SVS-Vistek ECO Series, Manual

Page: 21 / 104

SVS-VISTEK
Feature description 21
Flashing with Rolling Shutter
Scanning sensor lines takes time, an scanning time. There are 2 general
options for flashing:
1. Make sure your flash is ON and stable the whole period of time
while scanning/exposing. Minimum flash time is scanning time
plus exposure time. In this case, while flashing you will get
geometric distortions as mentioned above. Exposure will be
determined by camera exposure time and light intensity
2. If flash time is less than scanning time then exposure time has to
be at least scanning time + flash time, with a delay of scanning
time. In other words, your exposure time will be scanning time
plus flash time, while you use a flash delay of scanning time.
Thus flash release will start after the delay of scanning time, as
soon the sensor is fully open. You should keep the object in total
darkness while the first scanning time.
In this case, as all lines are sensitive to light at the same time
after the first scan time, flashing time can be as short as you like.
You will not see the typical geometric rolling shutter distortions as
shown above. Imaging will be similar to global shutter. Exposure
will be determined by flash time/intensity.
Figure 11: Rolling shutter lines light sensitivity versus time
As shown here, after triggering only part of the sensor is sensitive to light
(scanning time). As soon as scanning time has finished, all pixels are
sensitive to light, the sensor is fully open. While being fully open this is the
time where flashing should happen. In the final scanning time, less and
less pixels are sensitive to light until the sensor light sensitivity will finish.
Flashing of rolling shutter sensors is significantly different to global shutter
flashing!