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ISO Sensitivity / Noise levels


Standard Test

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 C-50 Zoom provides three selectable sensitivities of ISO 80, 160 and 320. Our noise comparison test involves shooting a color patch chart (a GretagMacBeth ColorChecker) at the full range of ISO sensitivities and then measuring luminance and RGB noise at a 'mid' grey patch.

Olympus C-50 Zoom vs. Pentax Optio 550

This is a slightly difficult comparison because the cameras don't share any ISO sensitivity. The C-50 Zoom has sensitivities of ISO 80, 160 and 320, the Optio 550 has 64, 100, 200 and 400. Please bear this in mind when looking at the comparison crops below.

Measurements taken at approximately 21°C (~70°F). Lighting was daylight. Manual white balance. Aperture Priority.

  n/a ISO 64
Olympus C-50 Zoom
n/a
Pentax Optio 550
1/35 sec, F5.6
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 80 ISO 100
Olympus C-50 Zoom
1/40 sec, F5.6
Pentax Optio 550
1/53 sec, F5.6
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 160 ISO 200
Olympus C-50 Zoom
1/80 sec, F5.6
Pentax Optio 550
1/105 sec, F5.6
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 320 ISO 400
Olympus C-50 Zoom
1/160 sec, F5.6
Pentax Optio 550
1/225 sec, F5.6
 Original crop
 Red channel
 Green channel
 Blue channel

This is an interesting comparison because both cameras used the same size (1/1.8", 7.2 x 5.3 mm) CCD sensor. While we can't be sure that the sensor is from the same manufacturer it's clear that both face the same physical challenges (photosensor size). A look at the graph below shows that Olympus are managing to either keep low (lower input noise) or tame (better noise reduction) noise far better than Pentax. Indeed the C-50 Zoom has approximately the same noise levels at ISO 160 as the Optio 550 does at ISO 64. Interestingly noise levels were virtually reversed at slower shutter speeds, see our studio comparison (1/4 sec exposures) later in this review.

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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