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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. The 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 ISO's. 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 measurement tool which measures the standard deviation (normalized) of the middle gray patch (indicated by the red rectangle above). Additionally we now have a 'detail crop', this is currently a postage stamp (lots of fine detail) but we may replace this at a future date. Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Test notes:

  • Shots taken at approximately 22°C (~72°F)
  • Lighting was simulated daylight measured as 10.1 EV (at ISO 100)

Nikon D50 vs. Nikon D70 (ISO 200 - 1600)

  • Nikon D50: Nikkor 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters, JPEG Large / Fine
  • Nikon D70: Nikkor 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters, JPEG Large / Fine
  Nikon D50
ISO 200
, 1/200 sec, F3.5
Nikon D70
ISO 200
, 1/200 sec, F3.5
Crops
  Nikon D50
ISO 400
, 1/400 sec, F3.5
Nikon D70
ISO 400
, 1/400 sec, F3.5
Crops
  Nikon D50
ISO 800
, 1/800 sec, F3.5
Nikon D70
ISO 800
, 1/800 sec, F3.5
Crops
  Nikon D50
ISO 1600
, 1/1600 sec, F3.5
Nikon D70
ISO 1600
, 1/1600 sec, F3.5
Crops

Very interesting results, without referring to the graphed results below you can already see that the D50 delivers a cleaner image than its 'bigger brother' the D70. Nikon has previously hinted that the sensor in the D50 is different than that of the D70 but are tight lipped about the exact differences. One thing you can see here (and is more obvious in the graphs) is that the D70's noise is more monochromatic (affects all color channels equally) where as the D50's noise has a more color mottle effect (see ISO 1600 gray crop).

Nikon D50 vs. Pentax *ist DS (ISO 200 - 3200)

  • Nikon D50: Nikkor 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters, JPEG Large / Fine
  • Pentax *ist DS: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters, JPEG Large / Fine
  Nikon D50
ISO 200
, 1/200 sec, F3.5
Pentax *ist DS
ISO 200
, 1/200 sec, F3.5
Crops
  Nikon D50
ISO 400, 1/400 sec, F3.5
Pentax *ist DS
ISO 400, 1/400 sec, F3.5
Crops
  Nikon D50
ISO 800
, 1/800 sec, F3.5
Pentax *ist DS
ISO 800
, 1/800 sec, F3.5
Crops
  Nikon D50
ISO 1600
, 1/1600 sec, F3.5
Pentax *ist DS
ISO 1600
, 1/1600 sec, F3.5
Crops
  Nikon D50
n/a
Pentax *ist DS
ISO 3200, 1/3200 sec, F4
Crops

The difference between the Pentax *ist DS and Nikon D50 is pretty clear here especially at ISO 400 and 800 where the D50 continues to deliver clean tones the *ist DS is already looking speckled and somewhat noisy. Additionally there's no loss of detail in the D50 images which hints to either a very good noise reduction system or minimal noise reduction.

The graph below supports what we've seen in visual comparison, the D50 delivering low luminance noise levels especially between ISO 200 and 800. At ISO 1600 noise levels are similar to the Canon EOS 350D and Nikon D70 although with no obvious loss of detail. As mentioned above the D50's noise is most noticeable in the red channel (luminance is mostly made up of green).

Luminance noise graph

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

RGB noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized image) are on the vertical axis.

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