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Appendix H DIF Camera 99
EEC (External Exposure Control)
Gives the user the ability to capture two images before readout with a different exposure
time for each. EEC uses the external trigger to control the exposure time of the first
image and the exposure time set in software to control the exposure time of the second
image. When the external trigger applied to Ext Sync is detected, the first exposure
begins. The end of the trigger marks the end of the first image and the start of the second.
After an interval equal to the exposure time set on the Experiment Setup Main tab page,
the shutter closes. As in the IEC mode, the system is receptive to an applied trigger when
goes low. Note that the shutter can be disabled open. With the shutter disabled
open, if reading out a full array, the second exposure time would actually last ~1.4 s. If
reading out a single strip, the readout time (and hence the second exposure) would be
much shorter, on the order of a few hundred microseconds. Generally though, the
experiment timing would be set up so that the second strobed event would occur during
the second image time as set by the Exposure Time parameter on the Experiment Setup
Main tab page.
Example: The exposure time for the first image is controlled with the signal applied to
the EXT. SYNC connector. The exposure time for the second image is the
exposure time set in software under Experiment Setup. An external trigger
supplied by the user is required to initiate the imaging process and control the
first image exposure time. The controller
signal goes low when the
camera is ready to begin imaging. Figure 58 illustrates an EEC timing
example.
EXT. SYNC. (A)
Images
t
exp
Mechanical
Shutter
8 ms
8 ms
NOTSCAN
Image 1
t
sync
Image 2
200 ns
READY
Figure 58. EEC Timing Example with Exposure Time in Software set to t
ex
Summary of EEC Timing mode
• Enables double image capture under external control.
• Requires that the switch, if present on the back of the camera, be set to INACTIVE.
• The width of the pulse applied to Ext Sync sets the exposure time of the first image.
The Exposure Time set in software on the Experiment Setup Main tab page sets the
second image time, at the end of which the shutter begins to close.
• An external trigger is required to initiate the imaging process. The
goes low
when the system is ready. Once
is low, an external trigger applied to the
Ext Sync connector initiates the double image capture.