Originally Posted by
Saorsa
In most cases, the focusing mechanism will extend more, much like a built in extension tube. Some of my zooms have a focus limit switch to that the AF doesn't move through the complete possible range. For example, the 200-500 has an option for FULL range or 6 meters to infinity. Putting limits on the AF helps it focus faster.
In the case of a P&S like the P900 I suspect that the macro setting is the limit control and operated by removing the block rather than setting it.