[The_bluester (Paul)]

Voyager uses one of two internal focus methods (Or you can set it up to call Focus Max, Maxim DL or one of the TheSky versions)

The internal versions first do a "First light" run which characterises your optics by slewing to a suitable focus star and running through the focus point via many small steps from well out of focus, through focus and out the other side. Then it can either use it's "robostar" routine which slews to a suitable star (And plate solves to center it) and focuses on that, but it does not do the SGP-like step off focus and run an number of data points, it steps slightly off focus and given the mag of the star is known it knows what HFR to expect at what point in the focus curve it characterised before using a given exposure it adjusts exposure time and focuser position to fit to the expected HFR, then exposes a number of "integration" images of the star, then moves the focuser to what should be the equivalent point on the other side of focus and does the integration routine again. From that it can work out where each side was compared to best focus. The benefit as well as what I have found to be really good focus is that it focuses really quickly with NB filters, it slews to brighter stars for NB so the focus exposure time stays about the same, usually two or three seconds at most. It generally only takes a couple of minutes to slew to a focus star, focus, and slew back.

The first light wizard also populates the step size for the SGP-like full field focus setup (Which focuses in place) but I never use that. If your optics are reasonably flat I think you are better off with the robostar routine, particularly for NB.