a simplified study of sorts. I wanted to illustrate how I understand atmospheric perspective. Using this quick abstracted mountain peak shape I tried to boil it down to the simplest concepts.
One of the biggest mistakes I see and have been guilty of is thinking of depth in terms of depth-of-field, or what is in focus and what's blurry. The trick has it's place, but it's something we understand because of cameras; it's not how our eyes and brains compose what we see. There are other things that happen that tell the viewer there is depth in an image.
True, our eyes only see little focused patches, no bigger than your thumbnail at arm's length. But as our eyes scan a scene our brains composite all those little pieces into a large image that we understand to be in focus everywhere.
So taking depth-of-field out of the equation, what else can we use?
The big image is all of these tools combined. Below are each tool that could stylistically be used all by itself.
'Fade to atmosphere'
Really simple, looks like fog. The object appears to recede as more atmosphere is put in front of it, the color of the sky. By atmosphere, that usually means water vapor. Water molecules absorb red wave lengths of light, leaving more blue wave length light to travel about; that's why the sky is blue.
'Fade lights'More like a spotlighting effect, dramatic. It appears as though there's something above and out of sight that is blocking the overhead light; the stuff far away is under it, the stuff nearer isn't. Coupled with interesting cloud cover, this effect can be really striking. And it can be reversed.
As you put more atmosphere between you and distant things, light scatters. This means the lights get darker and the darks get lighter. As the light from the lights travels to you it scatters into the space between you and the darks. A lot like 'fade to atmosphere,' but without introducing the color of the sky.
'Fade to light'
The opposite reasoning of 'fade to atmosphere.' At high and dry locations, like Utah, the mountains look really close because there is very little water vapor in the air, so they don't fade out very much at all. But a lot like 'compress contrast' in the scattering of light, this can introduce the color as well as the value of that scattering.