There is something wrong with FTA (Foucault Test Analysis) version 2.0A showing a negative Strehl.
Replace that with version 2.0B.
For all practical purposes I get the same anaysis with version B that you got with version A, except for Strehl.
There is some confusion in mixing/converting mm and inches.
Best to pick the one that matches your micrometer calibration and set the program for that measurement unit. That way you don't need to convert.
Whether the Z1 is set to zero or not is not important except that you need to under stand why. :-)
The wave front is calculated from measured difference from Z1 to Z2, Z2 to Zone 3, Zone 2 to Zone 4. The zones have finite width large enough to be seen from the tester. The knife edge is used to measure average ROC of the zone, and it is assumed that the measured average ROC for the zone is at some nearly equal distance from the inner radius and outer radius of the zone, and that is referred to in the programs as the zone's effective radius.
The mask has no Zone zero where the the exact center is both the inner and outer radius of the zone and also the effective radius, so we never really measure the ROC of the exact center when taking the test readings. We start with Z1 measuring the ROC for it's effective radius that is some distance from the mirror's center.
When you calculate the desired knife movements for the effective radius of each zone, the results for each zone will be a distance as measured fro the mirror's center. But you never measure the very center of the mirror, and Foucault analysis doesn't calculate from center, it calculates from movements between adjacent zones.
So all this means that you may if you wish just enter readings directly from your micrometer and let the program do what it does.
Or you can adjust your readings to have Z1 knife reading be zero. To do this you subtract the mircrometer reading of Z1 from the micrometer reading of each zone. This leaves intact the differences between zones.
You may ask "Why zero the first zone?"
When you compare raw readings from the micrometer, in various test sessions the readings from for Z1 might be very different and of course each of the other zones. It is difficult to look at the numbers and immediately see how far they are from the desired knife movements.
Zeroing the desired movements, and then each test session knife movements, you can look at the numbers and know immediately how well your numbers match the desired movements.
Some micrometers could be zeroed on the Z1 while testing, but the tester would likely be disturbed while zeroing. It is best not to zero the micrometer, but just note the raw reading from each zone.
Some consider it good practice to take readings in both directions. Start at Z1 and working outward, and then another set starting at the outermost zone and working inward.
In some cases the software will display the desired readings in the Z1 zeroed format, in some the desired readings are not zeroed but shown from mirror center.
All that is what has you confused.
I see why there is a FTA 2.00 version B. :-)
Delete FTA version 2.00A and get FTA version 2.00B.
I like FTA, but there are a couple of things about the wavefront graph that I don't like. One is that the zone boundaries are not shown. Another is that the lateral scale from mirror center to edge is is divided into 5 equal distances from center and the distance shown for each is rounded too coarsely. Otherwise It is a very good program.
You can also try FigureXP and see how you like that. I like the graph better. :-)
Edited by dogbiscuit, 29 March 2019 - 12:14 PM.