Just out of interest, is the autofocus on the DF+ considered to be not accurate enough for critical focusing on high megapixel backs when shooting wide open?
Gerald,
I have a DF+ with a 33 megapixel back. I haven't tried higher megapixels.
On the first (half) press of the shutter release button, you hear the auto focus motor moving the lens into position. On the second press, you hear it again briefly, making a small adjustment. Then it's probably done. But make a third press just to be sure the motor doesn't run again. Then shoot. If the motor doesn't run again, I would consider the focus to be accurate enough for critical focusing.
For subsequent shots, one half press to focus, and then keep pressing to shoot. One press will account for small movements of the subject or yourself so you will continue to get critical focus while working quickly. You only need two presses when the focus distance changes by larger amounts.
--Steve.