User`s guide

SHUTTER CONTROL
SDK SECTION 7
Page 61
SHUTTER TRANSFER TIME
Mechanical shutters take a finite time to open or close. This is sometimes called the Shutter Transfer Time
and can be of the order of tens to hundreds of milliseconds. The Transfer Time is important for many
reasons.
Firstly, if your shutter takes 40ms to open and you specify an exposure time of 20ms then the shutter will
simply not get the time to open fully. Similarly, if you are triggering a pulse light source via the Fire pulse then
you will want to ensure that the Fire pulse goes high only when the shutter is opened. Also, if you are
acquiring data in an imaging mode (Multi-Track, Random-Track, Single-Track or Image), with either a
continuous light source or a large high background illumination with a pulsed source, the shutter must be fully
closed before readout begins. Otherwise, a smeared image will result.
The
SetShutter and SetShutterEx functions allow you to specify a Transfer Time for both opening and closing
the shutter.
The time you specify for the shutter opening time will affect the minimum exposure time you can set via the
SetExposureTime function. For example, if you set the opening time to 0ms then the minimum exposure time
will be set to the amount of time needed to clean the shift register on the CCD. However, if the opening time
is set to a larger value than is needed to clean the shift register, say 50ms, then the minimum exposure time
will be 51ms i.e. 1ms more than the time needed to open the shutter.
The SetExposureTime is in effect setting the length of time the shutter output will be in the ‘open’ state. The
rising edge of the Fire output signal follows the start of the shutter open state after a delay, equal to the value
you set for the opening time via the SetShutter functions.
Andor SDK also automatically adds the Transfer Time for the closing of the shutter to the end of the
acquisition sequence, introducing an appropriate delay between the start of the shutter ‘closed’ state and the
commencement of the data being read out. This value is set via the closing time parameter in the SetShutter
and SetShutterEx functions.
Figures 10 & 11 on the next page show the timing sequence for both Internal and External triggering modes.