From the The 3-D Rebel’s Guide:
A shot is fusible if an audience member can merge the left and right eye streams in his brain. This is the point of 3-D production.
A shot is, or parts of it can become, infusible if the net separation is too wide. So, fusibility is not just how far you push stereo separation of the foreground or background separately, but how big the separation difference is between foreground and background together. In Prain Engrish again?
You can pop 3-D way out forward, or push it way out back, but you can’t do both at the same time in the same shot, unless you want people to leave the theater screaming, eyes bleeding as their heads catch on fire and explode.
There is a delicate balance for keeping your footage fusible, and this is probably the stickiest wicket in the 3-D game. Use your storyboards to plan for extreme pop or push, the big gimmicks of 3-D, if you must use them.
You can place an optical barrier plane in your shot like a door, a wall, a giant robot, or a clear blue sky. Or you can change your mind about having to pop the snot out of this particular sequence.
Remember those conversations that start with “Wouldn’t it be cool if-” that I warned you about? Well, you’ve now been doubly warned: If your shot isn’t fusible, there’s nothing remotely cool about it.
– -=Seth Estrada