When using back button focusing when does the IS engage? Is it when you are pressing the focus button or when you press the shutter? Just wondering because sometimes I lock in my focus with the back button then wait a couple seconds to hit the shutt...
Mine was the trust 17-40mm f/4 followed shortly (a couple months) by the 70-200mm f/4. Next on my list will be the 24-70 f/4 due to the size, weight, and the fact it can be used near macro for the rare times I want/need that ability.
