How can our eyes tell the difference between a close object and a far object
In: Biology
1. Your eyes point in a bit when you’re looking at something vaguely close so they’re both looking at the same thing. At the extreme this is you being cross eyed when you try look at the tip of your nose. Your brain measures this and can detect distance from it. This works for short to middle distances.
2. Lens focus. The amount that our lenses have to adjust to focus is an indicator of distance, your brain also measures this and estimates distance. This works for short to middle distances.
3. Experience. You know roughly how big certain things are, when they’re further away they look smaller. Your brain then uses expected size vs apparent size to gauge how far away something is. This works for longer distances.
It learns how to do this when you’re an infant and clumsily bumping into things or reaching for stuff that’s way out of your reach.
This is also how optical illusions like Forced Perspective work, the graphics/setup presents information that makes it seem something is at a different distance than it is, either by tricking size cues or perspective cues. Similarly this is why when you look at clouds from above when in an airplane it’s very difficult to work out how far away they are – the focal length is maxed out and there’s no frame of reference to compare sizes to, so although the clouds might be many miles away they can look relatively close.
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