ISO Sensitivity / Noise levels

Standard Test

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 measurement tool which measures the standard deviation (normalized) of the middle gray patch (indicated by the red rectangle above). Additionally we now have a 'detail crop', this is currently a postage stamp (lots of fine detail) but we may replace this at a future date. Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Test notes:

• Shots taken at approximately 22°C (~72°F)
• Lighting was simulated daylight measured as 10.1 EV (at ISO 100)

Canon EOS 350D (Digital Rebel XT) vs. Canon EOS 20D

• Canon EOS 350D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Parameters 1 (default), JPEG Large / Fine
  
• Canon EOS 20D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Parameters 1 (default), JPEG Large / Fine

	Canon EOS 350D ISO 100, 1/100 sec, F4	Canon EOS 20D ISO 100, 1/100 sec, F4
Crops
	Canon EOS 350D ISO 200, 1/200 sec, F4	Canon EOS 20D ISO 200, 1/200 sec, F4
Crops
	Canon EOS 350D ISO 400, 1/400 sec, F4	Canon EOS 20D ISO 400, 1/400 sec, F4
Crops
	Canon EOS 350D ISO 800, 1/800 sec, F4	Canon EOS 20D ISO 800, 1/800 sec, F4
Crops
	Canon EOS 350D ISO 1600, 1/1600 sec, F4	Canon EOS 20D ISO 1600, 1/1600 sec, F4
Crops
	Canon EOS 350D n/a	Canon EOS 20D ISO 3200, 1/3200 sec, F4
Crops

As you can see there's almost no visible difference in noise levels between the EOS 350D and EOS 20D, our measured results (see graph below) show that the 350D's noise levels are very slightly higher between ISO 800 and 1600. Image sharpness is also virtually identical with a slight softening at ISO 800 and 1600 but nothing like the levels we have seen from other cameras.

Canon EOS 350D (Digital Rebel XT) vs. Olympus E-300 EVOLT

• Canon EOS 350D: Canon 50 mm F1.4 lens, Aperture Priority, Manual WB,
  Parameters 1 (default), JPEG Large / Fine
   
• Olympus E-300: Olympus 50 mm F2.0 lens, Aperture Priority, Manual WB,
  Default Parameters, JPEG SHQ

	Canon EOS 350D ISO 100, 1/100 sec, F4	Olympus E-300 ISO 100, 1/100 sec, F3.5
Crops
	Canon EOS 350D ISO 200, 1/200 sec, F4	Olympus E-300 ISO 200, 1/200 sec, F3.5
Crops
	Canon EOS 350D ISO 400, 1/400 sec, F4	Olympus E-300 ISO 400, 1/400 sec, F3.5
Crops
	Canon EOS 350D ISO 800, 1/800 sec, F4	Olympus E-300 ISO 800, 1/800 sec, F3.5
Crops
	Canon EOS 350D ISO 1600, 1/1600 sec, F4	Olympus E-300 ISO 1600, 1/1600 sec, F3.5
Crops

At ISO 100 and 200 there's little visible difference in noise between the EOS 350D and the E-300, from ISO 400 upwards the EOS 350D looks cleaner and at maximum ISO 1600 there's a significant difference in noise. What's also noticeable is the gradual softening of the E-300's images at higher sensitivities.

Luminance noise graph

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

RGB noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized image) are on the vertical axis.