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

The only type of optic that doesn’t need to focus is the [pinhole](https://en.wikipedia.org/wiki/Pinhole_camera#History). It’s just a small aperture, and light travels straight through it (ideally).

But a pinhole only lets a tiny amount of light through. So it can take hours to collect enough light for a photo. If you want to take a photo more quickly, you need to use a larger aperture, and use some device to bend the path of light so it all converges onto a point. The amount of bending necessary to accomplish this depends on the distance to the subject.