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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.

As we have come to expect from Nikon digital SLRs the D40's indicated ISO sensitivity was the same as its actual sensitivity.

Indicated
sensitivity
Nikon D40
(actual sensitivity)
Canon EOS 350D
(actual sensitivity)
Pentax K100D
(actual sensitivity)
ISO 100 n/a ISO 125 n/a
ISO 200 ISO 200 ISO 250 ISO 200
ISO 400 ISO 400 ISO 500 ISO 400
ISO 800 ISO 800 ISO 1000 ISO 800
ISO 1600 ISO 1600 ISO 2000 ISO 1600
ISO 3200 ISO 3200 n/a ISO 3200

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.

Why no Canon EOS 400D (Rebel XTi)?

At this time this review was written the EOS 400D (Rebel XTi) Kit was a not inconsiderate $200 in the US (or £150 in the UK) more than the Nikon D40 and has a four megapixel advantage. For the purposes of this review we are only comparing the D40 to other cameras in the $600-$700 (£350-£400) Kit price range (Canon EOS 350D / Rebel XT and Pentax K100D).

Nikon D40 vs. Pentax K100D vs. Canon EOS 350D (Rebel XT)

  • Nikon D40: Nikkor 50 mm F1.8 lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), JPEG Large / Fine
     
  • Pentax K100D: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Vivid Tone), JPEG Large / Best
     
  • Canon EOS 350D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), JPEG Large / Fine
Nikon D40
n/a
Pentax K100D
n/a
Canon EOS 350D
ISO 100
(125 equiv.)
Nikon D40
ISO 200
Pentax K100D
ISO 200
Canon EOS 350D
ISO 200
(250 equiv.)
Nikon D40
ISO 400
Pentax K100D
ISO 400
Canon EOS 350D
ISO 400
(500 equiv.)
Nikon D40
ISO 800
Pentax K100D
ISO 800
Canon EOS 350D
ISO 800
(1000 equiv.)
Nikon D40
ISO 1600
Pentax K100D
ISO 1600
Canon EOS 350D
ISO 1600
(2000 equiv.)
Nikon D40
ISO 3200
Pentax K100D
ISO 3200
Canon EOS 350D
n/a

The Nikon D40 delivers cleaner images across the ISO range than the other two cameras here, and it does so while maintaining good detail (although I would say this is probably second to Pentax who have a very hands-off approach to noise reduction). At ISO 1600 the D40's grey and black patches are very clean with only a hint of chroma noise, this compares very well to the K100D and EOS 350D (Rebel XT).

The graphs below confirm the visual observation, the D40 has a very similar noise curve to the D50 which only exhibits more noise than the K100D and EOS 350D at ISO 3200 (HI 1).

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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