>It's easy to cause a mis-focus. A large percentage of the >time, the focus point that a tester has positioned on a 45 >degree target sheet is not actually locking on at that chosen >focus point. The camera may signal a confirmation (with the >focus dot), but the resulting shot appears >mis-/front-/back-focused because the lock signal was an >approximation. This has been demonstrated many, many times in >other threads on Nikonians - most or all of which predate your >other thread on the subject. Nothing new here.
So you did not actually test the method I proposed yourself?
The whole idea of leaving *only* one dot visible when focusing is to eliminate the typical errors coming from targets placed at 45 degrees. Indeed, the rest of the target is here pure white and cannot contribute to the phase detection of the focusing system. This is easily confirmed by the total inability of the camera to focus if the collimator is not on the dot.