of the Table. F should be read from the FREQUENCY display provided this indicates less
than 25 Hz (1500 r/ min) . Set FREQUENCY SELECTOR to one of the "Hz" positions. The
number of flashes which occur can be calculated from the formula F x T, where T is the
exposure-time in seconds .
If the flash rate F exceeds 25 Hz ( 1 500 r /min), then the exposure received by the film
will be independent of F provided at least three flashes occur while the shutter is open.
This is because the averaged ii luminance generated by the 491 2 is kept constant aboVe
25 Hz . In this situation the exposure should be taken from the column corresponding to