How to disable continuos autofocus during video shooting with Canon SX230 HS? I have a Canon SX230 HS camera and want to record a movie from a train driver's perspective on a model railway.

Everything is working fine, except that the camera refocuses continuously during the shoot, making your eyes hurt when watching the movie.

Is there any way to disable the continuous autofocus when recording a movie?
See "Shooting with the AF Lock" on p94 of the user manual.  This is linked from p120 which is for shooting movies so I would assume it works for movies as well as stills.