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Photographic tests

White balance

The SD870 IS has five white balance presets (daylight, cloudy, tungsten and two fluorescent settings) in addition to the default auto white balance. There is also a 'manual' white balance setting that allows you to point the camera at a neutral target to set the white balance. This manual setting is remembered even if you turn the camera off. In normal outdoor shooting the auto white balance works perfectly (as confirmed by our studio tests). Indoors it's a bit more hit and miss, as we've seen with most Canon PowerShots incandescent (tungsten) lighting causes a fairly strong orange color cast (and the appropriate preset only gives reasonable results). If you don't like the warm tone, you need to switch to manual WB.

Auto White Balance Fluo Preset Auto White Balance Incandescent preset
Fluorescent light - Auto white balance average,
Preset white balance average
Incandescent light - Auto white balance poor,
Preset white balance average

Flash

The SD870's built-in flash has a quoted working range of 0.3m - 4.0m (1.0 - 13 ft) at the wide end of the zoom and 0.3m - 2.0m (1.0 - 6.6 ft) at the tele end, which is a bit on the underpowered side The camera adjusts the ISO to keep the shutter speed at 1/60th which gives a reasonable balance of retaining ambient lighting and avoiding camera shake. That said, exposure is generally pretty good and flash recycling is pretty nippy (particularly if you turn the red eye reduction off). The AF illuminator works very well at distances of up to around 2m.

Click here for flash test chart

Skin tone -
Good color but slight under exposure (this is most likely caused by the white wall confusing the metering).

Macro

As is common to most compact digital cameras the SD870's macro mode is most effective at the wide end of the zoom, where you can get as close as 3cm, capturing an area 45mm across - not bad at all for an 'ultra-compact'. At the long end of the zoom the performance isn't too bad - 30cm subject distance capturing an area 10cm wide. There is inevitably some distortion when shooting very close up at the wide end, but it is not too strong, and certainly less so than many of its competitors. If you look at either of the samples below you'll also see some chromatic aberration and corner softness, though to be fair this is something we only really saw in the lab, not the real world.

Movie mode

As well as the 640x480, 30fps mode that has become standard on Canon's SD models, the 870 IS also features a 'long-play' mode that maintains the frame size and rate but reduces quality (increases compression) to keep the file size down.

'Compact' mode limits resolution to 160x120pixels and 15fps to keep files to an emailable size. There is also a time-lapse mode that records a single frame at one or two second intervals to demonstrate slowly unfolding events.

Overall quality is excellent, with movies very smooth and showing few compression artifacts. The AVI files are large - at the best quality setting (640x480 / 30fps) you're burning around 1.7MB every second.

The optical zoom locks in position once you're pressed the record button, but you can continue to use digital zoom throughout.

Sample movie: 640 x 480 pixels @ 30 fps
File size: 11 MB, 5 secs

Click on the thumbnail to view the movie (caution: large file!)

Resolution

Thanks to the extra million pixels the SD870 IS is pulling a touch more resolution out of our chart, and overall the results are a noticeable improvement (though how much of this is down to us having a 'better' sample of the SD870 IS than we had of the SD800 IS is open to debate). Again there's a little moiré at the highest frequencies, but overall these are better than we'd expect from a camera in this class, showing that the constant sensor upgrades we complain about all the time do bring some benefits!

Crops

Click here for the full resolution test chart

Horizontal LPH

Absolute resolution 1550 LPH
Extinction resolution 2000 LPH

 

Vertical LPH

Absolute resolution 1600 LPH
Extinction resolution 2100 LPH *

*moiré visible

Distortion and other image quality issues

Despite the wideangle lens the SD870IS exhibits only moderate distortion at the wide end of the zoom - 1.3% barrel distortion (click here for test chart) - nothing to worry about on a camera of this type. On a more positive note there is virtually no (0.1%) measurable distortion at all at telephoto end (click here for test chart).

General comments

On the whole, the SD870 IS produces decent results in a wide range of situations, and - perhaps more important - it does so reliably, shot after shot. Considering its relatively wide-angle lens, there is remarkably little in the way of chromatic aberration or fringing in the majority of photos. There is some, of course, but it's not something that you're likely to notice unless you really zoom in and start looking for it. For the typical user making prints the results are very good, with excellent color (not too overdone but bright enough to please the target market) and reliable focus, white balance and exposure (though see below).

The only real niggle is something that we noticed in the previous model - that faced with a hard-to-expose scene, the camera will tend to overexpose - which is probably the worst thing it can do. We also found a little corner softness in a couple of shots when shooting at the widest zoom setting and F2.8, but you need a lot of fine detail in the corner of the frame to see it.

Highlight clipping / contrast issues

Like all compact cameras the SD870's tiny sensor struggles to capture the full range of tones when faced with a scene containing a very wide dynamic range (from deep shadows to bright highlights). To make matters worse, there is fairly steep tone curve that makes for punchy, contrasty prints but exacerbates the problems of limited dynamic range by pushing near-whites to white and near blacks to black.

The SD 870IS has most difficulty in situations featuring deep shadows and bright sunlight in the same scene. These are the situations that any camera will find difficult but the Canon is prone to overexposing these scenes, letting large areas clip to white, rather than underexposing them and leaving some detail present. In some cases, the results can be improved using manual exposure compensation but it does mean certain scenes require a little more thought than simply pointing and shooting.

100% crop 28mm equiv., F2.8
100% crop 28mm equiv., F2.8

Channel clipping

Another result of the SD870's tendency to clip to white in high-contrast scenes is that individual color channels can also clip in certain circumstances. In this instance, a bright red region has completely overexposed and caused noticeable bleeding into surrounding pixels. To be fair, this happened only once in 400 or so photographs and with a brightly-lit red area in an otherwise shaded scene, which would be difficult to expose correctly. However, we can imagine other situations in which it might happen, so feel it is worth noting.

100% crop 105mm equiv., F5.6
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