While cruising the bottom of a deep ravine, I found places where my view distance gets reduced in a manner similar to the Void Fog. Thing is, the bottom of the ravine is flat where that occurs. I just walk, seeing the walls lit with dozens of torches on multiple levels, and then as I enter certain area, my view gets shorter, distant torches dim, then it all gets cut off, I see only like thirty blocks ahead, the rest swallowed by darkness. Then a little way further the vision gradually returns to normal. There are two such places in that ravine and I didn't find anything like that elsewhere.
This is fairly deep and I wouldn't be surprised to be affected by the Void Fog, but if I understand, the intensity of the Fog is directly proportional to your depth past certain threshold – and this seems as if I were entering some… hill of the fog? Also, there are no floating particles like in the deepest layers.
So, what can cause that local reduction of view distance?
Mobs spawn in this gigantic tower...
...and hit these fences. The water then funnels the items into the middle (which then connects to another stream flowing the lava you can see, to kill any mobs that fell through the middle).
Best Answer
This sounds like plain-old void fog, which is removed by exposure to the zenith. It gradually returns further away, similar to the light pattern around a torch.