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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 DiMAGE F100 provides four selectable ISO sensitivities of ISO 100, 200, 400 and 800.

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.

Minolta DiMAGE F100 vs. Canon PowerShot S45

Although the S45 provides an indicated sensitivity range of ISO 50 - 400 we have found that in reality this is closer to ISO 100 - 800. Indeed in the process of taking the shots (aperture locked at F4.5) it was observed that the S45's shutter speed was virtually always a stop faster at the same sensitivity. As most owners will use these cameras with Auto ISO or the lowest ISO it is fairer to compare the S45 samples to F100 samples with an indicated sensitivity one stop higher.

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 100 ISO 50
Minolta DiMAGE F100
1/20 sec, F4.5
Canon PowerShot S45
1/20 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200 ISO 100
Minolta DiMAGE F100
1/45 sec, F4.5
Canon PowerShot S45
1/40 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400 ISO 200
Minolta DiMAGE F100
1/90 sec, F4.5
Canon PowerShot S45
1/80 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 800 ISO 400
Minolta DiMAGE F100
1/180 sec, F4.5
Canon PowerShot S45
1/160 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. Overall the F100's noise levels are much as we would expect from an compact four megapixel.


White Balance

As we've come to expect from most compact digital cameras the F100's automatic white balance works best under natural light, incandescent or fluorescent light produces a muddy yellow cast. Switching to the pre-programmed white balance settings delivers good results, even under fluorescent light. Manual preset also works well although I found it to be a little inconsistent under incandescent light. Interestingly Minolta seem to have avoided any of the hue shift we normally associate white balance under with artificial light, Kudos.

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


Macro Focus

Engaging macro focus mode causes the camera to zoom to telephoto and lock the zoom at that position. We assume it does so because this is the optimum focal length for macro coverage with this lens system. One other advantage of being at telephoto (as opposed to wide angle macro seen on other compact digital cameras) is a lack of barrel distortion and generally better corner to corner sharpness. The F100's best frame coverage was approximately 40 mm (1.6 in). This is a good performance for this kind of camera and the resulting images are sharp.

 
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