Step size Maths calculation

I can’t figure the below maths out.
"Assuming that moving 1000 steps moved the focuser 40mm then you know that your focuser moves 4 microns (0.004mm) per step. "

If I divide 40 by 1000 I get 0.04 and not 0.004 as stated by the above instructions.
Please help me to understand the Maths.

I came out with a different figure.
1mm=1000 microns
40mm= 40 000 microns
40 000 Divided by 1000= 40
Therefore 1 step = 40 microns
Is this correct?


You’re right there is an arithmetical typo in the manual. I think this has been corrected in the new draft manual for the Beta.

To get a good AF v-curve, you need to set a step size that results in about a factor 3 time the lowest HFR value at the base of the ‘v’ to the highest HFR value at either start/end of the ‘v’. You should also bin your AF sub exposures and set any backlash you need for your focuser (this helps get a symmetrical v-curve).

Why not try, as a starter, something like: 30 step-size, bin 2, 9 focus points, 10 second exposure and see how you progress?

Good luck!