eli5 Why do camera lenses need to focus on something? Why can’t they just render an image in which everything is clear?

Question

Or maybe only some types of lenses work like that?

In: 281

Answer 1

Lenses capture many rays of light, but since light reflects off of many different things at once, the rays can mix together and appear blurry.

Focusing a camera basically redirects all the wrong light rays and only lets in light from a specific place, or depth.

[This diagram might help.](https://physics.highpoint.edu/~jregester/potl/Waves/Cameras/pinholecamera.png)

Imagine trying to fill a bathtub with a soda fountain. All the different sodas mix together and you’d have a muddy mixture. Now imagine if you had a hose you could hold under a specific nozzle and only fill the tub with your favorite soda. That’s focusing.