What do the 0.5x, 1x, 3x buttons do in the Camera app?

I'm confused about what the 0.5x, 1x, 3x buttons do in the Camera app on my iPhone 13 Pro. I had assumed that they were how I specified which lens I was using (what Apple misleadingly calls optical zoom) — i.e., they were how I selected the Ultra Wide, Wide, and Telephoto lenses, respectively.

This assumption is reenforced by the focal length indications on the focus dial, where for example 77 mm (Telephoto) is indicated at 3x.

But sometimes (in low light?) I get a different lens. For example I'll get the Wide less when I chose 3x.

What do the 0.5x, 1x, 3x buttons do? If they don't select a lens, is there a way to do that?

Solution 1:

They indicate zoom levels.

The lens chosen will be selected to obtain the best photograph. In some lighting situations, the photo quality from cropping the 1x lens to 3x will be higher than the quality from the 3x lens.