Opticstar PL-131 series. © Opticstar Ltd, 2021.
12
Updated: 07/09/2021
Exposure Time
The exposure time can be set by selecting
Options
> Video Capture Filter
under the
Exposure
tab.
The camera can operate using automatic exposure
or manual exposure. When using automatic
exposure, the only exposure related parameter that
the user can control is
Target
. The target slider
gives a delta value, up or down, to the automatic
exposure used by the camera. Effectively, the user
can affect the automatic exposure time by setting
the
Target
value. The target value can be set
between 50 and 200. The default value is 100
which leaves the default exposure time unchanged.
A
Target
value above 100 will increase the exposure time. A value below 100 will decrease it. The
Gain
value cannot be set by the user when the camera operates in automatic exposure mode.
Manual Exposure Time
The exposure time can also be set manually by un-ticking the
Auto Exposure
option. When the
camera operates in manual exposure mode, the
Target
value cannot be set since it has no
meaningful purpose in this context. The
Gain
value however can be set between 1 and 40. High
Gain
values increase the camera’s light sensitivity.
Timing Units and Exposure Time
The region of interest (ROI) modes, increase the frame rate dramatically. At 1280x1024 the frame
rate is 22 frames per second (FPS). When in 640x480 ROI mode the maximum frame rate increases
to 80FPS. An increase of 3.6 times (80 / 22 = 3.6). The exposure time per frame decreases
accordingly. Therefore, in 640x480 ROI the maximum exposure time of the camera is 3.6 times
less. Effectively, it is a trade-off between speed and exposure time (and hence sensitivity).
Similarly, at 320x240 ROI the frame rate increases to 220 FPS. Therefore, because the frame rate
increases by ten times, the exposure time per frame is reduced by 10 times (220 / 22 = 10).
The exposure control slide bar always displays the exposure time units between 0 and 3000. These
units relate to the camera's internal clock rather than actual milliseconds. The range of 3000 units
specifies different a exposure time depending on the camera mode. When the camera runs in high-
speed mode (the default mode), the maximum frame rates and the exposure times are outlined in
the table below.
Mode
Frame Rate (FPS)
Exposure Time (max)
Timing Units
1280 x 1024
22
500ms
3000
640 x 480 ROI
80
138ms
3000
320 x 240 ROI
220
50ms
3000
