With tiny, high pixel count chips noise is always going to be an issue, and to a large degree this is more a test of the effectiveness (both measurable and visible) of a camera's noise reduction system. Designers have to balance the desire to produce smooth, clean results with the need to retain as much detail as possible (if you blur away the noise, you blur away image detail too).

Noise is kept fairly low at ISO 80-400 with Canon concentrating mainly on the ugly chroma noise (color blobs) though as we've seen with other recent Powershots there's more luminance noise reduction than we're used to seeing on Canon compacts. The net result is that up to ISO 400 the output looks relatively sharp and clean, but at ISO 800 and above the impact of noise and noise reduction are taking a heavy toll. Compared to many of its competitors the noise reduction is applied with a relatively light touch, giving as good a balance as you're likely to get between noise and detail on a sensor this densely packed.

ISO 80 ISO 100 ISO 200 ISO 400 ISO 800 ISO 1600
100% Crops

Noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis.

The graphs confirm Canon's relatively light-handed approach to noise reduction. Measurable noise is low at base ISO up to ISO200 but then increases fairly smoothly as sensitivity rises. What might look bad on the graph is actually not quite as bad in the real world. As mentioned above the relatively subtle application of noise reduction preserves a reasonable amount of detail in the image. This approach leaves all the options to the user. You can always apply some more noise reduction in post production should you wish to do so. However, it is impossible to get any detail back that has been blurred away in the camera already.

Low contrast detail

What the crops and graph don't show is the effect of noise reduction on low contrast fine detail such as hair, fur or foliage. An inevitable side effect of noise removal is that this kind of detail is also blurred or smeared, resulting in a loss of 'texture'. In this test the crops below show the effect of the noise reduction on such texture (hair) as you move up the ISO range.

100% Crops
ISO 80 ISO 100 ISO 200
ISO 400 ISO 800 ISO 1600

Unsurprisingly, the SD850 is not significantly different from most digital compact cameras when it comes to the effect of noise reduction on low contrast detail. The ISO 80 and 100 images are clean with good detail. But from ISO 200 upwards it becomes obvious that the noise reduction algorithms are interfering. At ISO 200 there is already quite some blurring going on and the individual hairs are starting to merge into one large yellow mass. As expected this becomes worse at ISO 400 with the added bonus of some chroma noise color blobs appearing. ISO 800 and 1600 are firmly based in the emergency camp as far as fine texture goes, almost none of the detail has been preserved.

In summary, avoid shooting at anything higher than ISO 200 if fine textures or other detail are important elements of your photographs, you'll hardly recognize any of it on your screen/print.

Optical image stabilization

Like the SD700 IS before, the SD850 IS sports Canon's optical image stabilization system. The 140mm equivalent focal length at the long end of the lens is not exactly what you'd call a super zoom but nevertheless the stabilization system comes in handy in low light situations. At the wide end of the zoom (35mm equiv.), I was regularly getting acceptably sharp hand-held results at shutter speeds as slow as 1/8th sec. Undeniably, though, using the IS mode is more useful at the tele end of the zoom.

There are three modes: Continuous (IS on all the time), 'Shoot only' (IS is activated at the moment the exposure is made) and Panning (for horizontally panned shots). The first option makes framing easier - the IS system steadies the preview image - the second puts less strain on the batteries (by only activating itself once you press the shutter button) and the third option only counters vertical camera-shake so the system does not get confused when you pan a shot.

The SD850 IS does not offer any manual control of shutter speeds. So unfortunately we could not run our usual IS systems test but nevertheless we can say the SD850's stabilization works pretty efficiently in most situations. To a certain degree the effectiveness will obviously depend on a particular photographer's ' type of shake' but it's probably fair to say that the SD850's system will give you somewhere between approximately 2 and 3 stops advantage in most cases (1/30th sec exposures at the long end of the zoom were nearly all blur-free). Once shutter speeds get slower the hit rate decreases pretty rapidly. The stabilization system is also very helpful when recording movies - your footage will be much less jerky.

Just as with the competition's anti-shake solutions the Canon IS does not do any miracles but it significantly increases your chances of getting a usable shot. Even in marginal light situations you should at least get one 'keeper' (such as the one in our sample below, taken at 1/3rd sec) if you activate IS and take a few safety shots.

1/3rd sec, 140mm equiv., IS off, 100% crop 1/3rd sec, 140mm equiv., IS on, 100% crop