Huawei P9 Camera Pro Settings

I have this new smartphone and the camera system on it is pretty special. It has two "away-facing" cameras (one colour one monochrome, both 12 megapixel) and one "forward-facing" camera (or selfie camera if you like) which is 8 megapixel...

I have been playing with the pro features of the camera which allows full manual control of iso, shutter speed, focus, white balance, exposure and focal points.

Can anyone.explain why the image I'm trying to capture goes very very dark when I try tge very high shutter speeds ie anything shorter than 1/100 and the iris seems to start closing? See attached pics...

Cheers matt, i see what you're saying but the screenshots are of the phone camera screen as I'm adjusting the shutter speed, they aren't actual captured images... But i appreciate your input.

Yes. Its fine i just was curious why it went dark when its shutter speed im adjusting... I've already captured much better photos with this phone than i ever have with anything else...