As new features for v3 are being considered, I would like to propose that the current filter offset focusing routine be redesigned to make it easier to implement and more reliable in use.
In the Auto Focus Options dialog box, I would like to see a check box that clearly states:
“Use filter offset focusing.” When checked, a drop list allows the selection of the filter to be used for initial focusing; this would normally be the LUM filter. It might be useful to have a focuser position value for the LUM filter but that position would have to be temperature compensated.
In the Filter Setup dialog box, I want to be able to make entries that clearly identify that relative filter positions are being specified. For example:
LUM filter offset: 0
RED filter offset: +145
GRN filter offset: +88
BLU filter offset: -44
But filter offset focusing is a two part problem. You have to get accurate values for those filter offsets. Trying to run AF routines manually will typically result in values that may not be all that accurate. The better solution is to have a “Filter Offset Wizard” that would automatically run an entire series of AF runs for each filter and calculate an average value. This would be a fairly long process since you could be looking at 15+ second exposure times for NB filters. This also introduces the possibility of needing to take into account temperature compensation while the wizard is running.
All this relative movement also means using backlash control. If the focuser’s own ASCOM driver does not implement backlash adjustments, then SGP will need to do it. This might be part of the wizard.