NX500 - Disappointed by AF performance

I'm sorry to hear about your disappointment, and it's good that you are asking here. This image is certainly much worse than anything I've ever managed to "mis-produce" with the NX500 and the 30 mm, but the main reason for the misfocus are the dark subjects (the 30 AF is not great in low light anyway) in front of a strongly backlit scene. As it goes with such scenes, the cam tried to focus on the brightest spot, the window and curtains, but as it's too bright without sufficient contrast, it couldn't even find proper focus there.

This is a common problem with AF, in mirrorless cams especially, and Samsung's 30 mm lens in particular, and also the 50-200 mm. As your subjects are sitting and not really moving to and from the cam, half-pressing the shutter button until the AF square(s) are green before you press a way down, is recommended, and should yield better results, although focus may not be perfect still. Closing down the aperture would help, or using a different lens for such occasions, e.g. the 16 f2.4. Alternatively try the 12-24 if you don't mind increasing ISO. Or the fast 45 for portraits or even group shots if you have the space to move back. The 30 is really the worst of the lot in terms of AF speed and accuracy in backlit situations, as beautiful as it is otherwise.

You can also try different combinations of AF settings, but in my experience these don't make a whole lot of difference.

Andrea