How can I take 16:9 photos?

Hi,

Normally when I take photos they are 3264 × 2448 pixels = 4:3.

How can I take 16:9 photos?

I know I can crop a 4:3 photo later, but I would like to see the correct size before taking the photos.

Is there a way or do I need an extra app for that?

Many thanks!