Leginon

h1. Dose (Camera Sensitivity) Calibration

[[Faraday Cup Measurment Notes]]

Dose Calibration is a calibration of digital camera  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 but almost to 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 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 camera sensitivity (counts / electron) will display once the calculation is completed.

h2.  Enter pre-determined camera sensitivity value

#  Leginon/Dose/Calibrate/Camera Sensitivity> Enter Sensitivity values in counts per electron.

 

#  Leginon/Dose/Calibrate/Camera Sensitivity> Click on Save.

!predetermined-dose.png!

*Dose Calibration Need for the Example MSI:*

|_.Preset|_.magnification|

|*|any|

______

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

______