In Infinite you can have 3 separate maps: the environment map itself (which is the backdrop), the illumination map and the reflection map. By default, when you load the environment map, they are all made equal but you can chose to make them all diferent, if you like. Of course, if you just delete the environment map, you will have a black backdrop. Instead of deleting the environment map, you can put something (an object, a plane, whatever) in front of the camera that just blocks the backdrop. So, there are several ways of achieving the same result.