Click on the menu item “Camera” then “Acquire Ref” or Acquire References. Below is what you should see:
It is ultra critical that you find a blank area on your grid before shooting your flatfields/dark images. This means no specimen or other embedding material. Typically one leaves an empty area on their grid for this reason. If you are using a grid with no empty area then you may have to either switch to position 2 or switch to a different grid to acquire your flatfields and bias images. Set the brightness/current density to how you plan on shooting your images. It is advisable to choose around 12000-15000 counts and average about 2 frames for the flatfields.
When you click “Yes” you will notice that it will go through the process and you do not want to touch anything on the microscope as this is occurring. You will notice that at the bottom of your image it will display the exposure time that it used in order to achieve the number of counts that you specified. This is the exposure you should use for acquiring data. You may have to experiment with what current density and exposure time combination will work for you. If you notice that the exposure time was around 7 seconds or greater then you may have a problem with drift as you acquire your data set. You may have to increase your current density and retake your flatfields/dark images. Ideally you want to shoot your data with an exposure time between 2 seconds – 7 seconds.
Your flatfields and dark images are automatically saved every time you acquire a new set. Typically one just needs to acquire the flatfields and dark images at least once a day. If you plan on shooting data all day then just collect your flatfields and dark images first and it should work fine for your entire acquisition period.
Below is a sample of what you should see for the flatfield:
The following is the dark image: