Seeing underwater, dive mask helps it

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XTAR

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I'm a Fish!
Our eyes react to light and allow vision. The light is refracted the right amount so that it’s focused on the retina for us to see clearly. When light hits the retina, a series of chemical changes occur. It generates an electrical signal that’s transmitted to the brain. Through a very complex process, this signal is translated into the images we see. Then, when we see underwater, what happens?

For seeing underwater, the amount light is refracted, when it passes through the cornea, due to the difference in density between air and the cornea, the cornea has a density almost the same as water, therefore the difference in density between water and the cornea is very small. When light passes from water to the cornea, very little refraction occurs and the image will not be in focus until it is behind the retina. This is why everything appears blurry when we see underwater.

A good solution is to wear a dive mask. The dive mask creates airspace in front of the cornea, allowing the normal amount of refraction to occur when light passes from the air to the cornea, giving us the same vision as on the surface.

And we may notice that everything appears larger underwater than it does on land. Because glass has almost the same optical properties as water, very little refraction occurs, when light passes from water into the mask lens. However, the density of the mask lens is much greater than the density of the air inside the mask. As light passes from the mask lens into the air, it diverges. It results in objects appearing larger than they are out of water...

humen eyes.gif
 
https://www.shearwater.com/products/swift/

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