Instruction manual
Controlling image capture
MARLIN Technical Manual
Page 60
9.6 Jitter at start of exposure
The following chapter discusses the latency time which exists for all CCD-models when either a
hardware or software trigger is generated, until the actual image exposure starts.
Owing to the well-known fact that an Interline Transfer CCD-sensor has both a light sensitive
area and a separate storage area, it is common to interleave image exposure of a new frame and
output that of the previous one. It makes continuous image flow possible, even with an external
trigger.
This is different to the way the CMOS- sensor of the MF-131 works: the image sensitive area is
also the storage area, which means that it cannot be used for the integration of the new frame
until it has been read out.
Continuous image flow is thus only possible with the so-called rolling shutter.
Asynchronous image aqquisition only makes sense with the global shutter; leading to a non-
interleaving exposure – readout – exposure sequence. For every exposure cycle the sensor is
completely reset so that the camera needs to be idle.
For the CCD’s the uncertain time delay before the start of exposure depends on the state of the
sensor. A distinction is made as follows:
FVal is active the sensor is reading out, camera is busy
In this case the camera must not change horizontal timing so that the trigger event is
synchronized with the current horizontal clock. This introduces a max. uncertainty which is
equivalent to the line time. The line time depends on the sensor used and therefore can vary
frommodel to model.
FVal is inactive the sensor is ready, the camera is idle
In this case the camera can resynchronize the horizontal clock to the new trigger event, leaving
only a very short uncertainty time of the master clock period.
Model Camera idle Camera busy
MF-033 33,33 ns 27,03 µs
MF-046 33,33 ns 32,17 µs
MF-080 50 ns 63,50 µs
MF-131 25 ns Not possible
MF-145 50 ns 92,25 µs
Table 29: Jitter at exposure start
Jitter at the beginning of an exposure has no effect on the length of exposure, i.e. it is
always constant.
By default, the MF-131, the CMOS sensor uses global shutter, so it cannot be re-triggered
until the previous image has been read out.