I’ve dealt with this problem all my life – i have high powered glasses (-6 and – 8, with some cylindrical /spherical tweaks). My glasses work great. But i wore them while swimming in the crystal blue Mediterranean, and when I’m diving in, i realized the glasses aren’t effective. I understand the wavy reflective patterns interrupting, but why cant I focus on anything easily?
In: Physics
The focusing power of a lens depends on a few things. The diameter and the curvature of your glasses don’t change when you put them in water. Neither does the refractive index of the lens. What does change is the refractive index of the surrounding material.
Light is bent when it goes from one material to another. How much the light bends depends on the difference of their refractive indices. Refractive index is how quickly light travels in a material.
Water has a higher refractive index than air, so the light doesn’t bend as much when it goes from water to glass as it does when it goes from air to glass. That’s why your lenses don’t have as much power underwater. The power of a lens depends on the material surrounding it.
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