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70 PIXIS System Manual Version 2.C
External synchronization depends on an edge trigger (negative- or positive-going) which
must be supplied to the EXT SYNC connector on the back of the camera. The type of
edge must be identified in the application software to ensure that the shutter opening is
initiated by the correct edge (in WinX, this is done on the Experiment Setup|Timing
tab, in LightField on the Trigger expander). Since the shutter requires at least 8 ms to
fully open, the External Sync pulse provided by the experiment must precede the actual
signal by at least that much time. If not, the shutter will not be open for the duration of
the entire signal, or the signal may be missed completely.
Also, since the amount of time from initialization of the experiment to the first External
Sync pulse is not fixed, an accurate background subtraction may not be possible for the
first readout. In multiple-shot experiments this is easily overcome by simply discarding
the first frame.
In the PreOpen Shutter {Open Before Trigger} mode, on the other hand, shutter operation
is only partially synchronized to the experiment. As soon as the camera is ready to collect
data, the shutter opens. Upon arrival of the first External Sync pulse at the EXT SYNC
connector, the shutter remains open for the specified exposure period, closes, and the
CCD is read out. As soon as readout is complete, the shutter reopens and waits for the
next frame.
Figure 30. Chart Showing Two External Sync Timing Options