The Environment/Background Switcher map lets you use one map as a background and another as an environment map, to provide environmental reflections.
In typical usage, you use the Environment/Background Switcher as an Environment map. As the Background map you apply a background image, preferably using the Environment/Background Camera Map (mental ray) shader.
As the Environment/Reflections map, use an environment map. If you have a plain photograph of a chrome ball taken from a similar camera angle as the background, you can use Environment Probe / Chrome Ball (mental ray) shader for easy, automatic unwrapping, or, if you have a fully unwrapped environment-map image, use a Bitmap map in Spherical Environment mode.
For details, see the following procedure.
To use the Environment/Background Switcher map:
This procedure assumes you have two photographs: one of a background, and another an image of a mirror/chrome ball, both taken from roughly the same camera position. The photo of the chrome ball should be cropped so that it exactly touches the edges of the ball. The best result is obtained if at least the chrome ball photo is HDR, but good results can be achieved with a traditional, non-HDR phogograph.
The Environment Map button label now shows the name of the map.
This displays the map’s parameters rollout. Click the Map button (“Browse”) and choose a bitmap file for the background image. Ideally, the bitmap is an HDR photograph of a chrome or mirror ball taken from the camera perspective in the scene, but a non-HDR photo also works well.
Or, if you have a fully unwrapped environment map photo, use it as a Bitmap map and, on the Coordinates rollout, choose Environ and set Mapping to Spherical Environment.