My current belief is that C1 invokes center AF mode as indicated on this image, with the green square and text "AF" (at yellow arrow). Second image is another screen shot showing what could be metering mode (shown in yellow oval). Being Swedish I am not familiar with Dutch but both screenshots come from
rcblog.nl (youtube title shown top left).
Tapping the screen every now and then sounds like a really bad way of changing focus, though it at times could be helpful. But it seem like there is a "normal" AF mode though the manual dont elaborate about it.
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