reyalp,
Thanks for that. In the meantime I also found the 'get_zoom' uBASIC command, and tested this with a 'Zoom Stepping' script by Cythrelo. This works fine for my A470, which has 7 zoom steps (0 - 6). Though not the focal length I originally requested, I can, as you say, estimate the FL for each step, assuming they're equal FL steps between the lens's min and max zoom. Even if not exactly linear, this should be plenty good enough for my purpose (estimating the 'view' angle, to automatically rotate a motorised panorama head by the appropriate amount to achieve the desired overlap).
Daniel