Focusing with two eyes open makes sense with pistol shooting. It help one maintain situational awareness. Rifles with a scope could get debatable whether it is a benefit or not. With cameras I focus with one eye -- dominant eye -- no matter the type of camera. Right eye for SLRs; right eye for waist level screens on MF cameras; right eye for ground glass on view cameras. In the end... interesting discussion (as always, David) but whatever works best is what works best.