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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 Olympus C-5050 Zoom provides four selectable sensitivities of ISO 64, 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.

Olympus C-5050 Zoom vs. Sony DSC-F717

The C-5050 Zoom provides a 'lower than normal' ISO 64 but only goes up to ISO 400, thus two of the comparison crops below are of only one camera. To be fair it's also worth noting that the DSC-F717 has a 2/3" (8.8 x 6.6 mm) CCD versus the C-5050 Zoom's smaller 1/1.8" (7.2 x 5.3 mm) CCD.

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

  ISO 64
Olympus C-5050 Zoom
1/30 sec, F4.0
Sony DSC-F717
n/a
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 100
Olympus C-5050 Zoom
1/50 sec, F4.0
Sony DSC-F717
1/50 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200
Olympus C-5050 Zoom
1/100 sec, F4.0
Sony DSC-F717
1/80 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400
Olympus C-5050 Zoom
1/200 sec, F4.0
Sony DSC-F717
1/160 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 800
Olympus C-5050 Zoom
n/a
Sony DSC-F717
1/250 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel

It's interesting to note the difference in actual sensitivity between the two cameras, at ISO 100 both exposed at 1/50 sec, from then on upwards the C-5050 Zoom was a third of a stop more sensitive (not significant but notable). As you can see the DSC-F717 manages to keep noise levels lower than the C-5050 Zoom until ISO 400 where the C-5050 Zoom's noise reduction becomes more effective (and more noticeable).

The graph below tells an interesting story, firstly the C-5050 Zoom's noise levels are higher than we would have liked (especially at the expectedly clean ISO 64) but also that its noise reduction system is either 'turned up' or more effective at ISO 400 which pushes noise levels down below that of ISO 200. It would however be worth noting that such noise reduction often also sacrifices resolution. The DSC-F717 on the other hand has a fairly linear noise graph.

Luminance noise graph

Note that indicated ISO sensitivity is on the horizontal axis of this graph.

RGB noise graph

Note that indicated ISO sensitivity is on the vertical axis of this graph.

Olympus C-5050 Zoom vs. Canon PowerShot G3

This test was made far more complicated by the G3's higher than reported sensitivity. In effect the G3 was a full stop more sensitive than the C-5050 Zoom at the same indicated ISO, this meant that the G3 was shooting with a 1/50 sec, F4.0 exposure at it's ISO 50, the same exposure as the C-5050 Zoom at ISO 100. Thus to fairly compare the G3 and C-5050 Zoom we must compare crops from each camera a stop of sensitivity apart.

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

  ISO 64 n/a
Olympus C-5050 Zoom
1/30 sec, F4.0
Canon PowerShot G3
n/a
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 100 ISO 50
Olympus C-5050 Zoom
1/50 sec, F4.0
Canon PowerShot G3
1/50 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200 ISO 100
Olympus C-5050 Zoom
1/100 sec, F4.0
Canon PowerShot G3
1/100 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400 ISO 200
Olympus C-5050 Zoom
1/200 sec, F4.0
Canon PowerShot G3
1/200 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel
 
  n/a ISO 400
Olympus C-5050 Zoom
n/a
Canon PowerShot G3
1/400 sec, F4.0
 Original crop
 Red channel
 Green channel
 Blue channel

Very interesting results, the G3 delivers much less noise at the same effective sensitivity. Remember that the G3's ISO 50 is the same as the C-5050 Zoom's ISO 100 etc. With this in mind the luminance noise graph below has as second 'effective sensitivity' line on the graph to give you a fairer impression of noise levels and true sensitivity.

Luminance noise graph

Note that indicated ISO sensitivity is on the horizontal axis of this graph.

RGB noise graph

Note that indicated ISO sensitivity is on the vertical axis of this graph.

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