Le Kilt wrote:
You mean this one :
http://www.canon.com/camera-museum/camera/lens/ef/data/macro/ef_100_28macro.html ? That's pretty old.
My guess, "limited" limits AF to 0.3-0.5m, while "full" let's him hunt for focus in his entire reach (0.3 to infinity, which slows it down a lot).
For info, the equivalent switch on the USM version selects between 0.31m to infinity and 0.48m to infinity.
Thank you both for the info and link.