ISO / Sensitivity accuracy

In a new addition to our reviews we are now measuring the actual sensitivity of each indicated ISO sensitivity. This is achieved 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 Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV.

Just like almost every Nikon digital SLR past the D40X's indicated ISO sensitivities exactly match the camera's actual sensitivity across the range (from ISO 100 to 3200).

Indicated
sensitivity 		Nikon D40X
(actual sensitivity)		 Canon EOS 400D
(actual sensitivity)		 Olympus E-410
(actual sensitivity)
ISO 100 ISO 100 ISO 100 ISO 125
ISO 200 ISO 200 ISO 200 ISO 200
ISO 400 ISO 400 ISO 400 ISO 400
ISO 800 ISO 800 ISO 800 ISO 800
ISO 1600 ISO 1600 ISO 1600 ISO 1250
ISO 3200 ISO 3200 n/a n/a

ISO Sensitivity / Noise levels

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 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.

Nikon D40X vs. Canon EOS 400D (Digital Rebel XTi) vs. Olympus E-410

  • Nikon D40X: Nikkor 50 mm F1.8 lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), JPEG Large / Fine
     
  • Canon EOS 400D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), JPEG Large / Fine
     
  • Olympus E-410: Olympus 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
Nikon D40X
ISO 100		 Canon EOS 400D
ISO 100		 Olympus E-410
ISO 100 (ISO 125 equiv.)
Nikon D40X
ISO 200 		Canon EOS 400D
ISO 200 		Olympus E-410
ISO 200
Nikon D40X
ISO 400		 Canon EOS 400D
ISO 400		 Olympus E-410
ISO 400
Nikon D40X
ISO 800 		Canon EOS 400D
ISO 800 		Olympus E-410
ISO 800
Nikon D40X
ISO 1600 		Canon EOS 400D
ISO 1600 		Olympus E-410
ISO 1600 (ISO 1250 equiv.)
Nikon D40X
ISO 3200		 Canon EOS 400D
n/a		 Olympus E-410
n/a

Nikon's approach to high ISO noise on the D40X is pretty much the same as ever, mostly chroma noise reduction with very little luminance noise reduction. This leads to a lack of digital-looking chroma blobs while maintaining as much detail as possible (little luminance smearing here). Obviously this does mean that 'flat areas' can look noisier than the competition but this noise at least has a film-like grain rather than digital artifacts. Compared to the other cameras there's very little to choose although the EOS 400D does maintain more detail at ISO 1600 than the Nikon or Olympus.

Luminance noise graph

The graphs below demonstrate that the D40X's ten megapixel sensor with its smaller pixel pitch is naturally noisier than the D40, that said we're really talking about fractional differences between the two. The ISO 3200 option, indicated on the D40X as 'HI 1' is quite noisy and should really only be used in extreme situations.

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.