Or maybe only some types of lenses work like that?
In: 281
It has to do with the camera’s “aperture.”
The aperture are [those little blades inside of a camera](https://upload.wikimedia.org/wikipedia/commons/f/f8/Lenses_with_different_apertures.jpg) that control how big the hole is that lets light through. Some cameras like smartphone cameras might not have moving blades and instead just have a fixed size hole that light can pass through.
The way camera focus works is by [taking light from multiple directions, and focusing into a single point](https://www.androidauthority.com/wp-content/uploads/2020/04/Camera-Lens-Focusing.jpg) where it hits the film/digital-sensor.
Changing the size of the aperture has an [interesting side effect that it changes how many directions the light can come from](https://www.abc.net.au/science/askanexpert/img/aperture.jpg). Therefore, while a smaller aperture lets in less light (which will need to be compensated for by longer exposure times or boosting the brightness after the fact), more things will be in focus at once. The numbers listed as “f/X.X” in the following image are the aperture settings, with **lower** **numbers being a wider hole** and the other fraction representing how long the image was exposed for**:** [aperture comparison](http://1.bp.blogspot.com/-a4WUCHdyIzM/UbdpplzzCXI/AAAAAAAAAeY/PSXQKVRPhSg/s1600/equivalent%2Bexposure.jpg)
So depending on what the aperture size is, the point which light hits the sensor will be more or less narrow. Depending on how far away the object you want in focus is, that point may need to be adjusted to actually land on the sensor instead of coming together too early or too late and creating a blurry image.
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