Author Topic: PFE auto-focus parameters for JEOL 8900/8200/8500  (Read 2458 times)

John Donovan

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PFE auto-focus parameters for JEOL 8900/8200/8500
« on: January 18, 2018, 12:07:55 PM »
Paul Carpenter makes the following very helpful observations:

Here is the Autofocus section from the ini file for our 8200.

The offset is determined by first setting that to 0, then do autofocus on a nice flat smooth surface (like Si wafer). IF the autofocus solves to a consistently off position, then you use the offset value in microns to correct for this systematic offset.

I highly recommend using the maximum value (AutoFocusType=2) rather than any attempt to fit the data.

On the Carnegie Auto focus unit (which I assume you have access to), you should be seeing a fairly strong signal on the fluorescent meter and approximately equal signal strength for both X and Y which you select from the selector knob. Remember that the autofocus is using the reflected light brightness intensity, but it is sampled along the x-axis of the video camera image, so if the autofocus sample scan is rotationally misaligned from the signal you may not get a good solution.

Finally, in debug mode using Probe for EPMA, you can see the brightness profile from each autofocus scan; the profile should be smoothly peaked and not have bat ears or some funky non gaussian peak shape. Using the maximum value avoids problems in fitting but you really want to know if there is a hardware issue.

AutoFocusPresent=1                   ;is autofocus hardware present? no=0 yes=1
AutoFocusType=2                      ;0=parabolic 1=Gaussian 2=Maximum value
AutoFocusOffset=4.0                  ;offset in um (allowable range -100 to +100um) for autofocus z position relative to fitted parabola
AutoFocusMaxDeviation=30.0           ;max allowable deviation (range 1-60%) in fit to autofocus profile
AutoFocusThresholdFraction=0.33      ;threshold fraction (allowable range .1-.9) for fit to autofocus profile
AutoFocusMinimumPtoB=1.4             ;minimum P/B for autofocus profile (P=max count, B=average?) allowable range is 1.05-10, default 1.4
AutoFocusRangeFineScan=100           ;number of microns range for fine scan
AutoFocusRangeCoarseScan=600         ;number of microns range for coarse scan
AutoFocusPointsFineScan=200          ;number of points for fine scan
AutoFocusPointsCoarseScan=100        ;number of points for coarse scan
AutoFocusTimeFineScan=20             ;time per point for signal integration during autofocus routine: range 1-500 msec
« Last Edit: January 18, 2018, 12:14:18 PM by John Donovan »
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