so punch a hole through the 'visible fog' (so to speak) from the object to the camera? I don't know of any way other than using an Object Buffer for the object and doing a multipass render and using the object buffer to add a layer mask in the Atmosphere layer in post
I had this same question. in my context, I am producing a high resolution Planet Earth and I'm using a Light with Visible Light turned on to produce some Atmosphere lighting effects wrapping around the earth surface. I didn't like that the visible light some what lightened my blacks on the dark side of the planet, so I was looking for a solution where I could limit the fall off of my visible light.
I was searching and found this:
"In the Details tab of the light use Near Clipping."
This worked!! In my example, my planet is 1000 cm's and I set my Near Clip from 500cm to 500cm and boom, I got a perfect rim of visible light that I can now tighten or expand depending on these values, and I got the blacks back!!