New firmware released from SONY Japan.

update my u.s. version of 5N.

After update, I found the focus is indeed more stable than before, like the official statement: "AF動作の安定性向上".

It is not faster, especially when in low light. But before update, 5n occasionally gave false AF confirmation, which you can tell it was off-focus by judging the preview on LCD. After update, I try to focus it dozens of times, not a single false confirmation.