FEI Quanta FEG 250, User'S Operation Manual

Page: 80 / 228

Operating Procedures: Optimising an Image
5-8
Alternatively Magnification could be expressed as the Horizontal Field
Width (HFW), specifying dimension of the scanned area (see the
Preferences… / General tab).
The Quanta FEG supports two viewing sizes: Quad Image and
Single Image modes. Magnification is always adjusted in the databar
for the actual display, thus an image at 500× in Quad Image mode is
1000× in the Single Image mode as its size has doubled.
FIGURE 5-1 MONITOR IMAGE AND SCANNED SAMPLE
Changing Magnification
• The Toolbar list box is used to select from a predefined values.
• The Keyboard control ( + / - / * ): the numeric pad plus key (+) / the
minus key (-) increases / decreases the magnification 2× and
rounds the value (when using the HFW, no rounding takes place).
The star (
* ) key rounds the magnification / HFW value
(e.g. 10 063× becomes 10 000×).
• The Mouse wheel control: Coarse / fine control can be operated
by holding the Ctrl / Shift keyboard key and moving the mouse
wheel up / down to increase / decrease the magnification.
• The Selected Area Zooming In / Out is a quick way of zooming in
/ out on an area of interest. Press in the imaging area and drag to
make a dotted box over the area of interest (the cursor changes to
a magnifying glass with a + sign). Release the button and the
selected area increases to fill the whole quad (window) with respect
to the sides ratio. Using the Shift key while pressing consecutively
reverses the technique – the cursor changes to a magnifying glass
with a - sign (see above). The escape button cancels the operation
at any time.
• The Magnification module (see Chapter 4)
• The Digital Zoom module (see Chapter 4)
SCAN SPEED AND FILTERING
To make a good image it is necessary to find a balance between scan
speed, charge, sample damage and signal to noise ratio.
A noisy image can be improved by decreasing the scan speed. If charge or
sample damage are the limiting factors it is better to use a faster scan
speed in combination with an
Average or Integrate filter (see Chapter 4).