Distance from Camera
The Distance from Camera modifier alters the base property with a new one from a given range using the distance to the active camera.
Range Min and Range Max
The limits of the mapping from “distance to camera” to “property in mapping”. If the current point of the stroke is at Range Min or less from the active camera or the object, it will take the start value, and conversely, if it is at Range Max or more from the camera/object, it will take the end value. These values are in the current scene’s units, not in pixels!
Fill Range by Selection
Set the min/max range values from the distances between the current selected mesh vertices and the camera or the target.