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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" (gain) on the CCD's signal amplifiers. Nothing is without its price however and doing so also typically increases visible noise (random speckles visible all over the image).

We are now using a more reliable, repeatable and neutral method for evaluating noise. Shots are taken in daylight lighting in our studio. Noise is measured as the standard deviation of the medium gray patch on a Gretag MacBeth ColorChecker chart. The image is normalized before measurement of noise to remove the possibility of figures being affected by image contrast (one method of masking noise). Note that noise numbers shown on the graphs below can not be compared to those in older reviews.

Test notes:

  • Shots taken at approximately 21°C (~70°F)
  • Lighting was simulated daylight
  • Manual white balance
  • Aperture Priority

Sigma SD10 vs. Canon EOS 10D

It's worth noting that we had to use an aperture three quarters of a stop (0.7 EV) larger on the SD10 to deliver the same shutter speed and middle grey as the Canon EOS 10D at the same sensitivity. Thus ISO 100 on the EOS 10D would be roughly equivalent to ISO 160 on the SD10.

  • Sigma SD10: Sigma 50 mm F2.8 lens, Aperture Priority (F3.2), Manual WB,
    RAW converted to JPEG (Default settings in Photo Pro)
     
  • Canon EOS 10D: Canon 50 mm F1.4 lens, Aperture Priority (F4.0), Manual WB,
    Default Parameters (Standard), JPEG Large / Fine
  Sigma SD10
ISO
100, 1/100 sec, F3.2
Canon EOS 10D
ISO 100
, 1/100 sec, F4.0
 Partial crop
Red Green Blue
channels
  Sigma SD10
ISO
200, 1/200 sec, F3.2
Canon EOS 10D
ISO 200
, 1/200 sec, F4.0
 Partial crop
Red Green Blue
channels
  Sigma SD10
ISO
400, 1/400 sec, F3.2
Canon EOS 10D
ISO 400, 1/400 sec, F4.0
 Partial crop
Red Green Blue
channels
  Sigma SD10
ISO
800, 1/800 sec, F3.2
Canon EOS 10D
ISO 800
, 1/800 sec, F4.0
 Partial crop
Red Green Blue
channels
  Sigma SD10
ISO
1600, 1/1600 sec, F3.2
Canon EOS 10D
ISO 1600
, 1/1600 sec, F4.0
 Partial crop
Red Green Blue
channels
  Sigma SD10
n/a
Canon EOS 10D
ISO 3200
, 1/3200 sec, F4.0
 Partial crop
Red Green Blue
channels

As you can see the SD10 really does manage to keep noise levels under control even at higher sensitivities, this is a much better performance than the SD9. Note also that the SD10's noise is monochromatic compared to the EOS 10D's which gets progressively more color noise.

Luminance noise graph

Remember that the results below are measured from the 'middle grey' patch, see our note below "what the grey patch doesn't show".

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity (normalized) on the vertical axis. Note that we have standardized on a 0-10 scale.

RGB noise graph

As you would expect the Foveon X3 sensor produces almost identical noise levels across all three color channels, where as the Bayer pattern sensor will always have more noise in the red and blue channels as their are half the number of photosites for those colors compared to green.

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized) are on the vertical axis. Note that we have standardized on a 0-10 scale.

What the grey patch doesn't show

However, it's not all rosy for the SD10, what the crops above don't show is what happens to the color patches as ISO increases. The EOS 10D manages to maintain both the hue and saturation of the distinct red, green and blue patches all the way through to ISO 1600, at ISO 3200 all the patches are affected by the high noise level, noticably the blue patch is turning purple. The SD10 gradually loses both saturation and hue accuracy as sensitivity is increased, up to ISO 400 things appear to be acceptable, at ISO 800 it's borderline with the red patch taking quite a lot of yellow / green, at ISO 1600 noise levels in the color patches is quite strong.

  Sigma SD10
ISO
100, 1/100 sec, F3.2
Canon EOS 10D
ISO 100
, 1/100 sec, F4.0
Crops from
red, green, blue
patches
  Sigma SD10
ISO
200, 1/200 sec, F3.2
Canon EOS 10D
ISO 200
, 1/200 sec, F4.0
Crops from
red, green, blue
patches
  Sigma SD10
ISO
400, 1/400 sec, F3.2
Canon EOS 10D
ISO 400, 1/400 sec, F4.0
Crops from
red, green, blue
patches
  Sigma SD10
ISO
800, 1/800 sec, F3.2
Canon EOS 10D
ISO 800
, 1/800 sec, F4.0
Crops from
red, green, blue
patches
  Sigma SD10
ISO
1600, 1/1600 sec, F3.2
Canon EOS 10D
ISO 1600
, 1/1600 sec, F4.0
Crops from
red, green, blue
patches
  Sigma SD10
n/a
Canon EOS 10D
ISO 3200
, 1/3200 sec, F4.0
Crops from
red, green, blue
patches
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