eli5, how is it that cameras can see clearly underwater whereas human vision gets blurry?
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Cameras have the advantage of specialized lenses and technology, allowing them to maintain clarity underwater, while our human eyes lack the same adaptations.
There is a waterproof piece of glass between the water and the image sensor(or film) called a lens. The human eye does not have a waterproof lens, so the water touches the eye directly. However, when humans wear goggles, they can see much clearer underwater.
I can see pretty clearly underwater. I wear contacts.
Is my perspective underwater less distorted than someone who does not wear contacts?
Our eyes are designed to see in air, based on millions of years of evolution. When we are underwater, the light bends differently when it enters the eye than it does on land, and so it will be blurry when it hits the retina at the back of the eye.
Camera lenses can be designed to work underwater, so they can see clearly in water
Cameras underwater generally have a flat surface through which the light passes before entering the lens. This means there’s no effect on the focus of the lens and it can work as normal (though there is a slight magnification effect).
The front surface of an eye is curved and light passing in from the air is focused. Light passing from water into the eye is focused much less, because water and your eye’s lens are very similar, meaning light is bent less. You can fix this by wearing goggles or a mask with a flat front surface and air inside. Now the light is entering your eye from the air inside the goggles and focusing works normally (again, with some magnification).
Cameras will not see clearly underwater if the (rounded) lens contacts the water. They will only see clearly if a flat lens protector in front of the lens contacts the water.
Human eyes will not see clearly underwater if the (rounded) eye contacts the water. They will only see clearly if wearing goggles (which need to have a flat front surface).
The shifting of the light happens at the interface between materials. Our eyes evolved to account for bending light from air into our eyeballs. As are most cameras. But, if you have a thin, flat surface, light is not refracted.
This is why all goggles always need to be flat. There would be a substantial lensing effect if they weren’t.
Marine anomals presumably see fuzzily, as well, when not in water.
Underwater cameras are built to see underwater or in air. Eyes are way more adaptable, most people have “blurry” vision not because they can’t see underwater but because they don’t have enough practice. If you were (especially starting at a young age) to spend a few hours a day in the water you would learn to focus subliminally underwater as well as above. When I was little I could just see the blurs but after spending a considerable amount of time in the ocean I found I was able to see better and better until it wasn’t weird. This was after I was 12, there are tribes that swim long before they walk and they refuse to use goggles.
Underwater cameras have a flat piece of glass between the lens and the water – essentially the same as underwater goggles (you can also see clearly underwater when wearing goggles).
However, it is possible to see clearly underwater when the rounded lens touches the water directly, but it requires a much more rounded lens shape. For example, fish can see perfectly fine without a flat surface between the lens and the water. Note that the lenses of a fish are much more rounded than ours. If our eye muscles could pull our lens into such a round shape, we could also see clearly underwater.
Fun fact: there are fish that hunt by spitting water at low-flying insects. Their lenses are split horizontally, with two different curvatures: the top half can see clearly in air, while the bottom half can see clearly underwater.
there is a pocket of air inside the lens so actually lens doesn’t directly contact the water. human eye doesnt have that unless you put googles on
Because the refraction index of air is tightly accounted for by one of the cornea (which is basically water) shape, which is acting as a lense. When you are under water, the cornea is surrounded by water, effectively, almost completely nullifying the lens effect of it. If you add an air gap between the eye and the water (like a scuba diving mask), then the vision works fine. Similarly, the camera lenses are not directly exposed to the water. There is a flat surface, glass membrane that allows the lensing to occur unaffected.
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