Ulf W wrote:
Do you have some special version of Stackshot with smaller minimum step length?
The standard version of Stackshot, as far as I knows, can only do as fine as 10 µm steps (accomplished by 1/16 microsteps).
That is correct; see here
for the special (pre-production) version.
The link is correct but the numbers are not, or at least they don't go together like that.
In the rail itself, both old and new, 1 microstep is actually 0.000496 mm = 0.496 µm. This is documented in the StackShot manual, section 3.3.11 "Units of Measure", except that the manual says "step" rather than "microstep". Physically this number comes from using a screw at 16 rotations per inch, a stepper motor at 200 full steps per rotation, and 16 microsteps per full step.
If you set units to mm, then the standard controller has a minimum focus interval of 10 µm. If you set units to "steps" (actually microsteps), then it is possible to set an interval of one microstep = 0.496 µm. However, if you do that you'll discover that the resulting physical movements are not uniform, with physical steps occasionally being up to about 10X larger than the average step.
The recent modifications do not involve changes to the rail itself. Rather they are modifications to the controller that allow it to make the rail move with much more uniform microsteps. The movements are still not perfectly uniform, but they are now good enough to limit the maximum physical step to something like 0.0013 mm = 1.3 µm, at least in the unit that I have. In the Noctua pronuba
stack, I used 2 microsteps per focus interval, which (based on measurements made separately) resulted in actual focus intervals varying from roughly 0.6 to 1.9 µm.
Regarding the nature of the improvements, I'm treating that information as proprietary to Cognisys so I won't be explaining in any more detail.