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ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor to enable 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 noise and can also affect colour saturation.

The PowerShot S45 provides four selectable sensitivities of ISO 50, 100, 200 and 400.

Our noise comparison test involves shooting a colour patch chart (a GretagMacBeth ColorChecker) at the full range of ISO sensitivities and then measuring luminance and RGB noise at a 'mid' grey patch.

Note that this is a modification to our previous noise test which only measured luminance noise. The new test now provides a graph of luminance noise for each selectable sensitivity as well as individual RGB channel noise.

What is ISO 50?

In previous tests / comparisons of Canon consumer digital cameras we have observed that the indicated ISO 50 is actually just as sensitive as indicated ISO 100 of other digital cameras. Canon have explained this to me as their conservative approach to labelling sensitivity, while there is no standard among digital cameras for measuring sensitivity Canon prefer to 'round down'. This means that to compare the PowerShot S45 accurately we must compare shots one ISO sensitivity apart (one stop).

Canon PowerShot S45 vs. Minolta DiMAGE F100

Image sharpening set to 'Normal' on both cameras, white balance preset other settings as default. Measurements taken at approximately 21°C (~70°F). Lighting was daylight.

  ISO 50 ISO 100
Canon PowerShot S45
1/20 sec, F4.5
Minolta DiMAGE F100
1/20 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 100 ISO 200
Canon PowerShot S45
1/40 sec, F4.5
Minolta DiMAGE F100
1/45 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200 ISO 400
Canon PowerShot S45
1/80 sec, F4.5
Minolta DiMAGE F100
1/90 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400 ISO 800
Canon PowerShot S45
1/160 sec, F4.5
Minolta DiMAGE F100
1/180 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel

Using this 'fairer' shifted comparison it's clear to see that noise levels are very similar until you reach ISO 800 (indicated as ISO 400 on the S45) where the S45 manages to keep noise levels lower.


White Balance

Building on the strength of the G2 / S40 white balance algorithm the S45 exhibits extremely good white balance with one of the preset white balances or manual white balance, good grey balance and no noticeable hue shift. Automatic white balance is less good with a noticeable orange cast to tungsten / incandescent lit scenes and a yellowish green cast to fluorescent. My advice is to stick to the preset white balance settings when lighting conditions change.

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


Macro Focus

Just like the G2 / S40 the S45's lens system doesn't have much in the way of macro capability. The best frame coverage was found at the wide angle end of the zoom range (which means some distortion) and produced a closest horizontal frame coverage of approximately 9.2 cm (3.6 inches).

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