Quote - Or you can use a "persepctive zoom lens" prop in front of your camera. What I mean by that is you can keep your camera inside the room, but give the perspective of being somewhere outside the room, perhaps even a thousand miles away.

I did this trick when I built my GenIBL tool. For purposes of creating an IBl for an enclosed room, you have to have the camera and mirror inside the room. But the perspective needs to be infinitely far away, so that the view lines are parallel.

I put a one-sided square in front of my camera, very close, and it is parented to the camera. This square must be exactly perpendicular to the view plane. So you want to do this with the camera pointing in a precise direction. Once parented you can move the camera freely.

Then you put a Refract node on the square, turning it into a lens. (You have to turn Diffuse_Value and Specular_Value off as well.) With an IOR of 1.0, the lens does nothing.  As you increase the IOR, it creates exactly the same perspective change as moving the camera straight backwards. With an IOR of 1 million, the camera is effectively hundreds of miles away.

I'm just getting around to needing this trick because of a scene I have set in a rather confined space, and I really don't have other options for setting a camera up, but I can't get it to work.  Increasing the IOR of the lens zooms in, it doesn't "back" out.

Clearly I'm missing something blatantly obvious here.