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The combination of Canon's proprietary CMOS sensor technology and DIGIC 4 processor is intended to give the SX1 faster overall performance than the SX10, and it seems to have succeeded. Both start-up and shut-down times are comfortably under two seconds, which is impressive considering the size of the lens that has to be rolled out. The SX1 has the same single-point AF system as the SX10, and it too is impressively fast, resulting in a very quick single-shot cycle time of 1.4 seconds.
Some people seem to attach great significance to continuous shooting speed, which is odd considering how rarely it is actually useful. However Canon makes quite a big thing of the SX1's continuous mode, because it can shoot at four frames a second. This is indeed very impressive, considering the amount of data that is being processed and stored, but in this high-speed mode that camera doesn't focus between shots, so it's not particularly useful for moving subjects. It also has another continuous mode that includes motion-tracking AF, which is a lot more useful but somewhat slower, shooting at approximately 1.25 frames a second.
I'm not sure that the increase in continuous mode performance has been worth it, because I was somewhat surprised to find that the CMOS sensor seems to have sacrificed picture quality for shooting speed. At lower ISO settings there is no problem, and the camera performs brilliantly. I took a number of photos during the recent snow, a situation which can cause exposure and white balance problems for some cameras, but the SX1 coped perfectly, producing nice clean whites and clear accurate colours. It also performs well in low light, focusing quickly and accurately, and the iContrast feature is very good at capturing a nice balance between shadow and highlight detail in high-contrast conditions.
The problems only really start at about 400 ISO. Perhaps it's a feature of small CMOS sensors, but at higher ISO settings there were major problems with image noise, including what looked a lot like hot pixels. This is very surprising, since Canon cameras generally have excellent noise control. Fortunately the maximum ISO setting in normal mode is only 1600, so things don't get too messy, although there is high-ISO scene mode that pushes it up to 3200, with predictably horrible results.
The PowerShot SX1 IS comes closer than any other compact still camera to matching the video capabilities of a dedicated HD camcorder, and no doubt there are some people out there who will find the 4fps continuous mode very useful for something or other, but the loss of high-ISO picture quality is a sacrifice few will be willing to make, especially on a camera costing nearly £400.