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ISO (Sensitivity) Adjustment

ISO equivalence on a digital camera is the ability to increase the sensitivity of the CCD to allow for faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" on the CCD's signal amplifiers, nothing is without its price however and doing so also amplifies any noise that may be present and often affects colour saturation.

The IXUS 330 provides an 'Auto ISO' where the camera will automatically vary sensitivity between ISO 50 and ISO 150 depending on available light. You can also select ISO sensitivities ISO 50, 100, 200 and 400.

But what, or rather where is ISO 50?

When Canon introduced the PowerShot G1 they also broke the mold for selectable ISO sensitivity by providing an 'ISO 50' setting. This generated a lot of interest as it appears to deliver low noise levels and can still be useful as long as you are shooting in good light. Recently I have been comparing other camera models to the PowerShot G2 and S40 and have noticed that although Canon label their lowest sensitivity as ISO 50 that in fact this is just as sensitive as other cameras at ISO 100.

This was also true of the IXUS 330, with the camera set to ISO 50 it exposed as another camera would for ISO 100 (combination of shutter speed and aperture). For the shots below I used a light meter to take a (flat surface) reading from the subject, it was 4.0 EV (at ISO 100), taking shots the camera exposed 4.0 EV at ISO 50 and 5.0 EV at ISO 100 (etc.). I re-verified this by taking similar shots with other cameras (and indeed Canon's own EOS-D60 D-SLR), my results were reconfirmed. This means that in effect the IXUS 330's ISO 50 is actually equivalent to ISO 100, and so on up the scale. What is very curious is why Canon chose to label the camera sensitivity in this way.

Noise levels

Unfortunately I didn't have another (modern) 2 megapixel digital camera with selectable ISO sensitivities to do a direct comparison, so instead I have simply provided a montage of 60 x 60 pixel crops from our standard GretagMacBeth ColorChecker shot taken at each selectable sensitivity.

ISO 50
ISO 100
ISO 200
ISO 400

The ISO 50 setting provides a very clean almost completely noise free shooting mode, noise increases as we would expect in fairly consistent way all the way up the selectable sensitivities.


White Balance

Unfortunately the IXUS 330's automatic white balance did seem to fall over (quite badly) under both Incandescent and Fluorescent light. However, the news is better if you switch to one of the pre-programmed white balance settings. Pre-selecting white balance before shooting guarantees some of the best artificial light white balance I've seen in any consumer digital camera (check out that Incandescent shot, almost no hue shift). Additionally the IXUS 330 also has manual preset white balance which virtually guarantees perfect white balance. Canon lose one mark for poor Auto White balance but gain at least two for excellent pre-programmed settings!

Outdoors, Auto Outdoors, Sunny (or Cloudy) Outdoors, Manual
Incandescent, Auto Incandescent, Incandescent Incandescent, Manual
Fluorescent, Auto Fluorescent, Fluorescent Fluorescent, Manual


Macro Focus

Because of its extending compact lens design the IXUS 330 can't offer much in the way of macro ability. That said things do seem to be slightly improved over last years camera, at least now we can get close enough (at full telephoto) to produce a "macro" coverage of 8 cm (3.1 in) horizontally across the frame.


Low Light Focus

This test measures the minimum amount of light under which the camera can still focus. The focus target is our lens distortion test chart (shown here on the right), camera is positioned exactly 2 m (6.6 ft) away.

Light levels are gradually dropped until the camera can no longer focus. This is carried out at both wide angle and telephoto zoom positions (as more light reaches the focusing systems with a larger aperture).

This test target is the optimum type of subject for most "contrast detect" AF systems (as it has a vertical line at its center), you should consider the results below the best you could expect to achieve.

Lens position Aperture AF Assist lamp Lowest light focus
Wide angle (39 mm) F4.7 On 0.9 EV (4.7 Lux, 0.4 fc)
Telephoto (117 mm) F4.7 On 2.9 EV (18.7 Lux, 1.7 fc)
Wide angle (39 mm) F2.7 Off 1.9 EV (9.3 Lux, 0.9 fc)
Telephoto (117 mm) F4.7 Off 3.4 EV (26.4 Lux, 2.5 fc)

Light intensity (Lux) = 2.5 x 2^EV (@ ISO 100), 10.76391 Lux = 1 foot-candle (fc)

Surprisingly the IXUS 330's AF assist lamp didn't work in complete darkness, instead it managed to extend the camera's AF sensitivity by one stop at wide angle and about half a stop at telephoto. This is probably due to the fact that at 2 m from our AF target the beam cast by the lamp was looking slightly faint and didn't line up properly with the center AF point.


Flash Performance

The IXUS 330's flash unit has a quoted range of 3.5 m (12.5 ft) at wide angle and 2.0 m (6.6 ft) at telephoto. As you can see from our samples below exposures were accurate and consistent without any colour cast, there was some notable drop-off trying to shoot our white wall from 2 m away at full wide angle.

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