If I remember correctly, the easiest way would be...

1. turn of all lights
2. activate "DepthCue_On" (Atmosphere material)
3. set DepthCue_Color to white
4. set DepthCue_Start and _End distance
5. render

The hardest part is figuring out Start and End distance.
Usually I use the cameras "focus_distance" to figure out my start value.

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