Eli5 why do wee see things we dont focus on blurry ? Why cant our eyes see everything sharp ?



Eli5 why do wee see things we dont focus on blurry ? Why cant our eyes see everything sharp ?

In: Biology

Our eyes work by using a lens to focus light onto a light sensitive area at the back of them. Because a lens can only have exactly one distance in focus at a time, light from every other distance is either over focused or under focused causing it to be blurry. In practically there is a thin slice of distances that appear in focus but you can’t have everything from infinity to right in front of you be in focus at once.

It’s because the pupil of your eye is not infinitely small. This means that one side of your pupil is seeing the world from a slightly different point of view than the other. The lens of your eye can correct for the difference, but only for objects around a certain distance away.

In dim lighting, your pupils are large and this makes more things out of focus; photographers call it having a shallow depth of field. Outside, on a bright sunny day, your pupils shrink and much more of the world can be in focus at the same time. A pinhole camera sees everything in focus, at the cost of only having very dim images.

apart from what others have said, we’ve also evolved from carnivorous/omnivorous ancestors that practiced endurance hunting. One adaptation we’ve made are forward-facing eyes commonly seen on other omnivorous or carnivorous predators such as wolves, tigers, and bears, as opposed to side-facing eyes commonly found on omnivorous or herbivorous prey such as donkey, bison, elk, boar, etc. Forward-facing eyes have a point to allow us to focus on one thing to chase and remain focused on, where as side-facing eyes have a wider field of vision optimized to detect movement, but isn’t as clear.