New answers tagged focus-point-selection
It is perfectly possible to select one point and still use the viewfinder. I am attaching the manual page. Just make sure that you are in one of the letter modes (e.g. select P on the top dial) otherwise this wont' work at all.
Get a tilt lens and use the Scheimpflug Principle. You can even use this technique to keep only one target in focus even if they are on a parallel plane.
What you need is high depth of field. That means the distance range from the camera where subjects are acceptably in focus is longer. You say depth of field is not the issue since the background is just a wall. The background doesn't matter. It's the min and max distance of all intended subjects from the camera that matters. Clearly this is your problem ...
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