Originally posted by Sagitta I've found it easier to just turn SR off when using an old zoom and just compensating by not shooting as slow, because inevitably I'll be using, say, my 75-260mm at 75mm, forget I have SR set to 75mm, then shooting at 260 for a while and screwing up my shots.
While I haven't looked in detail into how the SR works, I imagine that if you set the focal length too low, it would just under-correct. So, if you shoot at 260mm with the SR set to 75mm, the SR will still help reduce shake - but by only a third or so of the correct amount.
However, if you set it took long (e.g. set it at 260mm but shoot at 75mm), it will severely over-correct, adding shake in the opposite direction to the original. If I'm understanding it correctly, you're always safe if you tell the Q that the focal length of the zoom is the short end of its range.
That said, I think if I personally was shooting at an effective field of view equivalent of 260mm x 4.6 (for the Q7, x 5.5 for the Q/Q10) then I'd want the camera on a tripod anyway.