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Dose (Camera Sensitivity) Calibration » History » Revision 3

Revision 2 (Amber Herold, 04/27/2010 10:51 AM) → Revision 3/14 (Amber Herold, 06/23/2010 02:28 PM)

h1. Dose (Camera Sensitivity) Calibration 



 Dose Calibration is a calibration of CCD sensitivity. This calibration is required only 
 once at each high tension per instrument. It can be used for three purposes: 


 




 *    To obtain a scaling factor between the scope screen current and the beam current 
 measured by a standardized equipment such as a Faraday cup. 


 *    To calibrate the camera sensitivity to electron. 


 *    If camera sensitivity is already calibrated, the value can be entered 
 directly. 



 







 h2.    Determine the screen current/beam current scale factor 



 The following uses a Faraday cup 



 




 *    Scope> Move the stage to an empty area or a broken hole. 


 *    Scope> Adjust the beam so that it passes through the measuring area of the 
 Faraday cup. 


 *    Scope> Choose a magnification so that the same beam will pass within the main 
 screen, too. 


 *    Leginon/Dose/Dose Calibrator> Beam Diameter = 0.16 m for Tecnai main 
 screen. 


 *    Leginon/Dose/Dose Calibrator> Enter Screen Current to Beam Current Scale 
 Factor as 1 as a starting point. 


 *    scope> Optionally lower the screen. Dose Calibrator will automatically do this 
 if the user forgets. 


 *    Leginon/Dose/Dose Calibrator> Click Measure Dose Rate. The Dose Rate, Beam 
 Current, and Screen Magnification will appear in the corresponding fields after they 
 have been calculated. 


 *    Leginon/Dose/Dose Calibrator> Adjust the Screen Current to Beam Current Scale 
 Factor so that the displayed beam current is equal to that of the Faraday cup 
 measurement. NRAMM Tecnai's value is 0.88. 



 









 h2.    Calibrate the camera sensitivity 



 





 *    Scope> Move the stage to an empty area or a broken hole. 


 *    Scope> Expand the beam so that it covers the main screen and illuminate it 
 uniformly. 


 *    Leginon/Dose/Settings> Configure camera with override overide preset activated. 


 *    Leginon/Dose/Dose Calibrator> 
 ** 



 Beam Diameter = 0.16 m for the Tecnai's main viewing screen. 
 ** 


 Screen Current to Beam Current Scale Factor = (as determined above or 1 to assume 
 good calibration by the microscope manufacturer) 


 *    scope> Optionally lower the screen. Dose Calibrator will automatically do this 
 if the user forgets. 


 *    Leginon/Dose/Dose Calibrator> Click Measure Dose Rate. The Dose Rate, Beam 
 Current, and Screen Magnification will appear in the corresponding fields after they 
 have been calculated. 


 *    Leginon/Dose/Dose Calibrator> Without changing the beam intensity, click on 
 "Calibrate". An image is acquired by Leginon. 
 


 *Leginon will automatically lift the main viewing screen on the microscope. Some 
 users report that the function does not work on their microscopes. Do it manually if 
 the automatic function does not work. 


 *    The calculated CCD sensitivity (counts / electron) will display once the 
 calculation is completed. 




 









 h2.    Enter pre-determined camera sensitivity value 


 





 *    Leginon/Dose/Dose Settings/Camera Sensitivity> Enter Sensitivity values in 
 counts per electron. 


 *    Leginon/Dose/Dose Settings/Camera Sensitivity> Click on Save. 

 Dose Calibration Need for the Example MSI: 

 







 |_.Preset|_.magnification| 
 |*|any| 




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 [[Autofocus Calibration with Beam Tilt Node|< Autofocus Calibration with Beam Tilt Node]] 

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