[Hatch]

For those that still have aproblem visualizing it, try this.

Set a (D)SLR camera to infinity and look through the viewfinder while keeping both eyes open.
( don't block your other eye with teh camera body LOL)

You'll have steropscopic vision with the viewfinder data superimposed.

Now try to read the numbbers in the viewfinder while keeping track of whats happening in the distance.

That's what requires training, not the actual superimpostioning.