White Balance

The S90 features eight preset white balance options plus an auto setting and the ability to set a custom (measured) white balance. In all cases you also get white balance fine-tuning options (B-A / G-M). We had no problems at all outdoors, with the Auto WB coping admirably in pretty much every situation we threw at it. Indoors under artificial light results were, as usual, less consistent. As with all Canons tungsten light produced very warm (orange) results when shooting with auto white balance, though the preset actually makes a pretty good effort of rendering a neutral (if slightly warm) result. the S90 fared a lot better under fluorescent lights, with both auto and preset white balance modes producing almost no color cast.

Incandescent - Auto WB
Red 10.8%, Blue -15.8% Poor
Incandescent - Incandescent preset WB
Red -2.3%, Blue -4.0% Average
Fluorescent - Auto WB
Red 0.0%, Blue 0.1% Excellent
Fluorescent - Fluorescent preset WB
Red 0.2%, Blue 0.0% Excellent

Flash Performance

The built-in flash unit has a specified range of 6.5m at wide angle and 2.5m at telephoto (when the ISO is set to auto) - which is fine for social snaps and the occasional bit of fill-in. In use the flash worked well enough in our indoor tests, with good skin tones, and good exposure, but 'in the field' we found it to be less than 100% reliable, and wouldn't recommend the S90 for anyone who does a lot of flash photography (not least because you always seem to have your finger over the flash when it tries to pop up). The FUNC menu allows the Flash Exposure Compensation to be set from -2 to +2, and an orange AF illuminator aids focus in low light.

The weak flash means that in Auto mode the camera has a tendency to set a higher ISO than you might choose yourself if you zoom in at all (the example below is ISO 800, for example). This isn't a problem for small prints but is something to be aware of. In auto mode the shutter speed tends to be chosen to balance flash and ambient light too, which can produce mild blur in dim conditions.

Skin tone - Slight warm tone. Color chart -good color, slight underexposure

Macro Focus

Although - like many very compact cameras - macro is not the S90's strongest point, with a minimum focus distance of 5cm at the wide end that allows you to capture an area around 65mm (2.6 inches across) it's useful for shooting everyday subjects such as flowers. At the long end the S90's close focus capabilities are less impressive (you can capture an area just under 10cm / 4" across, but in both cases corner to corner sharpness are good and distortion is relatively low.

Wide macro - 65 x 49 mm coverage
55 px/mm (1405 px/in)
Distortion: Low
Corner softness: Low
Equiv. focal length: 28 mm
Telephoto macro - 97 x 73 mm coverage
37 px/mm (947 px/in)
Distortion: Low
Corner softness: Low
Equiv. focal length: 105

Barrel and Pincushion Distortion

The S90, in common with many wide angle compacts (and an increasing number of mirrorless interchangeable lens cameras) uses software correction to remove distortion at short focal lengths. This design decision (which replaces bulky optics with fairly simple image processing routines) means that the measured distortion is very low in JPEGs. It's very low in raw files too, as long as you use one of the more common raw developers, such as the supplied Canon software or the latest version of Adobe Camera Raw. Switching to DCRaw reveals just how much correction the camera is doing - the first two examples below are the same shot. The distortion correction has no effect at the long end.

Barrel distortion JPEG - 0.5% at Wide angle
Equiv. focal length: 28 mm
Barrel distortion RAW - 3.5% at Wide angle
Equiv. focal length: 28 mm
Pincushion distortion JPEG - 0.1% at Tele
Equiv. focal length: 105 mm
Pincushion distortion RAW - 0.1% at Tele
Equiv. focal length: 105 mm

The examples below were converted using Adobe Camera Raw 5.6 (which doesn't appear to support the S90's distortion correction) - as you can see the real world ramifications can be pretty serious (though there is a side benefit - you get an even wider angle of view if you can live with the banana horizon). All taken at the widest (28mm) zoom position.

ACR 5.6 conversion Out of camera JPEG

Overall Image Quality / Specifics

Looking at the results it produces it's easy to forget all our quibbles about handling, pixel-level sharpness and speed, because - in most circumstances - the S90 really does impress, as long as you remember this is a small sensor compact and don't expect miracles.

The white balance, metering and focus accuracy, superb color (vibrant without being unnatural), consistent optical quality across the zoom range and pleasing tonality put it head and shoulders above most pocket cameras, and easily match the Panasonic LX3. Whilst it really shines when shooting landscapes and interiors (where the fast lens reduces the need for high ISO settings), the better-than-average ISO 800 performance and reliable image stabilization also means it does pretty well in low light too.

The negatives - blown highlights, slight blurring of low contrast fine detail in JPEGs, and occasional channel clipping in very bright conditions - are symptomatic of all small sensor compacts, and are less of a problem than we're used to seeing in this class of camera. Of the 1500 or so gallery shots taken for this review only a handful had issues serious enough to render images unusable.

The JPEGs are good enough that you don't really need to shoot raw at all, but storage is cheap and the raw mode fast enough that you may as well. In very bright light even the smallest amount of overexposure can cause very bright primary colors to clip in JPEGs (meaning the loss of tonality in, for example, a red flower). In these cases careful processing of the raw files will bring back just enough to rescue the shot (we found ACR's 'Recovery' tool useful for reducing hot spots in shots taken in bright sunlight).

As with many modern cameras there's a certain amount of digital trickery involved in optimizing the results from the S90. As shown above there's some heavy distortion correction (and the removal of corner shading) at the wide end. We also found - when using a raw converter (DCRaw) that doesn't support these automatic corrections - mild chromatic aberration and purple fringing at the wide end of the zoom. It's not a problem unless your workflow uses obscure raw converters (and even then, by compact camera standards the fringing is minimal). In extreme cases (as shown here) a hint of CA remains visible even in JPEGs, but you need to be looking very close to see it. We struggled to find any purple fringing in JPEGs at all.

Out of camera JPEG, 100% crop
28mm equivalent, F5.6
Raw converted (DCRaw), 100% crop
28mm equivalent, F5.6