BOBCAT Hardware User’s Manual
Imperx, Inc.
Rev. 1.0
6421 Congress Ave.
5/4/2010
Boca Raton, FL 33487
+1 (561) 989-0006
77 of 212
2.5 EXPOSURE CONTROL
2.5.1 Internal Exposure Control - Electronic Shutter
During normal camera operation, the exposure time is fixed and determined by the
readout (frame) time. The electronic shutter can be used to precisely control the
image exposure time under bright light conditions. The electronic shutter does not
affect the frame rate; it only reduces the amount of electrons collected. Positioning
a short pulse “SHUTTER”, with respect to the vertical transfer pulse, VCCD –
Figure 2.12, sets the exposure time. The electronic shutter pulse can be positioned
within the entire frame period with a precision of 1.0us. The maximum exposure is
frame time dependent and the minimum exposure is ~ 2 microseconds (camera
dependent).
VCCD
SHUTTER
Frame Time
Exposure
Figure 2.12 – Electronic shutter position
2.5.2 External exposure control
The camera exposure can be controlled using an external pulse, supplied to the
camera. The pulse duration determines the exposure. For stable operation, this pulse
MUST be synchronized with the camera frame timing. Please refer to “I/O Control”
section for pulse mapping information.
2.5.3 Variable Frame Time – Programmable Line and Frame Time
Variable frame time mode provides the ability to run the camera in full resolution
and a frame rate slower than the nominal camera frame. This has two effects: 1) it
reduces the bandwidth requirements on the camera output and 2) it increases the
exposure time for the frame. During normal camera operation (no shutter), the
nominal frame rate determines the integration time. The desired frame rate, and thus
the new integration time, can be achieved by moving the vertical transfer pulse,
