You do have to move the camera or change the focal length. Even if you change the rendering aspect ratio, Vue will attempt to keep the framing the same.

As in my above example, I had a 4:3 image. I needed to add to the sides to create a 16:9 image, but changing the aspect ratio in Vue simply cropped the top and bottom of the 4:3 image to make it 16:9! I could have achieved the same effect in photoshop, but obviously this isn't what I wanted. This is why I had to move the camera back and change the focal length.

That is the problem with 3D software...it all comes back to a camera. This is nice because if you are used to using cameras in the real world, you can transfer that knowledge to 3D...but if you don't know how to use cameras, it can bite you! Think of how you would achieve that effect in the real world...you would have to step back and take a larger picture.

Maybe you have seen these consumer film cameras several years ago that offered a "panoramic" view? All they did was crop the image in the middle. Vue does the same thing.