Can the PSM Find Best Focus of an F/25 Optical System?

Can the PSM find best focus of an f/25 optical system to less than ± 10 μm?

SOMEWHAT SURPRISINGLY, YES, TO ABOUT ± 2 ΜM.

You scan axially through best focus several times and plot the number of pixels above threshold versus scan distance.

The curve is quadratic and the derivative of the curve fit to the data gives the best focus position to even very slow systems.

The Axicon centering station and the associated LCS-PSM software make this an easy task.