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ISO Accuracy

The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). Measured ISO from all four cameras compared in these tests is within +/- 1/6 EV of indicated ISO, which we would expect from professional level equipment. The EOS-1D Mark IV gives almost exactly the same luminance readings from middle grey at ISO 51,200 as it does at ISO 100, only giving a slightly darker exposure at 102,400. As we noted with the D3S, this represents excellent consistency.

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 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 (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.6 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Canon EOS-1D Mark IV vs. Nikon D3S vs. Canon EOS-1D Mark III vs. Canon EOS 7D

  • Canon EOS-1D Mark IV: Canon 50 mm F1.4 lens, Manual Exposure, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (Standard), JPEG Large / 10
     
  • Nikon D3S: Nikkor 50 mm F1.4 G lens, Manual Exposure, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
     
  • Canon EOS-1D Mark III: Canon 50 mm F1.4 lens, Manual Exposure, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (Standard), JPEG Large / 10

  • Canon EOS 7D: Canon 50 mm F1.4 lens, Manual Exposure, Manual WB,
    Default Parameters (Standard PS), High ISO NR Default (Standard), JPEG Large / 10
  Canon EOS-1D Mk IV Nikon D3S Canon EOS-1D Mk III Canon EOS 7D
ISO 50    
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800  
ISO 25600    
ISO 51200    
ISO 102400    

The larger sensor of the 1D Mark IV means it noticeably out-performs the 7D as soon as the ISO starts to rise. The improved image processing of the newer Mark IV also means that it's producing cleaner images at the pixel level than the Mark III, with better detail retention and lower levels of chroma noise visible. The only camera it struggles against is Nikon's D3S. The larger sensor and lower pixel count of the D3S both help it to give a better performance at everything above ISO 6400. Downsizing the 1D IV images to the D3S' 12MP would even the field a little but that's still unlikely to make up for the considerably larger light-capturing area of the Nikon.

Noise graphs

Because this initial test is based on JPEG output, each camera has its own level of noise reduction applied. As a result, we often see some cameras getting better numerical noise results because they are applying more noise reduction. Unusually, here we're comparing cameras with different sensor sizes and that appears to be playing a large role in the outcome. So, despite the fact that the 7D is applying most noise reduction, it's also recording the highest noise figures. It's only in the higher ISO ranges that the D3S significantly out-performs the Mark IV (and the Mark IV's higher pixel count works against it in this test), so it's not a bad performance by any means.

ISO 50 - 1600

  Canon EOS 1D Mark IV
Chroma
Black
Gray

ISO 3200 - 102,400

  Canon EOS 1D Mark IV
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

RAW noise

Here we process the same shots through Adobe Camera Raw with noise reduction turned to a minimum, to give a clearer idea of the underlying sensor performance.

  EOS-1D Mark IV RAW D3S RAW EOS-1D Mark III RAW EOS 7D RAW
ISO 50    
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800  
ISO 25600    
ISO 51200    
ISO 102400    

Raw Noise graphs

Canon has told us that the 1D Mark IV's photosites have been maintained at the same size as those of the Mark III, making use of technology advances to reduce the surrounding circuitry to allow more pixels to be fitted into the same space. The RAW results certainly support that idea, with a very similar pixel-level noise characteristics between the two models (though bear in mind the Mark IV has more pixels, so is capturing more detail but only producing the same amount of noise, which would make the Mark IV cleaner at the whole-image scale). However, this isn't enough to counteract the D3S' larger sensor, with it producing similar amounts of noise to the Mark IV when ISO is set around 1 stop higher, all across the range.

ISO 50 - 1600

  Canon EOS 1D Mark IV
Chroma
Black
Gray

ISO 3200 - 102,400

  Canon EOS 1D Mark IV
Chroma
Black
Gray
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.
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