Cameras, Rendering, and Scenes - Mastering Unity Scripting - page 166

Start the project with a scene that contains two separate areas or regions, as shown
in the preceding screenshot. The sample project is included in the topic's companion
files (code bundle) inside the Cameras folder of this chapter. Each region of the scene
should be assigned a separate camera; this makes a total of two cameras in the scene,
and each camera component should be disabled. This will prevent the cameras from
rendering themselves automatically. Here, we'll be rendering the cameras manually;
this will allow the render from each camera to be composited and faded on top of
the other.
For each camera, the AudioListener component was removed,
because a Unity scene can have only one AudioListener active
at any one time.
Next, create a third camera tagged as MainCamera at the scene's origin and set with
a culling mask of nothing, making sure that the camera is active but can render
nothing. This will represent the central main scene camera that composites together
renders from all other cameras, as shown here:
Creating a third main camera for rendering