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.

Pentax K200D vs. Canon EOS 450D (Rebel XSi) vs. Olympus E-520 vs Nikon D60

  • Pentax K200D: Pentax 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Bright Tone), JPEG Large / Best
     
  • Canon EOS 450D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Standard PS), High ISO NR (Default; Off), JPEG Large/Fine
     
  • Olympus E-520: Olympus 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large/Fine

  • Nikon D60: Nikkor 50 mm F1.8 lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), JPEG Large / Fine
Pentax K200D
ISO 100		 Canon EOS 450D
ISO 100		 Olympus E-520
ISO 100		 Nikon D60
ISO 100

Pentax K200D
ISO 200		 Canon EOS 450D
ISO 200		 Olympus E-520
ISO 200		 Nikon D60
ISO 200

Pentax K200D
ISO 400		 Canon EOS 450D
ISO 400		 Olympus E-520
ISO 400		 Nikon D60
ISO 400

Pentax K200D
ISO 800		 Canon EOS 450D
ISO 800		 Olympus E-520
ISO 800		 Nikon D60
ISO 800

Pentax K200D
ISO 1600		 Canon EOS 450D
ISO 1600		 Olympus E-520
ISO 1600		 Nikon D60
ISO 1600

      Nikon D60
ISO 3200

The K200D's default output (Bright image mode) is quite heavily sharpened and contrasty. As a result noise and artifacts are being accentuated and you end up with an image that is visibly grainier than the competitors, even at base ISO. Purple chroma noise blotches appear on the scene at ISO 200 and become progressively more intrusive as you go up the sensitivity scale.

On the up-side the Pentax maintains a relatively good level of detail up into higher ISO regions by applying comparatively little noise reduction (even with High ISO NR switched off there is always some 'base' NR). The graphs below confirm the observations we made on our sample shots. Gray luminance and chroma noise measures pretty high on the K200D.

Gray luminance noise graph

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

Black 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.