Photometrics Cascade 128, User Manual, Page: 24 / 54

Chapter 3. Operating Features 13
Referring to Figure 4 , it can be seen that exposure and readout are carried out in
non-overlapped fashion. As a result, each frame in the sequence is precisely
exposed for the time specified (i.e., 10 ms).
Overlap Mode
(Simultaneous Exposure-
Readout)
Overlap mode is extremely useful in applications requiring continuous imaging
(100% duty cycle). Once a frame is exposed and transferred into the frame
transfer area, the next exposure immediately starts and continues until the
previous frame is read out or until the exposure time is finished, whichever is
longer (so the minimum effective exposure time in this mode is the readout
time). This mode of operation allows you to continuously image a specimen to
obtain better kinetic information about a process.
Figure 5 shows the required PVCAM settings for overlap mode. Note that the
clearing mode is set to "Pre-sequence" (as opposed to "Pre-exposure" in
Non-Overlap mode).
Figure 5. Required Settings for Overlap Mode Operation
Note: In Overlap mode, the minimum effective exposure time is the readout time.
The simultaneous exposure-readout mechanism is illustrated with two examples.
Example 1: Overlap Mode when Exposure Time < Readout Time
Consider a situation where full frame readout is 34.8 ms, the exposure time is 10 ms,
and three frames are taken in overlap mode. The first frame is exposed precisely for
the length of time entered into the software (10 ms) and all subsequent frames are
exposed for the readout time. The total time to acquire 3 frames is then 114.4 ms (3
×
34.8 ms + 10 ms), equivalent to a frame rate of 26.2 fps (3 frames
÷
0.114 seconds).
Note: Because the first frame is exposed for 10 ms and the others for 34.8 ms, the first
frame may look less bright compared to all other frames.
Select these parameters
to operate your
Cascade camera in
Overlap mode.