First experience with RX100, am I missing something?

You don't need an ISO that high in such a situation. Try ISO 200 at the highest or even lower. You could back off on the zoom a little and re-frame at a wider angle and the depth-of-focus would improve. Or zoom in on just one duck, that's separate in the frame. The F-stop setting is about right. By the faint shadows, it looks as though you were shooting towards an overcast Sun, which is not the best for focus or lighting the subject properly. But, you probably had no choice with these ducks. Don't expect good results when you're shooting with a disadvantage like this. Find some ducks with the light behind you.

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Steve McDonald
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