I was holding my 8 month old son today on balcony and started to wonder as his pupils changed size to focus on further objects, why light bouncing off surfaces near and far differ so, that the eye understands that difference and has to adjust to “see” and translate that light to brain. What causes the image to be blurry, if the pupil remains larger while we look at objects that are far?
In: 4
Adjusting pupil size is to correct for changes in brightness, not distance.
Focus is needed because the lens of your eye has a size, up to 7 mm across fully dilated. The world looks slightly different from one side of your lens than from the other, because of the different points of view or perspective. The lens can correct for this effect, but only for objects at certain distances. It’s fundamental geometry. It’s like the way your two eyes have to converge to look at nearby objects but then both eyes look in the same direction to look at distant objects.
In bright light, your pupils contract, making the lens of your eye effectively very small. This reduces the differences in points of view across the lens and focusing becomes much less critical and, outside on a sunny day, things both near and far can be in focus at once. In a darkened room, your pupils dilate and only objects at a very limited range of distances are in focus.
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