Princeton 4411-0106 User Manual

Chapter 5 

Operation 

57 

 

57 

For full-frame imaging CCDs, the standard PIXIS camera for imaging is equipped with 
an integral shutter. However, inasmuch as it is possible to order the camera without a 
shutter, the following general discussion of unshuttered operation is provided. 

Slow scan scientific cameras require a shutter to prevent "smearing" of features during 
readout. This is because during readout, charge is moved horizontally or vertically across 
the surface of the CCD. If light is falling on the CCD during readout then charge will 
continue to accumulate, blurring the image along one direction only.  

Because spectroscopy CCDs typically have their parallel shifting aligned vertically 
(perpendicular to the spectrum), smearing does not affect the spectral resolution, only the 
intensity level of the spectral features. When vertically binned, the readout generally 
takes a few milliseconds to tens of milliseconds. In experiments where the exposure time 
is much larger than the readout time, the smearing due to readout is insignificant, and the 
CCD can be operated without a shutter with very little loss of performance.   

If the CCD is set up for imaging mode (the WinSpec Imaging option has been installed 
and is selected on the Experiment Setup|ROI Setup tab), smearing may be more of a 
factor. In this case, controlling the light source so no light falls on the CCD during 
readout would minimize any smearing. If the light source can be controlled electronically 
via the output of the LOGIC OUT connector, the CCD can be read out in darkness.  

Exposure time, which is set on the 

 tab {

expander},  is the time between start acquisition and stop 

acquisition commands sent by the application software to the camera.  In combination 
with triggers, these commands control when continuous cleaning of the CCD stops and 
when the accumulated signal will be readout. The continuous cleaning prevents buildup 
of dark current and unwanted signal before the start of the exposure time. At the end of 
the exposure time, the CCD is readout and cleaning starts again. 

Because some PIXIS cameras do not incorporate an internal shutter, some signal may 
accumulate on the array while it is being readout. This continuous exposure of the array 
during readout may result in some smearing. However, exposures that are significantly 
longer than the readout time can be performed without a shutter, as the amount of 
smearing will be low.  

If smearing or other factors require a shutter, the 

 {

} or the 

 {

}signal at the 

 connector (on the rear of the PIXIS) 

can be used to control a customer-supplied external shutter. By using one of the signals to 
synchronize the shutter operation with exposure, the CCD can be read out in darkness.   

As stated before, lowering the temperature of the CCD 
will generally enhance the quality of the acquired 
signal. When WinX is the controlling software, 
temperature control is done via the 

 dialog (see Figure 23) accessed from the 

Setup menu. When LightField is being used, 
temperature control is done

on the

expander.