Most Often Asked Questions
UltraScan Use
r
’s Guide Reference Series Rev 1.0
5-5
binning mode) the CCD is saturated. Reduce the beam intensity or shorten
the exposure time.
3.
Why do I have to blank the beam when the CCD is reading
out?
You do not want to expose the CCD to a signal when it is reading out. It is
like continuing to expose the film during its retraction. Blanking the beam
will prevent any electrons from reaching the CCD.
4.
How often do I have to acquire a gain reference?
Whenever the image quality seems to be deteriorating. The most reliable
way to see if a new gain reference is advisable is to take a gain normalized
image of uniform illumination with no specimen in the beam and look for
any spurious pattern. If you see one, update the gain reference.
5.
What is the shortest and/or the longest exposure time I can
use?
The shortest time is actually determined by the shutter speed of the TEM
shutter (about 0.025 sec). Exposures over 1 minute are unusual.
6.
My images are noisy, what can I do?
Try increasing the exposure or current density of the beam.
7.
My images are slowly deteriorating, what should I do?
Determine if the CCD is warming up. Check the temperature display on the
controller. Check that the water lines are not clogged. Check the water
temperature of the chiller- should be approximately 20-23
°
C. Be sure to
acquire a new gain-reference image.
8.
The image is brighter (or darker) on the top than on the
bottom, what should I do?
Check that the CCD has been cooled for at least 2 hours.
Check that the shutter switch on the controller is set to AUTO.
It could be a bad reference image. Retake another one.
Check that the shutter is functioning correctly. If it is, the shutter indicator
light on the controller would go on and off as you take an image.
9.
When viewing, the image sometimes gets suddenly
bright/dark, what is happening?
Sudden changes in the contrast may be due to stray x-ray photons that
saturate some of the pixels.
10.
How long is the lifetime of the CCD?
None of Gatan’s CCDs has failed due to old age so it is hard to answer. So
far, there are no known mechanisms for aging.
11.
How often and for how long should the camera be warmed?
