You can use any camera and in fact every light has a camera already parented to it (for shadow map generation).

However, attempting to take a camera that already has some automation, such as the face camera, and parenting it to something else than the "current face" may cause grief that isn't worth trying to explain.

Any of the "usual" built-ins can be parented without any unexpected side effects. (main, dolly, aux) You can also make new cameras dedicated to whatever.

I once made a pair of cameras to demonstrate stereo rendering, that were parented to the main camera. You could then animate the main camera for a movie, and re-render with the stereo cameras to make the stereo version.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)