Originally posted by mattdm I suppose the autofocus system could stay active and blink a warning if it thinks your selected focus sensor is pointed at something too close.
I am not sure it can evaluate out of focus without changing the lens focus point transiently.
I think the way to do it would be via either the DOF preview or the green button. Have apature set, press green button or DOF and the lens would tell you as it moves from min to max focus if each focus point goes through the proper focus . whe you release the Button or what ever, the lens goes back to hyper focal.
Note for this it would need to know focal length, hence at present teleconverters are out because they have not yet made the adjustment for that.