There's is no setting in the camera for autofocus or similar options, but it's set to underwater mode.
I do have the square protector, but I didn't think it mattered which one I used because when I compare them it's the same result - allthough I only tested this on land.
So what you're saying is that the refraction of the light going into the camera is different on the two lenses, but only underwater? I had no idea that this would be reason why.
This was the first time I used it for diving and I was just trying out the headmount, and well, it mostly works, but the adjustment of the camera position is tricky when you can't see the screen. I'll try something else next time.
Thanks for your answers, I hope I get better results next time.