SpectraVideo Camera User’s Manual
Camera Exposure Control
10
4. C
AMERA
E
XPOSURE
C
ONTROL
4.1. E
XTERNAL
E
XPOSURE
C
ONTROL
Exposure may be controlled externally by supplying a TTL level to the “Exposure
In” connector on the back of the camera control box, with “Exposure Out”
disconnected. The TTL level is normally high; exposure will occur while the level
is pulled low. With a brief delay (typically 15
µ
s), as soon as the level goes low,
the camera will go into exposure mode and communication with the camera will
be suspended until exposure is discontinued and a frame readout is complete.
If you are running PixelView, exposure must be set to Externally Gated in the
Exposure Tab within the “Camera Setup” dialog box under the Control menu.
A new frame must then be acquired. The software will wait until an exposure has
occurred and will capture the frame. Pressing the Escape key will cancel the
acquisition. Once a single frame has been acquired, selecting the Continuous
(Ctrl-C) item from the Acquire menu makes continuous acquisitions.
The entrance into exposure mode may be delayed for as long as it takes the
parallel gate drivers to fall, typically 15
µ
s. Consequently, the exposure gate
should precede the external event by at least 15
µ
s.
After the exposure gate rises, the CCD will continue to expose to allow time for a
shutter to close, phosphor to decay, etc. The length of time is determined by the
value entered in the “After Exposure” box within the Rate Tab of the “Camera
Setup” dialog box under the Control menu. After exposure wait can also be
accessed by the user’s software. Figure 3 below shows the relationships between
the various waveforms.
Figure 3 Exposure Timing Relationships