How to Zoom on the iPhone's Camera

Open your iPhone's Camera. It's the camera icon on a grey background. You can open the Camera while your phone is locked by swiping the screen left.

Place two fingers on the camera screen. Ideally, you'll use your thumb and index finger.

Spread your fingers away from each other. Your screen should zoom in. You can repeat this gesture multiple times to keep zooming in. You can't zoom in on Time Lapse or Pano screens.

Tap and drag the slider at the bottom of the screen. This slider will appear after you zoom in initially. Dragging it left will zoom out, while dragging it right will zoom in.