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ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISOs. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (ie. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews). Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Sigma DP1 vs. Nikon D60 vs. Ricoh GR Digital II

  • Sigma DP1: Aperture Priority, Manual WB, Default Parameters,
    JPEG Hi / Fine
     
  • Nikon D60: Nikkor 50 mm F1.4 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
     
  • Ricoh GR Digital II: Aperture Priority, Manual WB, Default Parameters (Normal),
    JPEG Large / Fine
Sigma DP1
n/a
Nikon D60
n/a
Ricoh GR Digital II
ISO 80

Sigma DP1
ISO 100
Nikon D60
ISO 100
Ricoh GR Digital II
ISO 100
Sigma DP1
ISO 200
Nikon D60
ISO 200
Ricoh GR Digital II
ISO 200
Sigma DP1
ISO 400
Nikon D60
ISO 400
Ricoh GR Digital II
ISO 400
Sigma DP1
ISO 800
Nikon D60
ISO 800
Ricoh GR Digital II
ISO 800

Sigma DP1
n/a
Nikon D60
ISO 1600
Ricoh GR Digital II
ISO 1600

We are looking at output from three very different cameras here: The DP1 with its Foveon sensor, the Nikon D60 as a modern DSLR with an APS-C sized Bayer sensor and the compact Ricoh GR Digital II which squeezes 10MP onto its tiny 1/1.8" (Bayer-) sensor.

Thanks to the unique design of the Foveon sensor the DP1 resolves a remarkable amount of detail but there are traces of green and purple color blotches (chroma noise) visible even at base ISO (you have to look very closely though). They are much more clearly visible at ISO 400 and become unacceptably intrusive at ISO 800 which is the DP1's highest sensitivity setting.

Luminance noise (grain) on the other hand is not so much an issue on the Sigma. The images become slightly softer (due to noise reduction) at higher sensitivities but up to ISO 400 it is all within acceptable limits.

The Nikon's and Ricoh's output comes at a significantly higher resolution and cannot compete with the Sigma in terms of pixel-detail. The Nikon handles noise much better than the DP1 though and produces fairly clean results up to ISO 400. At higher sensitivities some softness caused by noise reduction becomes evident (something you can only solve by shooting raw), but on the plus side chroma and luminance noise are well under control and the results are more than usable.

The GR Digital II offers the same resolution as the D60 but individual photo sites are significantly smaller on the Ricoh's tiny sensor and find it much harder to 'gather' light. Therefore the image signal needs more amplification and the result of this are clearly visible in our crops. Shadow noise is visible even at the lowest ISO setting and the GR-D II is significantly noisier than the Sigma and Nikon at all sensitivities. From ISO 400 upwards noise reduction blurring becomes very evident.

Luminance noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Chroma (color) noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis.

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