This is the set (2) of 100mm mini clamps I just bought from B&Q. The top jaw is fitted with some BluTack and one of these plastic covers for philips screw heads. That's the jaw that will press down on the shutter button of my A540. The idea is to set the camera to repeat mode so that it keeps taking pictures as long as the shutter button is down. Night sky time-lapse photography should be much easier. It takes 15 seconds to expose and about 15 seconds to save the image on the internal card, so I expect a frame rate of 2 per minute. I've added a 12V adaptor (L17AR from Maplin) so that I can run the camera on external power from the Maplin 12V battery or a car cigar lighter socket. The PowerShot needs Tip-Positive external power and 3.15 Volts.