User`s manual

Basic Operation & Standard Features
3-4 BASLER A620
f
DRAFT
3.3 Exposure Control
3.3.1 Setting the Exposure Time
Exposure time is determined by a combination of two values. The first is the setting in the Value
field of the Shutter control register (see page 4-24). The second is the Shutter Time Base.
Exposure time is determined by the product of these two values:
Exposure Time = (Shutter Value Setting) x (Shutter Time Base)
The shutter time base is fixed at 20 µs. Exposure time is adjusted by changing the setting in the
Value field of the Shutter control register. The shutter value setting can range from 1 to 4095
(0x001 to 0xFFF). So if the Value field of the Shutter register is set to 100 (0x064), for example,
the exposure time will be 100 x 20 µs or 2000 µs.
If you are operating the camera at a standard frame rate, you can determine the maximum shutter
setting for that frame rate by reading the Max Value field of the Shutter Inquiry register (see page
4-16).
3.3.2 Effect of the Exposure Time Setting on the Camera’s
Maximum Frame Rate
The capture of a single frame (image) is a two part process. First, the pixels in the camera’s sensor
must be exposed to light for some period of time. Second, after exposure is complete, the charges
accumulated by the pixels during the exposure must be read out of the sensor and into the
camera’s image buffer. With the sensor used in A620
f cameras, the exposure of a new frame can
not begin until the readout of the previously captured frame is complete. This situation is illustrated
in Figure 3-3.
Figure 3-3: Frame Capture Sequence
A result of this sensor characteristic is that the exposure time setting will have a very direct effect
on the camera’s maximum allowed frame rate. At longer exposure times, the camera’s maximum
frame rate will be lower.
The formula on page 3-5 lets you calculate the camera’s maximum frame rate at full resolution for
a given exposure time. This is useful if you know the exposure time you want to use and you want
to determine the maximum frame rate you can achieve with that exposure time.
The formula on page 3-6 lets you calculate the camera’s maximum exposure time for a given
frame rate at full resolution. This is useful if you know the frame rate and you want to determine
the maximum exposure time you can use at that frame rate.
L
A camera signal called “trigger ready” indicates when sensor readout is complete and
it is safe to begin the next exposure. See Section 3.4 for more information on the trig-
ger ready signal.