Whenever I see some fog, it usually is very opaque when I am far away, like cloud, but when I am it, it’s far more transparent, though obviously visibility is decreased
In: Physics
From the outside, the fog boundary where it meets clear air is well lit, so the fog will reflect plenty of light into your eyes. When you’re inside the fog, most of the light has reflected or scattered out by the time it reaches the middle.
Your eyes distinguish contrast between objects with a biological equivalent to dynamic range – the darkest dark that can be seen in conjunction with the brightest bright. It’s a sliding scale. When it’s extremely bright, dark things can go missing, and it can be hard to tell the difference between 2 shades of ‘gray’ in the middle. When it’s very dark, everything with a little light stands out.
As such, once inside the fog, the darkness causes your irises to open up letting more light in, and the lower end of the range is where your sensitivity to subtle differences is higher. It’s the same as when you put on sunglasses and suddenly can see details a lot more clearly – you’re putting your eyes in the most sensitive range where they aren’t being starved for light nor blown out by too much.
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