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Set the pk to pk range for the scan. The value refers to the maximum Z-axis distance
will move during the scan. Refer to the Z position field in the main PureFocus850 GUI.
The default setting, 10, gives a peak to peak range of 1 micron.
WARNING: when the search begins the focus will move half the peak to peak range
relative to the starting position, and then scan through the starting position for the full
peak to peak range specified. Take care to ensure that a crash does not occur in the
peak to peak range.
Set the maximum speed for the scan. Lower speeds will increase the chance of a
successful focus search but decrease the overall speed of the scan. Higher speeds will
make the scan run more quickly, but focus search may be unsuccessful if the sample
flag threshold is high.
Click’ search and lock’. The PureFocus850 will adjust focus until the sample flag is active
(green), then activate the servo and begin to autofocus.
If the search is unsuccessful consider increasing the peak to peak range or decreasing
the focus speed.
8.2.2 Fast Capture
Fast capture can be used when the sample flag is true but the sample is far from focus. In this
scenario the focus error signal may be falling off and driving the sample to focus may be slow,
even with the maximum stable gain settings. This routine will drive the Z-axis towards focus at
a specified speed, with the direction specified by the current sign of the error signal. When the
sign of the error signal changes PureFocus detects it has just passed through focus, ending
the routine and activating the focus servo.
Ensure the sample flag is active, either by bringing the sample closer to focus or by
making the sample detection threshold less stringent. Ensure that the sample detection
threshold is appropriate for your sample.
WARNING: Ensure the focus flag it set up correctly. If it is not set this procedure may
result in a crash.
Open the Search submenu. Refer to the Fast Capture section of the submenu.
Set the maximum speed for the scan. Lower speeds will increase the chance of a
successful focus recapture but decrease the overall speed of the scan. Higher speeds
will make the scan run more quickly, but focus recapture may be unsuccessful if the
focus flag settings are stringent.
Click ‘capture’. The PureFocus850 will adjust focus until the error value sign changes,
then activate the servo and begin to autofocus.
If the fast capture is unsuccessful, refer to section 7.3 to refine the focus flag settings.
