Trying to get this effect
 

Sorry I don't know the name of the effect I am after but a description is:
You have, say, a head and shoulders shot of someone looking at the camera then the background zooms in or out with the person remaining stationary / unchanged.

Any pointers?

subject shot on blue screen, composited over changing background?
I've wondered how they've done this as well.... seen it in movies.

This has to be done in-camera. It is called a dolly-zoom (and others) and involves dollying a shot one way and zooming the other way. Very difficult to pull off, but quite effective for indicating confusion, fear, disorientation or vertigo.

Basically, you dolly in and zoom out, or dolly out and zoom in. It really needs a dolly though, the hero element should stay as much in the same place and the same size as possible.

Just search for "dolly zoom" on YouTube, there's a lot of examples.

Good luck =)

Thanks Craig. I guess the hard part is timing. I am thinking that the 'art is to match the speed the dolly zooms in has to marry with the speed that your lens zooms out (and vice-versa)

Hmmm.....maybe Sam's idea of blue screening might be easier as the shot I want involves a stationary person within an empty hallway background

The hard parts are timing and consistency/smoothness. Depending on your camera style, it might just not be possible to get an even zoom in or out at an appropriate speed.

I don't mean to imply it's impossible, but it will take a few attempts. Try either sitting in a wheelchair with the camera, or even propped up on one of those cargo carts (small platform at the bottom and a high back kind of one). Then, have someone run you back and forth a few times, while you focus on smoothly and consistently zooming. Once the two of you get matching speeds and have your rhythm, it is quite possible to achieve.

Doing it as a keyed shot might work, but I still think the background would need to zoom, and that means perspective changing, not just the size of things. So just making the background bigger (or smaller) might not look right. And frequently, when it just doesn't look "right" but you can't tell why, it will put people off. I'm honestly not sure though, it might work OK if all the background elements started and ended far enough away from the hero element that the lack of perspective change wasn't noticed.

And remember, you don't have to achieve the speed you want in camera, that can be fiddled with in post. Generally, the hero element is moving very little, so speed-up artifacts will mostly be confined to the background, and therefore not nearly so noticeable.