I think I have found the problem...me! lol. I just tried again and I think I actually noticed a difference in the DOF. It definetely gets darker, and the difference in DOF is slight but apparant. The stuff outside the focus area becomes a bit clearer when using the button. The amount of change depends on the aperature as it should. It is just hard to tell when it gets darker. I must start paying better attention! I believe it was working correctly the entire time but I wasn't. :-)